JP2019117360A - Acoustic device, acoustic controller and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it difficult to reduce the sound pressure of sound emitted by a piezoelectric element in an audio device. An acoustic device (1) includes a piezoelectric element (11) and a control unit (14). The piezoelectric element 11 receives a periodic drive voltage and vibrates, and outputs a sound having a sound pressure corresponding to the drive voltage. The control unit 14 controls the drive voltage. The control unit 14 controls the drive voltage so as to repeat the constant period T0 including the first period T1 and the second period T2. The first period T1 is a period in which the piezoelectric element 11 outputs the reference sound having the first sound pressure. The second period T2 is a period in which the piezoelectric element 11 outputs a sound having a second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element 11 is placed. [Selection diagram] Figure 1

Description

  The present disclosure generally relates to an acoustic device, an acoustic control device, and a program, and more particularly to an acoustic device, an acoustic control device, and a program using a piezoelectric element.

  Patent Document 1 discloses a ringing device (sound device) having a configuration in which a sound pressure is changed by giving a signal in which the duty ratio (duty ratio) is switched in the same cycle to the sounding body. The ringing device described in Patent Document 1 includes a sounding body that generates sound, a sounding body driving AMP for supplying a current of a level sufficient to drive the sounding body, and a sound pressure control circuit. There is. The sound pressure control circuit switches the duty ratio of the sound signal according to the sound pressure control signal.

Japanese Patent Application Laid-Open No. 11-153994

  In the ringing device described in Patent Document 1, for example, when the sounding body (piezoelectric element) is driven in a state where the sound pressure is maximized, the temperature of the environment in which the piezoelectric element is placed is increased to emit the piezoelectric element. The problem could occur that the sound pressure of the sound decreased.

  This indication is made in view of the above-mentioned point, and an object of the present indication is to provide an acoustic device, an acoustic control device, and a program in which sound pressure of a sound which a piezoelectric element emits in an acoustic device does not fall easily.

  An acoustic device according to an aspect of the present disclosure includes a piezoelectric element and a control unit. The piezoelectric element vibrates upon receiving a periodic drive voltage, and outputs a sound with a sound pressure corresponding to the drive voltage. The control unit controls the drive voltage. The control unit controls the drive voltage so as to repeat a fixed cycle including the first period and the second period. The first period is a period in which the piezoelectric element outputs the sound of the first sound pressure as a reference. The second period is a period in which the piezoelectric element outputs the sound of the second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element is placed.

  An acoustic control device according to an aspect of the present disclosure receives a periodic drive voltage to vibrate, and controls a drive voltage to be applied to a piezoelectric element that outputs a sound with a sound pressure corresponding to the drive voltage. The acoustic control device has a function of controlling the drive voltage so as to repeat a constant cycle including the first period and the second period. The first period is a period in which the piezoelectric element outputs the sound of the first sound pressure as a reference. The second period is a period in which the piezoelectric element outputs the sound of the second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element is placed.

  A program according to an aspect of the present disclosure is a program for controlling a drive voltage applied to a piezoelectric element that vibrates upon receiving a periodic drive voltage and outputs a sound with a sound pressure according to the drive voltage. The program causes the computer system to execute a process of controlling the drive voltage so as to repeat a fixed cycle including the first period and the second period. The first period is a period in which the piezoelectric element outputs the sound of the first sound pressure as a reference. The second period is a period in which the piezoelectric element outputs the sound of the second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element is placed.

  The present disclosure has the advantage that the sound pressure of the sound emitted by the piezoelectric element in the acoustic device does not easily decrease.

FIG. 1A is a block diagram showing a schematic configuration of an acoustic device according to an embodiment of the present disclosure. FIG. 1B is a conceptual diagram showing a change in drive frequency in the above-described acoustic device. FIG. 2 is a view showing a schematic configuration of a drive circuit and a piezoelectric element in the above-described acoustic device. FIG. 3A is a diagram showing a waveform of a drive voltage when the duty ratio of the first drive signal and the second drive signal is 50% in the acoustic device of the above. FIG. 3B is a diagram showing a waveform of a drive voltage when the duty ratio of the first drive signal and the second drive signal is 40% in the acoustic device of the above. FIG. 4 is a waveform diagram of the first drive signal and the second drive signal in the case where the environmental temperature is the first stage in the acoustic device of the above. FIG. 5A is a waveform diagram of the first drive signal and the second drive signal in the second period when the environmental temperature is the second stage in the acoustic device of the above. FIG. 5B is a waveform diagram of the first drive signal and the second drive signal in the second period when the environmental temperature is in the third stage in the acoustic device of the above. FIG. 6A is a waveform diagram of the first drive signal and the second drive signal in the second period in the case where the environmental temperature is the fourth stage in the acoustic device same as the above. FIG. 6B is a waveform diagram of the first drive signal and the second drive signal in the second period in the case where the environmental temperature is the fifth stage in the acoustic device of the above. FIG. 7 is another waveform diagram of the first drive signal and the second drive signal when the environmental temperature is the fourth stage in the acoustic device of the above.

