Object detection system

Abstract

The object detection system (1) includes a processing circuit (30) that performs object detection processing including wave transmission processing and determination processing. In the wave transmission processing, the sound wave generating device (10) is controlled to generate a series of sound waves (P1) with a frequency that varies with time at a target sound pressure, and the target sound pressure is associated with the frequencies corresponding to the series of sound waves (P1). In the determination processing, a received signal representing the sound waves received by the receiving device (20) from the object space is acquired, and the presence of an object in the object space is determined based on the received signal. Based on the frequency characteristics of the receiving device (20)'s sensitivity to a sound wave at a given sound pressure, the target sound pressure is set such that the sensitivity of the receiving device (20) to the sound wave at the target sound pressure is within a given range including a given value. The frequency of the series of sound waves (P1) varies within the given frequency range. The given value is the maximum value of the sensitivity of the receiving device (20) to the sound wave (P1) at a given sound pressure within the given frequency range.

Description

Technical Field

[0001] This disclosure generally relates to object detection systems. More specifically, this disclosure relates to object detection systems that utilize sound waves for object detection. Background Technology

[0002] Patent Document 1 discloses an object detection device (object detection system). The object detection device of Patent Document 1 uses multiple ultrasonic sensors to detect objects existing around a moving body based on reflected waves (echoes) received by the ultrasonic sensors (receiving devices). The ultrasonic sensors generate ultrasonic waves from an oscillator and generate a received signal along with the vibration of the oscillator.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-105703 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] This disclosure provides an object detection system that can improve the detection accuracy of objects.

[0008] Technical solutions for solving the problem

[0009] One aspect of this disclosure is an object detection system comprising: a sound wave generating device that generates sound waves by heating when energized; and a processing circuit that performs object detection processing to detect objects in an object space using the sound waves from the sound wave generating device. The object detection processing includes a wave transmission process and a determination process. In the wave transmission process, the sound wave generating device is controlled to generate a series of sound waves with frequencies varying over time at a target sound pressure level, and a correlation is established between the target sound pressure level and the frequencies corresponding to the series of sound waves. In the determination process, a received signal representing the sound waves received by the receiving device is obtained from a receiving device that receives sound waves from the object space, and an object is determined to exist in the object space based on the received signal. Based on the frequency characteristics of the receiving device's sensitivity to sound waves of a given sound pressure level, the target sound pressure level is set such that the sensitivity of the receiving device to sound waves of the target sound pressure level is within a given range including a given value. The frequencies of the series of sound waves vary within the given frequency range. The given value is the maximum value of the receiving device's sensitivity to sound waves of a given sound pressure level within the given frequency range.

[0010] One aspect of this disclosure is an object detection system comprising: a sound wave generating device that generates sound waves by heating when energized; and a processing circuit that performs object detection processing to detect objects in an object space using the sound waves from the sound wave generating device. The object detection processing includes a wave transmission process and a determination process. In the wave transmission process, the sound wave generating device is controlled to generate a series of sound waves with a target sound pressure level whose frequency varies over time, and the target sound pressure level is associated with the frequencies corresponding to the series of sound waves. In the determination process, a received signal representing the sound waves received by the receiving device is obtained from a receiving device that receives the sound waves from the object space, and an object is determined to exist in the object space based on the received signal. The frequency of the series of sound waves varies within a given frequency range. Based on the frequency characteristics of the receiving device's sensitivity to sound waves of a given sound pressure level, the target sound pressure level is set such that the sensitivity of the receiving device to sound waves of the target sound pressure level is consistent with a given value. The given value is the maximum value of the receiving device's sensitivity to sound waves of a given sound pressure level within the given frequency range.

[0011] Invention Effects

[0012] The method disclosed herein can improve the accuracy of object detection. Attached Figure Description

[0013] Figure 1 This is a block diagram illustrating a structural example of an object detection system according to one implementation method.

[0014] Figure 2 yes Figure 1 The circuit diagram of the acoustic wave generator in the object detection system is shown.

[0015] Figure 3 This is an explanation Figure 1 The timing diagram of the operation of the sound wave generating device.

[0016] Figure 4 It is shown Figure 1 The curve of the frequency characteristics of the receiving device of the object detection system.

[0017] Figure 5 This is a block diagram of the structure of the sound wave generating device in Modified Example 1.

[0018] Figure 6 This is a block diagram of the structure of the sound wave generating device in Modified Example 2. Detailed Implementation

[0019] (Implementation Method)

[0020] [1. Summary]

[0021] Previously, cross-correlation processing using cross-correlation functions was proposed as one method for high-precision object detection or distance measurement. In this method, the transmitted signal representing the sent sound wave and the received signal representing the echo are compared. The higher the consistency between the transmitted and received signals, the higher the S / N ratio becomes. When transmitting the sound wave, a linearly modulated frequency signal whose frequency varies with time is used, and the echo is received by a microphone. In this case, the sound pressure level of the sound wave has a flat frequency response with little variation relative to frequency, but the microphone has a frequency response with a large variation in sensitivity relative to frequency. Therefore, even if the frequency response of the sound pressure level is flat, the received signal will be distorted due to the microphone's frequency response. Thus, when comparing this distorted received signal with the transmitted signal, the S / N ratio decreases, and the accuracy of object detection and distance measurement decreases.

[0022] The purpose of the object detection system 1 described in this embodiment is to reduce the distortion of the received signal caused by the frequency characteristics of receiving devices such as microphones, and to improve the object detection accuracy.

[0023] Figure 1 This is a block diagram illustrating a structural example of the object detection system 1 according to this embodiment. The object detection system 1 is capable of detecting objects in an object space using sound waves. For example, the object detection system 1 is used to detect objects such as obstacles in a moving body. Examples of moving bodies include vehicles such as cars, unmanned aerial vehicles such as drones, and autonomous mobile robots. An example of an autonomous mobile robot is a cleaning robot.

[0024] like Figure 1 As shown, the object detection system 1 includes: a sound wave generating device 10 that generates sound waves by heating up when energized; and a processing circuit 30 that performs object detection processing to detect objects in an object space using sound waves from the sound wave generating device 10. The object detection processing includes a wave transmission process and a determination process. In the wave transmission process, the sound wave generating device 10 is controlled to generate a series of sound waves P1 with a target sound pressure level whose frequency varies over time, and the target sound pressure level is associated with the frequencies corresponding to the series of sound waves P1. In the determination process, a received signal representing the sound waves received by the receiving device 20 is acquired from the receiving device 20 that receives the sound waves from the object space, and the presence of an object in the object space is determined based on the received signal. Based on the frequency characteristics of the receiving device 20's sensitivity to sound waves of a given sound pressure level, a target sound pressure level is set such that the sensitivity of the receiving device 20 to the sound waves of the target sound pressure level is within a given range including the given value. The frequency of the series of sound waves P1 varies within the given frequency range. The given value is the maximum value of the sensitivity of the receiving device 20 to the sound wave P1 at a given sound pressure within a given frequency range.

[0025] Figure 1 The object detection system 1 can set the sound pressure of each of the series of sound waves P1 output from the sound wave generator 10, whose frequency varies with time, to a target sound pressure correlated with the frequency. In other words, the sound pressure can be set according to the frequency of the sound wave P1. Therefore, the influence of the frequency characteristics of the sensitivity of the receiving device 20 can be reduced, and the decrease in object detection accuracy caused by distortion of the received signal can be suppressed. As described above, the object detection system 1 can improve the object detection accuracy.

[0026] [2. Details]

[0027] The object detection system 1 will now be described with reference to the accompanying drawings. Figure 1 As shown, the object detection system 1 includes a sound wave generator 10, a wave receiver 20, and a processing circuit 30.

