JP2023176726A - object detection device - Google Patents

Abstract

To provide an object detection device capable of detecting vibrations with frequencies different from a resonance frequency.SOLUTION: An object detection device includes: a transceiver; a first signal generation unit that generates a transmission signal, which is a signal for causing the transceiver to transmit ultrasound; a second signal generation unit that generates a first impedance measurement signal, which is a signal for detecting vibrations applied to the transceiver; a frequency setting unit 84 that sets a frequency fi of the first impedance measurement signal based on an impedance of the transceiver; an amplitude conversion unit 82 that converts the output signal of the transceiver into an amplitude signal; and a vibration detection determination unit 88 that detects and determines the vibrations applied to the transceiver based on fluctuations in the amplitude signal.SELECTED DRAWING: Figure 4

Description

The present invention relates to an object detection device that detects an object by transmitting and receiving ultrasonic waves.

Technology has been proposed for self-driving cars that detects contact with other vehicles based on vibrations transmitted to the car body, and reduces impact by changing direction or the like based on the detection results. For example, a condenser microphone can be used to detect such vibrations.

On the other hand, an object detection device that detects obstacles and the like using an ultrasonic sensor has also been proposed, and if the microphone used in the ultrasonic sensor can also be used for the above-mentioned vibration detection, cost reduction can be expected.

In the ultrasonic sensor, a piezoelectric microphone is used (for example, see Patent Document 1). In an object detection device using a piezoelectric microphone, ultrasonic waves are transmitted by applying an alternating current voltage to the microphone. Further, the microphone outputs a received signal corresponding to the received ultrasonic wave, and by comparing the amplitude of the received signal with a predetermined threshold, reflected waves from an object can be detected.

Patent No. 4274679

Piezoelectric microphones have narrowband frequency characteristics. That is, high output and high sensitivity can be obtained by applying an alternating current voltage to the microphone at a resonant frequency. On the other hand, reception sensitivity becomes low at frequencies other than the resonant frequency. Therefore, it is difficult to detect vibrations at a frequency different from the resonant frequency using a method in which the amplitude of the output signal of the microphone is directly compared with a threshold value, similar to the detection of reflected waves.

In view of the above-mentioned points, an object of the present invention is to provide an object detection device capable of detecting vibrations at a frequency different from the resonance frequency.

In order to achieve the above object, the invention according to claim 1 provides an object detection device that detects an object by transmitting and receiving ultrasonic waves, the object detecting device detecting an object by transmitting and receiving ultrasonic waves. a transmitter/receiver (4) that outputs a signal according to the ultrasonic wave; a first signal generator (71) that generates a transmission signal that is a signal for causing the transmitter/receiver to transmit ultrasonic waves; a second signal generation section (72) that generates a first impedance measurement signal that is a signal for detection; and a frequency setting section (84) that sets the frequency fi of the first impedance measurement signal based on the impedance of the transceiver. , an amplitude converter (82) that converts the output signal of the transceiver into an amplitude signal, and a vibration detection/judgment unit (88) that detects and determines the vibration applied to the transceiver based on fluctuations in the amplitude signal. Be prepared.

The impedance of a transceiver changes depending on the frequency, and the impedance changes sharply depending on the frequency. By setting the frequency at which the impedance changes sensitively as the frequency of the first impedance measurement signal based on the frequency-impedance characteristics of the transceiver, the amplitude of the output signal becomes steep when vibration is applied to the transceiver. It fluctuates. Therefore, it is possible to detect vibrations at a frequency different from the resonant frequency of the transceiver based on fluctuations in the amplitude signal.

Note that the reference numerals in parentheses attached to each component etc. indicate an example of the correspondence between the component etc. and specific components etc. described in the embodiments to be described later.

FIG. 1 is a block diagram of an object detection device according to a first embodiment. FIG. 2 is a block diagram of the receiving circuit shown in FIG. 1. FIG. FIG. 2 is a block diagram of a signal generation unit shown in FIG. 1. FIG. FIG. 2 is a block diagram of a signal processing unit shown in FIG. 1. FIG. FIG. 3 is a diagram showing frequency characteristics of impedance of a transducer. It is a flowchart of frequency setting processing. FIG. 5 is a diagram showing an example of output signals of the BPF, amplitude converter, HPF, and root mean square device shown in FIG. 4; FIG. 5 is a diagram showing an example of output signals of the BPF, amplitude converter, HPF, and root mean square device shown in FIG. 4; FIG. 3 is a diagram showing a change in impedance of a transducer due to application of vibration. FIG. 3 is a diagram showing an output signal of a transducer. It is a timing chart of a transmission signal and a 1st impedance measurement signal. FIG. 3 is a diagram showing frequency characteristics of impedance of a transducer.

