JP2020168927A - Muffler for propeller - Google Patents

Abstract

To reduce the noise caused by propeller rotation by using a small calculation amount and a small scale constitution.SOLUTION: A muffler for a propeller comprises: a propeller having plural impeller blades; a duct with a peripheral surface surrounding the propeller; plural speakers arranged in a concentrically circular manner on the peripheral surface; one or more error microphones arranged on the exterior of the peripheral surface; and a signal processing circuit for generating a signal indicating control sound to be output by the plural speakers. The number of error microphones is less than the number of speakers. The signal processing circuit generates a first signal which indicates control sound to be output by a first speaker among the plural speakers, so that residual noise collected by the one or more error microphones is minimized, by using transfer characteristics of the sound from the first speaker to the one or more error microphones. Further, the signal processing circuit generates a signal obtained by differing a phase of the first signal by only an amount according to the number of blades, as a second signal which indicates control sound to be output by a second speaker different from the first speaker among the plural speakers.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to a propeller silencer that reduces noise generated by the rotation of a propeller.

Conventionally, for example, a technique for reducing noise generated by rotation of a propeller by arranging a tubular duct so as to surround the propeller has been known. In this technology, the noise generated by the rotation of the propeller is attenuated in the duct, and the noise is reflected on the inner wall of the duct to generate the noise of the opposite phase, so that the noise can be canceled.

Further, in recent years, for example, as described in Patent Document 1, noise is reduced by outputting a control sound having a phase opposite to that of noise by a speaker, and residual noise collected by an error microphone is minimized. An active noise control (hereinafter referred to as ANC) technique for updating the control sound is known.

Japanese Unexamined Patent Publication No. 7-160273

However, depending on the load capacity of the propeller device equipped with the propeller or the surrounding space, the length (for example, 2.5 m) that can attenuate the noise generated by the rotation of the propeller (hereinafter, propeller noise) as in the prior art. It may not be possible to provide a large duct with.

Therefore, as a method of reducing the noise of the propeller by using the above-mentioned ANC technology, it is conceivable to output a control sound for reducing the propeller noise by a speaker arranged around the propeller. However, the wave surface of a certain phase of the control sound at a certain point in time exists concentrically from the center of the output surface of the speaker. On the other hand, the wave plane of the propeller noise having a phase opposite to that of the propeller noise at a certain time point exists on a spiral line centered on the rotation axis of the propeller. Therefore, the wave surface of the control sound in a certain phase and the wave surface of the propeller noise in the opposite phase can intersect at a slight position, and there is a problem that the propeller noise cannot be sufficiently reduced by a simple ANC system. there were.

In order to solve this problem, it is conceivable to arrange as many speakers as possible around the propeller to increase the intersecting positions. However, in ANC technology, as the number of speakers to be arranged increases, the number of signal processing circuits that generate control sounds to be output to each speaker increases, and it is necessary to perform enormous calculations.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a small-scale propeller muffling device capable of reducing noise generated by rotation of a propeller with a small amount of calculation.

The sound deadening device for a propeller according to one aspect of the present disclosure includes a propeller having a plurality of blades, a duct having a peripheral surface surrounding the propeller, a plurality of speakers arranged concentrically on the peripheral surface, and the peripheral surface. One or more error microphones arranged outside the above, and a signal processing circuit for generating a signal indicating a control sound to be output to the plurality of speakers are provided, and the number of the one or more error microphones is the plurality. The signal processing circuit outputs a control sound to the first speaker of the plurality of speakers so as to minimize the residual noise collected by the one or more error microphones. The first signal shown is generated by using the sound transmission characteristics from the first speaker to the one or more error microphones, and the phases of the first signal are different by an amount corresponding to the number of blades. Is generated as a second signal indicating a control sound to be output to a second speaker different from the first speaker among the plurality of speakers.

According to the present disclosure, it is possible to provide a small-scale sound deadening device for a propeller that can reduce the noise generated by the rotation of the propeller with a small amount of calculation.

It is a perspective view which shows an example of the appearance of a drone. It is a top view which shows an example of the appearance of a drone. It is a block diagram which shows an example of the functional structure of a drone. It is a top view which shows an example of a propeller apparatus. FIG. 3A is a cross-sectional view taken along the line BB of FIG. 3A. It is a circuit diagram which shows an example of a signal processing circuit. It is a figure which shows an example of the phase distribution of the control sound reproduced by a plurality of speakers. It is a figure which shows the modification of the arrangement position of an error microphone. It is a circuit diagram which shows the modification of the signal processing circuit. It is a figure which shows an example of the sound pressure frequency characteristic of a propeller noise. It is a figure which shows an example of the ANC control circuit which includes four speakers and four error microphones. It is a figure which shows an example of the phase distribution of propeller noise.

(Background to this disclosure)
The present inventor has developed a technique for reducing noise generated by rotation of a propeller (hereinafter referred to as propeller noise). As such a technique, a technique for reducing propeller noise by arranging a tubular duct so as to surround the propeller, for example, has been conventionally known. In this technology, the propeller noise is attenuated in the duct, and the propeller noise is reflected by the inner wall of the duct to generate the noise of the opposite phase, so that the noise can be canceled.

FIG. 8 is a diagram showing an example of sound pressure frequency characteristics of propeller noise. As shown in the lower right figure of FIG. 8, the sound pressure frequency characteristic is set at a position 2 m away from the rotation axis of the propeller in each of the case where the duct is provided so as to surround the propeller and the case where the duct is not provided. The measurement result when the propeller noise is measured by the arranged microphone is shown. The horizontal axis of FIG. 8 indicates the frequency, and the vertical axis of FIG. 8 indicates the sound pressure. In FIG. 8, the graph G81 shows the sound pressure frequency characteristic when the duct is not provided, and the graph G82 shows the sound pressure frequency characteristic when the duct is provided. As shown in FIG. 8, when the duct is provided, the sound pressure of the noise of each frequency included in the propeller noise can be reduced as compared with the case where the duct is not provided. In particular, when a duct is provided, the sound pressure of propeller noise in the mid-high range of 100 Hz to 1000 Hz can be reduced.