[0028] [2-1. Sound wave generating device]

[0029] Figure 1 The sound wave generating device 10 includes a sound wave source 11, a drive circuit 12, an adjustment circuit 13, and a control circuit 14.

[0030] The sound source 11 generates sound waves by heating up when energized. More specifically, the sound source 11 is a thermally excited element that generates sound waves by heating air. The sound source 11 is a so-called thermoelectric sound generator. The sound source 11 includes, for example, a heating element, a substrate, a pair of electrodes, and an insulating layer. The heating element is a resistive element that heats up by allowing current to flow through it. The heating element is disposed on the substrate, for example, so that it is in contact with air. The air surrounding the heating element expands or contracts according to the temperature change of the heating element. This generates air pressure waves, i.e., sound waves. The insulating layer suppresses heat conduction from the heating element to the substrate. The pair of electrodes are electrodes for allowing current to flow from the outside of the sound source 11 to the heating element. The pair of electrodes are disposed on both sides of the heating element. The sound source 11 may also have a conventionally known structure, therefore a detailed description of the sound source 11 is omitted.

[0031] Figure 2 This is a circuit diagram illustrating an example of the structure of the sound wave generator 10. (Example:) Figure 2 As shown, the sound source 11 is electrically connected between the DC power supply V1 and ground.

[0032] The DC power supply V1 includes various power circuits and / or batteries. These power circuits may include, for example, an AC / DC converter, a DC / DC converter, a regulator, and a battery. The voltage of the DC power supply V1 is, for example, 5V.

[0033] The drive circuit 12 supplies power to the sound source 11, causing the sound source 11 to generate sound waves. For example... Figure 2As shown, the drive circuit 12 includes a capacitor C1, a drive switching element T1, and a resistor R1.

[0034] Capacitor C1 is used to supply power to the sound source 11. Capacitor C1 is electrically connected between the DC power supply V1 and the connection point of the sound source 11 and ground. Capacitor C1 is, for example, an electrolytic capacitor or a ceramic capacitor.

[0035] A driving switch element T1 is used to drive the sound wave source 11 by controlling the power supply to it. The driving switch element T1 is electrically connected between the sound wave source 11 and ground. The driving switch element T1 is, for example, an n-type MOSFET. When the driving switch element T1 is turned on, power is supplied to the sound wave source 11. Figure 2 As shown by arrow A1, current flows from capacitor C1 to sound source 11, supplying power to sound source 11. If the drive switching element T1 is open, no power is supplied to sound source 11. By turning the drive switching element T1 on / off, sound source 11 generates sound wave P1. In this disclosure, "sound wave" is a periodic sine wave. In contrast, "a series of sound waves" is a multi-period sine wave.

[0036] Resistor R1 forms an overcurrent protection element electrically connected between capacitor C1 and DC power supply V1. Resistor R1 limits the current flowing directly from DC power supply V1 to sound source 11. Resistor R1 prevents excessive heating of sound source 11. The resistance value of resistor R1 is, for example, 50Ω or more and 5kΩ or less.

[0037] In the drive circuit 12, current flows from capacitor C1 to sound source 11, supplying power to sound source 11. Therefore, the sound pressure of the sound wave output from sound source 11 depends on the voltage V2 between the two ends of capacitor C1.

[0038] The adjustment circuit 13 adjusts the sound pressure of the sound wave from the sound wave generator 10 by adjusting the voltage V2 across capacitor C1 in the drive circuit 12. Figure 2 As shown, the adjustment circuit 13 includes an inductor L1, an adjustment switching element T2, and a diode D1. The inductor L1 is electrically connected between the DC power supply V1 and the capacitor C1. Figure 2 In this circuit, inductor L1 is electrically connected between resistor R1 (which serves as an overcurrent protection element) and DC power supply V1. Adjustment switch T2 is electrically connected in parallel with the series circuit of inductor L1 and DC power supply V1. Adjustment switch T2 is, for example, an n-type MOSFET. Inductor L1, DC power supply V1, and adjustment switch T2 form a closed loop. If adjustment switch T2 is turned on, energy is stored in inductor L1. Figure 2As shown by arrow A2, current flows through the closed loop of DC power supply V1, inductor L1, and adjusting switch element T2, accumulating energy in inductor L1. If the adjusting switch element T2 changes from closed to open, an induced electromotive force is generated in inductor L1. Therefore, as shown by arrow A3, current flows from inductor L1 to capacitor C1, charging capacitor C1. Figure 2 The adjustment circuit 13 can charge capacitor C1, thereby allowing adjustment of the voltage V2 across capacitor C1. The energy stored in inductor L1 is adjusted by regulating the period during which the switching element T2 is on. Diode D1 is electrically connected between inductor L1 and capacitor C1. Specifically, the anode of diode D1 is electrically connected to inductor L1, and the cathode of diode D1 is electrically connected to capacitor C1. Diode D1 reduces the possibility of current flowing from capacitor C1 to inductor L1, thus preventing accidental discharge of capacitor C1.

[0039] The control circuit 14 is configured to control the drive circuit 12 and the adjustment circuit 13. The control circuit 14 may include, for example, an oscillator for outputting the drive signals S1 and S2 described later. The control circuit 14 may be, for example, an integrated circuit such as an FPGA (field-programmable gate array). While controlling the switching of the drive switching element T1 of the drive circuit 12, causing the sound source 11 to generate a series of sound waves P1, the control circuit 14 also controls the adjustment circuit 13 to make the voltage V2 across the capacitor C1 of the drive circuit 12 a value corresponding to the target sound pressure level.

[0040] The control circuit 14 controls the switching (on / off) of the drive switching element T1 of the drive circuit 12. By controlling the drive switching element T1 of the drive circuit 12, the control circuit 14 executes the action of generating a series of sound waves P1 from the sound wave source 11.

[0041] like Figure 1 As shown, the control circuit 14 outputs a drive signal S1 to control the switching of the drive switching element T1. The switching frequency of the drive switching element T1 corresponds to the frequency of a series of sound waves P1. Therefore, in order to generate a series of sound waves P1 whose frequency varies with time, it is only necessary to change the switching frequency of the drive switching element T1 with time. The frequency of the series of sound waves P1 is set to vary within a given frequency range. The given frequency range is, for example, 20 kHz or higher and 150 kHz or lower. In this case, the switching frequency of the drive switching element T1 is also set to vary within this given frequency range.

[0042] In this embodiment, the driving switching element T1 is a MOSFET, and the driving signal S1 is input to the gate of the driving switching element T1. During the period when the driving signal S1 is high, the driving switching element T1 is turned on. During the period when the driving signal S1 is low, the driving switching element T1 is turned off. Figure 2 In the diagram, the drive signal S1 is represented as a DC power supply.

[0043] like Figure 3 As shown, the drive signal S1 is a pulse train with a period varying over time. Such a signal is, for example, called a linear frequency modulated (LFM) signal. The period of the pulse train of the drive signal S1 is set according to the switching frequency of the drive switching element T1. Figure 3 In this process, the period of the driving signal S1 increases with time to T11, T12, T13, ... . Therefore, Figure 3 The driving signal S1 is a pulse train with a period that increases with time. According to... Figure 3 The drive signal S1 drives the switching frequency of the switching element T1 to decrease over time, thereby outputting a series of sound waves P from the sound source 11 with a frequency decreasing over time. Furthermore, the length of the drive signal S1 can be set to, for example, 5ms to 30ms. The pulse width of the drive signal S1 is set according to the target duty cycle of the driving switching element T1.