(1) Outline Hereinafter, the outline of the acoustic device 1 of the present embodiment will be described with reference to FIGS. 1A and 1B. The sound device 1 of the present embodiment is a device that outputs a sound (for example, an alarm sound). The acoustic device 1 includes a piezoelectric element 11 and a control unit 14 as shown in FIG. 1A.

  The piezoelectric element 11 vibrates upon receiving the periodic drive voltage V1, and outputs a sound with a sound pressure corresponding to the drive voltage V1. In the present embodiment, when the piezoelectric element 11 receives the rectangular wave drive voltage V1 from the drive circuit 13 described later, it vibrates due to the piezoelectric effect, and the magnitude (amplitude) of the drive voltage V1 and the time for receiving the drive voltage V1. Output sound of sound pressure according to.

  The control unit 14 controls the drive voltage V1. In the present embodiment, the control unit 14 controls the magnitude of the drive voltage V1 by controlling a booster circuit 12 described later. The control unit 14 also controls the drive circuit 13 to control the duty ratio of the drive voltage V1, that is, the time for applying the drive voltage V1 to the piezoelectric element 11.

  Then, as shown in FIG. 1B, the control unit 14 controls the drive voltage V1 so as to repeat a constant cycle T0 including the first period T1 and the second period T2. The first period T1 is a period in which the piezoelectric element 11 outputs the sound of the first sound pressure as a reference. In the present embodiment, the first sound pressure is, for example, the maximum sound pressure that can be output by the piezoelectric element 11 when assuming that the drive frequency described later is constant. The second period T2 is a period in which the piezoelectric element 11 outputs a sound of a second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element 11 is placed. That is, in the second period T2, the second sound pressure output by the piezoelectric element 11 changes in accordance with the environmental temperature.

  The "environmental temperature" in the present disclosure may be the temperature of the piezoelectric element 11 itself. Further, the “environmental temperature” in the present disclosure may be, for example, the temperature in the case or the temperature outside the case when the piezoelectric element 11 is housed in the case. That is, the "environmental temperature" may be a temperature that directly or indirectly indicates the temperature of the piezoelectric element 11 itself.

  As described above, in the present embodiment, the piezoelectric element 11 outputs the sound of the first sound pressure in the first period T1 in the constant cycle T0, and in the second period T2, according to the environmental temperature, it outputs more than the first sound pressure. Output low second sound pressure sound. Therefore, in the present embodiment, for example, the sound of the maximum sound pressure that can be output by the piezoelectric element 11 can be suppressed compared to the case where the piezoelectric element 11 continues outputting, and as a result, the piezoelectric element 11 can be suppressed. There is an advantage that the output sound of the is difficult to reduce.

(2) Details Hereinafter, the acoustic device 1 of the present embodiment will be described using FIGS. 1A to 3B. The acoustic device 1 of the present embodiment includes a piezoelectric element 11, a booster circuit 12, a drive circuit 13, a control unit 14, and a temperature sensor 15. In the present embodiment, the piezoelectric element 11, the booster circuit 12, the drive circuit 13, the control unit 14, and the temperature sensor 15 are all housed in a common case. The sound output from the piezoelectric element 11 is output to the outside of the case, for example, through a sound hole provided in the case.

  The piezoelectric element 11 is a piezoelectric buzzer, and as shown in FIG. 2, is a bimorph type piezoelectric element in which a first piezoelectric plate 111 and a second piezoelectric plate 112 are provided on both sides in the thickness direction of the diaphragm 113. . The first piezoelectric plate 111 and the second piezoelectric plate 112 are electrically connected to a connection point between a first switching element Q1 and a third switching element Q3 of the drive circuit 13 described later. In other words, the first piezoelectric plate 111 and the second piezoelectric plate 112 are electrically connected to one end on the high voltage side of the booster circuit 12 through the first switching element Q1. The diaphragm 113 is electrically connected to a connection point between a second switching element Q2 and a second switching element Q4 of the drive circuit 13 described later. In other words, the diaphragm 113 is electrically connected to one end (reference potential) of the low voltage side of the booster circuit 12 via the fourth switching element Q4. The diaphragm 113 vibrates by applying a rectangular wave drive voltage V 1 between the first piezoelectric plate 111 and the second piezoelectric plate 112 and the diaphragm 113. The piezoelectric element 11 vibrates the diaphragm 113 according to the drive voltage V1 to output a sound with a sound pressure according to the drive voltage V1.

  The booster circuit 12 is a DC / DC converter, which boosts the input DC voltage and outputs the boosted DC voltage to the drive circuit 13. The booster circuit 12 includes a switching element. Then, the booster circuit 12 outputs a DC voltage of a magnitude corresponding to the control signal by switching on / off the switching element in accordance with a control signal from the control unit 14 described later. In the present embodiment, a DC voltage from a battery as a power supply of the acoustic device 1 is input to the booster circuit 12.

