Object detection device

Abstract

An object detection device that detects an object through transmission and reception of a sound wave, the object detection device comprising: a wave transmitter (10) that generates a sound wave as a signal wave (W1) on the basis of a prescribed wave transmission signal (Sd) and transmits the generated sound wave to an object; a wave receiver (11) that receives the sound wave and generates a wave reception signal, the wave receiver being provided separately from the wave transmitter; and a control unit (13) that generates the wave transmission signal so as to control the signal wave from the wave transmitter. The wave receiver has frequency characteristics such that the wave reception signal fluctuates when resonance occurs. The wave transmission signal is set in accordance with the frequency characteristics of the wave receiver such that resonance of the wave receiver is suppressed during reception of the signal wave from the wave transmitter.

Description

Technical Field

[0001] The present invention relates to an object detection device that detects an object by transmitting and receiving sound waves such as ultrasonic waves.

Background Art

[0002] Patent Document 1 discloses a transmission / reception control device that controls transmission and reception in an ultrasonic sensor. The ultrasonic sensor includes an ultrasonic microphone configured to transmit a detection wave that is an ultrasonic wave and receive a received wave. This transmission / reception control device sets the frequency of the detection wave to a transmission frequency different from the resonance frequency of the ultrasonic microphone, processes the reception result of the received wave based on the detection wave transmitted at the transmission frequency, and detects an object based on the processing result. As a result, the reverberation time of the ultrasonic microphone caused by the transmission of the detection wave is shortened compared to the case where the transmission frequency is the resonance frequency. In this way, it is intended to suppress the adverse effects caused by reverberation in the ultrasonic sensor as much as possible.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 assumes a configuration in which the ultrasonic microphone that transmits the detection wave also receives the reflected wave. The inventor of the present application has found new problems that do not occur in such a conventional configuration in the detection of an object by transmitting and receiving sound waves, and has devised the present invention.

[0005] An object of the present invention is to provide an object detection device capable of suppressing a situation in which it is difficult to detect an object by transmitting and receiving sound waves due to the influence of the received sound waves.

Means for Solving the Problems

[0006] In one aspect of the present invention, an object detection device that detects an object by transmitting and receiving sound waves is provided. The object detection device includes a transmitter that generates a sound wave as a signal wave based on a predetermined transmission signal and transmits it to the object, a receiver that is provided separately from the transmitter and receives the sound wave to generate a reception signal, and a control unit that generates the transmission signal so as to control the signal wave from the transmitter. The receiver has a frequency characteristic in which the reception signal fluctuates when it resonates. The transmission signal is set so as to suppress the resonance of the receiver when the signal wave from the transmitter is received, according to the frequency characteristic of the receiver.

Advantages of the Invention

[0007] According to the object detection device of the present invention, it is possible to suppress a situation in which it is difficult to detect an object by transmitting and receiving sound waves due to the influence of the received sound wave.

Brief Description of the Drawings

[0008]

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Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the object detection device according to the present invention will be described with reference to the accompanying drawings.

[0010] Each embodiment is an exemplification, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. In the following embodiments from Embodiment 2 onwards, descriptions of matters common to Embodiment 1 will be omitted, and only the different points will be explained. In particular, for the same operational effects due to the same configurations, they will not be sequentially mentioned for each embodiment.

[0011] (Embodiment 1) The configuration and operation of the object detection device according to Embodiment 1 will be described below.

[0012] 1. Configuration 1-1. Overview The overview of the object detection device according to Embodiment 1 will be described with reference to FIG. 1.

[0013] FIG. 1 is a diagram for explaining the overview of the object detection device 1 of the present embodiment. The object detection device 1 is a device that detects the distance to an object 3 by transmitting and receiving sound waves such as ultrasonic waves.

[0014] The object detection device 1 of this embodiment can be applied to various applications for detecting various objects 3. For example, in an application where it is mounted on a moving body such as a robot arm or a robot hand, the object detection device 1 can detect the distance to a nearby object 3 such as an object to be grasped. Moreover, the object detection device 1 is not limited to the above, and can be applied to various moving bodies such as a robot cleaner, an automatic guided vehicle, and a personal mobility. For example, it can detect the distance at which the moving body approaches surrounding objects 3, the presence or absence of obstacles, or the road surface condition. Further, the object detection device 1 can also be appropriately applied to various applications other than the mounting application of the moving body.

[0015] The object detection device 1 emits, from a transmitter 10, a sound wave, that is, a signal wave W1, whose signal waveform is set in advance according to each detection application, toward the object 3 side, and receives, by a receiver 11 provided separately from the transmitter 10, a reflected wave W2 of the signal wave W1 from the object 3, thereby detecting the object 3. At this time, a direct wave W0 in which the signal wave W1 from the transmitter 10 reaches the receiver 11 directly without passing through reflection at the object 3 in particular is generated.

[0016] Regarding the influence of the direct wave W0, which is peculiar to the configuration in which the transmitter 10 and the receiver 11 are separate bodies, on the short-distance detection of the object 3 and the like, the inventor of the present application conducted intensive research and found a new problem. The inventor of the present application repeated intensive research to solve this new problem and arrived at devising the object detection device 1 of this embodiment capable of suppressing the influence of the direct wave W0. Hereinafter, the configuration of the object detection device 1 of this embodiment will be described.

[0017] 1-2. Device Configuration The configuration of the object detection device 1 of this embodiment will be described with reference to FIG. 2. FIG. 2 is a block diagram illustrating the configuration of the object detection device 1 of this embodiment.

[0018] As shown in, for example, Fig. 2, the object detection device 1 of this embodiment includes a transmitter 10, a receiver 11, a control unit 13, a storage unit 14, a transmission circuit 15, and a reception circuit 16. The transmitter 10 and the receiver 11 are arranged at a distance, for example, on the same main surface of a substrate. The distance between the transmitter 10 and the receiver 11 can be measured as the distance between reference positions such as the center position of the transmitter 10 and the center position of the receiver 11.

[0019] The transmitter 10 is composed of, for example, a thermophone which is a sound wave source that generates sound waves such as ultrasonic waves by heating air and then stopping the heating. The thermophone generates a sound wave of a pressure wave that expands the surrounding air at the start of heat generation and contracts the surrounding air at the stop of heat generation as a signal wave W1 (see Fig. 3(B)). According to such a transmitter 10 of a thermophone, sound waves can be controlled by heat generation and heat generation stop without using resonance, and reverberation during transmission can be easily avoided. Also, by using a thermophone, it is easy to broaden the bandwidth of sound waves, reduce the size and weight of the transmitter 10, etc.