[0044] The period of the drive signal S1 includes the on-time T1on and the off-time T1off of the drive switching element T1. The on-time T1on is the period during which the drive switching element T1 is turned on. During the on-time T1on, current flows from capacitor C1 to the sound source 11, supplying power to the sound source 11. The off-time T1off is the period during which the drive switching element T1 is turned off. During the off-time T1off, no current flows from capacitor C1 to the sound source 11, and no power is supplied to the sound source 11.

[0045] Control circuit 14 controls the switching (on / off) of the adjustment switching element T2 of adjustment circuit 13. By controlling the adjustment switching element T2 of adjustment circuit 13, control circuit 14 adjusts the voltage V2 across capacitor C1 in drive circuit 12. Figure 1 As shown, the control circuit 14 outputs a drive signal S2 to control the switching of the adjustment switching element T2. In this embodiment, the adjustment switching element T2 is a MOSFET, and the drive signal S2 is input to the gate of the adjustment switching element T2. During the period when the drive signal S2 is high, the adjustment switching element T2 is turned on. During the period when the drive signal S2 is low, the adjustment switching element T2 is turned off. Figure 2 In the diagram, the drive signal S2 is represented as a DC power supply.

[0046] During the on-time T1on, power is supplied to the sound source 11 from the capacitor C1, and the sound source 11 outputs a sound wave P1. Before the on-time T1on begins, the control circuit 14 adjusts the voltage V2 across the capacitor C1 via the adjustment circuit 13. In order to control the adjustment circuit 13 to adjust the voltage V2 across the capacitor C1, the control circuit 14 outputs a drive signal S2 to the adjustment switching element T2.

[0047] exist Figure 3 In this circuit, the drive signal S2 is a pulse train signal. Drive signal S2 is synchronized with drive signal S1. Therefore, the period of drive signal S2 is equal to the period of drive signal S1. For each period, the adjusting switch element T2 switches from on to off before the on-time T1on of the drive switch element T1. The period of drive signal S2 includes the on-time T2on and the off-time T2off of the adjusting switch element T2. The on-time T2on is the period during which the adjusting switch element T2 is on. During the on-time T2on, current flows from the DC power supply V1 to the inductor L1, where energy is stored. The off-time T2off is the period during which the adjusting switch element T2 is off. During the off-time T2off, current flows from the inductor L1 to the capacitor C1, where the capacitor C1 is charged. Therefore, the voltage V2 across capacitor C1 can be adjusted by the length of the on-time T2on. If the on-time T2on of the drive signal S2 is long, more energy can be stored in the inductor L1 of the adjustment circuit 13.

[0048] like Figure 3 As shown, the control circuit 14 switches the adjustment switch element T2 from on to off before the on-time T1on of the drive switch element T1. Therefore, the voltage V2 across the capacitor C1 can be set to a voltage corresponding to the on-time T2on of the adjustment switch element T2.

[0049] [2-2. Wave receiving device]

[0050] The receiving device 20 receives the sound wave and outputs the received signal representing the sound wave to the processing circuit 30. Figure 1 The receiving device 20 includes multiple (two in the illustrated example) microphones 21, multiple (two in the illustrated example) amplifier circuits 22, multiple (two in the illustrated example) filters 23, an AD converter 24, and a control circuit 25.

[0051] Microphone 21 is an acoustic-to-electrical conversion element that converts sound waves into electrical signals. If microphone 21 receives a sound wave, it outputs a received signal in analog form representing the received sound wave. Microphone 21 is used to detect sound waves reflected by an object after being output from sound source 11. Amplifier circuit 22 amplifies and outputs the received signal in analog form from microphone 21. Filter 23 allows signals in the passband containing the frequency band of the sound wave to pass through. Filter 23 is, for example, a bandpass filter. AD converter 24 converts the received signal in analog form, which has passed through filter 23, into a received signal in digital form and outputs it to control circuit 25. Microphone 21, amplifier circuit 22, filter 23, and AD converter 24 can also be conventionally known structures, therefore detailed descriptions are omitted.

[0052] Control circuit 25 controls AD converter 24, causing AD converter 24 to output the received signal in digital form to control circuit 25. Control circuit 25 outputs the received signal in digital form from AD converter 24 to processing circuit 30. Control circuit 25 is, for example, an integrated circuit such as an FPGA. Alternatively, control circuit 14 and control circuit 25 can be integrated into a single chip. For example, control circuit 14 and control circuit 25 can also be implemented by a single FPGA.

[0053] [2-3. Processing Circuit]

[0054] The processing circuit 30 is a circuit that controls the operation of the object detection system 1. The processing circuit 30 can be implemented, for example, by a computer system containing one or more processors (microprocessors) and one or more memories. The function of the processing circuit 30 is achieved by executing programs through one or more processors.

[0055] The processing circuit 30 performs object detection processing, which uses sound waves from the sound wave generator 10 to detect objects in the object space. The object detection processing includes wave transmission processing and determination processing.

[0056] In the wave transmission process, the sound wave generating device 10 is controlled to generate a series of sound waves P1 with a frequency that varies over time at a target sound pressure level. A correlation is established between the target sound pressure level and the frequencies corresponding to the series of sound waves P1. More specifically, in the wave transmission process, the voltage V2 across capacitor C1 is adjusted by adjustment circuit 13 so that the sound pressure of the sound waves P1 from the sound wave generating device 10 becomes the target sound pressure level. This drives the switching element T1 of the drive circuit 12, causing sound waves to be generated from the sound wave source 11. In the wave transmission process, for example, processing circuit 30 sends a command to control circuit 14, whereby control circuit 14 executes the control of drive circuit 12 and adjustment circuit 13. The establishment of the correlation between frequency and target sound pressure level will be described later in "[3. Establishment of Correlation between Frequency and Target Sound Pressure Level]".

[0057] In the determination process, a received signal representing the sound waves received by the receiving device 20 is acquired from the receiving device 20 that receives sound waves from the object space. For example, the received signal in digital form from the receiving device 20 is acquired in the determination process. If an object exists in the object space, the sound waves from the object space include a reflected wave (also called an echo) of the sound waves output from the sound wave generator 10 at the object. In the determination process, the presence of an object in the object space is determined based on the acquired received signal. In this embodiment, for example, in the determination process, if the peak value of the cross-correlation function representing a series of sound waves P1 and the received signal is above a threshold, it is determined that an object exists in the object space. For example, the main lobe of the cross-correlation function can be used as the peak value of the cross-correlation function. Furthermore, in the determination process, if it is determined that an object exists in the object space, the distance to the object is determined based on the received signal. In the determination process, for example, the distance to the object is calculated using Time of Flight (TOF) technology based on the peak occurrence time of the cross-correlation function of the transmitted and received signals. As mentioned above, the frequency of a series of sound waves P1 varies with time. In this case, compared to using a series of sound waves P1 with a frequency that does not change with time, that is, compared to using sound waves P1 with a fixed frequency, the sidelobes of the cross-correlation function can be reduced. Therefore, it becomes easier to distinguish the main lobe from the sidelobes of the cross-correlation function, thereby improving the accuracy of object detection. Furthermore, conventionally known techniques can be applied to the detection of objects using sound waves and the determination of the distance to the object, so detailed explanations are omitted.