  The drive circuit 13 is a full bridge inverter including four switching elements Q1 to Q4 as shown in FIG. Hereinafter, the four switching elements Q1 to Q4 are also referred to as "first switching element Q1", "second switching element Q2", "third switching element Q3", and "fourth switching element Q4", respectively. The drive circuit 13 switches on / off of the switching elements Q1 to Q4 according to a first drive signal S1 and a second drive signal S2 from the control unit 14 described later, whereby the output voltage of the booster circuit 12 is a rectangular wave drive voltage. The voltage is converted into V1 and the drive voltage V1 is applied to the piezoelectric element 11. The first drive signal S1 and the second drive signal S2 are both PWM (Pulse Width Modulation) signals and are 180 degrees out of phase with each other. Therefore, the output voltage of the booster circuit 12 and a voltage obtained by inverting the polarity of the output voltage are alternately applied to the piezoelectric element 11.

  The control unit 14 is configured of, for example, a microcomputer whose main configuration is a processor and a memory. That is, the control unit 14 is realized by a computer system having a processor and a memory. The computer system functions as the control unit 14 by the processor executing an appropriate program. The program may be pre-recorded in a memory, or may be provided through a telecommunication line such as the Internet or in a non-transitory recording medium such as a memory card.

  The control unit 14 controls the drive voltage V1 by controlling the booster circuit 12 and the drive circuit 13. Specifically, control unit 14 applies control signal S0 to the switching element included in step-up circuit 12 to turn on / off the switching element, thereby controlling the magnitude of the output voltage of step-up circuit 12. The magnitude of the output voltage of the booster circuit 12 is substantially equal to the maximum value of the magnitude of the drive voltage V1. Further, the control unit 14 supplies the first drive signal S1 to the first switching element Q1 and the fourth switching element Q4 of the drive circuit 13 described later, and the second drive signal S2 described later of the second switching The element Q2 and the third switching element Q3 are provided. Thus, the control unit 14 applies the rectangular wave drive voltage V1 to the piezoelectric element 11 by turning on / off the switching elements Q1 to Q4 of the drive circuit 13.

  FIG. 3A shows the waveform of the drive voltage V1 when the duty ratio of the first drive signal S1 and the second drive signal S2 is 50%, as an example. FIG. 3B shows the waveform of the drive voltage V1 when the duty ratio of the first drive signal S1 and the second drive signal S2 is 40%, as an example.

  In the present embodiment, the frequency of the drive voltage V1 is equal to the switching frequency of the drive circuit 13, that is, the frequencies of the first drive signal S1 and the second drive signal S2. Hereinafter, the frequency of the drive voltage V1 (frequency of the first drive signal S1 and the frequency of the second drive signal S2) is also referred to as a “drive frequency”. Further, in the present embodiment, the “duty ratio of the drive voltage V1” is occupied by a period in which the drive voltage V1 is applied to the piezoelectric element 11 in one cycle of the drive voltage V1 (that is, a period when the drive voltage V1 is not zero). Say the percentage. The duty ratio of the drive voltage V1 corresponds to twice the duty ratio of the first drive signal S1 and the second drive signal S2. That is, the duty ratio of the drive voltage V1 shown in FIG. 3A is 50 × 2 = 100 [%], and the duty ratio of the drive voltage V1 shown in FIG. 3B is 40 × 2 = 80 [%]. In the present embodiment, when the magnitude of the drive voltage V1 is constant, the duty ratio of the drive voltage V1 is 100% (that is, the duty ratio of the first drive signal S1 and the second drive signal S2 is 50%). When it becomes, the sound pressure of the sound which the piezoelectric element 11 outputs becomes the largest.

  The temperature sensor 15 is a thermistor, and is mounted on a substrate housed in a case. The booster circuit 12, the drive circuit 13, and the control unit 14 are also mounted on this substrate. The temperature sensor 15 detects the environmental temperature in which the piezoelectric element 11 is placed directly or indirectly by detecting the temperature in the case. The detection result of the temperature sensor 15 is given to the control unit 14.

  The acoustic device 1 of the present embodiment is used, for example, as an on-vehicle device provided in a vehicle such as a car. In this case, the acoustic device 1 is an alarm in an intrusion detection system, and is installed at a location that is not easily visible, such as on a tire house (wheel well) of a vehicle. When the intrusion detection sensor provided in the vehicle detects an intrusion by a suspicious person, the sound device 1 generates an alarm sound to threaten the intruder or to notify the surrounding that there is an intruder. Do.