[0020] The transmission circuit 15 is a drive circuit for the transmitter 10, and drives the transmitter 10 based on, for example, a transmission signal Sd input from the control unit 13. For example, the transmission circuit 15 when the transmitter 10 is a thermophone can be configured using a switching transistor, a capacitor, an inductor, etc., and on / off controls the current flowing through the thermophone according to the transmission signal Sd.

[0021] The transmission circuit 15 may set the time length, intensity, time interval, frequency band, directivity, etc. of the sound waves generated by the transmitter 10. Part or all of the functions of the transmission circuit 15 may be integrally configured with the transmitter 10 or the control unit 13. The transmission signal Sd may be supplied from the transmission circuit 15 to the transmitter 10 as a drive signal for the transmitter 10, or may be directly supplied from the control unit 13 to the transmitter 10.

[0022] The receiver 11 is composed of a microphone element such as a MEMS (Micro Electro Mechanical System) microphone. The receiver 11 has frequency characteristics that resonate with a structure such as a cap (see FIG. 4 etc.). The receiver 11 may include a plurality of microphone elements, and for example, may have common frequency characteristics with each other among the same type of products. The frequency characteristics of the receiver 11 may vary within an appropriate tolerance range as appropriate.

[0023] The receiver 11 receives an external sound wave and generates a reception signal Sr indicating the reception result. The receiver 11 is not limited to a MEMS microphone, and may be composed of other microphone elements having frequency characteristics capable of receiving ultrasonic waves transmitted from the transmitter 10, for example. For example, a condenser microphone may be used for the receiver 11. The receiver 11 may be omnidirectional or may have various directivities as appropriate.

[0024] The receiving circuit 16 includes, for example, a sensor amplifier that amplifies the reception signal Sr from the receiver 11, and outputs the reception signal Sr generated within a predetermined dynamic range to the control unit 13. The receiving circuit 16 may include various drive circuits for the receiver 11. Part or all of the functions of the receiving circuit 16 may be integrally configured with the receiver 11 or the control unit 13.

[0025] The control unit 13 controls the overall operation of the object detection device 1. The control unit 13 is composed of, for example, a microcomputer, and realizes a predetermined function in cooperation with software. The control unit 13 reads out the data and programs stored in the storage unit 14, performs various arithmetic processes, and realizes various functions. For example, the control unit 13 generates a transmission signal Sd for generating the signal wave W1 in the transmitter 10 based on the data about the signal waveform stored in the storage unit 14, and outputs it to the transmission circuit 15. Also, the control unit 13 has an arithmetic function for detecting the object 3 based on the reception signal Sr from the receiving circuit 16.

[0026] Note that the control unit 13 may be a hardware circuit such as a dedicated electronic circuit or a reconfigurable electronic circuit designed to implement a predetermined function. The control unit 13 may be composed of various semiconductor integrated circuits such as a CPU, MPU, DSP, FPGA, ASIC, etc. Further, the control unit 13 may be configured to include an analog / digital (A / D) converter and a digital / analog (D / A) converter.

[0027] The storage unit 14 is a storage medium that stores programs and data necessary to implement the functions of the control unit 13, and is composed of, for example, a flash memory. For example, the storage unit 14 stores data indicating the transmission wave signal Sd. The storage unit 14 may be an internal memory of the control unit 13.

[0028] 2. Operation The operation of the object detection device 1 configured as described above will be described below.

[0029] In the object detection device 1 of the present embodiment, the control unit 13 generates a transmission wave signal Sd and controls the transmission circuit 15 to cause the transmitter 10 to generate a corresponding signal wave W1 (see FIGS. 3(A) and (B)). In the present embodiment, the transmission wave signal Sd has an impulse waveform that forms the signal wave W1 as a single pulse.

[0030] The signal wave W1 from the transmitter 10 is transmitted to the object 3 and becomes a reflected wave W2, or becomes a direct wave W0 without passing through the object 3. In the object detection device 1, the receiver 11 receives sound waves such as the reflected wave W2 and the direct wave W0, generates a reception wave signal Sr indicating the reception result, and outputs it to the control unit 13 via, for example, the reception circuit 16.

[0031] Based on the received wave signal Sr from the wave receiver 11, the control unit 13 detects the timing when the reflected wave W2 from the object 3 is received, for example, by threshold determination with respect to the signal intensity, and performs distance measurement using the TOF (Time Of Flight) method. For example, the control unit 13 uses the period from the transmission timing of the signal wave W1 to the detected reception timing as the round-trip period of the signal wave W1 between the object detection device 1 and the object 3, and calculates the distance to the object 3 from conversion based on the speed of sound or the like.

[0032] According to the operation of the object detection device 1 as described above, the distance to the object 3 can be detected by a simple signal process that applies TOF-based distance measurement to the transmission and reception of the signal wave W1 based on the impulse waveform transmission signal Sd. Such object detection operation of the present embodiment is useful for detecting an object at a short distance where it is easy to ensure the sound pressure of the reflected wave W2, for example.

[0033] 2-1. Regarding the influence of the direct wave In the object detection operation as described above, due to the reception of the direct wave W0, when the reflected wave W2 from an object 3 at a relatively short distance is received, it is difficult to discriminate between the reflected wave W2 and the direct wave W0 in the received wave signal Sr, and it is considered that there will be a period during which it is difficult to detect the object 3. The object detection device 1 of the present embodiment can control the signal wave W1 to shorten such a difficult detection period and expand the detectable range of the object 3 in a closer distance range.

[0034] As an example of such a countermeasure, for example, according to the transmission signal Sd of the impulse waveform (see Fig. 3(A)), the period during which the direct wave W0 is received by the wave receiver 11 can be shortened compared to the case where pulses of the same waveform are repeated multiple times in the signal wave W1. Also, by adopting a thermophone for the wave transmitter 10, reverberation due to resonance of the wave transmitter 10 in the signal wave W1 can be avoided (see Fig. 3(B)), and the reception period of the direct wave W0 considering reverberation during transmission can be shortened.

[0035] 2-1-1. Problems of ringing According to the above measures, it is considered that the influence of the direct wave W0 in short-distance detection can be reduced to a certain extent. However, even after taking the above measures, new problems in which the direct wave W0 still affects short-distance detection have been found through the intensive research of the inventor of the present application. These problems will be described with reference to FIG. 3.

