JP2019200059A - Object detection device - Google Patents

Abstract

To provide an object detection device that can improve the identification accuracy of a received wave.SOLUTION: An object detection device comprises: a transmitting-receiving wave unit 1 that transmits an ultrasonic wave as a survey wave including an identification code for distinguishing it from an ultrasonic wave transmitted from other devices, and that, after receiving the ultrasonic wave, outputs a signal according to the received wave; a first filtering unit 6 and a second filtering unit 7 that filter the output signal of the transmitting-receiving wave unit 1; an amplitude determination part 10 that detects a reflection wave on the basis of the amplitude information included in the output signal of the first filtering unit 6; and a signal determination unit 11 that determines whether or not the received wave is a reflection wave of the survey wave on the basis of the code information included in the output signal of the second filtering unit 7. The first filtering unit 6 and the second filtering unit 7 have different properties from each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an object detection device.

  For vehicle-mounted object detection devices that detect obstacles by sending and receiving ultrasonic waves, change the frequency of the exploration wave with time, compare the frequency of the received wave and the exploration wave, and send other vehicles traveling around A technique for avoiding interference with ultrasonic waves has been proposed (see, for example, Patent Document 1).

European Patent No. 2373434

  However, in an object detection apparatus that transmits and receives ultrasonic waves using a resonance type microphone, the frequency waveform of the received signal may change in the same manner as the exploration wave when reception of the reflected wave starts and when reception ends. Therefore, in the method of identifying a received wave only by frequency comparison, there is a possibility that the detection accuracy of an object may be reduced due to a decrease in received wave identification accuracy.

  In this regard, the present inventors detect the amplitude peak based on the amplitude gradient of the received wave, etc., and compare the frequencies in the time range near the amplitude peak, thereby improving the identification accuracy of the received wave. It was confirmed.

  To detect the propagation time of ultrasonic waves and the peak of amplitude, the amplitude waveform generated from the received signal is used, but when generating the amplitude waveform, in order to reduce the influence of noise and overlapping of multiple ultrasonic waves, It is desirable to use a filter with a narrow BW (bandwidth).

  On the other hand, the frequency waveform generated from the received signal is used to compare the frequency of the exploration wave and the received wave. When generating the frequency waveform, a filter with a wide BW is used to suppress the loss of frequency modulation information. It is desirable to use it. In order to further suppress the loss of frequency information, it is desirable to use a filter that complements the frequency characteristics of the resonant microphone. In addition, it is desirable to use a filter with a wide BW even when a search wave is transmitted by changing the phase or amplitude instead of the frequency and the change patterns of the phase of the search wave and the received wave are compared.

  Therefore, if an amplitude waveform used for detection of an amplitude peak and a waveform such as a frequency used for pattern comparison are generated using the same filter, the detection accuracy of the amplitude peak or pattern may be lowered. Such a decrease in detection accuracy causes a decrease in received wave identification accuracy, so there is room for improvement in received wave identification accuracy.

  In view of the above points, an object of the present invention is to provide an object detection device capable of improving the identification accuracy of received waves.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided an object detection device that is mounted on a vehicle and detects an object outside the vehicle, for discrimination from an ultrasonic wave transmitted from another device. And transmitting / receiving ultrasonic waves as exploration waves, receiving ultrasonic waves and outputting signals corresponding to the received waves, and a first filter for filtering the output signals of the transmitting / receiving units Unit (5, 6), second filter unit (5, 7), and amplitude determination unit (10) that measures the propagation time or amplitude value of the reflected wave based on the amplitude information included in the output signal of the first filter unit ) And a signal determination unit (11) that determines whether the received wave is a reflected wave of the exploration wave based on code information included in the output signal of the second filter unit, the first filter unit And the second filter unit have different characteristics.

  According to this, since the first filter unit and the second filter unit corresponding to the amplitude determination unit and the signal determination unit are provided, the amplitude information and the code information are generated using a filter having characteristics suitable for the application. be able to. Thereby, the detection accuracy of the peak of amplitude and the code can be improved, and the identification accuracy of the received wave can be improved.

  Reference numerals in parentheses attached to each component and the like indicate an example of a correspondence relationship between the component and the like and specific components described in the embodiments described later.

It is a figure which shows the structure of the object detection apparatus concerning 1st Embodiment. It is a figure which shows the structure of a receiving circuit. It is a figure which shows the structure of a signal processing part. It is a figure which shows the filter characteristic when BW is changed. It is a figure which shows the filter characteristic when changing Q value. It is a figure which shows the structure of an amplitude production | generation part and an amplitude determination part. It is a figure which shows the structure of a frequency generation part. It is a figure which shows the amplitude waveform and frequency waveform in a comparative example. It is a figure which shows the amplitude waveform and frequency waveform in 1st Embodiment. It is a figure which shows the filter characteristic in other embodiment. It is a figure which shows the filter characteristic in other embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In 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 of the present embodiment is an ultrasonic sonar device that is mounted on a vehicle and detects an object outside the vehicle.