(3) Operation Hereinafter, the operation of the acoustic device 1 of the present embodiment will be described with reference to FIGS. 1B and 4 to 6B. In the present embodiment, when the predetermined condition is satisfied, the control unit 14 controls the drive voltage V1 so as to repeat the constant period T0 including the first period T1 and the second period T2, thereby the sound from the piezoelectric element 11 is generated. (In this case, an alarm sound) is output. In the present embodiment, the predetermined condition is that an intrusion detection sensor detects intrusion of a suspicious person. Further, in the present embodiment, the control unit 14 causes the piezoelectric element 11 to output sound for several tens of seconds after the predetermined condition is satisfied. Moreover, in the present embodiment, the fixed period T0 includes one first period T1 and one second period T2. That is, in the present embodiment, the control unit 14 controls the drive voltage V1 so as to alternately repeat the first period T1 and the second period T2.

  As shown in FIG. 1B and FIG. 4, the control unit 14 changes the drive frequency for each third period T3 in each of the first period T1 and the second period T2 to obtain a drive frequency from the first frequency f11 It is continuously changed to the second frequency f12. The third period T3 corresponds to one cycle of the first drive signal S1 and the second drive signal S2, and the length changes according to the drive frequency. That is, the third period T3 becomes shorter as the drive frequency increases from the first frequency f11 to the second frequency f12. As described above, the control unit 14 repeats control for continuously changing the sound output from the piezoelectric element 11 from bass to treble every sweep period T11. In the present embodiment, the sweep period T11 corresponds to the first period T1 and also corresponds to the second period T2. Further, in the present embodiment, the first frequency f11 is, for example, 2.6 kHz, and the second frequency f12 is, for example, 3.4 kHz. In FIG. 1B, although it appears that the drive frequency is changing in the third period T3, it is merely expressed in this way to represent a continuous change of the drive frequency, and in fact, The driving frequency is constant in the third period T3.

  As described above, in the present embodiment, the sound output from the piezoelectric element 11 is continuously changed from bass to treble, but this has the following advantages. For example, when the acoustic device 1 is an in-vehicle device, the sound output from the piezoelectric element 11 is output to the outside through a body or the like that constitutes a vehicle. Therefore, when the drive frequency substantially matches the resonance frequency determined by the piezoelectric element 11 and the vehicle, the sound output from the piezoelectric element 11 is most efficiently output to the outside of the vehicle. The resonant frequency is, for example, about 3 kHz.

  Here, since the resonance frequency varies depending on the type of vehicle, when the sound output from the piezoelectric element 11 is a single sound, that is, a sound with a constant drive frequency, the sound output from the piezoelectric element 11 may be out of the vehicle It may be difficult to output. Therefore, in the present embodiment, by continuously changing the drive frequency from the first frequency to the second frequency lower than the resonance frequency, the sound output from the piezoelectric element 11 can be transmitted to the outside of the vehicle regardless of the type of the vehicle. And make it easy to output.

  In the present embodiment, the control unit 14 controls the drive voltage V1 by controlling the booster circuit 12 and the drive circuit 13 based on data stored in the memory as shown in Table 1 below. The “drive voltage” in Table 1 represents the drive voltage V1 in the second period T2, and the drive voltage V1 in the first period T1 is constant at 65 [V]. The data shown in Table 1 is an example, and the control unit 14 may control the drive voltage V1 based on data different from the data shown in Table 1.

  In the first period T1, the control unit 14 sets the duty ratio of the first drive signal S1 and the second drive signal S2 to 50 [%] and the magnitude of the drive voltage V1 to 65 [V] regardless of the environmental temperature. As described above, the booster circuit 12 and the drive circuit 13 are controlled. Therefore, in the first period T1, the piezoelectric element 11 outputs the sound of the reference sound pressure (first sound pressure) regardless of the environmental temperature.

  In the second period T2, the control unit 14 drives the booster circuit 12 and the drive so as to change the duty ratio of the first drive signal S1 and the second drive signal S2 and the magnitude of the drive voltage V1 according to the environmental temperature. The circuit 13 is controlled. Therefore, in the second period T2, the piezoelectric element 11 outputs the sound of the second sound pressure lower than the first sound pressure according to the environmental temperature.

  Specifically, the control unit 14 reduces the second sound pressure in the second period T2 as the environmental temperature detected by the temperature sensor 15 increases. Here, the environmental temperature is divided into a plurality of (here, five) stages as shown in Table 1.

  The first stage is a stage when the environmental temperature is -40 [C] to 40 [C]. In the first stage, the control unit 14 sets the duty ratio of the first drive signal S1 and the second drive signal S2 to be 50% and the magnitude of the drive voltage V1 to be 65V in the second period T2. Control the booster circuit 12 and the drive circuit 13 (see FIG. 4). That is, in the first stage, the control unit 14 performs control similar to that in the first period T1 also in the second period T2. Therefore, in the first stage, the second sound pressure in the second period T2 is the same as the first sound pressure in the first period T1.

  The second stage is a stage where the ambient temperature is 41 ° C to 50 ° C. In the second stage, the control unit 14 controls the drive circuit 13 to reduce the duty ratio of the first drive signal S1 and the second drive signal S2 to 40% in the second period T2 (see FIG. 5A). ). Further, in the second stage, the control unit 14 controls the booster circuit 12 so as to maintain the magnitude of the drive voltage V1 in the first stage in the second period T2. For this reason, in the second stage, the second sound pressure in the second period T2 is lower than in the first stage. Therefore, in the second stage, the second sound pressure in the second period is lower than the first sound pressure in the first period T1.