[0058] [3. Establishing a correlation between frequency and target sound pressure level]

[0059] Reference Figure 4 The relationship between frequency and target sound pressure level is explained. Figure 4 This is a graph showing the frequency characteristics of the receiving device 20 in the object detection system 1. The frequency characteristics of the receiving device 20 are mainly determined by the frequency characteristics of the microphone 21 included in the receiving device 20. Figure 4In this context, G1 represents the frequency response of the receiving device 20 to a sound wave with a given sound pressure level. In other words, G1 shows the change in sensitivity of the receiving device 20 when the sound pressure level is fixed and the frequency of the sound wave varies. According to G1, the sensitivity at 60 kHz is lower than the sensitivity at 40 kHz. Since G1 represents a fixed, given sound pressure level, the sensitivity of the receiving device 20 can be adjusted by adjusting the sound pressure level of the sound wave P1 according to the frequency response of the microphone 21. Based on this, a target sound pressure level is set according to the frequency response of the receiving device 20 to a sound wave with a given sound pressure level. The target sound pressure level is set such that the sensitivity of the receiving device 20 to the sound wave with the target sound pressure level is within a given range including the given value Vs. As described above, the frequencies of a series of sound waves P1 vary within the given frequency range. The given frequency range is, for example, 40 kHz to 80 kHz. Figure 4 In the range of 40kHz to 80kHz, the sensitivity of the receiving device 20 is lower than the given value Vs. For example... Figure 4As shown in G2, it is preferable to set the target sound pressure level so that the sensitivity of the receiving device 20 is consistent with the given value Vs. In practice, the target sound pressure level can also be set so that the sensitivity of the receiving device 20 is within a given range that includes the given value Vs. The given value Vs is the maximum value within a given frequency range of the sensitivity of the receiving device 20 to the sound wave P1 at the given sound pressure level. This allows for a larger sensitivity within the given frequency range. In this case, the target sound pressure level of the sound wave at a frequency where the sensitivity of the receiving device 20 to the sound wave at the given sound pressure level is insufficient is set to be greater than the given sound pressure level. Alternatively, the given range can be set such that the given value Vs is between the upper limit and the middle value of the given range. That is, the upper limit of the given range can be above the given value, and the middle value of the given range can be below the given value. In this embodiment, the upper limit of the given range is the given value Vs (that is, the maximum value within a given frequency range of the sensitivity of the receiving device 20 to the sound wave P1 at the given sound pressure level). The lower limit of the given range is below a given value and greater than the minimum value of the sensitivity of the receiving device 20 to the sound wave P1 at a given sound pressure within a given frequency range. If the difference between the maximum and minimum values ​​of the sensitivity of the receiving device 20 to the sound wave P1 at a given sound pressure within a given frequency range is set as d, then the lower limit of the given range is Vs-k·d (0≤k<1). If k is 0.5 or less, the range of variation of the sensitivity of the receiving device 20 to the sound wave at the target sound pressure within a given frequency range can be set to less than half of the range of variation of the sensitivity of the receiving device 20 to the sound wave at a given sound pressure within a given frequency range. That is, the given range is narrower than the range of variation of the sensitivity of the receiving device 20 to the sound wave at a given sound pressure within a given frequency range. As a result, the influence caused by the frequency characteristics of the sensitivity of the receiving device 20 can be reduced, and the decrease in object detection accuracy caused by the distortion of the received signal can be suppressed. As a result, the object detection accuracy can be improved. Furthermore, the given range can also be ±10% of the given value Vs. That is, the lower limit of the given range can be 0.9 × Vs, and the upper limit of the given range can be 1.1 × Vs.

[0060] By establishing a correlation between frequency and target sound pressure in this way, the influence of the frequency characteristics of the receiver 20's sensitivity can be reduced, and the decrease in object detection accuracy caused by distortion of the received signal can be suppressed. As a result, object detection accuracy can be improved.

[0061] [4. Effects, etc.]

[0062] The object detection system 1 described above includes: a sound wave generating device 10, which generates sound waves by heating up when energized; and a processing circuit 30, which performs object detection processing to detect objects in an object space using the sound waves from the sound wave generating device 10. The object detection processing includes: a wave transmission process, controlling the sound wave generating device 10 such that it generates a series of sound waves P1 with a target sound pressure level whose frequency varies over time, and establishing a correlation between the target sound pressure level and the frequencies corresponding to the series of sound waves P1; and a determination process, acquiring a received signal representing the sound waves received by the received device 20 from the receiving device 20 that receives the sound waves from the object space, and determining whether an object exists based on the received signal. According to this structure, the object detection accuracy can be improved. Based on the frequency characteristics of the receiving device 20's sensitivity to sound waves of a given sound pressure level, a target sound pressure level is set such that the sensitivity of the receiving device 20 to the sound waves of the target sound pressure level is within a given range including the given value. The frequency of the series of sound waves P1 varies within the given frequency range. The given value is the maximum value of the sensitivity of the receiving device 20 to the sound wave P1 at a given sound pressure within a given frequency range.

[0063] Furthermore, in object detection system 1, the upper limit of the given range is above a given value, and the central value of the given range is below the given value. This structure improves the accuracy of object detection.

[0064] Furthermore, in object detection system 1, the lower limit of a given range is less than a given value, but greater than the minimum value of the sensitivity of the receiving device 20 to the sound wave P1 at a given sound pressure within a given frequency range. This structure improves the accuracy of object detection.

[0065] Furthermore, in object detection system 1, the upper limit of a given range is a given value. This structure improves the accuracy of object detection.

[0066] Furthermore, in the object detection system 1, the sensitivity of the receiving device 20 to a sound wave with a given sound pressure is insufficient for a target sound pressure greater than a given sound pressure for a sound wave of a frequency with a given sound pressure. Based on this structure, the object detection accuracy can be improved.

[0067] Furthermore, in object detection system 1, the given range is ±10% of a given value Vs. This structure improves the accuracy of object detection.

[0068] Furthermore, the object detection system 1 includes: a sound wave generating device 10 that generates sound waves by heating up when energized; and a processing circuit 30 that performs object detection processing to detect objects in an object space using sound waves from the sound wave generating device 10. The object detection processing includes: a wave transmission process that controls the sound wave generating device 10 to generate a series of sound waves P1 with a target sound pressure level whose frequency varies over time, establishing a correlation between the target sound pressure level and the frequencies corresponding to the series of sound waves P1; and a determination process that acquires a received signal representing the sound waves received by the receiving device 20 from the receiving device 20 that receives the sound waves from the object space, and determines whether an object exists based on the received signal. The frequency of the series of sound waves P1 varies within a given frequency range. Based on the frequency characteristics of the receiving device 20's sensitivity to sound waves at a given sound pressure level, a target sound pressure level is set such that the sensitivity of the receiving device 20 to sound waves at the target sound pressure level matches a given value. The given value is the maximum value within a given frequency range of the sensitivity of the receiving device 20 to a sound wave P1 at a given sound pressure. Based on this structure, the detection accuracy of objects can be improved.

[0069] Furthermore, in object detection system 1, during the determination process, if the peak value of the cross-correlation function representing a series of sound waves P1 (the transmitted and received signals) exceeds a threshold, an object is determined to exist. This structure improves the accuracy of object detection.

[0070] Furthermore, in the object detection system 1, during the determination process, if an object is determined to exist, the distance to the object is determined based on the received wave signal. Based on this structure, the distance to the object can be obtained.

[0071] Furthermore, in the object detection system 1, the sound wave generating device 10 includes: a drive circuit 12 having a capacitor C1 charged by a DC power supply V1 and a drive switching element T1 that supplies power from the capacitor C1 to a sound wave source 11 that generates sound waves by heating when energized; and an adjustment circuit 13 that adjusts the sound pressure of the sound wave from the sound wave generating device 10 by adjusting the voltage V2 across the capacitor C1 in the drive circuit 12. In the wave transmission process, the voltage V2 across the capacitor C1 is adjusted by the adjustment circuit 13 to make the sound pressure of the sound wave from the sound wave generating device 10 the target sound pressure, thereby driving the drive switching element T1 of the drive circuit 12 to generate sound waves from the sound wave source 11. With this structure, the sound pressure of the sound wave output from the sound wave generating device 10 can be easily adjusted.