Embodiments of the present invention will be described below based on the drawings. Note that in each of the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
A first embodiment will be described. The object detection device 1 of this embodiment shown in FIG. 1 is mounted on a vehicle (not shown) and is configured to detect an object B around the vehicle. The vehicle equipped with the object detection device 1 will be referred to as the "host vehicle" hereinafter. The vehicle (not shown) is, for example, an automobile.

The object detection device 1 also has a function of detecting vibrations applied to the vehicle. This vibration is, for example, vibration caused by contact with another vehicle or vibration caused by audible sound such as an alarm sound of an emergency vehicle.

The object detection device 1 includes an ultrasonic sensor 2 and a control section 3 that controls the operation of the ultrasonic sensor 2. The ultrasonic sensor 2 is configured to detect the object B by transmitting an exploration wave that is an ultrasonic wave and receiving a reflected wave of the exploration wave from the object B.

The ultrasonic sensor 2 includes a transducer 4, a transmitter circuit 5, a receiver circuit 6, a signal generator 7, and a signal processor 8.

The transducer 4 is a transmitter/receiver that has the function of a transmitter that transmits an ultrasonic wave to the outside according to an input signal, and the function of a receiver that outputs a signal according to the received ultrasonic wave. , are electrically connected to the transmitting circuit 5 and the receiving circuit 6. That is, the ultrasonic sensor 2 has a so-called integrated transmitting and receiving configuration.

Specifically, the transducer 4 is configured as an ultrasonic microphone incorporating an electro-mechanical energy conversion element such as a piezoelectric element. The transducer 4 is disposed at a position facing the outer surface of the vehicle so that it can transmit exploration waves to the outside of the vehicle and receive reflected waves from outside the vehicle. For example, the transducer 4 is placed in the bumper of the host vehicle.

The transmitting circuit 5 is provided to drive the transducer 4 based on the input signal, thereby causing the transducer 4 to emit a probe wave. Specifically, the transmitting circuit 5 includes a digital/analog conversion circuit and the like. That is, the transmitting circuit 5 is configured to perform signal processing such as digital/analog conversion on the signal output from the signal generating section 7 to generate an element input signal. The element input signal is an AC voltage signal for driving the transducer 4. The transmitting circuit 5 is configured to apply the generated element input signal to the transducer 4 to excite the electro-mechanical energy conversion element in the transducer 4, thereby generating a probe wave.

The receiving circuit 6 is provided to generate a received signal corresponding to the result of receiving the ultrasound by the transducer 4 and output it to the signal processing section 8 . Specifically, as shown in FIG. 2, the receiving circuit 6 includes an amplifier 61 and an ADC (AD converter) 62, and the element output signal outputted by the transducer 4 is amplified by the amplifier 61, and is converted into a digital signal by

Note that the amplifier 61 performs STC processing that takes into account distance attenuation. STC is an abbreviation for Sensitivity Time Control. That is, the amplifier 61 is set to increase the gain over time from when a transmission signal is generated until when the next transmission signal is generated.

The element output signal converted into a digital signal is input to the signal processing section 8. The element output signal is an AC voltage signal generated by the electro-mechanical energy conversion element provided in the transducer 4 upon reception of the ultrasonic wave.

The signal generation section 7 is provided to generate a digital signal and output it to the transmission circuit 5. Further, the signal generation section 7 is provided to generate an analog signal and output it to the transducer 4. As shown in FIG. 3, the signal processing section 7 includes a first signal generation section 71, a second signal generation section 72, and an attenuator 73.

The first signal generation unit 71 generates a transmission signal that is a signal for causing the transducer 4 to transmit ultrasound. The transmission signal is, for example, a sine signal. The frequency fc of the transmission signal is set by a frequency setting section 84, which will be described later. The signal generated by the first signal generation section 71 is input to the transmission circuit 5.

The second signal generation unit 72 generates an impedance measurement signal that is a signal for measuring the impedance of the transducer 4. The impedance measurement signal is, for example, a sin signal.

Specifically, the second signal generation unit 72 generates a first impedance measurement signal that is a signal for detecting vibrations applied to the transducer 4. The frequency fi of the first impedance measurement signal is set by a frequency setting section 84, which will be described later.