[0036] FIG. 3(A) illustrates the transmission signal Sd in the object detection device 1. FIG. 3(B) illustrates the signal wave W1 from the transmitter 10 corresponding to the transmission signal Sd in FIG. 3(A). FIG. 3(C) illustrates the received wave signal Sr of the receiver 11 that responds to the signal wave W1 in FIG. 3(B).

[0037] In the received wave signal Sr illustrated in FIG. 3(C), a ringing period T2 occurs after a period T1 during which the signal wave W1 (FIG. 3(B)) transmitted based on the transmission signal Sd in FIG. 7(A) is received as the direct wave W0 (FIG. 1). The ringing period T2 is a period during which the receiver 11 resonates when receiving the direct wave W0, and ringing occurs in which the received wave signal Sr fluctuates unstably.

[0038] The ringing period T2 in FIG. 3(C) lasts for a longer period than, for example, the time length of the signal wave W1 (FIG. 3(B)). During such a ringing period T2, it is difficult to detect the reflected wave W2 even if it is received. Thus, due to the influence of the ringing in which the received wave signal Sr becomes unstable due to the resonance of the receiver 11 when receiving the direct wave W0, the problem that it becomes difficult to detect an object 3 at a relatively short distance has been newly found through the intensive research of the inventor of the present application.

[0039] 2-2. Setting of impulse waveform The inventor of the present application has conducted intensive research on such problems of ringing due to the reception of the direct wave W0, and has devised the object detection device 1 of the present embodiment. In the object detection device 1 of the present embodiment, in consideration of the frequency characteristics of the receiver 11, an impulse waveform of the transmission signal Sd is set to shorten the ringing period T2 due to the reception of the direct wave W0. This will be described with reference to FIGS. 4 to 11.

[0040] FIG. 4 shows an example of the frequency characteristics of the receiver 11 in the object detection device 1. In this example, the frequency characteristics when a microphone SPU0410LR5H manufactured by Knowles is used for the receiver 11 are illustrated. The horizontal axis in FIG. 4 indicates the frequency, and the vertical axis indicates the sensitivity. In the example of FIG. 4, the resonance frequency fr of the receiver 11 at which the frequency characteristics peak is around 25 kHz.

[0041] FIG. 5 illustrates the impulse waveform of the transmission signal Sd. In this example, the pulse width, which is a parameter of the time length in the impulse waveform of the transmission signal Sd, is set to "2a". The pulse width 2a is an example of the signal length indicating the time length of one signal wave W1. The frequency spectrum obtained by expanding such a transmission signal Sd into components for each frequency f is expressed, for example, by the following equation (1). G(f)=sin(2πa*f) / (2πa*f) …(1) In the above equation (1), sin() is the sine function, and π is the ratio of the circumference of a circle to its diameter. The frequency spectrum of the transmission signal Sd with such an impulse waveform is illustrated in FIG. 6.

[0042] In FIG. 6, considering the frequency characteristics of the receiver 11 in FIG. 4, the case where the pulse width 2a is set to 40 μs is illustrated. In the frequency spectrum F1 of the transmission signal Sd with an impulse waveform, the frequency f = 0 Hz is the maximum, and as the frequency f increases, the intensity |G(f)| of the frequency component vibrates and attenuates. The frequency spectrum F1 has portions where the intensity |G(f)| is reduced to near zero, that is, nodal portions F10, at every predetermined period (1 / 2a) corresponding to the pulse width 2a. Therefore, in the present embodiment, such nodal portions F10 are utilized to suppress the frequency component G(f = fr) of the resonance frequency fr of the receiver 11 in the transmission signal Sd.

[0043] For example, in the object detection device 1 of the present embodiment, the pulse width 2a of the transmission signal Sd is set as follows based on the above frequency spectrum F1 and the resonance frequency fr of the receiver 11. 2a = 1 / fr …(2)

[0044] According to the setting of the above formula (2), the pulse width 2a of the transmission wave signal Sd matches the period 1 / fr corresponding to the resonance frequency fr. In this case, as illustrated in FIG. 6, in the frequency spectrum F1 of the transmission wave signal Sd, the intensity |G(fr)| of the frequency component of the resonance frequency fr of the receiver 11 can be reduced to zero together with its harmonics. The effect of such a setting will be described with reference to FIG. 7.

[0045] FIGS. 7(A) to (D) are graphs showing an example of the experimental results of the operation of the object detection device 1. The inventor of the present application conducted an experiment to confirm the effect of considering the frequency characteristics of the receiver 11 as described above in the object detection device 1. The frequency characteristics of FIG. 4 were adopted for the receiver 11. The distance between the transmitter 10 and the receiver 11 was set to 35 mm.

[0046] FIG. 7(A) shows an example of the signal waveform of the transmission wave signal Sdx when the frequency characteristics of the receiver 11 are not considered. FIG. 7(B) illustrates the signal waveform of the received wave signal Sr corresponding to the transmission wave signal Sdx of FIG. 7(A). The transmission wave signal Sdx in FIG. 7(A) has a pulse width of 10 μs with respect to the resonance frequency fr in FIG. 4, and significantly deviates from the above formula (2). In the received wave signal Srx in this case, as shown in FIG. 7(B), a long ringing period T2x occurs from the time of receiving the direct wave W0.

[0047] On the other hand, in the object detection device 1 of the present embodiment, the signal waveform of the transmission wave signal Sd is set in consideration of the frequency characteristics of the receiver 11. FIG. 7(C) shows an example of the signal waveform of the transmission wave signal Sd by the object detection device 1 of the present embodiment. FIG. 7(D) illustrates the signal waveform of the received wave signal Sr corresponding to the transmission wave signal Sdx of FIG. 7(A).

[0048] In the operation examples of FIGS. 7(C) and (D), the transmission wave signal Sd was set to have a pulse width 2a = 40 μs according to the frequency characteristics of FIG. 4. The pulse width 2a of the transmission wave signal Sd in this example is longer than that in the example of FIG. 7(A), while satisfying the above formula (2) for the resonance frequency fr of the receiver 11 in the example of FIG. 4.

[0049] According to the object detection device 1 of this embodiment, as shown in FIG. 7(D), the ringing period T2 due to the reception of the direct wave W0 is shortened by about 80 μs from the example of FIG. 7(B). By reducing the influence of ringing due to the reception of the direct wave W0 in this way, it was confirmed that object detection at a closer distance than the operation examples of FIGS. 7(A) and 7(B) can be facilitated by about 2.76 cm in terms of distance conversion corresponding to the shortening of the ringing period T2.