  The third stage is a stage where the ambient temperature is 51 ° C to 60 ° C. In the third stage, the control unit 14 reduces the duty ratio of the first drive signal S1 and the second drive signal S2 to 30% and the magnitude of the drive voltage V1 to 55V in the second period T2. The booster circuit 12 and the drive circuit 13 are controlled so as to lower to (see FIG. 5B). Therefore, in the third stage, the second sound pressure in the second period T2 is lower than the first sound pressure in the first period T1, and compared with the second stage, the second sound pressure in the second period T2 2 Sound pressure is further reduced.

  The fourth stage is a stage when the ambient temperature is 61 ° C to 75 ° C. In the fourth stage, the control unit 14 controls the drive circuit 13 to lower the duty ratio of the first drive signal S1 and the second drive signal S2 to 20% in the second period T2 (see FIG. 6A). ). In the fourth stage, the control unit 14 controls the booster circuit 12 to maintain the magnitude of the drive voltage V1 in the third stage in the second period T2. Therefore, in the fourth step, the second sound pressure in the second period T2 is lower than the first sound pressure in the first period T1 and compared to the third step in the second period T2. Sound pressure is further reduced.

  The fifth step is a step when the environmental temperature is 76 ° C. or higher. In the fourth stage, the control unit 14 reduces the duty ratio of the first drive signal S1 and the second drive signal S2 to 10% and the magnitude of the drive voltage V1 to 40V in the second period T2. The booster circuit 12 and the drive circuit 13 are controlled so as to lower the voltage (see FIG. 6B). Therefore, in the fifth step, the second sound pressure in the second period T2 is lower than the first sound pressure in the first period T1, and compared with the fourth step, the second sound pressure in the second period T2 2 Sound pressure is further reduced.

(4) Advantages As described above, in the present embodiment, the piezoelectric element 11 outputs the sound of the first sound pressure in the first period T1 in the constant cycle T0, and in the second period T2, according to the environmental temperature. The sound of the second sound pressure lower than the sound pressure is output. Therefore, in the present embodiment, for example, the sound of the maximum sound pressure that can be output by the piezoelectric element 11 can be suppressed compared to the case where the piezoelectric element 11 continues to output, and the increase of the environmental temperature can be suppressed. There is an advantage that the sound output from the piezoelectric element 11 in the above is hardly reduced.

  The advantages will be specifically described below. The environmental temperature is raised mainly by the heat generation of the piezoelectric element 11 and the drive circuit 13. Then, in a state where the environmental temperature is excessively raised, the piezoelectric element 11 is also excessively heated to a temperature, and the piezoelectric plate (here, the first piezoelectric plate 111 and the second piezoelectric plate 111 are A crack may occur in the piezoelectric plate 112). If a crack is generated in the piezoelectric plate, the sound output from the piezoelectric element 11 may be reduced.

  Here, the piezoelectric element 11 generates heat mainly by mechanical vibration. And the piezoelectric element 11 outputs the sound of high sound pressure, so that a vibration is large. That is, the piezoelectric element 11 generates heat as the sound pressure of the sound to be output is higher.

  In addition, the drive circuit 13 generates heat mainly when current flows. A larger current flows in the drive circuit 13 as the sound pressure of the sound output from the piezoelectric element 11 is higher. That is, the drive circuit 13 generates heat as the sound pressure of the sound output from the piezoelectric element 11 is higher.

  And when the piezoelectric element 11 and the drive circuit 13 are accommodated in a case like this embodiment, the heat which the piezoelectric element 11 and the drive circuit 13 emit in a case is easy to be stagnant. For this reason, the environmental temperature rises with an increase in the amount of heat generation of the piezoelectric element 11 and the drive circuit 13. Therefore, in order to prevent the environmental temperature from rising excessively to such an extent that a crack is generated in the piezoelectric plate, it is necessary to control so that the amounts of heat generation of the piezoelectric element 11 and the drive circuit 13 do not increase excessively.

  So, in this embodiment, the 1st period T1 which outputs the 1st sound pressure used as a reference, and the 2nd period T2 which outputs the 2nd sound pressure lower than the 1st sound pressure according to environmental temperature are included. The drive voltage V1 is controlled so as to repeat the constant cycle T0. Therefore, in the present embodiment, the piezoelectric element 11 and the drive are not attenuated without attenuating the peak sound pressure (first sound pressure) (that is, while securing a period in which the sound of the first sound pressure is output at a constant period T0). It is possible to suppress the amount of heat generation of the circuit 13 and to suppress the rise of the environmental temperature.