Further, in recent years, for example, as described in Patent Document 1, noise is reduced by outputting a control sound having a phase opposite to that of noise by a speaker, and residual noise collected by an error microphone is minimized. An active noise control (hereinafter referred to as ANC) technique for updating the control sound is known.

FIG. 9 is a diagram showing an example of an ANC control circuit including four speakers and four error microphones. For example, as shown in FIG. 9, four speakers OUT1 to OUT4 and four error microphones ERR1 to ERR4 are arranged to reduce noise by using ANC technology. In this case, the control sounds output from the four speakers OUT1 to OUT4 are transmitted to the four error microphones ERR1 to ERR4, respectively. That is, there are 16 control sound transmission paths as shown by the broken line portion in FIG. Therefore, in order to update the control sound output to the four speakers OUT1 to OUT4 so as to minimize the residual noise collected by the four error microphones ERR1 to ERR4, the number of control sound transmission paths is adjusted. 16 signal processing circuits V11 to V14, V21 to V24, V31 to V34, and V41 to V44 are provided.

However, depending on the load capacity of the propeller device such as a cooling fan, drone, and ventilation fan provided in electronic devices such as a personal computer and a projector, or the surrounding space, the length is sufficient to attenuate the propeller noise as in the prior art. For example, it may not be possible to provide a large duct having 2.5 m). Therefore, it is conceivable to reduce propeller noise by using ANC technology, but there are the following problems.

FIG. 10 is a diagram showing an example of the phase distribution of propeller noise. This phase distribution shows the phase distribution at a certain time point of the propeller noise having a frequency of 300 Hz, which is generated when one blade rotates a propeller of 30 cm. FIG. 10 is a view of the rotating surface of the propeller viewed from above, and the center G101 of FIG. 10 shows the rotation axis of the propeller. The horizontal axis of FIG. 10 indicates the relative distance from the rotation axis of the propeller in the left-right direction, the right side of the rotation axis is indicated by a positive value, and the left side is indicated by a negative value. The vertical axis of FIG. 10 shows the relative distance of the propeller from the rotation axis in the front-rear direction, the front side of the rotation axis is shown by a positive value, and the rear side is shown by a negative value. In FIG. 10, the spiral graph G102 shows a wave surface having a propeller noise phase of 60 ° (π / 3) at the time point, and the spiral graph G103 shows a propeller noise phase of 180 ° (π / 3) at the time point. ) Shows the wave surface. As shown in FIG. 10, the wave front of each phase of the propeller noise at a certain time point has a characteristic that it exists on a spiral line centered on the rotation axis of the propeller.

Therefore, it is assumed that the ANC technology is used to output a control sound that reduces propeller noise from a speaker arranged around the propeller. In this case, the wave plane of a certain phase at a certain point in time of the control sound output from the speaker exists concentrically from the center of the output plane of the speaker. On the other hand, the wave plane of the propeller noise having a phase opposite to that of the propeller noise at a certain time point exists on a spiral line centered on the rotation axis of the propeller, as shown in FIG. Therefore, the wave surface of the certain phase of the control sound at a certain time point and the wave surface of the opposite phase of the propeller noise can intersect only at a slight position, and the propeller noise cannot be sufficiently reduced.

Therefore, it is conceivable to arrange as many speakers as possible around the propeller to increase the position where the wave surface of the certain phase of the control sound and the wave surface of the opposite phase of the propeller noise intersect at a certain time point. However, as the number of speakers to be arranged increases, as shown in FIG. 9, the transmission path of the control sound becomes enormous, and the signal processing circuit provided to update the control sound to be output to each speaker accordingly. The number of is huge. As a result, there is a problem that the circuit for reducing the propeller noise becomes large-scale and the amount of calculation for updating the control sound output to each speaker becomes enormous. In particular, in a device that drives a propeller with electric power supplied by a secondary battery such as a drone, there is a problem that when the amount of calculation becomes enormous, the electric power used for driving the propeller is reduced and the operating time is shortened.

The present disclosure has been made to solve the above problems, and an object of the present invention is to provide a small-scale propeller muffling device capable of reducing noise generated by rotation of a propeller with a small amount of calculation.

The sound deadening device for a propeller according to one aspect of the present disclosure includes a propeller having a plurality of blades, a duct having a peripheral surface surrounding the propeller, a plurality of speakers arranged concentrically on the peripheral surface, and the peripheral surface. One or more error microphones arranged outside the above, and a signal processing circuit for generating a signal indicating a control sound to be output to the plurality of speakers are provided, and the number of the one or more error microphones is the plurality. The signal processing circuit outputs a control sound to the first speaker of the plurality of speakers so as to minimize the residual noise collected by the one or more error microphones. The first signal shown is generated by using the sound transmission characteristics from the first speaker to the one or more error microphones, and the phases of the first signal are different by an amount corresponding to the number of blades. Is generated as a second signal indicating a control sound to be output to a second speaker different from the first speaker among the plurality of speakers.

According to this aspect, only the first signal indicating the control sound to be output to the first speaker is described from the first speaker so as to minimize the residual noise collected by one or more error microphones, which is less than the speaker. Generated using the sound transfer characteristics up to one or more error microphones. On the other hand, the second signal indicating the control sound to be output to the second speaker different from the first speaker is generated by making the phase of the first signal different by an amount corresponding to the number of blades of the propeller.

For this reason, a plurality of speakers and error microphones are arranged, and each speaker is output using the sound transmission characteristics from all the speakers to all the error microphones so as to minimize the residual noise collected by the plurality of error microphones. The amount of calculation required to generate the signal indicating the control sound can be reduced as compared with the case of generating the signal indicating the control sound.

Further, the wave front of each phase of the propeller noise at a certain point in time exists on a spiral line centered on the rotation axis of the propeller. In this embodiment, control sounds having different phases by an amount corresponding to the number of blades are output from a plurality of speakers arranged concentrically so as to surround the propeller. Therefore, similarly to the propeller noise, the wave surface of each phase of the control sound can exist on the spiral line centered on the rotation axis of the propeller at a certain time point. Thereby, the propeller noise can be effectively reduced.