[0050] The object detection device 1 of this embodiment is not limited to the above example, and the transmission signal Sd can be set to various pulse widths 2a in consideration of the frequency characteristics of the receiver 11. For example, the transmission signal Sd of this embodiment does not necessarily have to strictly satisfy the above formula (2), and may be satisfied within an appropriate allowable error range. The node F10 of the frequency spectrum can be defined so as to include such an allowable range. This allowable range will be described with reference to FIG. 8.

[0051] FIG. 8 illustrates the frequency spectra F2 and F3 of the upper and lower limits of the allowable range of the above formula (2) with respect to the frequency characteristics of FIG. 4. In this example, the pulse width 2a of the upper limit frequency spectrum F2 is 44 μs, and the pulse width 2a of the lower limit frequency spectrum F3 is 36 μs.

[0052] For example, the allowable range of the pulse width 2a of the above formula (2) may be within the range of ±10% from the period 1 / fr corresponding to the resonance frequency fr. In this case, the intensity |G(fr)| of the frequency component of the resonance frequency fr in the transmission signal Sd can be reduced to 50% or less of the second peak value Y in the frequency spectra F1 to F3 as shown in FIG. 8, and the influence of the direct wave W0 can be suppressed.

[0053] Alternatively, in this embodiment, the pulse width 2a may be set to 80% or more of the period 1 / fr corresponding to the resonance frequency fr. Thereby, the influence of the direct wave W0 can be suppressed to the extent of being equal to or less than the second peak value Y in the frequency spectra F1 to F3. Further, the object detection device 1 of this embodiment may appropriately satisfy the following formula (3) within an allowable error range for an integer M of 2 or more instead of the above formula (2). 2a = M / fr …(3)

[0054] That is, the pulse width 2a may be set such that the resonance frequency fr of the receiver 11 is included in any one of a plurality of nodal points F10 (FIG. 6) in the frequency spectra F1 to F3. Also by this, the intensity |G(fr)| of the frequency component of the resonance frequency fr in the transmission signal Sd can be reduced, and the influence of the direct wave W0 can be suppressed.

[0055] Further, the object detection device 1 of the present embodiment can be configured by applying the above setting of the transmission signal Sd to various frequency characteristics of the receiver 11. Such a modification will be described with reference to FIGS. 9 to 10.

[0056] FIG. 9 shows another example of the frequency characteristics of the receiver 11 in the object detection device 1. FIG. 10 shows another example of the setting of the transmission signal Sd according to the frequency characteristics of FIG. 9.

[0057] In FIG. 9, the frequency characteristics in the case where the microphone IM73A135V01 manufactured by Infineon Technologies is used for the receiver 11 are illustrated. According to the frequency characteristics of FIG. 9, the resonance frequency fr of the receiver 11 is considered to be in the vicinity of 35 kHz. In this case, in the object detection device 1 of the present embodiment, for example, as shown in FIG. 10, the pulse width 2a of the transmission signal Sd is set in the vicinity of 28.5 μs (see Equation (2)), and is set to 26.7 μs or more and 31.4 μs or less as an allowable range of, for example, ±10%. Within such an allowable range, as illustrated in FIG. 10, the intensity of the frequency component of the resonance frequency fr can be sufficiently reduced.

[0058] FIGS. 11(A) to (D) illustrate the results of a confirmation experiment when the modified receiver 11 is used. In this experiment, when the microphone IM73A135V01 manufactured by Infineon Technologies was used for the receiver 11, the same experiment as in FIGS. 7(A) to (D) was conducted. At this time, the frequency characteristics in which the receiver 11 resonates at the resonance frequency of 21 kHz were actually confirmed.

[0059] Figs. 11(A) and (B) illustrate a transmitted wave signal Sdx with a pulse width 2a and a received wave signal Srx that responds thereto, similar to Figs. 7(A) and (B). In this case, ringing occurs for a long time until the signal intensity Vp when the direct wave W0 is received is halved in the received wave signal Srx.

[0060] Figs. 11(C) and (D) illustrate the transmitted wave signal Sd and the received wave signal Sr in the object detection device 1 of the present embodiment. In Figs. 11(C) and (D), in the same wave receiver 11 as in Figs. 11(A) and (B), the pulse width 2a is set to 48 μs according to the actually confirmed frequency characteristics (see Equation (2)).

[0061] According to the object detection device 1 of the present embodiment, as shown in Fig. 11(D) for example, the ringing is shortened by 128 μs from the example of Fig. 11(B). It was confirmed that in a distance range of about 4.35 cm in terms of this distance conversion, the object detection device 1 of the present embodiment can facilitate the detection of an object at a closer distance than the examples of Figs. 11(A) and (B).

[0062] 3. Summary As described above, the object detection device 1 in the present embodiment is a device that detects the object 3 by transmitting and receiving sound waves. The object detection device 1 includes a transmitter 10, a receiver 11, and a control unit 13. The transmitter 10 generates a sound wave as a signal wave W1 based on a predetermined transmitted wave signal Sd and transmits it to the object 3. The receiver 11 is provided separately from the transmitter 10, receives a sound wave including a reflected wave W2 and a direct wave W0 of the signal wave W1 at the object 3, and generates a received wave signal Sr. The transmitted wave signal Sd is generated so as to control the signal wave W1 from the transmitter 10. The receiver 11 has a frequency characteristic in which the received wave signal Sr fluctuates when it resonates (see Fig. 4). The transmitted wave signal Sd is set so as to suppress the resonance of the receiver 11 when the signal wave W1 from the transmitter 10 is received, according to the frequency characteristic of the receiver 11 (see Fig. 6).

[0063] According to the above object detection device 1, for example, when the signal wave W1 is received by the receiver 11 as the direct wave W0 without passing through the object 3, it is possible to suppress the situation where the ringing due to the resonance of the receiver 11 becomes prolonged. Thus, it is possible to suppress the situation where it is difficult to detect the object 3 by transmitting and receiving sound waves due to the influence of the received sound waves.

[0064] In the object detection device 1 of the present embodiment, the transmission signal Sd has a frequency spectrum F1 including a node portion F10 where the intensity of the frequency component is lower than the surroundings (see FIG. 6). The transmission signal Sd is set so that the resonance frequency fr in the frequency characteristics of the receiver 11 is included in the node portion F10 (see FIGS. 6 and 8). Thereby, the frequency component that causes the resonance of the receiver 11 in the transmission signal Sd can be reduced, and it is easier to suppress the ringing at the time of reception of the receiver 11.