[0072] Furthermore, in the object detection system 1, the adjustment circuit 13 includes: an inductor L1 electrically connected between a DC power supply V1 and a capacitor C1; and an adjustment switch element T2 electrically connected in parallel with the series circuit of the inductor L1 and the DC power supply V1. The adjustment circuit 13 adjusts the voltage V2 across the capacitor C1 by adjusting the on-time T2on of the adjustment switch element T2. This structure simplifies the circuit configuration.

[0073] Furthermore, in the object detection system 1, the adjustment circuit 13 includes a diode D1, the anode of which is electrically connected to the inductor L1, and the cathode of which is electrically connected to the capacitor C1. This structure reduces the possibility of current flowing from the capacitor C1 to the inductor L1, thus accidentally discharging the capacitor C1.

[0074] Furthermore, in the object detection system 1, the adjustment switch element T2 switches from on to off before the on-time T1on of the drive switch element T1. According to this structure, the adjustment of the sound pressure level of the sound wave becomes easy.

[0075] Furthermore, in the object detection system 1, the switching frequency of the drive switching element T1 is 20 kHz or higher. This structure improves the object detection accuracy.

[0076] (Modified Example)

[0077] The embodiments disclosed herein are not limited to the embodiments described above. Various modifications can be made to the embodiments described above, depending on the design, etc., as long as the objectives of this disclosure are achieved. Hereinafter, variations of the embodiments described above are given. The variations described below can be appropriately combined and applied.

[0078] [1. Variation Example 1]

[0079] Figure 5 This is a circuit diagram of a structural example of the sound wave generator 10A, as shown in Modification 1. The sound wave generator 10A includes a sound wave source 11, a drive circuit 12A, and an adjustment circuit 13A. Like the sound wave generator 10, the sound wave generator 10A also includes a control circuit 14, but... Figure 5 The diagram of control circuit 14 is omitted.

[0080] The drive circuit 12A has a drive switching element T1 that supplies power to a sound source 11 from a given capacitor. The sound source 11 heats up and generates sound waves when energized. The drive switching element T1 controls the power supply to the sound source 11. The drive switching element T1 is connected between the sound source 11 and ground. If the drive switching element T1 is on, power is supplied to the sound source 11. If the drive switching element T1 is off, no power is supplied to the sound source 11. By turning the drive switching element T1 on / off, the sound source 11 generates sound waves. The drive switching element T1 is, for example, an n-type MOSFET.

[0081] The adjustment circuit 13A adjusts the sound pressure of the sound wave from the sound wave generator 10 by selecting at least one of a plurality of capacitors C1-1 to C1-3 (hereinafter referred to as C1 in the drawing) that are charged by a plurality of DC power supplies V1-1 to V1-3 (hereinafter collectively referred to as V1) with different voltages as a given capacitor. Figure 5 As shown, the adjustment circuit 13A includes multiple capacitors C1-1 to C1-3 and a switching circuit 131.

[0082] Multiple capacitors C1-1 to C1-3 are charged by multiple DC power supplies V1-1 to V1-3 with different voltages. Capacitor C1 is used to supply power to the sound source 11. Capacitor C1 is electrically connected between the connection point of the DC power supply V1 and the sound source 11 and ground. Capacitor C1 is charged by the DC power supply V1. Capacitor C1 is, for example, an electrolytic capacitor or a ceramic capacitor.

[0083] The switching circuit 131 selects a power supply source from a plurality of capacitors C1 to supply power to the sound source 11. More specifically, the switching circuit 131 electrically connects at least one of the plurality of capacitors C1 to the sound source 11, such that the sound generating device 10A generates sound waves with a target sound pressure level correlated with a frequency. For example, multiple groups of capacitors C1 and DC power supply V1 are used to achieve target sound pressure levels correlated with different frequencies.

[0084] like Figure 5 As shown, the switching circuit 131 includes multiple (three in the illustrated example) switches SW1-1 to SW1-3 (hereinafter referred to collectively as SW1). The multiple switches SW1'1 to SW1-3 are electrically connected between the sound source 11 and the multiple capacitors C1-1 to C1-3. In the switching circuit 131, one of the multiple switches SW1-1 to SW1-3 is set to ON, and the others are set to OFF. Thus, one of the multiple capacitors C1-1 to C1-3 is electrically connected to the sound source 11.

[0085] Control circuit 14 controls the switching circuit 131 of drive circuit 12A and adjustment circuit 13A. Control circuit 14 controls the switch SW1 of switching circuit 131, thereby electrically connecting at least one of the multiple capacitors C1 to sound source 11, so that sound wave generating device 10 generates a series of sound waves P1 with a frequency that varies with time at the target sound pressure, and a correlation is established between the target sound pressure and the frequencies corresponding to the series of sound waves P1.

[0086] When the object detection system 1 is equipped with a sound wave generator 10A, the processing circuit 30 controls the control circuit 14 of the sound wave generator 10A to perform the following wave transmission process. In the wave transmission process, the adjustment circuit 13A selects a capacitor C1 corresponding to the target sound pressure from a plurality of capacitors C1 as a given capacitor, and drives the drive switching element T1 of the drive circuit 12A to generate a sound wave from the sound wave source 11.

[0087] In this way, the object detection system 1 can set the sound pressure of each of the series of sound waves P1 output from the sound wave generator 10A, whose frequency varies with time, to a target sound pressure correlated with the frequency. That is, the sound pressure can be set according to the frequency of the sound wave P1. Therefore, the influence of the frequency characteristics of the sensitivity of the receiving device 20 can be reduced, and the decrease in object detection accuracy caused by the distortion of the received signal can be suppressed. As described above, the object detection system 1 can improve the object detection accuracy.

[0088] In the object detection system 1 described above, the sound wave generating device 10A includes: a drive circuit 12A having a drive switching element T1 that supplies power from a given capacitor C1 to a sound wave source 11 that generates sound waves by heating when energized; and an adjustment circuit 13A that adjusts the sound pressure of the sound wave from the sound wave generating device 10A by selecting at least one of a plurality of capacitors C1 charged by a plurality of DC power supplies V1 with different voltages as the given capacitor C1. In the wave transmission process, the adjustment circuit 13A selects a capacitor C1 corresponding to the target sound pressure from the plurality of capacitors C1 as the given capacitor C1, and drives the drive switching element T1 of the drive circuit 12A to generate sound waves from the sound wave source 11. With this structure, the sound pressure of the sound wave output from the sound wave generating device 10A can be easily adjusted.

[0089] [2. Variation Example 2]

[0090] Figure 6This is a circuit diagram of the structure of the sound wave generator 10B, which is a modified example 2. The sound wave generator 10B includes multiple (three in the illustrated example) sound wave sources 11-1 to 11-3 (hereinafter collectively referred to as 11), a drive circuit 12, and an adjustment circuit 13B. The sound wave generator 10B, like the sound wave generator 10, includes a control circuit 14, but... Figure 6 The diagram of control circuit 14 is omitted.

[0091] Multiple sound wave sources 11-1 to 11-3 are electrically connected between the DC power supply V1 and ground. For example... Figure 6 As shown, multiple sound wave sources 11-1 to 11-3 are connected in parallel.

[0092] The drive circuit 12 includes a capacitor C1 charged by a DC power supply V1 and a drive switching element T1 that supplies power from the capacitor C1 to a given sound source 11. A given sound source 11 is selected from a plurality of sound sources 11-1 to 11-3. The drive circuit 12 supplies power to the given sound source 11, causing the given sound source 11 to generate sound waves. Furthermore, the drive circuit 12 includes a resistor R1. The resistor R1 constitutes an overcurrent protection element electrically connected between the capacitor C1 and the DC power supply V1.