(5) Modification The embodiment described above is only one of the various embodiments of the present disclosure. The above-mentioned embodiment can be variously changed according to design etc. if the object of the present disclosure can be achieved. For example, the acoustic device 1 may be the acoustic control device 100 including only the control unit 14 (see FIG. 1A). That is, the acoustic control device 100 according to an aspect vibrates by receiving the periodic drive voltage V1, and controls the drive voltage V1 applied to the piezoelectric element 11 that outputs the sound of the sound pressure according to the drive voltage V1. The acoustic control device 100 has a function of controlling the drive voltage V1 so as to repeat a constant cycle T0 including the first period T1 and the second period T2. The first period T1 is a period in which the piezoelectric element 11 outputs the sound of the first sound pressure as a reference. The second period T2 is a period in which the piezoelectric element 11 outputs a sound of a second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element 11 is placed.

  In addition, the same function as the control unit 14 may be embodied by a computer program or a non-temporary recording medium or the like recording the computer program. That is, the program according to one aspect is a program for controlling the drive voltage V1 applied to the piezoelectric element 11 that vibrates upon receiving the periodic drive voltage V1 and outputs a sound with a sound pressure according to the drive voltage V1. is there. The program causes the computer system to execute a process of controlling the drive voltage V1 so as to repeat a constant cycle T0 including the first period T1 and the second period T2. The first period T1 is a period in which the piezoelectric element 11 outputs the sound of the first sound pressure as a reference. The second period T2 is a period in which the piezoelectric element 11 outputs a sound of a second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element 11 is placed.

  Hereinafter, modifications of the above-described embodiment will be listed. The modifications described below can be applied in combination as appropriate.

  The acoustic device 1 in the present disclosure includes a computer system in the control unit 14. The computer system mainly includes a processor and memory as hardware. The processor executes the program stored in the memory of the computer system to implement the function as the control unit 14 in the present disclosure. The program may be pre-recorded in the memory of the computer system, may be provided through a telecommunication line, and recorded in a non-transitory recording medium such as a computer system-readable memory card, an optical disc, a hard disk drive, etc. It may be provided. A processor of a computer system is configured of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large scale integrated circuit (LSI). The plurality of electronic circuits may be integrated into one chip or may be distributed to a plurality of chips. The plurality of chips may be integrated into one device or may be distributed to a plurality of devices.

  In the above embodiment, the piezoelectric element 11 is not limited to a bimorph type piezoelectric element, and is a monomorph (unimorph) type piezoelectric element in which one piezoelectric plate is provided on one surface in the thickness direction of one diaphragm. May be In this case, the control unit 14 may be configured to supply only one of the first drive signal S1 and the second drive signal S2 to the drive circuit 13 by doubling the duty ratio.

  In the above-described embodiment, the control unit 14 changes the duty ratio of the first drive signal S1 and the second drive signal S2 and the magnitude of the drive voltage V1 in accordance with the environmental temperature, in the second period T2. The second sound pressure is changed, but the present invention is not limited to this. For example, the control unit 14 changes only the duty ratio of the first drive signal S1 and the second drive signal S2 according to the environmental temperature without changing the drive voltage V1, and thereby the second in the second period T2 is performed. Sound pressure may be changed. In addition, the control unit 14 changes only the magnitude of the drive voltage V1 according to the environmental temperature without changing the duty ratio of the first drive signal S1 and the second drive signal S2, in the second period T2. The second sound pressure may be changed.

  In the above-described embodiment, the control unit 14 changes the drive frequency every third period T3 in each of the first period T1 and the second period T2. And in the above-mentioned embodiment, as shown in Drawing 7, control part 14 may change sound pressure synchronizing with the 3rd period T3.

  In the example shown in FIG. 7, in each of the first period T1 and the second period T2, the duty ratio of the first drive signal S1 and the second drive signal S2 is 50 [%] in the first third period T3. On the other hand, in the second third period T3, the duty ratio of the first drive signal S1 and the second drive signal S2 is 20 [%]. As described above, the control unit 14 controls the drive voltage V1 so as to alternately repeat the third periods T3 having different sound pressures in each of the first period T1 and the second period T2. That is, here, the control unit 14 changes the sound pressure every third period T3. Of course, the control unit 14 may change the sound pressure for each of the plurality of third periods T3.

  Further, in the above-described embodiment, the control unit 14 changes the ratio of the first period T1 to the second period T2 (hereinafter, also simply referred to as a “ratio”) in the fixed cycle T0 according to the environmental temperature. The second sound pressure in the second period T2 may be changed. For example, the control unit 14 may increase the proportion of the second period T2 in the constant period T0 as the environmental temperature rises. In this case, the control unit 14 may change not only the ratio but also the duty ratio of the first drive signal S1 and the second drive signal S2 and the magnitude of the drive voltage V1 according to the environmental temperature. That is, the control unit 14 changes the duty ratio of the first drive signal S1 and the second drive signal S2, the magnitude of the drive voltage V1, and at least one of the ratio according to the environmental temperature, thereby the second period. The second sound pressure at T2 may be changed.