As described above, according to this aspect, the propeller noise can be reduced with a small amount of calculation by a small-scale configuration in which a duct long enough to attenuate the propeller noise is not provided.

In the above aspect, the plurality of speakers are arranged at equal intervals on the peripheral surface, and the amount corresponding to the number of blades is smaller as the number of blades is larger and the number of the plurality of speakers is larger. It may be smaller and larger as the number of speakers existing between the first speaker and the second speaker is larger.

When a plurality of speakers are arranged at equal intervals on the peripheral surface, the larger the number of blades of the propeller and the larger the number of speakers, the more each blade of the propeller passes in the vicinity of the first speaker. The time from when it reaches the vicinity of the second speaker is shortened.

According to this aspect, the phase difference between the first signal and the second signal can be reduced as the number of blades of the propeller increases and the number of speakers increases accordingly. As a result, the control sound can be output from each speaker at the timing when noise is generated by each blade passing in the vicinity of each speaker.

Further, when a plurality of speakers are arranged at equal intervals on the peripheral surface, the larger the number of speakers existing between the first speaker and the second speaker, the closer each blade of the propeller is to the vicinity of the first speaker. It takes a long time to reach the vicinity of the second speaker after passing through.

According to this aspect, the larger the number of speakers existing between the first speaker and the second speaker, the more the phase difference between the first signal and the second signal output to the second speaker. Can be increased. As a result, it is possible to output a control sound for reducing the noise from the second speaker at the timing of generating noise when each blade passes in the vicinity of the second speaker.

In the above aspect, the signal processing circuit includes a control filter that performs signal processing on a reference signal indicating noise generated by rotation of the propeller using a predetermined control coefficient, and one or more of the reference signal and the first speaker. The output of the control filter is provided with a coefficient update circuit that updates the control coefficient so as to minimize the residual noise by using the sound transmission characteristic to the error microphone and the error signal indicating the residual noise. The signal may be generated as the first signal.

According to this aspect, a control filter that performs signal processing using a predetermined control coefficient for the reference signal, a reference signal, a sound transmission characteristic from the first speaker to one or more error microphones, and an error signal are used. , A known signal processing circuit used in ANC technology including a coefficient updating circuit that updates the control coefficient so as to minimize the residual noise indicated by the error signal can be applied to the signal processing circuit in this embodiment. it can.

In the above aspect, the reference signal may be a drive signal for rotating the propeller.

According to this aspect, the signal processing circuit generates a signal after performing signal processing using a predetermined control coefficient for the drive signal for rotating the propeller, and is generated as a first signal, which is in phase with the first signal. A different signal is generated as the second signal. Therefore, even if the noise generated by the wind generated by the rotation of the propeller colliding with the error microphone (hereinafter referred to as wind noise) is included in the residual noise collected by the error microphone, the wind noise is included. It can be ignored to reduce noise having a frequency component similar to that of the drive signal.

In the above aspect, the reference signal may be a detection signal indicating that it has detected that any one of the plurality of blades has passed in the vicinity.

According to this aspect, a signal after performing signal processing using a predetermined control coefficient for a detection signal indicating that one of a plurality of blades has been detected to have passed in the vicinity by the signal processing circuit. However, a signal having a phase different from that of the first signal is generated as a second signal. Therefore, even if the wind noise is included in the residual noise collected by the error microphone, the wind noise can be ignored and the noise having the same frequency component as the detection signal can be reduced.

In the above aspect, the reference signal may be a voice signal indicating a sound collected by a microphone arranged in the vicinity of the propeller.

According to this aspect, the signal after performing signal processing using a predetermined control coefficient on the voice signal indicating the sound collected by the microphone arranged in the vicinity of the propeller by the signal processing circuit is the first signal. A signal having a phase different from that of the first signal is generated as a second signal. Therefore, even if the wind noise is included in the residual noise collected by the error microphone, the wind noise is ignored and the noise having the same frequency component as the sound collected in the vicinity of the propeller is reduced. be able to.

The sound deadening device for a propeller according to another aspect of the present disclosure includes a propeller having a plurality of blades, a duct having a peripheral surface surrounding the propeller, a plurality of speakers arranged concentrically on the peripheral surface, and the above. The signal processing circuit includes a signal processing circuit that generates a signal indicating a control sound to be output to a plurality of speakers, and a sensor that outputs a detection signal indicating that any one of the plurality of blades has passed in the vicinity. The circuit includes a control filter that performs signal processing using a predetermined control coefficient for the detection signal, and indicates a control sound for outputting the output signal of the control filter to the first speaker among the plurality of speakers. A control sound generated as a signal and having the phase of the first signal different by an amount corresponding to the number of blades is output to a second speaker different from the first speaker among the plurality of speakers. The control coefficient is generated as the second signal to be shown, and the detection signal, the sound transmission characteristic from the first speaker to the position of a predetermined error microphone outside the peripheral surface, and the first signal to the first speaker. It is predetermined to minimize the residual noise by using an error signal indicating the residual noise at the position of the error microphone when the control sound indicated by is output.

In this embodiment, the control coefficient is a detection signal indicating that one of a plurality of blades has passed in the vicinity and a sound from the first speaker to a predetermined error microphone position outside the peripheral surface of the duct. It is predetermined to minimize the residual noise by using the transmission characteristic and the error signal indicating the residual noise at the position of the error microphone when the control sound indicated by the first signal is output to the first speaker. .. Then, the first signal indicating the control sound to be output to the first speaker is generated by performing signal processing on the detection signal using the predetermined control coefficient. Further, the second signal indicating the control sound to be output to the second speaker is generated by making the phase of the first signal different by an amount corresponding to the number of blades of the propeller.