[0065] In the object detection device 1 of the present embodiment, the transmission signal Sd is set so as to include the resonance frequency fr in the lowest-frequency node portion F10 among the plurality of periodically arranged node portions F10 in the frequency spectrum F1 (see FIGS. 6 and 8). Thereby, for example, the time length of the signal wave W1 can be made shorter, and it is easier to perform the operation of detecting the object by transmitting and receiving sound waves by the object detection device 1.

[0066] In the object detection device 1 of the present embodiment, the transmission signal Sd is set to the pulse width 2a which is an example of the signal length indicating the time length of the signal wave W1 so as to suppress the resonance of the receiver 11 at the time of reception of the signal wave W1. By setting the signal length in this way, it is possible to suppress the situation where it is difficult to detect the object 3 and it is easier to detect the object 3 by transmitting and receiving sound waves.

[0067] In the object detection device 1 of the present embodiment, the transmission signal Sd has an impulse waveform with the pulse width 2a set as the signal length. By controlling the transmission signal Sd in this way, it is possible to easily suppress the ringing of the receiver 11.

[0068] In the object detection device 1 of the present embodiment, the control unit 13 detects, as the distance to the object 3, the distance corresponding to the period from when the signal wave W1 is transmitted from the transmitter 10 until it is received by the receiver 11 via reflection from the object 3 based on the transmitted wave signal Sd and the received wave signal Sr. By such distance measurement using the TOF method, it is possible to easily detect the distance of the object 3 by transmitting and receiving sound waves. The object detection device 1 may perform various object detections by transmitting and receiving sound waves, not limited to the TOF method of distance measurement in particular.

[0069] In the object detection device 1 of the present embodiment, the transmitter 10 is a thermophone that generates the signal wave W1 by heat generation and heat stop. Thereby, it is easy to avoid the reverberation of the transmitted signal wave W1, and it is possible to suppress a situation where it is difficult to detect the object 3 by transmitting and receiving sound waves due to the influence of reverberation at the time of transmission.

[0070] (Embodiment 2) Hereinafter, Embodiment 2 will be described with reference to FIGS. 12 to 16. In Embodiment 1, an example of a detection method for measuring the distance of the object 3 with the signal wave W1 was described. In Embodiment 2, an object detection device 1A that combines and uses the detection method of Embodiment 1 and another detection method will be described.

[0071] 1. Configuration FIG. 12 illustrates the configuration of the object detection device 1A of Embodiment 2. The object detection device 1A of the present embodiment has, for example, the same configuration as that of Embodiment 1, and includes first and second detection units 31 and 32 that respectively execute two types of detection methods as functional configurations in the control unit 13.

[0072] Similar to the object detection device 1 of Embodiment 1, the first detection unit 31 controls the transmission and reception of the signal wave W1 based on the impulse waveform transmitted wave signal Sd, and detects the object 3 by performing distance measurement using the TOF method.

[0073] The second detection unit 32 detects the object 3 by controlling the transmission and reception of the signal wave W1 based on a modulated carrier signal Se such as a chirp waveform, and performing distance measurement by correlation processing. For example, the storage unit 14 of the present embodiment stores data indicating the carrier signal Se of the chirp waveform. The data of such a carrier signal Se is illustrated in FIG. 13.

[0074] In the example of FIG. 13, the signal waveform of the carrier signal Se for generating the down-chirp signal wave W1 in pulse interval modulation is illustrated. In the transmitter 10 of the thermophone, for example, by applying pulse interval modulation to keep the pulse width short, it is easy to suppress heat generation and power consumption.

[0075] The modulation method of the carrier signal Se by the second detection unit 32 is not particularly limited to the above, and various modulation methods may be used. For example, an up-chirp may be used, or a spreading code such as an M-sequence code may be used. Further, pulse width modulation may be used instead of pulse interval modulation. Furthermore, not limited to frequency modulation, amplitude modulation or the like may be performed.

[0076] FIG. 14 is a block diagram illustrating the configuration of the second detection unit 32. The second detection unit 32 includes, for example, as functional units, fast Fourier transform (FFT) units 131a, 131b, a cross-spectrum calculation unit 132, a Hilbert transform unit 133, inverse Fourier transform (IFFT) units 134a, 134b, and an analysis processing unit 135. Hereinafter, the general names of the FFT units 131a, 131b are referred to as the FFT unit 131, and the general names of the IFFT units 134a, 134b are referred to as the IFFT unit 134.

[0077] The second detection unit 32 inputs, for example, the transmission signal Se from the storage unit 14 and the reception signal Sr from the reception circuit 16, and performs signal processing by each functional unit 131 to 135. Each functional unit 131 to 135 can operate periodically, for example, in a predetermined frame period (for example, 1 / 30 second). For example, a series of processes from the FFT unit 131 to the IFFT unit 134 are performed to generate an analysis signal based on the transmission signal Se and the reception signal Sr for each frame. The analysis signal is composed of the cross-correlation function between the transmission signal Se and the reception signal Sr. The cross-correlation function is a function that shows the correlation between the two signals Se and Sr in the time domain.

[0078] The FFT unit 131a converts the transmission signal Se from the time domain to the frequency domain by calculating the fast Fourier transform for the transmission signal Se input to the second detection unit 32, and outputs the conversion result to the cross-spectrum calculation unit 132. The FFT unit 131b performs the same calculation as the FFT unit 121a on the reception signal Sr input to the second detection unit 32, and outputs the conversion result to the cross-spectrum calculation unit 132.

[0079] The cross-spectrum calculation unit 132 calculates the cross-spectrum from the results of the Fourier transform of the signals Se and Sr by the FFT unit 131, and outputs the calculation result to the IFFT unit 134a and the Hilbert transform unit 133. The cross-spectrum corresponds to the frequency components by the Fourier transform of the cross-correlation function between the transmission signal Se and the reception signal Sr.

[0080] The IFFT unit 134a calculates the inverse fast Fourier transform for the input cross-spectrum, and outputs the signal I of the conversion result that returns from the frequency domain to the time domain to the analysis processing unit 135. The signal I output in this way indicates the cross-correlation function between the transmission and reception signals Se and Sr (hereinafter also referred to as "in-phase component I").

[0081] The Hilbert transform unit 133 calculates the Hilbert transform of the input cross-spectrum, and outputs the conversion result in which each frequency component of the cross-spectrum is shifted by π / 2 to the IFFT unit 134b.