Further, the second signal generation unit 72 generates a second impedance measurement signal that is a signal for measuring the frequency-impedance characteristic of the transducer 4. The frequency of the second impedance measurement signal is swept in a band including the design value of the resonance frequency of the transducer 4.

As will be described later, the object detection determination unit 85 of the signal processing unit 8 compares the amplitude signal with an object detection threshold to determine object detection. The amplitude of the impedance measurement signal is set so that the amplitude value after converting the output signal of the transducer 4 according to the impedance measurement signal into an amplitude signal is less than this threshold value. Specifically, the first and second impedance measurement signals generated by the second signal generation section 72 are attenuated by the attenuator 73 so that the above amplitude value becomes less than the threshold value, and then input to the transducer 4. .

The signal processing unit 8 uses the signal output from the receiving circuit 6 to measure the impedance of the transducer 4, set the frequencies of the transmission signal and the first impedance measurement signal, and perform object detection determination and vibration detection determination. As shown in FIG. 4, the signal processing section 8 includes a BPF (band pass filter) 81, an amplitude conversion section 82, an impedance measurement section 83, a frequency setting section 84, and an object detection determination section 85. . Further, the signal processing unit 8 includes an HPF (high pass filter) 86, a root mean square unit 87, and a vibration detection determination unit 88.

The signal output from the receiving circuit 6 is input to the BPF 81. The band of the BPF 81 is set to include the frequencies of the transmission signal and the first and second impedance measurement signals. The signal that has passed through the BPF 81 is input to the amplitude conversion section 82.

The amplitude converter 82 converts the output signal of the transducer 4 into an amplitude signal. Specifically, the amplitude converter 82 performs envelope detection on the output signal of the BPF 81 to remove phase and frequency information, extracts and outputs only the amplitude. The output signal of the amplitude conversion section 82 is input to the impedance measurement section 83, the object detection determination section 85, and the HPF 86.

The impedance measurement section 83 measures the impedance of the transducer 4 based on the voltage between the terminals of the transducer 4 generated by inputting an impedance measurement signal. Specifically, when measuring the impedance of the transducer 4, only the second impedance measurement signal among the transmission signal, first and second impedance measurement signals is generated and input to the transducer 4. Then, the output signal of the transducer 4 while the second impedance measurement signal is being input to the transducer 4 is inputted to the impedance measuring section 83, which is converted into an amplitude signal. The impedance measuring section 83 converts the amplitude value of this amplitude signal into the impedance of the transducer 4. As a method for converting the amplitude value into impedance, for example, the method described in Japanese Patent Laid-Open No. 2022-16127 can be used.

The impedance of the transducer 4 changes depending on the frequency of the input impedance measurement signal, and has minimum points and maximum points as shown in FIG. The frequency fmin at the minimum point is the actual resonant frequency of the transducer 4, and the frequency fmax at the maximum point is the anti-resonance frequency. Let the resonant frequency and anti-resonant frequency of the transducer 4 be fr and fa, respectively.

As shown in FIG. 5, the impedance of the transducer 4 changes sharply near the frequency fmin, that is, the resonant frequency fr, and near the frequency fmax, that is, the anti-resonant frequency fa. Further, the impedance of the transducer 4 changes sharply between the frequency fmin and the frequency fmax, that is, between the resonant frequency fr and the anti-resonant frequency fa.

The frequency of the impedance measurement signal is swept, for example, within a range of ±10% of the design value of the resonance frequency fr, and as a result, the impedance measurement section 83 obtains a signal within the region R1 in FIG. The impedance measuring section 83 extracts the frequency fmin of the minimum point and the frequency fmax of the maximum point from the impedance measurement results, and inputs them to the frequency setting section 84.

The frequency setting unit 84 sets the frequency fc of the transmission signal generated by the first signal generation unit 71 and the first impedance measurement signal generated by the second signal generation unit 72 based on the impedance measured by the impedance measurement unit 83. This is to set the frequency fi. The frequency setting unit 84 sets the frequency fi to a value different from the frequency fc. Specifically, the frequency setting unit 84 sets the frequencies fc and fi based on the frequencies fmin and fmax extracted by the impedance measurement unit 83. The frequency setting unit 84 sets the frequency fmin of the minimum point as the frequency fc of the transmission signal.