For this reason, a plurality of speakers and error microphones are arranged, and each speaker is output using the sound transmission characteristics from all the speakers to all the error microphones so as to minimize the residual noise collected by the plurality of error microphones. The amount of calculation required to generate the signal indicating the control sound can be significantly reduced as compared with the case of generating the signal indicating the control sound.

Further, the wave front of each phase of the propeller noise at a certain point in time exists on a spiral line centered on the rotation axis of the propeller. In this embodiment, control sounds having different phases by an amount corresponding to the number of blades are output from a plurality of speakers arranged concentrically so as to surround the propeller. Therefore, similarly to the propeller noise, the wave surface of each phase of the control sound can exist on the spiral line centered on the rotation axis of the propeller at a certain time point. Thereby, the propeller noise can be effectively reduced.

As described above, according to this aspect, the propeller noise can be reduced with a small amount of calculation by a small-scale configuration in which a duct long enough to attenuate the propeller noise is not provided.

In the above aspect, the signal processing circuit includes an amplifier that amplifies a signal indicating a control sound to be output to the plurality of speakers with a predetermined gain, a sound pressure characteristic of the output sound by the first speaker, and an output by the second speaker. A correction unit that corrects the gain when the amplifier amplifies the signal of the error microphone among the first signal and the second signal may be further provided according to the difference from the sound pressure characteristic of the sound.

According to this aspect, even if there is a difference between the sound pressure characteristic of the output sound of the first speaker and the sound pressure characteristic of the output sound of the second speaker, the gain can be corrected so as to eliminate the difference. .. As a result, it is possible to eliminate variations in the sound pressure of the control sounds output from the plurality of speakers.

In the above aspect, the propeller may be a propeller included in the drone.

According to this aspect, in the drone, the propeller noise can be reduced with a small amount of calculation by a small-scale configuration in which a duct long enough to attenuate the propeller noise is not provided. Therefore, it is possible to reduce the electric power required for the calculation required to reduce the propeller noise and suppress the reduction of the electric power required for the rotation of the propeller of the drone. As a result, it is possible to suppress the shortening of the flight time of the drone due to the rotation of the propeller in order to reduce the propeller noise.

It should be noted that all of the embodiments described below show a specific example of the present disclosure. The numerical values, shapes, components, and the like shown in the following embodiments are examples, and are not intended to limit the present disclosure. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components. Moreover, in all the embodiments, each content can be combined.

(Embodiment)
Hereinafter, the drone 1 according to the embodiment of the silencer for propeller of the present disclosure will be described with reference to the drawings. FIG. 1A is a perspective view showing an example of the appearance of the drone 1. FIG. 1B is a top view showing an example of the appearance of the drone 1. As shown in FIGS. 1A and 1B, the drone 1 includes a main body 90 and four propeller devices 10 that generate propulsive force for the drone 1. The propeller device 10 includes a cylindrical duct 19 having a peripheral surface 191 surrounding the propeller 11 having four blades. The peripheral surface 191 of the duct 19 is attached to the tip of the support portion 99 extending from the main body 90 in all directions. The duct 19 is not limited to this, and may be a truncated cone-shaped duct having a peripheral surface surrounding the propeller 11.

FIG. 2 is a block diagram showing an example of the functional configuration of the drone 1. FIG. 3A is a top view showing an example of the propeller device 10. FIG. 3B is a sectional view taken along line BB of FIG. 3A. As shown in the solid line portion of FIG. 2, the propeller device 10 further includes a motor 12, a speaker 13, and an error microphone 14.

As shown in FIGS. 3A and 3B, the motor 12 is attached to the tip of a support portion 121 extending from the inside of the peripheral surface 191 of the duct 19 to the inside of the duct 19, and rotates the rotating shaft 111 of the propeller 11. As a result, the motor 12 rotates the propeller 11.

As shown in FIGS. 3A and 3B, a plurality of speakers 13 are arranged at equal intervals on the peripheral surface 191 of the duct 19. FIG. 3A shows an example in which 12 speakers 13 are arranged at equal intervals on the peripheral surface 191. The speaker 13 outputs the control sound indicated by the control sound signal generated by the signal processing circuit 93 described later.

As shown in FIG. 3B, the error microphone 14 is located outside the peripheral surface 191 of the duct 19 and below the speaker 13. In this embodiment, two error microphones 14 are arranged as shown in FIG. 3B. However, the number of error microphones 14 is not limited to this, and may be one, or may be smaller than the number of speakers 13. The error microphone 14 collects residual noise remaining around the position where it is installed, and outputs an error signal indicating the collected residual noise to the signal processing circuit 93.

As shown in FIG. 2, the main body 90 includes a communication unit 94, a drive circuit 92, a signal processing circuit 93, a control unit 91, and a power supply unit 95.

The communication unit 94 is composed of a communication interface circuit that performs wireless communication such as infrared communication or Bluetooth (registered trademark), and performs wireless communication with a remote control device (not shown). Specifically, when the communication unit 94 receives the operation instruction of the drone 1 from the remote control device, the communication unit 94 outputs the received operation instruction to the control unit 91.

The drive circuit 92 rotates the motor 12 in the instructed direction and rotation speed in accordance with the instruction indicated by the drive signal input from the control unit 91.

The signal processing circuit 93 generates a signal indicating a control sound to be output to the speaker 13 based on the error signal output by the error microphone 14 and the reference signal indicating the propeller noise. In the present embodiment, the reference signal is assumed to be the same drive signal as the drive signal input from the control unit 91 to the drive circuit 92. The details of the signal processing circuit 93 will be described later.

The control unit 91 is composed of a processor such as a CPU and a microcomputer provided with a memory such as RAM and ROM, and controls the entire drone 1 according to an operation instruction of the drone 1 received from the communication unit 94.

For example, when the control unit 91 receives an instruction to fly the drone 1 upward from the communication unit 94, the control unit 91 sets the motor 12 included in each of the four propeller devices 10 in a predetermined direction (for example, clockwise) according to the instruction. , A drive signal indicating an instruction to rotate at a predetermined rotation speed is output to the drive circuit 92. In response to this, the drive circuit 92 rotates the motor 12 included in each of the four propeller devices 10 in the instructed direction at the instructed rotation speed according to the instruction indicated by the drive signal received from the control unit 91.