[0082] The IFFT unit 134b performs the same operations as the IFFT unit 134a on the Hilbert-transformed cross-spectrum, and outputs the signal Q of the conversion result to the analysis processing unit 135. The signal Q output in this way is in a quadrature relationship with the in-phase component I (hereinafter also referred to as the "quadrature component Q").

[0083] The analysis processing unit 135 generates an analysis signal having the in-phase component I as the real part and the quadrature component Q as the imaginary part, and performs processing on the analysis signal. The analysis signal generated based on the transmitted wave signal Se and the received wave signal Sr in this way represents an analytical function in the complex domain (see FIG. 16).

[0084] The second detection unit 32 is not limited to the functional configuration described above. For example, in the second detection unit 32, the cross-correlation function may be calculated directly from the transmitted and received signals Se and Sr by a sum-of-products operation, instead of performing an inverse Fourier transform after calculating the cross-spectrum after Fourier transform. Further, the generation of the analysis signal in the second detection unit 32 is not limited to Hilbert transform, and may be realized by, for example, the function of quadrature detection.

[0085] 2. Operation The operation of the object detection device 1A according to the second embodiment will be described below.

[0086] When the object detection device 1A of the present embodiment detects an object 3 at a relatively short distance, the first detection unit 31 is operated, and when detecting up to a long distance, the second detection unit 32 is operated. In this way, by switching the detection method according to the distance of the detection target, the object detection device 1A of the present embodiment can perform an object detection operation with good energy efficiency over a wide range from a short distance to a long distance.

[0087] FIG. 15 is a flowchart exemplifying the operation of the object detection device 1A in the present embodiment. Hereinafter, an operation example of detecting the distance to the object 3 a preset number of times N in the object detection device 1A will be described. The processing shown in this flowchart starts, for example, in a state where the detection count n managed in the storage unit 14 is set to "0", and is executed by the control unit 13 of the object detection device 1A.

[0088] First, the control unit 13 selects the second detection unit 32 out of the first and second detection units 31 and 32 (S1). By the selection in step S1, the object detection device 1A is set to an operation mode (i.e., long-distance mode) capable of detecting the object 3 up to a long distance.

[0089] In such a long-distance mode, the control unit 13 operates as the second detection unit 32 and controls the chirp transmission of the signal wave W1 from the transmitter 10 (S2). In the control of chirp transmission (S2), the control unit 13 generates a carrier signal Se of a chirp waveform and supplies it to the carrier circuit 15. By driving from the carrier circuit 15 according to the carrier signal Se, the transmitter 10 generates a chirp-modulated signal wave W1.

[0090] Furthermore, the control unit 13 as the second detection unit 32 acquires, for example, a reception signal Sr indicating the reception result by the receiver 11 via the reception circuit 16 (S3). The receiver 11 receives an acoustic wave including the reflected wave W2 of the signal wave W1 by chirp transmission in a predetermined frame period and generates a reception signal Sr.

[0091] Next, the control unit 13 calculates the distance to the object 3 by correlation processing between the respective signals Sd and Sr in the second detection unit 32 based on the carrier signal Sd of the chirp waveform and the acquired reception signal Sr (S4). For example, the second detection unit 32 performs the operations of the respective functional units 131 to 135 for each frame period and generates an analysis signal indicating the analysis result of the correlation between the carrier signal Sd and the reception signal Sr in the frame period.

[0092] FIG. 16 is a graph for explaining the analysis signal z(t) in the second detection unit 32. In FIG. 16, the analysis signal z(t) for one frame is illustrated. The analysis signal z(t) has a complex number value range based on the real part of the in-phase component I(t) indicating the cross-correlation function between the carrier signal Sd and the received signal Sr, and the imaginary part of the corresponding quadrature component Q(t).

[0093] In step S4, the second detection unit 32 obtains, for example, the envelope E(t)=|z(t)| of the analysis signal z(t) and detects the peak time t 0 . The peak time t 0 is the timing at which the amplitude |z(t)| becomes maximum in the analysis signal z(t) of one frame. Thus, by analyzing the timing corresponding to the reflection by the object 3 in the transmission and reception of the signal wave W1 of the frame, for example, the propagation period until the transmitted signal wave W1 is received as the reflected wave W2 from the object 3 can be measured.

[0094] Through the analysis of the correlation processing as described above, the second detection unit 32 can accurately detect the distance to the object 3 from the propagation period of the reflected wave W2 that has reached from the object 3 (S4). Also, according to the distance measurement in step S4, even if the reception times of a plurality of sound waves partially overlap due to the correlation processing over the chirp waveform during the frame period, each sound wave can be discriminated and the corresponding object 3 etc. can be detected.

[0095] Returning to FIG. 15, the control unit 13 increments, for example, the detection count n and determines whether the current detection count n has reached the specified count N (S5). If the current detection count n has not reached the specified count N (NO in S5), the control unit 13 determines, based on the distance calculated by the correlation processing (S4), whether there is an object 3 at a distance closer than a predetermined distance, for example (S6). The predetermined distance is set as a near-distance threshold, for example, from the viewpoint of the distance range that the first detection unit 31 can accurately detect.

[0096] If the control unit 13 determines that the object 3 is not at a near distance (NO in S6), the control unit 13 performs the processing after step S2 again as the second detection unit 32. Thereby, the object detection device 1A continues to operate in the long-distance mode.

[0097] On the other hand, when the control unit 13 determines that the object 3 is at a short distance (YES in S6), it selects the first detection unit 31 out of the first and second detection units 31 and 32 (S7). By the selection in step S7, the object detection device 1A is set to an operation mode (i.e., short-distance mode) capable of efficiently detecting the object 3 at a short distance.

[0098] In such a short-distance mode, the control unit 13 operates as the first detection unit 31 and controls the impulse transmission of the signal wave (S8). In the control of impulse transmission (S8), the control unit 13 supplies the same transmission wave signal Sd as in the first embodiment to the transmission circuit 15, and causes the transmitter 10 to transmit the signal wave W1 in an impulse waveform.

[0099] Furthermore, the control unit 13, as the first detection unit 31, acquires a reception signal Sr including the reception result of the reflected wave W2 by the receiver 11 (S9), and calculates the distance to the object 3 that is the reflection source of the reflected wave W2 by distance measurement using the TOF method (S10). The operation of the object detection device 1A in steps S8 to S10 is the same as the operation of the object detection device 1 in the first embodiment.