[0093] The adjustment circuit 13B adjusts the sound pressure level of the sound wave from the sound wave generating device 10B by selecting at least one of the plurality of sound wave sources 11-1 to 11-3 as a given sound wave source 11. For example... Figure 6 As shown, the adjustment circuit 13B selects the destination of the power supply from the capacitor C1 from a plurality of sound wave sources 11-1 to 11-3. More specifically, the adjustment circuit 13B electrically connects at least one of the plurality of sound wave sources 11-1 to 11-3 to the capacitor C1, such that the sound wave generating device 10B generates sound waves with a target sound pressure level correlated with a frequency. The plurality of sound wave sources 11 are used to achieve target sound pressure levels correlated with different frequencies.

[0094] like Figure 6 As shown, the adjustment circuit 13B includes multiple (three in the illustrated example) switches SW2-1 to SW2-3 (hereinafter referred to collectively as SW2). The multiple switches SW2-1 to SW2-3 are electrically connected between the multiple sound wave sources 11-1 to 11-3 and the capacitor C. In the adjustment circuit 13B, one of the multiple switches SW2-1 to SW2-3 is set to ON, and the others are set to OFF. Thus, one of the multiple sound wave sources 11-1 to 11-3 is electrically connected to the capacitor C1.

[0095] The control circuit 14 controls the drive circuit 12 and the adjustment circuit 13B. The control circuit 14 controls the switch SW2 of the adjustment circuit 13B, thereby electrically connecting at least one of the plurality of sound wave sources 11 to the capacitor C1, so that the sound wave generating device 10B generates sound waves with a target sound pressure that is correlated with the frequency.

[0096] When the object detection system 1 is equipped with a sound wave generator 10B, the processing circuit 30 controls the control circuit 14 of the sound wave generator 10B to perform the following wave transmission process. In the wave transmission process, the adjustment circuit 13B selects a sound wave source 11 corresponding to the target sound pressure from a plurality of sound wave sources 11 as a given sound wave source 11, and drives the drive switching element T1 of the drive circuit 12 to generate a sound wave from the given sound wave source 11.

[0097] In this way, the object detection system 1 can set the sound pressure of each of the series of sound waves P1 output from the sound wave generator 10B, whose frequency varies with time, to a target sound pressure correlated with the frequency. That is, the sound pressure can be set according to the frequency of the sound waves P1. Therefore, the influence of the frequency characteristics of the sensitivity of the receiving device 20 can be reduced, and the decrease in object detection accuracy caused by distortion of the received signal can be suppressed. As described above, the object detection system 1 can improve the object detection accuracy.

[0098] In the object detection system 1 described above, the sound wave generating device 10B includes: a plurality of sound wave sources 11, each of which heats up when energized and generates sound waves with different sound pressures; a drive circuit 12, having a capacitor C1 charged by a DC power supply V1 and a drive switching element T1 that supplies power from the capacitor C1 to a given sound wave source 11; and an adjustment circuit 13B, which adjusts the sound pressure of the sound wave from the sound wave generating device 10B by selecting at least one of the plurality of sound wave sources 11 as the given sound wave source 11. In the wave transmission process, the adjustment circuit 13B selects a sound wave source 11 corresponding to the target sound pressure from the plurality of sound wave sources 11 as the given sound wave source 11, and drives the drive switching element T1 of the drive circuit 12 to generate a sound wave from the given sound wave source 11. According to this structure, the sound pressure of the sound wave output from the sound wave generating device 10B can be easily adjusted.

[0099] [3. Other variations]

[0100] In the above embodiment, the frequency of a series of sound waves P decreases with time, but it is not limited to this and can also increase with time.

[0101] In one variation, the given value may not be a representative value within a given frequency range of the sensitivity of the receiving device 20 to the sound wave at a given sound pressure. That is, the given value may be any desired value. However, if the given value is a representative value within a given frequency range of the sensitivity of the receiving device 20 to the sound wave at a given sound pressure, the difference between the given sound pressure and the target sound pressure can be reduced, making it easier to set the target sound pressure.

[0102] In one variation, a given range is set by considering the frequency characteristics of the sensitivity of the receiving device 20 to a sound wave of a given sound pressure, so that the influence caused by the frequency characteristics of the sensitivity of the receiving device 20 can be reduced.

[0103] In Modification 1, the number of DC power supplies V1 and the number of capacitors C1 are not particularly limited. Adjustment circuit 13A can also connect two or more capacitors C1 to the sound source 11 as needed. In Modification 1, multiple capacitors C1 are connected in parallel with the sound source 11, but they can also be connected in series with the sound source 11. In this case, the number of capacitors C1 connected in series can be changed by switching circuit 131, thereby adjusting the voltage applied to the sound source 11. The structure of Modification 1 can also be applied to sound wave generating device 10 and sound wave generating device 10B.

[0104] In Modification 2, the number of sound wave sources 11 is not particularly limited. The adjustment circuit 13B can also connect two or more sound wave sources 11 to the capacitor C1 as needed. In Modification 2, multiple sound wave sources 11 are connected in parallel with the capacitor C1, but they can also be connected in series with the capacitor C1. In this case, the number of multiple sound wave sources 11 connected in series can be changed by adjusting the adjustment circuit 13B, thereby adjusting the sound pressure. The structure of Modification 2 can also be applied to the sound wave generating device 10 and the sound wave generating device 10A.

[0105] In a variation, other overcurrent protection components can be used instead of resistor R1. Examples of overcurrent protection components include current fuses, fusible resistors, and bimetallic components. However, overcurrent protection components are not always necessary.

[0106] (Way)

[0107] As can be seen from the above embodiments and variations, this disclosure includes the following methods. Hereinafter, reference numerals are used in parentheses only to illustrate the correspondence with the embodiments.

[0108] The first method is an object detection system (1), comprising: a sound wave generating device (10; 10A; 10B) that generates sound waves by being powered on; and a processing circuit (30) that performs object detection processing to detect objects in an object space using sound waves from the sound wave generating device (10; 10A; 10B). The object detection processing includes: a wave transmission process that controls the sound wave generating device (10; 10A; 10B) to generate a series of sound waves (P1) with a target sound pressure level whose frequency varies with time, wherein the target sound pressure level is associated with the frequencies corresponding to the series of sound waves (P1); and a determination process that obtains a received signal representing the sound waves received by the received device (20) from a receiving device (20) that receives sound waves from the object space, and determines whether the object exists based on the received signal. Based on the frequency characteristics of the sensitivity of the receiving device (20) to a sound wave of a given sound pressure, the target sound pressure is set such that the sensitivity of the receiving device (20) to the sound wave of the target sound pressure is within a given range including a given value. The frequency of the series of sound waves (P1) varies within the given frequency range. The given value is the maximum value of the sensitivity of the receiving device (20) to the sound wave (P1) of the given sound pressure within the given frequency range. In this manner, the detection accuracy of objects can be improved.

[0109] The second method is an object detection system (1) based on the first method. In the second method, the upper limit of the given range is above the given value, and the middle value of the given range is below the given value. According to this method, the object detection accuracy can be improved.

[0110] The third method is an object detection system (1) based on either the first or second method. In the third method, the lower limit of the given range is below the given value and greater than the minimum value of the sensitivity of the receiving device to the sound wave of a given sound pressure within the given frequency range. According to this method, the detection accuracy of the object can be improved.

[0111] The fourth method is an object detection system (1) based on the third method. In the fourth method, the upper limit of the given range is the given value. According to this method, the object detection accuracy can be improved.