The frequency setting unit 84 sets the frequency at which the impedance of the transducer 4 sharply changes as the frequency fi of the first impedance measurement signal. Specifically, the frequency setting unit 84 sets a frequency between the actual resonant frequency fr and the anti-resonant frequency fa as the frequency fi. For example, the frequency setting unit 84 sets fi=(fr+fa)/2. Alternatively, the frequency setting unit 84 sets the frequency fi to a frequency within a range of ±5% of the resonance frequency fr. That is, the frequency fi is set to be greater than or equal to 0.95×fr and less than or equal to 1.05×fr. Alternatively, the frequency setting unit 84 sets the frequency fi to a frequency within a range of ±5% of the anti-resonance frequency fa. That is, the frequency fi is set to be greater than or equal to 0.95×fa and less than or equal to 1.05×fa.

Note that among the frequencies fc and fi, only the frequency fc may be set based on the first-order resonance frequency, and the frequency fi may be set based on the higher-order resonance frequency. For example, the frequency of the second impedance measurement signal is swept in a band including the design value of the secondary resonance frequency, and the frequencies of the minimum and maximum points of the signal in the region R2 in FIG. 5 are determined as the resonance frequency fr and the antiresonance frequency fa. do. The frequency fi may be a frequency between the resonant frequency fr and the anti-resonant frequency fa, or the frequency fi may be greater than or equal to 0.95×fr and less than or equal to 1.05×fr. When setting the frequency fi based on a high-order resonance frequency, the band of the BPF 81 is set wide so as to include the frequency fi. The values of frequencies fc and fi set by the frequency setting section 84 are input to the first signal generation section 71 and the second signal generation section 72.

The object detection determination section 85 performs object detection determination based on the amplitude signal. Specifically, the object detection determination unit 85 compares the amplitude signal with a predetermined threshold value, and determines that an object exists around the vehicle if the amplitude value is larger than the threshold value. This threshold value is defined as an object detection threshold value. On the other hand, if the amplitude value is less than or equal to the object detection threshold, the object detection determination unit 85 determines that there is no object around the vehicle that is likely to come into contact with the vehicle. Furthermore, when it is determined that an object exists, the object detection determination unit 85 calculates the distance between the vehicle and the object. For example, the object detection determination unit 85 calculates the distance to the object using the TOF method based on the time when the amplitude value exceeds the object detection threshold. TOF is an abbreviation for Time of Flight. The object detection determination result and distance calculation result by the object detection determination section 85 are transmitted to the control section 3.

The HPF 86 is provided to remove low frequency components from the output signal of the amplitude converter 82 and pass high frequency components. The cutoff frequency of the HPF 86 is set so that fluctuations in the amplitude signal when vibrations are applied to the transducer 4 can be detected. The signal that has passed through the HPF 86 is input to a root mean square unit 87 and a vibration detection determination section 88 .

The root mean square unit 87 is provided to square the signal that has passed through the HPF 86 and then perform averaging processing and LPF (low pass filter) processing on the signal. This LPF removes amplitude fluctuations due to reception of reflected waves from the signal that has passed through the HPF 86. For example, if the signal width of the reflected wave is expected to be about 0.2 msec, set the cutoff frequency of the LPF to a value less than 5 kHz, for example 2.5 kHz, so that the signal with a frequency of 5 kHz can be removed from the amplitude signal. good. By removing high frequency components using the LPF, the vibration detection and determination section 88 can easily detect and determine vibrations. The signal that has passed through the mean square unit 87 is input to a vibration detection determination section 88 .

The vibration detection and determination section 88 detects and determines the vibration applied to the transducer 4 based on fluctuations in the amplitude signal. Specifically, the vibration detection determination unit 88 compares the input signal with a predetermined threshold value, and determines that vibration has been applied to the transducer 4 if the signal is larger than the threshold value. This threshold value is defined as the vibration detection threshold value. On the other hand, if the signal is less than or equal to the vibration detection threshold, the vibration detection determination unit 88 determines that no vibration is applied to the transducer 4. Further, if it is determined that vibration is applied to the transducer 4, the vibration detection determination unit 88 identifies the type of vibration based on the signal input from the HPF 86. For example, the vibration detection determination unit 88 identifies the alarm sound of an emergency vehicle using a known voice recognition technique using frequency analysis or the like. The vibration detection determination result by the vibration detection determination section 88 is transmitted to the control section 3.

The signal generation unit 7 and the signal processing unit 8 are configured by a DSP programmed with functions such as transmission signal generation, impedance measurement signal generation, impedance measurement, object detection determination, vibration detection determination, and the like. DSP is an abbreviation for Digital Signal Processor.