[0100] Also, the control unit 13 increments the detection count n and determines whether the specified number of times N has been reached, for example, in the same manner as in step S5 (S11). When the current detection count n has not reached the specified number of times N (NO in S11), the control unit 13 determines whether the object 3 is at a short distance, for example, in the same manner as in step S6, based on the distance calculated by the TOF method (S10) (S12).

[0101] When the control unit 13 determines that the object 3 is at a short distance (YES in S12), it performs the processing after step S8 again as the first detection unit 31. Thereby, the object detection device 1A continues to operate in the short-distance mode.

[0102] On the other hand, when it is determined that the object 3 is not at a short distance (NO in S12), the process returns to step S1. Thereby, the object detection device 1A is reset to the long-distance mode and the processing after step S2 is performed again.

[0103] When the current number of detections n reaches the specified number N (YES in S5 and S11), the control unit 13 ends the processing shown in this flow.

[0104] According to the operation of the object detection device 1A in the above-described embodiment, the first detection unit 31 is used in the short-distance mode, and the second detection unit 32 is used in the long-distance mode for proper use. First, the second detection unit 32 can detect the object 3 from a short distance to a long distance by chirp transmission (S2) and correlation processing-based distance measurement (S4). On the other hand, since the chirp transmission (S2) includes a large number of pulses per time, the power consumption is relatively high. Also, the correlation processing-based distance measurement (S4) is considered to have a relatively high computational load.

[0105] Therefore, when the object 3 is at a short distance, the object detection device 1A of the present embodiment uses the first detection unit 31 instead of the second detection unit 32. Thereby, the power consumption during wave transmission can be reduced by impulse transmission (S8) instead of chirp transmission (S2). Also, the computational load can be reduced by TOF method-based distance measurement (S10) instead of correlation processing-based distance measurement (S4). Thus, according to the object detection device 1A of the present embodiment, energy-efficient object detection can be realized over a wide range from a short distance to a long distance.

[0106] Also, in the short-distance mode of the object detection device 1A, as described in Embodiment 1, the influence of the direct wave W0 can be considered. In contrast, in the object detection device 1A of the present embodiment, in the impulse transmission (S8) as the short-distance mode, the pulse width 2a of the transmission wave signal Sd is set in the same manner as in Embodiment 1. Thereby, the influence of the direct wave W0 can be suppressed, and short-distance detection can be made accurate.

[0107] Also, when the object detection device 1A of the present embodiment performs chirp transmission (S2), it is not necessary to adopt the settings of the first embodiment for the individual pulse widths of a particularly large number of pulses. For example, a relatively narrow pulse width may be adopted. Thereby, the power consumption during chirp transmission (S2) can be reduced. Also, even in this case, the direct wave W0 and the reflected wave W2 can be discriminated even when they overlap by correlation processing for distance measurement (S4), and object detection can be performed with high accuracy.

[0108] 3. Summary As described above, in the object detection device 1A of the present embodiment, the control unit 13 determines whether the object 3 is at a distance closer than a predetermined distance (S6, S12). When the control unit 13 determines that the object 3 is at a short distance (YES in S6, S12), it generates a transmission signal Sd that suppresses the resonance of the wave receiver 11 due to the reception of the signal wave W1 as the first transmission signal Sd (S8). When the control unit 13 determines that the object 3 is not at a short distance (NO in S6, S12), it generates a second transmission signal Se different from the first transmission signal Sd (S2). Thereby, according to whether the object 3 is at a short distance or not, transmission signals Sd, Se, etc. of the signal wave W1 are properly used, and object detection can be efficiently performed.

[0109] In the object detection device 1A of the present embodiment, the control unit 13 causes the wave transmitter 10 to transmit the signal wave W1 by the second transmission signal Se (S2), and performs correlation processing based on the received wave signal Sr indicating the reception result of the subsequent wave receiver 11 to detect the distance to the object 3 (S4). Thereby, in the object detection device 1A, high-precision object detection can be performed using correlation processing.

[0110] (Other Embodiments) In the above-described Embodiment 2, as the operation of the second detection unit 32 by the object detection device 1A, an operation using a complex cross-correlation function was exemplified. However, the operation of the second detection unit 32 is not particularly limited to this. For example, the object detection device 1 of the present embodiment may use the cross-correlation function without particularly complexifying it. For example, instead of detecting the peak of the envelope E(t), the second detection unit 32 may calculate the distance to the object 3 by detecting the peak of the real part signal I. In this case, for example, the Hilbert transform unit 133 and the subsequent IFFT unit 134b in the functional configuration of the control unit 13 can be omitted.

[0111] Further, the second detection unit 32 may analyze the phase ∠z(t) in addition to the envelope E(t) in the analytic signal z(t) obtained by complexifying the cross-correlation function, and for example, calculate the phase difference between consecutive frames. Thereby, for example, a minute displacement of the object 3 can be detected with high accuracy.

[0112] Also, in each of the above embodiments, the pulse width 2a was exemplified as an example of the signal length of the carrier signal Sd. However, the signal length set in the object detection device 1 of the present embodiment is not particularly limited to this. For example, although a rectangular wave having a pulse width 2a is exemplified as the signal waveform of the carrier signal Sd in FIG. 5, the signal waveform of the carrier signal Sd is not particularly limited to a rectangular wave and may be various signal waveforms such as a triangular wave. In the present embodiment, the same setting as the above-described pulse width 2a is applicable to various signal lengths indicating the time length of the signal wave W1 in the carrier signal Sd regardless of the details of the signal waveform of the carrier signal Sd.

[0113] Moreover, in the object detection device 1 of the present embodiment, the parameter for setting the transmission signal Sd is not necessarily limited to the signal length. In the present embodiment, the transmission signal Sd is not limited to an impulse waveform and may include two or more pulses. In this case, the setting of the transmission signal Sd in consideration of the frequency characteristics of the receiver 11 similar to those in the above embodiments may be performed for each individual pulse width or for the total time length of a plurality of pulses. Further, the period of a plurality of pulses may also be set in consideration of the frequency characteristics of the receiver 11. Moreover, the transmission signal Sd is not particularly limited to a pulse waveform and may have a continuous waveform such as a sine wave.