  As shown in FIG. 1, the object detection apparatus includes a microphone 1, a transmission circuit 2, a signal generation unit 3, and a control unit 4. The object detection apparatus includes a receiving circuit 5, a signal processing unit 6, a signal processing unit 7, an amplitude generation unit 8, an amplitude determination unit 9, a frequency generation unit 10, and a signal determination unit 11. Yes.

  The control unit 4, the signal processing unit 6, and the like are configured by a known microcomputer including a CPU, a ROM, a RAM, an I / O, and the like, and execute processes such as various calculations according to a program stored in the ROM or the like. ROM and RAM are non-transitional physical storage media. Further, the control unit 4 or the like may be configured by an ASIC including a signal processing circuit.

  The object detection device includes, for example, a microphone 1 and a plurality of sensor units arranged in each part of the vehicle and a calculation unit arranged in the ECU. Among the components shown in FIG. Other than the above may be arranged in the sensor unit or arranged in the calculation unit.

  The microphone 1 transmits and receives ultrasonic waves and outputs a signal corresponding to a received wave, and corresponds to a wave transmitting / receiving unit. The microphone 1 is disposed so as to face the outer surface of the vehicle, and transmits an ultrasonic wave that is an exploration wave for detecting an object toward the outside of the vehicle. Specifically, the microphone 1 includes a piezoelectric element (not shown) having a configuration in which a piezoelectric layer is disposed between two electrodes facing each other. The two electrodes are connected to the transmission circuit 2, and an ultrasonic voltage is transmitted from the microphone 1 to the outside of the vehicle by applying an AC voltage from the transmission circuit 2 and deforming the piezoelectric layer.

  The transmission circuit 2 performs processing such as boosting on the input signal and outputs it. The transmission circuit 2 is connected to a signal generation unit 3 that generates a pulse signal. The transmission circuit 2 converts the pulse signal input from the signal generation unit 3 into an AC signal, and then boosts the signal to generate the pulse signal. An alternating voltage is applied to the microphone 1.

  Note that the signal generation unit 3 generates a pulse signal in accordance with a transmission instruction from the control unit 4 so that an ultrasonic identification code is included. This code is for identifying the reflected wave of the exploration wave transmitted from the microphone 1 and the ultrasonic wave transmitted from another object detection device. The identification of the received wave using the identification code enables simultaneous measurement with a plurality of microphones, improves the measurement reliability, and shortens the measurement cycle.

  Specifically, the identification code is represented by a pattern such as an amplitude, a frequency, and a phase. The signal generation unit 3 of the present embodiment generates a pulse signal including a chirp signal whose frequency changes in a predetermined pattern with time. Thereby, an ultrasonic wave including a chirp signal whose frequency changes with time in a predetermined pattern is transmitted from the microphone 1 as an exploration wave.

  As the chirp signal, an upstream chirp signal representing a code “0” and a downstream chirp signal representing a code “1” are used. The upstream chirp signal is a signal whose frequency increases with the passage of time, and the downstream chirp signal is a signal whose frequency decreases with the passage of time.

  Two electrodes of the piezoelectric element included in the microphone 1 are also connected to the receiving circuit 5. When the microphone 1 receives ultrasonic waves, the piezoelectric layer is deformed to generate a voltage between the two electrodes, and this voltage is input to the receiving circuit 5.

  The receiving circuit 5 performs processing such as amplification and filtering on the output signal of the microphone 1. As shown in FIG. 2, the reception circuit 5 includes a DC cut unit 12, a clamp protection circuit 13, an amplifier 14, a BPF (band pass filter) 15, an amplifier 16, and an ADC (AD converter) 17. The output signal of the microphone 1 is input to the DC cut unit 12.

  The DC cut unit 12 removes an offset component included in the output signal of the microphone 1 and protects a subsequent stage from an excessive DC current. The DC cut unit 12 is an LPF (low-pass filter) and HPF (high-pass filter) with fixed characteristics. It is configured. The output signal of the DC cut unit 12 is input to the clamp protection circuit 13.

  The clamp protection circuit 13 defines an upper limit of the signal magnitude and protects the subsequent stage from an excessive input. The output signal of the clamp protection circuit 13 is amplified by the amplifier 14 and then input to the BPF 15.