[0112] The fifth method is an object detection system (1) based on either the third or fourth method. In the fifth method, the sensitivity of the receiving device (20) to a sound wave with a given sound pressure is insufficient for a target sound pressure greater than the given sound pressure of a sound wave at a given frequency. According to this method, the detection accuracy of the object can be improved.

[0113] The sixth method is an object detection system (1) based on the first method. In the sixth method, the given range is a range of ±10% of the given value. According to this method, the object detection accuracy can be improved.

[0114] The seventh method is an object detection system (1), comprising: a sound wave generating device (10; 10A; 10B) that generates sound waves by being energized; and a processing circuit (30) that performs object detection processing to detect objects in an object space using sound waves from the sound wave generating device (10; 10A; 10B). The object detection processing includes: a wave transmission process that controls the sound wave generating device (10; 10A; 10B) to generate a series of sound waves (P1) with a target sound pressure level whose frequency varies over time, wherein the target sound pressure level is associated with the frequencies corresponding to the series of sound waves (P1); and a determination process that obtains a received signal representing the sound waves received by the received device (20) from a receiving device (20) receiving sound waves from the object space, and determines whether the object exists based on the received signal. The frequency of the series of sound waves (P1) varies within a given frequency range. Based on the frequency characteristics of the sensitivity of the receiving device (20) to a sound wave of a given sound pressure, the target sound pressure is set such that the sensitivity of the receiving device (20) to the sound wave of the target sound pressure is consistent with the given value. The given value is the maximum value of the sensitivity of the receiving device (20) to the sound wave (P1) of the given sound pressure within the given frequency range. In this manner, the detection accuracy of the object can be improved.

[0115] The eighth method is an object detection system (1) based on any one of the methods 1 to 7. In the eighth method, during the determination process, if the peak value of the cross-correlation function representing the transmitted signal and the received signal of the series of sound waves (P1) is above a threshold, then the presence of the object is determined. According to this method, the object detection accuracy can be improved.

[0116] The ninth method is an object detection system (1) based on any one of the first to eighth methods. In the ninth method, the sound wave generating device (10) includes: a drive circuit (12) having a capacitor (C1) charged by a DC power supply (V1) and a drive switching element (T1) that supplies power from the capacitor (C1) to a sound wave source (11) that generates sound waves by heating up when energized; and an adjustment circuit (13) that adjusts the sound pressure of the sound wave from the sound wave generating device (10) by adjusting the voltage (V2) between the two ends of the capacitor (C1) of the drive circuit (12). In the wave transmission process, the voltage (V2) between the two ends of the capacitor (C1) is adjusted by the adjustment circuit (13) so that the sound pressure of the sound wave from the sound wave generating device (10) becomes the target sound pressure, and the drive switching element (T1) of the drive circuit (12) is driven to generate sound waves from the sound wave source (11). According to this method, the sound pressure of the sound wave output from the sound wave generator (10) can be easily adjusted.

[0117] The tenth method is an object detection system (1) based on the ninth method. In the tenth method, the adjustment circuit (13) includes: an inductor (L1) electrically connected between the DC power supply (V1) and the capacitor (C1); and an adjustment switch element (T2) electrically connected in parallel with the series circuit of the inductor (L1) and the DC power supply (V1). The adjustment circuit (13) adjusts the voltage (V2) across the capacitor (C1) by the on-time (T2on) of the adjustment switch element (T2). According to this method, the circuit structure can be simplified.

[0118] The 11th method is an object detection system (1) based on the 10th method. In the 11th method, the adjustment circuit (13) has a diode (D1), the anode of which is electrically connected to the inductor (L1), and the cathode of which is electrically connected to the capacitor (C1). According to this method, the possibility of the capacitor (C1) accidentally discharging due to current flowing from the capacitor (C1) to the inductor (L1) can be reduced.

[0119] The 12th method is an object detection system (1) based on the 10th or 11th method. In the 12th method, the adjustment switch element (T2) is turned on during the on-time (T1on) of the drive switch element (T1), and simultaneously switches on with the drive switch element (T1). According to this method, the adjustment of the sound pressure of the sound wave becomes easier.

[0120] The 13th method is an object detection system (1) based on any one of the 1st to 8th methods. In the 13th method, the sound wave generating device (10A) includes: a drive circuit (12A) having a drive switching element (T1) that supplies power from a given capacitor (C1) to a sound wave source (11) that generates sound waves by heating up when energized; and an adjustment circuit (13A) that adjusts the sound pressure of the sound wave from the sound wave generating device (10A) by selecting at least one of a plurality of capacitors (C1) charged by a plurality of DC power supplies (V1) with different voltages as the given capacitor (C1). In the wave transmission process, the adjustment circuit (13A) selects a capacitor (C1) corresponding to the target sound pressure from the plurality of capacitors (C1) as the given capacitor (C1), and drives the drive switching element (T1) of the drive circuit (12A) to generate sound waves from the sound wave source (11). According to this method, the sound pressure of the sound wave output from the sound wave generator (10A) can be easily adjusted.

[0121] The 14th method is an object detection system (1) based on any one of the 1st to 8th methods. In the 14th method, the sound wave generating device (10B) includes: a plurality of sound wave sources (11), each of which heats up by being energized and generates sound waves with different sound pressures; a drive circuit (12) having a capacitor (C1) charged by a DC power supply (V1) and a drive switching element (T1) for supplying power from the capacitor (C1) to a given sound wave source (11); and an adjustment circuit (13B) for adjusting the sound pressure of the sound wave from the sound wave generating device (10B) by selecting at least one of the plurality of sound wave sources (11) as the given sound wave source (11). In the wave transmission process, the adjustment circuit (13B) selects a sound wave source (11) from the plurality of sound wave sources (11) that corresponds to the target sound pressure as the given sound wave source (11), and drives the drive switching element (T1) of the drive circuit (12) to generate a sound wave from the given sound wave source (11). In this manner, the sound pressure of the sound wave output from the sound wave generator (10B) can be easily adjusted.

[0122] The 15th method is an object detection system (1) based on any one of the 9th to 14th methods. In the 15th method, the switching frequency of the driving switching element (T1) is 20 kHz or higher. According to this method, the object detection accuracy can be improved.

[0123] Industrial availability

[0124] This disclosure can be applied to sound wave generating devices. Specifically, this disclosure can be applied to object detection systems that use sound waves to detect objects.

[0125] Explanation of reference numerals in the attached figures

[0126] 1: Object detection system;

[0127] 10, 10A, 10B: Sound wave generating device;

[0128] 11: Sound wave source;

[0129] 12, 12A: Drive circuit;

[0130] 13, 13A, 13B: Adjustment circuit;

[0131] V1: DC power supply;

[0132] V2: Voltage between the two terminals;

[0133] C1: Capacitor;

[0134] T1: Switching element for driving;

[0135] T1on: During connection period;

[0136] L1: Inductor;

[0137] T2: Adjustment switching element;

[0138] T2on: During connection period;

[0139] D1: Diode;

[0140] 20: Wave receiving device;

[0141] 30: Processing circuit;

[0142] PI: sound wave.

Claims

1. An object detection system, comprising: A sound wave generating device that generates heat and produces sound waves by being powered on; and The processing circuit performs object detection processing, which uses sound waves from the sound wave generator to detect objects in the object space. The object detection process includes: The sound wave generator is controlled to generate a series of sound waves with frequencies varying over time at a target sound pressure level. A correlation is established between the target sound pressure level and the frequencies corresponding to the series of sound waves. The determination process involves acquiring a received signal representing the sound waves received by the receiving device from the object space, and determining whether the object exists in the object space based on the received signal. Based on the frequency characteristics of the receiving device's sensitivity to sound waves of a given sound pressure, the target sound pressure is set such that the receiving device's sensitivity to the sound waves of the target sound pressure is within a given range that includes the given value. The frequency of the series of sound waves varies within a given frequency range. The given value is the maximum value of the sensitivity of the receiving device to a sound wave of a given sound pressure within the given frequency range.