The control unit 3 is connected to the ultrasonic sensor 2 via an in-vehicle communication line so as to be able to communicate information, and is configured to control the transmission and reception operations of the ultrasonic sensor 2.

The control unit 3 is provided as a sonar ECU, and includes an on-vehicle microcomputer including a CPU, ROM, RAM, nonvolatile rewritable memory, etc. (not shown). ECU is an abbreviation for Electronic Control Unit. Examples of the nonvolatile rewritable memory include EEPROM and flash ROM. EEPROM stands for Electronically Erasable and Programmable Read Only Memory.

The control unit 3 issues a transmission instruction to the signal generation unit 7 and detects the approach of an obstacle or an emergency vehicle based on the determination result transmitted from the signal processing unit 8.

The operation of the object detection device 1 will be explained. When the object detection device 1 is started, it executes the process shown in FIG. 6 and sets the frequency fc and the frequency fi.

First, in step S1, the second signal generation unit 72 generates a second impedance measurement signal by sweeping the frequency in a band of ±10% of the design value of the resonance frequency fr. The second impedance measurement signal generated by the second signal generator 72 is attenuated by the attenuator 73 and then input to the transducer 4 . The output signal of the transducer 4 is input to the signal processing unit 8 via the receiving circuit 6, converted into an amplitude signal by the amplitude conversion unit 82, and input to the impedance measurement unit 83.

In subsequent step S2, the impedance measuring section 83 converts the input amplitude signal into the impedance of the transducer 4, extracts the frequency fmin of the minimum point of impedance and the frequency fmax of the maximum point, and inputs them to the frequency setting section 84. .

In subsequent step S3, the frequency setting unit 84 sets frequencies fc and fi based on the frequencies fmin and fmax extracted in step S2. Specifically, the frequency setting unit 84 sets fc=fmin and fi=(fmin+fmax)/2, for example. The process then ends. When the process shown in FIG. 6 is completed, object detection process and vibration detection process are started. Note that the process shown in FIG. 6 is executed repeatedly at a predetermined cycle after being executed when the object detection device 1 is started.

In the object detection process, a transmission signal having the frequency fc set in step S3 is generated by the first signal generation section 71 and input to the transducer 4 via the transmission circuit 5. As a result, the transducer 4 transmits ultrasonic waves. When the reflected wave is received by the transducer 4, a signal corresponding to the reflected wave is output from the transducer 4, converted into an amplitude signal, and input to the object detection determination section 85. The object detection determination unit 85 compares the amplitude value of the amplitude signal with the object detection threshold, and if the amplitude value is larger than the object detection threshold, determines that an object exists around the vehicle, and transmits the determination result to the control unit 3. Send to. The control unit 3 performs avoidance control etc. according to the determination result.

In the vibration detection process, the first impedance measurement signal having the frequency fi set in step S3 is generated by the second signal generation section 72 and input to the transducer 4. Then, a signal corresponding to the impedance is output from the transducer 4, converted into an amplitude signal, processed by the HPF 86 and the root mean square unit 87, and then input to the vibration detection determination section 88.

When no vibration is applied to the transducer 4, the amplitude of the output signal is approximately constant, so the amplitude signal is removed by the HPF 86. Specifically, the BPF 81 outputs a sine signal with a constant amplitude as shown in FIG. 7(a), and the amplitude converter 82 outputs a signal with a constant amplitude as shown in FIG. 7(b). Then, the amplitude of the output signal of the HPF 86 and the root mean square unit 87 becomes 0 as shown in FIGS. 7(c) and 7(d), respectively, and the vibration detection determination unit 88 determines that no vibration is applied to the transducer 4. judge.

On the other hand, when vibration is applied to the transducer 4, the amplitude of the output signal changes due to a change in the impedance of the transducer 4. Then, the BPF 81 and the amplitude converter 82 output signals whose amplitudes change as shown in FIGS. 8(a) and 8(b), respectively, and the HPF 86 outputs signals whose amplitudes change to a certain extent as shown in FIG. 8(c). Outputs a signal with . Then, as shown in FIG. 8D, when the amplitude of the output signal of the root mean square unit 87 becomes larger than the vibration detection threshold, the vibration detection determination unit 88 determines that vibration has been applied to the transducer 4. In this way, when vibration is applied to the transducer 4, a signal corresponding to the vibration passes through the HPF 86, making it possible to detect the vibration.