  In the above-described embodiment, the control unit 14 continuously changes the drive frequency from the first frequency f11 to the second frequency f12 in each of the first period T1 and the second period T2, but this is limited to this. It is not the purpose. For example, the control unit 14 discretely changes the drive frequency from the first frequency f11 to the second frequency f12 by making the third period T3 relatively long in each of the first period T1 and the second period T2. May be

  In the above-described embodiment, the control unit 14 may control the drive voltage V1 so as to have a constant drive frequency in each of the first period T1 and the second period T2. That is, the control unit 14 may control the drive voltage V1 so that the sound output from the piezoelectric element 11 is a single sound.

  In the above-mentioned embodiment, although acoustic device 1 is provided with temperature sensor 15, it is not the meaning limited to this. That is, the acoustic device 1 may incorporate the temperature sensor 15 or may be configured to receive a detection signal from an external temperature sensor. In the latter case, the control unit 14 may control the drive voltage V1 using the temperature detected by the external temperature sensor as the ambient temperature.

  In the above-mentioned embodiment, although the acoustic device 1 is provided with the booster circuit 12, it is not the meaning limited to this. For example, a voltage necessary to drive the piezoelectric element 11 can be supplied directly to the drive circuit 13, and the duty ratio of the first drive signal S1 and the second drive signal S2 alone can be used for the second period T2. When performing control to change the sound pressure, the booster circuit 12 is unnecessary.

  In the above-mentioned embodiment, although the drive circuit 13 is a full bridge type inverter, it is not the meaning limited to this. For example, if the piezoelectric element 11 is a monomorph type piezoelectric element as described above, the drive circuit 13 may not be a full bridge type inverter.

  In the above-mentioned embodiment, although drive circuit 13 is stored in the case of acoustic device 1, it is not the meaning limited to this. For example, the drive circuit 13 may be disposed outside the case. In this case, the heat generated by the drive circuit 13 is less likely to be transmitted to the inside of the case, so it is possible to suppress the rise of the environmental temperature. In order to miniaturize the acoustic device 1, it is desirable to dispose the drive circuit 13 in the case.

  In the above-mentioned embodiment, although acoustic device 1 is installed in vehicles, it is not the meaning limited to this. The acoustic device 1 is preferably installed in an environment where the temperature of the environment in which the acoustic device 1 is placed is likely to be raised by driving the acoustic device 1, such as a highly airtight place, for example.

  In the above-mentioned embodiment, although acoustic device 1 is used as an alarm for vehicles, it is not the meaning limited to this. For example, the acoustic device 1 is used as an alarm device for moving objects other than vehicles such as drones, flying objects such as airplanes, or ships, as well as moving objects running on land such as trains, linear motor cars, and autonomous traveling robots. May be

(Summary)
As described above, the acoustic device (1) according to the first aspect includes the piezoelectric element (11) and the control unit (14). The piezoelectric element (11) vibrates upon receiving a periodic drive voltage (V1), and outputs a sound with a sound pressure corresponding to the drive voltage (V1). The control unit (14) controls the drive voltage (V1). The control unit (14) controls the drive voltage (V1) to repeat a fixed cycle (T0) including the first period (T1) and the second period (T2). The first period (T1) is a period during which the piezoelectric element (11) outputs the sound of the first sound pressure as a reference. The second period (T2) is a period in which the piezoelectric element (11) outputs a sound of a second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element (11) is placed.

  According to this aspect, there is an advantage that the sound pressure of the sound emitted by the piezoelectric element (11) in the acoustic device (1) is hardly reduced.

  In the acoustic device (1) according to the second aspect, in the first aspect, the control unit (14) changes the duty ratio of the drive voltage (V1) to change the second sound pressure.

  According to this aspect, there is an advantage that the second sound pressure can be changed by simple control of changing the duty ratio of the drive voltage (V1).

  In the sound device (1) according to the third aspect, in the first or second aspect, the control unit (14) changes the magnitude of the drive voltage (V1) to change the second sound pressure.

  According to this aspect, there is an advantage that the second sound pressure can be changed by the simple control of changing the magnitude of the drive voltage (V1).

  In the sound device (1) according to the fourth aspect, in any of the first to third aspects, the control unit (14) drives in each of the first period (T1) and the second period (T2). The frequency (drive frequency) of the voltage (V1) is changed every third period (T3), and the sound pressure is changed in synchronization with the third period (T3).

  According to this aspect, there is an advantage that the sound pressure of the sound output from the piezoelectric element (11) can be changed in accordance with the change in the height of the sound output from the piezoelectric element (11).

  In the acoustic device (1) according to the fifth aspect, in the fourth aspect, the control unit (14) changes the sound pressure every third period (T3).

  According to this aspect, there is an advantage that the sound pressure of the sound output from the piezoelectric element (11) can be changed in accordance with the change in the height of the sound output from the piezoelectric element (11).

  In the sound device (1) according to the sixth aspect, in any of the first to fifth aspects, the control unit (14) selects a first period (T1) in a predetermined period (T0) according to the environmental temperature. And the second period (T2).