The power supply unit 95 is composed of a rechargeable secondary battery such as a lithium ion secondary battery or a nickel hydrogen secondary battery. The power supply unit 95 supplies electric power to each unit 91 to 94 included in the main body 90 and each component 12 to 14 included in the propeller device 10.

Next, the details of the signal processing circuit 93 will be described. FIG. 4 is a circuit diagram showing an example of the signal processing circuit 93. As shown in FIG. 4, the signal processing circuit 93 includes an input terminal 30, an ANC control circuit 31, a first amplifier 32-1 (amplifier), (m-1) delay circuits 33, and (m-). 1) It is provided with (m-1) second amplifiers 32-2 (amplifiers) connected to each of the delay circuits 33. Note that m indicates the number of speakers 13.

A reference signal indicating propeller noise is input to the input terminal 30. In the present embodiment, it is assumed that the same drive signal as the drive signal input from the control unit 91 to the drive circuit 92 is input to the input terminal 30 as a reference signal.

The ANC control circuit 31 minimizes the error signal indicating the residual noise collected by the first error microphone 14-1 and the second error microphone 14-2, which are the two error microphones 14 shown in FIG. 3B. In addition, a control sound signal (hereinafter, the first signal) indicating a control sound to be output to the first speaker 13-1 of the m speakers 13 is generated.

Specifically, the ANC control circuit 31 includes a control filter 310, a convolution circuit 311 (coefficient update circuit), and an LMS arithmetic unit 312 (coefficient update circuit).

The control filter 310 performs convolution processing (signal processing) on the reference signal input to the input terminal 30 by using a predetermined control coefficient. The control filter 310 outputs the signal after the convolution process as the first signal to the first amplifier 32-1. Further, the control filter 310 outputs a control sound that outputs the signal after the convolution process to the second speaker 13-2 (m-1) different from the first speaker 13-1 of the m speakers 13. It is output to (m-1) delay circuits 33 as a reference signal of the control sound signal (hereinafter, the second signal) shown.

The convolution circuit 311 convolves the reference signal input to the input terminal 30 with a coefficient C1 that simulates the sound transmission characteristics from the first speaker 13-1 to the first error microphone 14-1. Further, the convolution circuit 311 convolves the reference signal input to the input terminal 30 with a coefficient C2 simulating the sound transmission characteristics from the first speaker 13-1 to the second error microphone 14-2. The convolution circuit 311 outputs a signal obtained by adding a signal obtained by convolving the coefficient C1 to the reference signal and a signal obtained by convolving the coefficient C2 to the reference signal to the LMS calculator 312.

The LMS calculator 312 uses the signal input from the convolution circuit 311 and the error signal input from the first error microphone 14-1 and the second error microphone 14-2, and uses the LMS (Least Mean Square) algorithm (minimum). A control filter is executed so as to minimize the residual noise indicated by the error signals input from the first error microphone 14-1 and the second error microphone 14-2 by executing a known coefficient update algorithm such as the square method). The control coefficient used by 310 is updated.

The first amplifier 32-1 amplifies the control sound signal input from the ANC control circuit 31 at a predetermined amplification factor (gain), and outputs the amplified control sound signal to the first speaker 13-1. As a result, the first speaker 13-1 outputs (reproduces) the control sound indicated by the amplified control sound signal.

The (m-1) delay circuits 33 generate a second signal by delaying the phase of the reference signal input from the ANC control circuit 31.

Specifically, the first speaker 13-1 is referred to as the first speaker 13. Then, the second speaker 13-2 adjacent to the first speaker 13-1 in the rotation direction of the propeller 11 is designated as the second speaker 13 and the first second speaker 13-2. Similarly to this, the remaining second speakers 13-2 are sequentially ordered in the rotation direction of the propeller 11.

The delay circuit 33- (m-1) is a delay circuit 33 that generates a second signal indicating a control sound to be output to the (m-1) th second speaker 13-2, which is the mth speaker 13. The delay circuit 33- (m-1) delays the phase of the input reference signal by the time (m-1) Δt indicated by the product of the predetermined delay time Δt and (m-1). The delay circuit 33- (m-1) is connected to itself as a second signal indicating a control sound for outputting the signal whose phase is delayed to the (m-1) th second speaker 13-2. Output to the second amplifier 32-2. The second amplifier 32-2 amplifies the input second signal at a predetermined amplification factor (gain), and outputs the amplified second signal to the second speaker 13-2 connected to itself. As a result, the second speaker 13-2 outputs (reproduces) the control sound indicated by the second signal after the amplification.

Therefore, for example, the second signal indicating the control sound to be output to the second second speaker 13-2 becomes a signal in which the phase of the reference signal is delayed by 2Δt of time, and the third second speaker 13-2 The second signal indicating the control sound to be output is a signal in which the phase of the reference signal is delayed by 3Δt for a time. As described above, the second signal indicating the control sound to be output to the second speaker 13-2 is a speaker existing between the first speaker 13-1 and the second speaker 13-2 in the rotation direction of the propeller 11. The larger the number of 13, the larger the phase of the first signal, which is the reference signal, is delayed.

The delay time Δt is determined by the following equation (1).

For example, as shown in FIG. 3A, it is assumed that the number of blades of the propeller 11 is four and the number of speakers 13 is twelve. Further, it is assumed that the rotation speed of the motor 12 per second is 50 times. In this case, the delay time Δt is set to 0.00417 (= 1/4 × 12 × 50) seconds using the equation (1). On the other hand, it is assumed that the number of blades of the propeller 11 is 5, the number of speakers 13 is 12, and the number of rotations of the motor 12 per second is 50. In this case, the delay time Δt is set to 0.000333 (= 1/5 × 12 × 50) seconds using the equation (1). As described above, the delay time Δt is set to be smaller as the number of blades of the propeller 11 increases. Therefore, as the number of blades of the propeller 11 increases, the second signal becomes a signal in which the phase of the first signal is delayed by a small amount.