  The BPF 15 is an analog filter that removes noise from an input signal. The BPF 15 may be configured by a combination of LPF and HPF. The BPF 15 may be a characteristic that complements the frequency characteristic of the microphone 1. The center frequency, BW, and complementary characteristics of the BPF 15 are variable and are set by an input signal from the control unit 4. The output signal of the BPF 15 is amplified by the amplifier 16, converted into a digital signal by the ADC 17, and then input to the signal processing units 6 and 7. The reference clock for measuring the amplification factor of the amplifier 16, the sampling rate of the ADC 17, and the propagation time is set by an input signal from the control unit 4.

  Note that the receiving circuit 5 may have another configuration. For example, a plurality of amplifiers 16 may be arranged. Further, an amplifier 16 may be disposed in front of the BPF 15.

  The signal processing units 6 and 7 perform processing such as amplification and filtering on the output signal of the receiving circuit 5, and correspond to a first filter unit and a second filter unit, respectively. As shown in FIG. 3, the signal processing unit 6 includes a BPF 18 and an amplitude offset correction unit 19.

  The BPF 18 is a digital filter that removes noise from an input signal. The BPF 18 may have a characteristic that complements the frequency characteristic of the microphone 1. The center frequency, BW, and complementary characteristics of the BPF 18 are set by an input signal from the control unit 4. The output signal of the BPF 18 is input to the amplitude offset correction unit 19.

  The amplitude offset correction unit 19 amplifies the input signal from the BPF 18 and corrects the amplitude offset. The amplification factor and the amplitude offset correction amount of the amplitude offset correction unit 19 are set by an input signal from the control unit 4. The output signal of the amplitude offset correction unit 19 is input to the amplitude generation unit 8.

  As shown in FIG. 3, the signal processing unit 7 includes a BPF 20 and an amplitude offset correction unit 21. The amplitude offset correction unit 21 of the signal processing unit 7 has the same configuration as the amplitude offset correction unit 19 of the signal processing unit 6.

  The BPF 20 of the signal processing unit 7 has different characteristics from the BPF 18 of the signal processing unit 6. Specifically, the BPF 20 is set to have a wider BW than the BPF 18. For example, the BPFs 18 and 20 are biquadratic filters having the same center frequency, and the BPF 20 has a wider BW than the BPF 18 as shown in FIG. Alternatively, as shown in FIG. 5, the BPF 20 is set to have a larger reverse characteristic that complements the frequency characteristic of the microphone 1 than the BPF 19.

  The broken lines in FIGS. 4 and 5 indicate threshold values for defining the BW of the filter. The characteristics of the BPFs 18 and 20 are set so that most of the range in which the frequency of the exploration wave changes is included in the pass band, where the frequency range in which the gain is greater than the threshold is defined as the pass band of the filter.

  If the complementary characteristic of the filter is increased and the gain graph is M-shaped, a signal of a part of the frequency is amplified. However, the filter characteristic is combined with the characteristic of the microphone 1 shown in FIG. Amplification is reduced. As shown in FIG. 5, the characteristics of the BPFs 18 and 20 are set so that most of the range in which the frequency of the exploration wave changes is included in the pass band of the synthesis characteristics with the microphone 1.

  The signal input from the reception circuit 5 to the signal processing unit 7 is processed by the BPF 20, amplified and corrected by the amplitude offset correction unit 21, and input to the frequency generation unit 10.

  As shown in FIG. 6, the amplitude generation unit 8 includes an amplitude conversion unit 22 and an LPF 23. The amplitude converter 22 extracts amplitude information from the output signal of the signal processor 6 and generates an amplitude waveform of the received wave. The amplitude waveform generated by the amplitude converting unit 22 is smoothed by the LPF 23 and then input to the amplitude determining unit 9. The characteristics of the LPF 23 are set by an input signal from the control unit 4.

  The amplitude determination unit 9 measures the propagation time and amplitude value of the reflected wave based on the amplitude waveform generated by the amplitude generation unit 8. As shown in FIG. 6, the amplitude determination unit 9 includes a threshold determination unit 24, a time measurement unit 25, and a peak detection unit 26.

  The threshold determination unit 24 determines whether or not the amplitude of the received wave is larger than a predetermined amplitude threshold based on the amplitude waveform generated by the amplitude generation unit 8. The amplitude threshold is set by an input signal from the control unit 4. The threshold determination unit 24 measures the amplitude value of the amplitude waveform.

  The determination result of the threshold determination unit 24 is input to the time measurement unit 25 and the peak detection unit 26. The time measuring unit 25 measures the time from when the microphone 1 transmits the exploration wave until the threshold determining unit 24 determines that the amplitude of the received wave is larger than the amplitude threshold as the propagation time, and the measurement result Transmit to the control unit 4.