At this time, since the frequency fi of the first impedance measurement signal is set to be a frequency at which the impedance of the transducer 4 changes sensitively to the application of vibration, the amplitude of the output signal changes sensitively in response to the vibration. It becomes easier to be detected by the detection determination unit 88.

For example, assume that vibration is applied to the transducer 4 having the frequency-impedance characteristic shown by the solid line in FIG. 9, and the frequency-impedance characteristic changes as shown by the one-dot chain line or the two-dot chain line. In this case, if the frequency f1 at which the change in impedance is small is set as the frequency fi, it is difficult to detect the vibration because the change in impedance due to the application of vibration is small. On the other hand, if the frequency f2 at which the impedance changes sharply is the frequency fi, the impedance changes greatly due to the application of vibration, so that the vibration can be detected with high sensitivity. The determination result in the vibration detection determination section 88 is transmitted to the control section 3, and the control section 3 performs avoidance control etc. according to the determination result.

The object detection process is repeatedly executed at a predetermined period, and the first signal generation unit 71 intermittently generates a transmission signal. On the other hand, the vibration detection process is always executed except while the frequency setting process is being performed. That is, the second signal generation section 72 constantly generates the first impedance measurement signal and inputs it to the transducer 4.

In this way, the output signal of the transducer 4 becomes as shown in FIG. In FIG. 10, the solid line is an amplitude signal corresponding to the reception of reverberation and reflected waves caused by transmission of ultrasonic waves, and the broken line is an amplitude signal corresponding to the first impedance measurement signal.

As shown in FIG. 10, after the transmission signal is generated at time t1 and the ultrasonic wave is transmitted from the transducer 4, the output signal of the transducer 4 is becomes larger than the object detection threshold.

On the other hand, the first impedance measurement signal is constantly generated, and the transducer 4 outputs the signal at all times in response to the first impedance measurement signal. However, the first impedance measurement signal is attenuated by the attenuator 73, and the amplitude of the output signal of the transducer 4 according to the first impedance measurement signal is less than the object detection threshold, so the first impedance measurement signal has no effect on the object detection process. The impact is minor.

Further, when the reflected wave is received and the amplitude signal increases, the frequency of the amplitude signal temporarily increases and the amplitude signal passes through the HPF 86. However, since the amplitude signal with a short signal width is removed by the root mean square unit 87, only the vibration with a long signal width is detected by the vibration detection determination unit 88.

Note that, as shown in FIG. 11, the input of the first impedance measurement signal to the transducer 4 may be stopped until a predetermined time period elapses after the transmission signal is input to the transducer 4. In FIG. 11, the solid line portion is the time when the signal is generated, and the broken line portion is the time when the signal generation is stopped.

Further, as described above, the amplifier 61 is set to increase the gain as time passes from the generation of a transmission signal until the generation of the next transmission signal. When this gain becomes higher than a predetermined value, input of the first impedance measurement signal to the transducer 4 may be stopped as shown in FIG.

As explained above, in this embodiment, by setting the frequency at which the impedance of the transducer 4 sharply changes as the frequency fi of the first impedance measurement signal, the amplitude of the output signal when vibration is applied to the transducer 4 is set as the frequency fi of the first impedance measurement signal. fluctuates rapidly. Therefore, it is possible to detect vibrations at a frequency different from the resonant frequency of the transducer 4 based on the amplitude signal.

Further, according to the above embodiment, the following effects can be obtained.

(1) The impedance measurement unit 83 measures the impedance of the transducer 4 based on the voltage between the terminals of the transducer 4 generated by inputting the second impedance measurement signal. This makes it possible to extract frequencies where the impedance changes sharply.

(2) The frequency setting unit 84 sets the frequency fi to a value greater than or equal to 0.95×fr and less than or equal to 1.05×fr. In this range, the impedance of the transducer 4 changes sharply depending on the frequency, and the influence of changes in the frequency-impedance characteristics caused in the transducer 4 due to vibration becomes large. This allows the impedance to change sensitively in response to vibrations, improving vibration detection accuracy.

(3) The frequency setting unit 84 sets the frequency fi to a value different from the frequency fc. According to this, object detection and vibration detection can be performed in parallel.

(4) The frequency setting unit 84 sets the frequency fi to a value between the resonant frequency fr and the anti-resonant frequency fa. In this range, the impedance of the transducer 4 changes sharply depending on the frequency, so vibration detection accuracy improves.