Further, it is assumed that the number of blades of the propeller 11 is 4, the number of speakers 13 is 15, and the number of rotations of the motor 12 per second is 50. In this case, the delay time Δt is set to 0.000333 (= 1/4 × 15 × 50) seconds using the equation (1). On the other hand, as described above, when the number of blades of the propeller 11 is 4, the number of speakers 13 is 12, and the rotation speed of the motor 12 per second is 50, the delay time Δt is determined. It is set to 0.00417 (= 1/4 × 12 × 50) seconds. As described above, the delay time Δt is set to be smaller as the number of speakers 13 increases. Therefore, as the number of speakers 13 increases, the second signal becomes a signal in which the phase of the first signal is delayed by a small amount.

In the configuration of the above embodiment, only the first signal has two errors from the first speaker 13-1 so as to minimize the residual noise collected by the two error microphones 14, which are smaller than the number of speakers 13. It is generated using the sound transmission characteristics up to the microphone 14. On the other hand, the second signal has the phase of the first signal between the first speaker 13-1 and the second speaker 13-2 in the number of blades of the propeller 11, the number of speakers 13, and the rotation direction of the propeller 11. It is generated by delaying by an amount corresponding to the number of speakers 13 to be used.

Therefore, in the convolution circuit 311 and the LMS calculator 312, 2 m of sounds from the m speakers 13 to the two error microphones 14 are minimized so as to minimize the residual noise collected by the two error microphones 14. The amount of calculation required to generate the control sound signal can be reduced as compared with the case of generating the first signal and (m-1) second signals by using the transmission characteristics of.

FIG. 5 is a diagram showing an example of the phase distribution of the control sound reproduced by the plurality of speakers 13. In the configuration of the present embodiment, the phase distribution of the 12 speakers 13 (FIG. 3A) concentrically arranged so as to surround the propeller 11 is sequentially different in phase by a delay time Δt in the rotation direction of the propeller 11. It shows the phase distribution of the control sound at a certain point in time when the control sound is output. FIG. 5 is a view of the rotating surface of the propeller 11 as viewed from above, and the center G51 of FIG. 5 shows the rotating shaft 111 of the propeller 11. The horizontal axis of FIG. 5 indicates the relative distance of the propeller 11 from the rotation axis 111 in the left-right direction, the right side of the rotation axis 111 is indicated by a positive value, and the left side is indicated by a negative value. The vertical axis of FIG. 5 shows the relative distance of the propeller 11 from the rotation axis 111 in the front-rear direction, the front side of the rotation axis 111 is shown by a positive value, and the rear side is shown by a negative value. In FIG. 5, the spiral graph G52 shows a wave surface in which the phase of the control sound at the time point is 60 ° (π / 3).

As shown in FIG. 5, according to the configuration of the present embodiment, the wave surface of each phase of the control sound at a certain time point is centered on the rotation axis 111 of the propeller 11 as in the phase of the propeller noise (FIG. 10). It can be present on a spiral. As a result, the wave surface of each phase of the control sound at a certain time point and the wave surface of the opposite phase of the propeller noise are overlapped on the spiral line centered on the rotation axis 111 of the propeller 11, and the propeller noise is effectively reduced. be able to.

As described above, according to the configuration of the present embodiment, the propeller noise can be reduced with a small amount of calculation in a small-scale configuration in which the duct 19 long enough to attenuate the propeller noise is not provided.

Further, in the configuration of the present embodiment, 12 speakers 13 (FIG. 3A) are arranged at equal intervals on the peripheral surface 191 of the duct 19. Therefore, in the rotation direction of the propeller 11, as the number of the speakers 13 existing between the first speaker 13-1 and the second speaker 13-2 increases, each blade of the propeller 11 becomes the first speaker 13-1. It takes a long time to reach the vicinity of the second speaker 13-2 after passing through the vicinity of the second speaker.

According to the configuration of the present embodiment, the larger the number of speakers 13 existing between the first speaker 13-1 and the second speaker 13-2 in the rotation direction of the propeller 11, the first. The phase difference between the signal and the second signal output to the second speaker 13-2 can be increased. As a result, the control sound for reducing the noise can be output from the second speaker 13-2 at the timing when the noise is generated when each blade passes in the vicinity of the second speaker 13-2.

Further, according to the configuration of the present embodiment, the signal processing circuit 93 generates a signal after performing signal processing using a predetermined control coefficient for the drive signal for rotating the propeller 11, as the first signal. Further, a signal having a phase different from that of the first signal is generated as the second signal. Therefore, even if the noise generated by the wind generated by the rotation of the propeller 11 colliding with the error microphone 14 (hereinafter referred to as wind noise) is included in the residual noise collected by the error microphone 14, the said noise. Wind noise can be ignored and noise having a frequency component similar to that of the drive signal can be reduced.

(Modified Embodiment)
It should be noted that the above embodiment is merely an example of the embodiment according to the present disclosure, and does not mean that the present disclosure is limited to the above embodiment. For example, it may be a modified embodiment shown below. In the following description, the same components as those described above will be designated by the same reference numerals, and the description thereof will be omitted.

(1) In the above embodiment, an example in which 12 speakers 13 are arranged on the peripheral surface 191 at equal intervals has been described, but the number of speakers 13 is not limited to this. Further, although the example in which the number of blades of the propeller 11 is four has been described, the number of blades of the propeller 11 is not limited to this. Using the above equation (1), the delay time Δt may be determined according to the number of speakers 13 arranged at equal intervals on the peripheral surface 191 and the number of blades of the propeller 11.

When a plurality of speakers 13 are arranged on the peripheral surface 191 at equal intervals, the larger the number of blades of the propeller 11 and the larger the number of speakers 13, the more each blade of the propeller 11 becomes the first speaker. The time from passing the vicinity of 13-1 to reaching the vicinity of the second speaker 13-2 is shortened. If the delay time Δt is determined using the above equation (1), the larger the number of blades of the propeller 11 and the larger the number of speakers 13, the greater the difference in phase between the first signal and the second signal. It can be made smaller. As a result, the control sound can be output from each speaker at the timing when noise is generated by each blade passing in the vicinity of each speaker 13.