  According to this aspect, there is an advantage that it is easy to suppress the rise of the environmental temperature without reducing the second sound pressure.

  In the sound device (1) according to the seventh aspect, in any of the first to sixth aspects, the environmental temperature is divided into a plurality of stages. The control unit (14) reduces the second sound pressure as the environmental temperature rises.

  According to this aspect, there is an advantage that the control of the drive voltage (V1) becomes easy as compared with the case where the second sound pressure is continuously reduced according to the change of the environmental temperature.

  The acoustic control device (100) according to the eighth aspect vibrates upon receiving a periodic drive voltage (V1) and applies it to a piezoelectric element (11) that outputs a sound with a sound pressure corresponding to the drive voltage (V1). Control the driving voltage (V1). The acoustic control device (100) has a function of controlling the drive voltage (V1) so as to repeat a constant period (T0) including a first period (T1) and a second period (T2). The first period (T1) is a period during which the piezoelectric element (11) outputs the sound of the first sound pressure as a reference. The second period (T2) is a period in which the piezoelectric element (11) outputs a sound of a second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element (11) is placed.

  According to this aspect, even if the temperature of the environment in which the piezoelectric element (11) controlled by the acoustic control device (100) is raised, the sound pressure of the sound emitted by the piezoelectric element (11) is unlikely to decrease. It has the advantage of

  The program according to the ninth aspect vibrates upon receiving a periodic drive voltage (V1), and applies a drive voltage (V1) to a piezoelectric element (11) that outputs a sound with a sound pressure corresponding to the drive voltage (V1). ) Is a program for controlling the The program causes the computer system to execute a process of controlling the drive voltage (V1) so as to repeat a fixed cycle (T0) including the first period (T1) and the second period (T2). The first period (T1) is a period during which the piezoelectric element (11) outputs the sound of the first sound pressure as a reference. The second period (T2) is a period in which the piezoelectric element (11) outputs a sound of a second sound pressure lower than the first sound pressure according to the environmental temperature in which the piezoelectric element (11) is placed.

  According to this aspect, there is an advantage that the sound pressure of the sound emitted by the piezoelectric element (11) is hardly reduced even if the temperature of the environment in which the piezoelectric element (11) controlled by the program is increased.

  About the structure which concerns on a 2nd-7th aspect, it is not an essential structure for acoustic device (1), and can be abbreviate | omitted suitably.

DESCRIPTION OF SYMBOLS 1 acoustic apparatus 11 piezoelectric element 14 control part 15 temperature sensor 100 acoustic control apparatus T0 fixed period T1 1st period T2 2nd period T3 3rd period V1 drive voltage

Claims (9)

A piezoelectric element that vibrates upon receiving a periodic drive voltage and outputs a sound of sound pressure according to the drive voltage;
A control unit that controls the drive voltage;
The control unit
A first period in which the piezoelectric element outputs a sound of a first sound pressure as a reference;
A second period in which the piezoelectric element outputs a sound of a second sound pressure lower than the first sound pressure according to an environmental temperature in which the piezoelectric element is placed;
Controlling the drive voltage so as to repeat a fixed cycle including
Sound equipment. The control unit changes the second sound pressure by changing a duty ratio of the driving voltage.
An acoustic device according to claim 1. The control unit changes the magnitude of the driving voltage to change the second sound pressure.
The acoustic device according to claim 1. The control unit changes the frequency of the drive voltage every third period in each of the first period and the second period, and changes the sound pressure in synchronization with the third period.
The acoustic device according to any one of claims 1 to 3. The control unit changes the sound pressure every third period,
The acoustic device according to claim 4. The control unit changes a ratio between the first period and the second period in the predetermined cycle according to the environmental temperature.
The acoustic device according to any one of claims 1 to 5. The environmental temperature is divided into multiple stages,
The control unit reduces the second sound pressure as the environmental temperature rises.
The acoustic device according to any one of claims 1 to 6. An acoustic control device that controls a drive voltage applied to a piezoelectric element that vibrates upon receiving a periodic drive voltage and outputs a sound with a sound pressure according to the drive voltage,
A first period in which the piezoelectric element outputs a sound of a first sound pressure as a reference;
A second period in which the piezoelectric element outputs a sound of a second sound pressure lower than the first sound pressure according to an environmental temperature in which the piezoelectric element is placed;
Control the drive voltage to repeat a fixed cycle including
Acoustic control device. A program for controlling a drive voltage applied to a piezoelectric element that vibrates upon receiving a periodic drive voltage and outputs a sound with a sound pressure corresponding to the drive voltage,
Computer system,
A first period in which the piezoelectric element outputs a sound of a first sound pressure as a reference;
A second period in which the piezoelectric element outputs a sound of a second sound pressure lower than the first sound pressure according to an environmental temperature in which the piezoelectric element is placed;
Controlling the drive voltage so as to repeat a fixed cycle including
Program to run.

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