(5) Set the frequency fi based on the high-order resonance frequency of the transducer 4. By setting the frequency fi to a frequency near the high-order resonance frequency and separating the frequencies for object detection and vibration detection, the detection accuracy when object detection and vibration detection are performed in parallel is improved.

(6) The frequency setting unit 84 sets the frequency fi to a value greater than or equal to 0.95×fa and less than or equal to 1.05×fa. In this range, the impedance of the transducer 4 changes sharply depending on the frequency, so vibration detection accuracy improves.

(7) Measurement of the impedance of the transducer 4 and setting of the frequency fi are performed periodically. This makes it possible to appropriately set the frequencies fc and fi in response to changes in impedance characteristics due to temperature changes, mud adhesion to the transducer 4, etc., and improves object detection accuracy and vibration detection accuracy. Further, by comparing the measurement result with the previous measurement result, it is possible to detect substances attached to the transducer 4. For example, if the variation in frequency fmin is larger than a specified value, it is determined that mud or the like has adhered to the transducer 4.

(8) The amplitude of the impedance measurement signal is set so that the amplitude value after converting the output signal of the transducer 4 according to the impedance measurement signal into an amplitude signal is less than the object detection threshold. This makes it possible to perform object detection and vibration detection in parallel.

(9) The input of the first impedance measurement signal to the transducer 4 is stopped until a predetermined time period elapses after the transmission signal is input to the transducer 4. Immediately after the transmission signal is input to the transducer 4, the output signal of the transducer 4 increases due to reverberation, making vibration detection difficult. Therefore, by stopping input of the first impedance measurement signal in this manner, processing efficiency is improved.

(10) The first signal generation unit 71 intermittently generates a transmission signal, and the amplifier 61 has a gain that increases over time from generation of a transmission signal until generation of the next transmission signal. However, when the gain is higher than a predetermined value, input of the first impedance measurement signal to the transducer 4 is stopped. Thereby, saturation of the amplitude signal due to reception of reflected waves and application of vibration can be suppressed.

(11) The transducer 4 is a microphone having a piezoelectric element, and is mounted on the bumper of the vehicle. Unlike when the transducer 4 is configured with a capacitor type microphone, when the transducer 4 is configured with a piezoelectric type microphone, dustproof, drip-proof, and chipping-proof measures are possible, and it can also be placed on the bumper of a vehicle. I can do it.

(Other embodiments)
Note that the present invention is not limited to the embodiments described above, and can be modified as appropriate within the scope of the claims. Furthermore, in the above embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where it is specifically specified that they are essential or where they are clearly considered essential in principle. . In addition, in the above embodiments, when numerical values such as the number, numerical value, amount, range, etc. of the constituent elements of the embodiment are mentioned, it is especially specified that they are essential, or it is clearly limited to a specific number in principle. It is not limited to that specific number, except in cases where

The frequency fi may be set by measuring the frequency-impedance characteristic of the transducer 4 before shipping the object detection device. In this case, the object detection device does not need to have the function of measuring the frequency-impedance characteristic of the transducer 4.

The frequency fc of the transmission signal and the frequency fi of the first impedance measurement signal may be set to the same value. In this case, object detection and vibration detection can be performed by shifting the timing of generation of the transmission signal and generation of the first impedance measurement signal.

The transmission signal may be a signal whose frequency changes over time. For example, an up-chirp signal whose frequency monotonically increases over time or a down-chirp signal whose frequency monotonically decreases over time can be used as the transmission signal. In this case, even if the frequency fi is included in the frequency band of the transmitted signal, by using a composite filter etc., the signal corresponding to the reflected wave and the signal corresponding to the vibration are extracted separately from the amplitude signal, Object detection and vibration detection can be performed in parallel.

Depending on the circuit configuration of the transmitting circuit 5, two anti-resonance points may appear as shown in FIG. 12 in the measurement results of the frequency-impedance characteristics of the transducer 4. That is, in addition to the frequency fmax1 higher than the frequency fmin, the impedance may take a maximum value also at the frequency fmax2 lower than the frequency fmin. In this case, the frequency fi may be set to a value between the frequency fmin and the frequency fmax1, or may be set to a value between the frequency fmin and the frequency fmax2. Even at frequencies between the frequency fmin and the frequency fmax2, the impedance of the transducer 4 changes sharply depending on the frequency, so setting the frequency fi as described above improves vibration detection accuracy. Further, the frequency fi may be set to a value of 0.95×fmax1 to 1.05×fmax1, or may be set to a value of 0.95×fmax2 to 1.05×fmax2. Since the impedance of the transducer 4 changes sharply depending on the frequency even in the range from 0.95 x fmax2 to 1.05 x fmax2, vibration detection accuracy is improved by setting the frequency fi as above. . Even when two anti-resonance points appear on both sides of the high-order resonance frequency, the frequency fi can be similarly set.