(2) In the above embodiment, the case where the reference signal input to the input terminal 30 of the signal processing circuit 93 is the same drive signal as the drive signal input from the control unit 91 to the drive circuit 92 has been described as an example. The reference signal is not limited to the drive signal, and may be another signal indicating propeller noise.

For example, the propeller device 10 may include an optical sensor 15 (sensor) that outputs a detection signal indicating that the blades of the propeller 11 have passed in the vicinity to the control unit 91. In accordance with this, the control unit 91 may output the detection signal input from the optical sensor 15 to the signal processing circuit 93 as a reference signal.

Specifically, as shown by the broken lines in FIGS. 2 and 3B, the optical sensor 15 is arranged inside the peripheral surface 191 of the duct 19 and at a position facing the blades of the propeller 11. The optical sensor 15 includes, for example, a light emitting unit and a light receiving unit, irradiates light from the light emitting unit toward the propeller 11, and when the light receiving unit receives the reflected light, the blades of the propeller 11 have passed in the vicinity. The indicated detection signal is output to the control unit 91.

In this case, the signal processing circuit 93 generates a signal after performing signal processing on the detection signal output by the optical sensor 15 using a predetermined control coefficient as the first signal. Further, a signal having a phase different from that of the first signal is generated as the second signal. Therefore, even if the wind noise is included in the residual noise collected by the error microphone 14, the wind noise can be ignored and the noise having the same frequency component as the detection signal can be reduced.

Further, for example, when the drone 1 is flown in a windy environment, the propeller 11 may not rotate at the rotation speed indicated by the drive signal depending on the surrounding environment. In this case, if the drive signal is used as the reference signal as in the above embodiment, there is a possibility that the propeller noise actually generated cannot be reduced accurately. However, in this modification, the detection signal output at the timing corresponding to the speed at which the propeller 11 is actually rotating is used as the reference signal. Therefore, the propeller noise actually generated can be reduced more accurately than in the above embodiment.

Therefore, the control unit 91 further counts the number of times the detection signal is input from the optical sensor 15 per predetermined time (for example, 1 second), and divides the counted number of times by the number of blades of the propeller 11. The result may be measured as the rotation speed of the propeller 11.

Then, every time the test flight of the drone 1 was performed and the control coefficient used by the control filter 310 (FIG. 4) was updated by the convolution circuit 311 and the LMS calculator 312 (FIG. 4), the control unit 91 was updated. The control coefficient and the rotation speed of the propeller 11 measured when the control coefficient is updated may be associated with each other and stored in a memory or the like provided by the propeller.

Then, after the test flight, when the drone 1 is flying and the control coefficient associated with the rotation speed of the propeller 11 measured by the control unit 91 is stored in the memory, the convolution circuit 311 and the LMS The update of the control coefficient by the arithmetic unit 312 (FIG. 4) may be stopped. Then, the control coefficient associated with the rotation speed of the propeller 11 measured by the control unit 91, which is stored in the memory, may be used as the control coefficient used by the control filter 310.

In this way, the control filter 310 may be configured to use the (predetermined) control coefficients that are updated by the convolution circuit 311 and the LMS calculator 312 (FIG. 4) in the test flight and stored in the memory in advance. .. In this case, the chances of the convolution circuit 311 and the LMS calculator 312 (FIG. 4) executing the LMS algorithm for updating the control coefficients can be significantly reduced. As a result, the power supplied from the power supply unit 95 (FIG. 2) to the signal processing circuit 93 can be reduced. As a result, the electric power supplied from the power supply unit 95 (FIG. 2) to the motor 12 is reduced, so that it is possible to suppress the reduction in the time required for the drone 1 to fly.

Alternatively, the reference microphone may be arranged on the support portion 121 (FIG. 3B) to which the motor 12 is attached. Then, an audio signal indicating the sound collected by the reference microphone may be output to the control unit 91, and the control unit 91 may output the audio signal as a reference signal to the signal processing circuit 93. Alternatively, the audio signal may be output directly from the reference microphone to the signal processing circuit 93.

In this case, the signal after the signal processing circuit 93 performs signal processing on the voice signal indicating the sound collected by the reference microphone arranged in the vicinity of the propeller 11 using a predetermined control coefficient is the first signal. A signal having a phase different from that of the first signal is generated as a second signal. Therefore, even if the wind noise is included in the residual noise collected by the error microphone 14, the noise having the same frequency component as the sound collected in the vicinity of the propeller 11 is ignored by ignoring the wind noise. It can be reduced.

(3) FIG. 6 is a diagram showing a modified example of the arrangement position of the error microphone 14. The arrangement position of the error microphone 14 is not limited to the position shown in FIG. 3B. For example, as shown in FIG. 6, the error microphone 14 may be attached to the tip of an arm 193 attached to the lower end of the peripheral surface 191 of the duct 19 and forming a predetermined angle θ with the inner wall 192 of the peripheral surface 191 of the duct 19. Good. The predetermined angle θ is preferably 30 degrees or more.

In this case, it is possible to reduce the possibility that the error microphone 14 collects the wind noise generated by the wind generated by the rotation of the propeller 11 colliding with the error microphone 14 as residual noise. As a result, it is possible to reduce the possibility that the signal processing circuit 93 will generate a control sound signal that reduces wind noise.

(4) FIG. 7 is a circuit diagram showing a modified example of the signal processing circuit 93. As shown in FIG. 7, the signal processing circuit 93 has the sound pressure characteristic of the output sound from the first speaker 13-1 and the second of any one of the (m-1) second speakers 13-2. The first amplifier 32-1 is provided with a correction unit 34-1 that corrects the amplification factor (gain) when amplifying the first signal according to the difference from the sound pressure characteristic of the output sound by the speaker 13-2. It may be. In accordance with this, the signal processing circuit 93 sets the amplification factor when each second amplifier 32-2 amplifies the second signal according to the difference in the sound pressure characteristics of the output sound by each second speaker 13-2. A correction unit 34-2 for correction may be provided.