2. The object detection system according to claim 1, wherein, The upper limit of the given range is above the given value. The central value of the given range is below the given value.

3. The object detection system according to claim 1 or 2, wherein, The lower limit of the given range is below the given value and greater than the minimum value of the sensitivity of the receiving device to the sound wave of the given sound pressure within the given frequency range.

4. The object detection system according to claim 3, wherein, The upper limit of the given range is the given value.

5. The object detection system according to claim 3, wherein, The sensitivity of the receiving device to a sound wave at a given sound pressure level is insufficient for a target sound pressure level greater than the given sound pressure level for a sound wave at a given frequency.

6. The object detection system according to claim 1, wherein, The given range is the range of ±10% of the given value.

7. The object detection system according to claim 1 or 2, wherein, In the determination process, if the peak value of the cross-correlation function representing the series of sound waves transmitted and received is above a threshold, then it is determined that the object exists.

8. The object detection system according to claim 1 or 2, wherein, The sound wave generating device includes: The drive circuit includes a capacitor charged by a DC power supply and a drive switching element that supplies power from the capacitor to a sound wave source that heats up and generates sound waves when energized; and The adjustment circuit adjusts the sound pressure level of the sound waves from the sound wave generator by adjusting the voltage across the capacitor in the drive circuit. In the wave transmission process, The voltage across the capacitor is adjusted by the adjustment circuit so that the sound pressure of the sound wave from the sound wave generator becomes the target sound pressure. The driving switching element of the driving circuit is used to generate sound waves from the sound wave source.

9. The object detection system according to claim 8, wherein, The adjustment circuit has: An inductor, electrically connected between the DC power supply and the capacitor; and The adjusting switching element is electrically connected in parallel with the series circuit of the inductor and the DC power supply. The adjustment circuit adjusts the voltage across the capacitor by controlling the on / off period of the adjustment switching element.

10. The object detection system according to claim 9, wherein, The adjustment circuit has diodes. The anode of the diode is electrically connected to the inductor. The cathode of the diode is electrically connected to the capacitor.

11. The object detection system according to claim 9 or 10, wherein, The adjustment switch element is turned on during the period when the drive switch element is turned on, and switches to be turned on simultaneously with the drive switch element.

12. The object detection system according to claim 1 or 2, wherein, The sound wave generating device includes: A drive circuit having a drive switching element that supplies power from a sound wave source that heats up and generates sound waves when a given capacitor pair is energized. as well as The adjustment circuit adjusts the sound pressure of the sound waves from the sound wave generator by selecting at least one of a plurality of capacitors, each charged by a plurality of DC power supplies with different voltages, as the given capacitor. In the wave transmission process, The adjustment circuit selects a capacitor from the plurality of capacitors that corresponds to the target sound pressure as the given capacitor. The driving switching element of the driving circuit is used to generate sound waves from the sound wave source.

13. The object detection system according to claim 1 or 2, wherein, The sound wave generating device includes: Multiple sound wave sources generate heat and produce sound waves with different sound pressures when energized. A drive circuit having a capacitor charged by a DC power supply and a drive switching element for supplying power from the capacitor to a given sound wave source. as well as The adjustment circuit adjusts the sound pressure level of the sound wave from the sound wave generating device by selecting at least one of the plurality of sound wave sources as the given sound wave source. In the wave transmission process, The adjustment circuit selects the sound source corresponding to the target sound pressure from the plurality of sound sources as the given sound source. The driving switching element of the driving circuit is driven to generate sound waves from the given sound wave source.

14. The object detection system according to claim 8, wherein, The switching frequency of the drive switching element is 20kHz or higher.

15. An object detection system, comprising: A sound wave generating device that generates heat and produces sound waves by being powered on; and The processing circuit performs object detection processing, which uses sound waves from the sound wave generator to detect objects in the object space. The object detection process includes: The sound wave generator is controlled to generate a series of sound waves with frequencies varying over time at a target sound pressure level. A correlation is established between the target sound pressure level and the frequencies corresponding to the series of sound waves. The determination process involves acquiring a received signal representing the sound waves received by the receiving device from the object space, and determining whether the object exists in the object space based on the received signal. The frequency of the series of sound waves varies within a given frequency range. Based on the frequency characteristics of the receiving device's sensitivity to sound waves at a given sound pressure, the target sound pressure is set such that the receiving device's sensitivity to the sound waves at the target sound pressure is consistent with the given value. The given value is the maximum value of the sensitivity of the receiving device to a sound wave of a given sound pressure within the given frequency range.

16. The object detection system according to claim 15, wherein, In the determination process, if the peak value of the cross-correlation function representing the series of sound waves transmitted and received is above a threshold, then it is determined that the object exists.

17. The object detection system according to claim 15 or 16, wherein, The sound wave generating device includes: The drive circuit includes a capacitor charged by a DC power supply and a drive switching element that supplies power from the capacitor to a sound wave source that heats up and generates sound waves when energized; and The adjustment circuit adjusts the sound pressure level of the sound waves from the sound wave generator by adjusting the voltage across the capacitor in the drive circuit. In the wave transmission process, The voltage across the capacitor is adjusted by the adjustment circuit so that the sound pressure of the sound wave from the sound wave generator becomes the target sound pressure. The driving switching element of the driving circuit is used to generate sound waves from the sound wave source.

18. The object detection system according to claim 17, wherein, The adjustment circuit has: An inductor, electrically connected between the DC power supply and the capacitor; and The adjusting switching element is electrically connected in parallel with the series circuit of the inductor and the DC power supply. The adjustment circuit adjusts the voltage across the capacitor by controlling the on / off period of the adjustment switching element.

19. The object detection system according to claim 18, wherein, The adjustment circuit has diodes. The anode of the diode is electrically connected to the inductor. The cathode of the diode is electrically connected to the capacitor.

20. The object detection system according to claim 18 or 19, wherein, The adjustment switch element is turned on during the period when the drive switch element is turned on, and switches to be turned on simultaneously with the drive switch element.

21. The object detection system according to claim 15 or 16, wherein, The sound wave generating device includes: A drive circuit having a drive switching element that supplies power from a sound wave source that heats up and generates sound waves when a given capacitor pair is energized. as well as The adjustment circuit adjusts the sound pressure of the sound waves from the sound wave generator by selecting at least one of a plurality of capacitors, each charged by a plurality of DC power supplies with different voltages, as the given capacitor. In the wave transmission process, The adjustment circuit selects a capacitor from the plurality of capacitors that corresponds to the target sound pressure as the given capacitor. The driving switching element of the driving circuit is used to generate sound waves from the sound wave source.

22. The object detection system according to claim 15 or 16, wherein, The sound wave generating device includes: Multiple sound wave sources generate heat and produce sound waves with different sound pressures when energized. A drive circuit having a capacitor charged by a DC power supply and a drive switching element for supplying power from the capacitor to a given sound wave source. as well as The adjustment circuit adjusts the sound pressure level of the sound wave from the sound wave generating device by selecting at least one of the plurality of sound wave sources as the given sound wave source. In the wave transmission process, The adjustment circuit selects the sound source corresponding to the target sound pressure from the plurality of sound sources as the given sound source. The driving switching element of the driving circuit is driven to generate sound waves from the given sound wave source.

23. The object detection system according to claim 17, wherein, The switching frequency of the drive switching element is 20kHz or higher.

Images