The impedance measurement unit 83 may extract the frequencies fmin and fmax without converting the amplitude value of the amplitude signal into the impedance of the transducer 4. Since the amplitude value and impedance are in a proportional relationship, the frequency of the minimum point and the frequency of the maximum point of the amplitude value become the frequency fmin of the minimum point and the frequency fmax of the maximum point of impedance, respectively.

Each of the functional configurations and methods described above may be implemented by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. . Alternatively, each of the functional configurations and methods described above may be implemented by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, each of the functional configurations and methods described above may be implemented in a single unit configured by a combination of a processor and memory configured to perform one or more functions and a processor configured by one or more hardware logic circuits. It may be implemented by more than one dedicated computer. The computer program may also be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium.

4 Transducer 71 First signal generation section 72 Second signal generation section 82 Amplitude conversion section 84 Frequency setting section 88 Vibration detection determination section

Claims (12)

An object detection device that detects an object by transmitting and receiving ultrasonic waves,
a transceiver (4) that transmits ultrasonic waves according to the input signal and outputs a signal according to the received ultrasonic waves;
a first signal generation unit (71) that generates a transmission signal that is a signal for causing the transceiver to transmit ultrasound;
a second signal generation unit (72) that generates a first impedance measurement signal that is a signal for detecting vibrations applied to the transceiver;
a frequency setting unit (84) that sets a frequency fi of the first impedance measurement signal based on the impedance of the transceiver;
an amplitude converter (82) that converts the output signal of the transceiver into an amplitude signal;
An object detection device comprising: a vibration detection determination section (88) that performs a detection determination of vibration applied to the transmitter/receiver based on fluctuations in the amplitude signal. In addition to the first impedance measurement signal, the second signal generation unit generates a second impedance measurement signal that is a signal for measuring the frequency-impedance characteristic of the transceiver,
The frequency setting unit sets the frequency fi based on the impedance of the transceiver measured based on the voltage between terminals of the transceiver generated by inputting the second impedance measurement signal. Object detection device. The resonant frequency of the transceiver is fr,
The object detection device according to claim 1 or 2, wherein the frequency setting unit sets the frequency fi to a value of 0.95×fr or more and 1.05×fr or less. The object detection device according to claim 3, wherein the frequency setting section sets the frequency fi to a value different from a frequency of the transmission signal. The resonant frequency of the transceiver is fr,
The anti-resonant frequency of the transmitter and receiver is fa,
The object detection device according to claim 1 or 2, wherein the frequency setting section sets the frequency fi to a value between the resonance frequency fr and the anti-resonance frequency fa. The object detection device according to claim 3, wherein the resonant frequency fr is a higher-order resonant frequency of the transceiver. The anti-resonant frequency of the transmitter and receiver is fa,
The object detection device according to claim 1 or 2, wherein the frequency setting unit sets the frequency fi to a value of 0.95×fa or more and 1.05×fa or less. The object detection device according to claim 1 or 2, wherein the measurement of the impedance of the transceiver and the setting of the frequency fi are performed periodically. an object detection determination unit (85) that compares the amplitude signal with a threshold value to determine object detection;
The amplitude of the second impedance measurement signal is set such that the amplitude value after converting the output signal of the transceiver according to the second impedance measurement signal into the amplitude signal is less than the threshold value. The object detection device described in . The object detection device according to claim 1 or 2, wherein input of the first impedance measurement signal to the transceiver is stopped until a predetermined time period elapses after the transmission signal is input to the transceiver. comprising an amplifier (61) that amplifies the output signal of the transceiver,
the first signal generation unit intermittently generates the transmission signal;
The amplifier has a gain that increases over time from generation of the transmission signal to generation of the next transmission signal,
The object detection device according to claim 1 or 2, wherein input of the first impedance measurement signal to the transceiver is stopped when the gain is higher than a predetermined value. 3. The object detection device according to claim 1, wherein the transceiver is a microphone having a piezoelectric element, and is mounted on a bumper of a vehicle.

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