[0114] In each of the above embodiments, the transmitter 10 constituted by a thermophone has been described. In the present embodiment, the transmitter 10 is not limited to a thermophone and may be various sound wave generators such as, for example, a piezoelectric resonance type ultrasonic transducer. The transmitter 10 of the present embodiment may be various non-directional sound sources that do not particularly have directivity. The transmitter 10 may be a variable or fixed directional sound source. For example, even when a sound wave generator having reverberation characteristics inferior to those of a thermophone is used as the transmitter 10, the influence of ringing at the time of receiving the direct wave W0 can be suppressed by setting the transmission signal Sd in the same manner as in Embodiment 1 or the like. Therefore, even in this case, it is possible to suppress a situation where it is difficult to detect an object by transmitting and receiving sound waves due to the influence of the received sound waves.

[0115] (Summary of aspects) Hereinafter, various aspects according to the present invention will be appended.

[0116] A first aspect is an object detection device that detects an object by transmitting and receiving sound waves, including a transmitter that generates a sound wave as a signal wave based on a predetermined transmission signal and transmits it to the object, a receiver that is provided separately from the transmitter and receives the sound wave to generate a received wave signal, and a control unit that generates the transmission signal so as to control the signal wave from the transmitter. The receiver has a frequency characteristic in which the received wave signal fluctuates when resonating, and the transmission signal is set so as to suppress the resonance of the receiver at the time of receiving the signal wave from the transmitter according to the frequency characteristic of the receiver.

[0117] In a second aspect, in the object detection device according to the first aspect, the transmission signal has a frequency spectrum including nodes where the intensity of the frequency components is lower than that of the surroundings, and the transmission signal is set so that the resonance frequency in the frequency characteristics of the receiver is included in the nodes.

[0118] In a third aspect, in the object detection device according to the second aspect, the transmission signal is set so that the resonance frequency is included in the lowest-frequency node among a plurality of nodes arranged periodically in the frequency spectrum.

[0119] In a fourth aspect, in the object detection device according to any one of the first to third aspects, the transmission signal is set with a signal length indicating the time length of the signal wave so as to suppress the resonance of the receiver when receiving the signal wave.

[0120] In a fifth aspect, in the object detection device according to the fourth aspect, the transmission signal has an impulse waveform with a pulse width set as the signal length.

[0121] In a sixth aspect, in the object detection device according to any one of the first to fifth aspects, the control unit detects, as the distance to the object, the distance corresponding to the period from when the signal wave is transmitted from the transmitter until it is received by the receiver via reflection from the object, based on the transmission signal and the received signal.

[0122] In a seventh aspect, in the object detection device according to any one of the first to sixth aspects, the control unit determines whether the object is at a distance closer than a predetermined distance. When it is determined that the object is at a close distance, a transmission signal that suppresses the resonance of the receiver due to the reception of the signal wave is generated as a first transmission signal. When it is determined that the object is not at a close distance, a second transmission signal different from the first transmission signal is generated.

[0123] In an eighth aspect, in the object detection device according to the seventh aspect, the control unit transmits the signal wave to the transmitter with the second transmission signal, and performs correlation processing based on the received signal indicating the reception result of the receiver thereafter to detect the distance to the object.

[0124] In the ninth aspect, in the object detection device according to any one of the first to eighth aspects, the transmitter is a thermophone that generates a signal wave by heat generation and heat stop.

Explanation of symbols

[0125] 1, 1A Object detection device 10 Transmitter 11 Receiver 13 Control unit 14 Memory unit 15 Transmission circuit 16 Reception circuit

Claims

1. An object detection device that detects an object by transmitting and receiving sound waves, a transmitter provided on the object side of the object detection device, which generates a sound wave as a signal wave based on a predetermined transmission signal without using resonance and transmits it to the object, a receiver provided separately from the transmitter on the object side of the object detection device, which receives a sound wave and generates a received wave signal, a control unit that generates the transmission signal so as to control the signal wave from the transmitter and comprising the receiver having a frequency characteristic in which the received wave signal fluctuates when resonating, the transmission signal is set so as to suppress the fluctuation of the received wave signal due to the resonance of the receiver at the time of receiving the signal wave from the transmitter according to the frequency characteristic of the receiver, the transmission signal has a frequency spectrum including a node portion where the intensity of the frequency component is lower than the surroundings, the transmission signal is set so as to include the resonance frequency in the node portion of the frequency characteristic of the receiver object detection device.

2. The transmission signal is set so as to include the resonance frequency in the lowest frequency node portion among a plurality of periodically arranged node portions in the frequency spectrum The object detection device according to claim 1.

3. The transmission signal is set with a signal length indicating the time length of the signal wave so as to suppress the resonance of the receiver at the time of receiving the signal wave The object detection device according to claim 1 or 2.

4. The transmission signal has an impulse waveform with a pulse width set as the signal length The object detection device according to claim 3.

5. An object detection device that detects an object by transmitting and receiving sound waves, a transmitter provided on the object side of the object detection device, which generates a sound wave as a signal wave based on a predetermined transmission signal without using resonance and transmits it to the object, a receiver provided separately from the transmitter on the object side of the object detection device, which receives a sound wave and generates a received wave signal, a control unit that generates the transmission signal so as to control the signal wave from the transmitter and comprising the receiver having a frequency characteristic in which the received wave signal fluctuates when resonating, the transmission signal is set so as to suppress the fluctuation of the received wave signal due to the resonance of the receiver at the time of receiving the signal wave from the transmitter according to the frequency characteristic of the receiver, The transmission signal is set with a signal length indicating the time length of the signal wave so as to suppress fluctuations in the received signal due to resonance of the receiver when receiving the signal wave. The transmission signal has a pulse waveform with a pulse width set as the signal length. Object detection device. **Claim 6** Based on the transmission signal and the received signal, the control unit detects, as the distance to the object, the distance corresponding to the period from when the signal wave is transmitted from the transmitter until it is received by the receiver via reflection by the object. The object detection device according to claim 1 or 5. **Claim 7** The control unit determines whether the object is at a distance closer than a predetermined distance, when it is determined that the object is at the short distance, generates, as a first transmission signal, a transmission signal in which resonance of the receiver due to reception of the signal wave is suppressed, when it is determined that the object is not at the short distance, generates a second transmission signal different from the first transmission signal. The object detection device according to claim 1 or 5. **Claim 8** The control unit transmits the signal wave to the transmitter using the second transmission signal, and performs correlation processing based on a received signal indicating a reception result of the receiver thereafter, to detect the distance to the object. The object detection device according to claim 7. **Claim 9** The transmitter is a thermophone that generates the signal wave by heat generation and heat stop. The object detection device according to claim 1 or 5.

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