For example, it is assumed that the sound pressure characteristic of the output sound by the first speaker 13-1 is the characteristic of outputting the control sound at a sound pressure 1.1 times the sound pressure of the output sound by the first second speaker 13-2. Further, it is assumed that the sound pressure characteristics of the output sounds of the second speakers 13-2 from the second speaker to the (m-1) th speaker are the same. However, the sound pressure characteristic of the output sound from the first speaker 13-1 is 1.2 times the sound pressure of the output sound from the second speaker 13-2 from the second speaker to the (m-1) th speaker. It is assumed that it is a characteristic to be output.

In this case, the correction unit 34-1 connected to the first speaker 13-1 may correct the amplification factor of the first amplifier 32-1 by 1.2 times. Further, the correction unit 34-2 connected to the first second speaker 13-2 corrects the amplification factor of the second amplifier 32-2 connected to itself 1.2 / 1.1 times. do it.

According to the configuration of this modified embodiment, there is a difference between the sound pressure characteristic of the output sound of the first speaker 13-1 and the sound pressure characteristic of the output sound of the (m-1) second speakers 13-2. Even so, the amplification factor can be corrected so as to eliminate the difference. As a result, it is possible to eliminate variations in the sound pressure of the control sounds output from all the m speakers 13.

(5) In the above embodiment, the drone 1 has been described as an example of the embodiment of the propeller muffling device of the present disclosure, but the propeller muffling device of the present disclosure is not limited to the drone 1, but a propeller such as a personal computer and a projector It may be a device for rotating a propeller such as an electronic device having a cooling fan and a ventilation fan.

The propeller silencer of the present disclosure is useful for reducing noise generated by the rotation of a propeller regardless of the load capacity of the propeller device equipped with the propeller or the surrounding space.

1 Drone (silencer for propeller)
11 Propeller 111 Rotating axis 13 Speaker 13-1 First speaker 13-2 Second speaker 14 Error microphone 15 Optical sensor (sensor)
19 Duct 191 Peripheral surface 31 ANC control circuit 310 Control filter 311 Convolution circuit (coefficient update circuit)
312 LMS calculator (coefficient update circuit)
32-1 First amplifier (amplifier)
32-2 Second amplifier (amplifier)
33 Delay circuit 34 Correction unit 93 Signal processing circuit

Claims (9)

A propeller with multiple blades and
A duct with a peripheral surface surrounding the propeller and
A plurality of speakers arranged concentrically on the peripheral surface,
With one or more error microphones located outside the peripheral surface,
A signal processing circuit that generates a signal indicating a control sound to be output to the plurality of speakers, and
With
The number of the one or more error microphones is less than the number of the plurality of speakers.
The signal processing circuit outputs a first signal indicating a control sound to be output to the first speaker among the plurality of speakers so as to minimize the residual noise collected by the one or more error microphones. Of the plurality of speakers, a signal generated by using the sound transmission characteristics from one speaker to the one or more error microphones and having the phase of the first signal different by an amount corresponding to the number of blades is generated. Is generated as a second signal indicating a control sound to be output to a second speaker different from the first speaker.
Mute device for propellers. The plurality of speakers are arranged at equal intervals on the peripheral surface.
The amount corresponding to the number of blades is smaller as the number of blades is larger, and is smaller as the number of the plurality of speakers is larger, and the speaker exists between the first speaker and the second speaker. The larger the number, the larger
The muffling device for a propeller according to claim 1. The signal processing circuit
A control filter that performs signal processing using a predetermined control coefficient for the reference signal indicating noise generated by the rotation of the propeller, and
The control coefficient is updated so as to minimize the residual noise by using the reference signal, the sound transmission characteristic from the first speaker to the one or more error microphones, and the error signal indicating the residual noise. With a coefficient update circuit,
The output signal of the control filter is generated as the first signal.
The muffling device for a propeller according to claim 1 or 2. The reference signal is a drive signal for rotating the propeller.
The sound deadening device for a propeller according to claim 3. The reference signal is a detection signal indicating that it has been detected that any one of the plurality of blades has passed in the vicinity.
The sound deadening device for a propeller according to claim 3. The reference signal is an audio signal indicating a sound collected by a microphone arranged in the vicinity of the propeller.
The sound deadening device for a propeller according to claim 3. A propeller with multiple blades and
A duct with a peripheral surface surrounding the propeller and
A plurality of speakers arranged concentrically on the peripheral surface,
A signal processing circuit that generates a signal indicating a control sound to be output to the plurality of speakers, and
A sensor that outputs a detection signal indicating that any one of the plurality of blades has passed in the vicinity, and
With
The signal processing circuit includes a control filter that performs signal processing using a predetermined control coefficient for the detection signal, and outputs a control sound for outputting the output signal of the control filter to the first speaker among the plurality of speakers. A signal generated as the first signal to be shown and having the phases of the first signal differed by an amount corresponding to the number of blades is output to a second speaker different from the first speaker among the plurality of speakers. Generated as a second signal indicating the control sound,
The control coefficient causes the detection signal, the sound transmission characteristic from the first speaker to the position of a predetermined error microphone outside the peripheral surface, and the first speaker to output the control sound indicated by the first signal. It is predetermined to minimize the residual noise by using an error signal indicating the residual noise at the position of the error microphone.
Mute device for propellers. The signal processing circuit
An amplifier that amplifies a signal indicating a control sound to be output to the plurality of speakers with a predetermined gain, and
The amplifier amplifies the error microphone signal among the first signal and the second signal according to the difference between the sound pressure characteristic of the output sound from the first speaker and the sound pressure characteristic of the output sound from the second speaker. A correction unit that corrects the gain when
Further prepare
The sound deadening device for a propeller according to any one of claims 1 to 7. The propeller is a propeller provided in the drone.
The sound deadening device for a propeller according to any one of claims 1 to 8.