  The peak detector 26 detects the peak of the amplitude of the received wave. In addition to the determination result of the amplitude determination unit 25, the amplitude waveform generated by the amplitude generation unit 8 is also input to the peak detection unit 26 via the amplitude determination unit 25. A peak is detected from the amplitude waveform.

  For example, the peak detector 26 detects a portion of the amplitude waveform where the absolute value of the slope is equal to or smaller than a predetermined value as an amplitude peak. In addition, the peak detector 26 calculates, for example, a residual sum of squares between the reference waveform stored in the control unit 4 and the amplitude waveform of the received wave, and the residual sum of squares of the amplitude waveform is equal to or less than a predetermined value. The part is detected as an amplitude peak.

  Further, the peak detector 26 measures a peak value having an amplitude larger than the amplitude threshold. The peak detection unit 26 transmits the amplitude peak detection result, the amplitude peak value, the determination result of the amplitude determination unit 25, the wave width value, and the like to the control unit 4.

  As shown in FIG. 7, the frequency generation unit 10 includes a phase difference conversion unit 27 and a frequency conversion unit 28. The phase difference conversion unit 27 mixes the pulse signal generated by the signal generation unit 3 with the signal input from the signal processing unit 7 and extracts phase difference information from the input signal. The phase difference information is input to the signal determination unit 11 and the frequency conversion unit 28. A reference clock used for conversion by the phase difference conversion unit 27 is input from the control unit 4.

  The frequency converter 28 calculates the frequency of the received wave based on the frequency of the pulse signal generated by the signal generator 3 and the phase difference input from the phase difference converter 27, and generates a frequency waveform. is there. The frequency waveform generated by the frequency conversion unit 28 is transmitted to the signal determination unit 11.

  The signal determination unit 11 determines whether or not the received wave is a reflected wave of the exploration wave based on the code information included in the output signal of the signal processing unit 7. As described above, the signal generation unit 3 of the present embodiment generates a pulse signal so that the identification code is represented by a change in frequency. And if the change pattern of the frequency showing this code | symbol is detected from a frequency waveform, the signal generation part 11 will determine with the code | symbol same as a transmission wave being included in the frequency waveform of a received wave.

  For example, the reference waveform corresponding to the codes “0” and “1” is input from the control unit 4 to the signal determination unit 11, and the signal determination unit 11 stores the remaining reference waveform and the frequency waveform of the received wave. Calculate the difference sum of squares. Then, when the residual sum of squares for the code “0” is equal to or less than a predetermined threshold, the signal determination unit 11 determines that the code “0” is included in the frequency waveform of the received wave, and the signal “11” When the residual sum of squares is equal to or smaller than the threshold value, it is determined that the code “1” is included in the frequency waveform of the received wave.

  Further, for example, the signal determination unit 11 receives a frequency change pattern representing the codes “0” and “1” from the control unit 4. Then, when a pattern similar to the pattern representing the code “0” is detected from the frequency waveform, the signal determination unit 11 determines that the code “0” is included in the frequency waveform of the received wave. Further, when a pattern similar to the pattern representing the code “1” is detected from the frequency waveform, the signal determination unit 11 determines that the code “1” is included in the frequency waveform of the received wave.

  Note that the frequency between the pulse signal generated by the signal generation unit 3 and the signal output when the microphone 1 receives the reflected wave of the exploration wave is low due to the low follow-up performance with respect to the input signal of the microphone 1. There is a difference. Specifically, when the microphone 1 receives the reflected wave of the exploration wave, the frequency of the output signal of the microphone 1 changes in the opposite direction to the pulse signal with time or more slowly than the pulse signal. Changes in the same manner as the pulse signal. Therefore, the reference waveform and pattern of the frequency input from the control unit 4 to the signal determination unit 11 are changed as described above.

  The signal determination unit 11 is configured to transmit the detection result of the amplitude peak from the amplitude determination unit 9, and the signal determination unit 11 receives the amplitude peak from the amplitude waveform of the received wave. The code is detected. For example, the signal determination unit 11 responds to the reference waveform when the residual sum of squares of the frequency waveform of the received wave and the reference waveform is equal to or less than a predetermined value in a predetermined time range including the time when the amplitude reaches the peak. It is determined that the code is included in the received wave. The determination result of the signal determination unit 11 is transmitted to the control unit 4.

  The control unit 4 determines whether an object exists within the detection range based on the information transmitted from the amplitude determination unit 9 and the signal determination unit 11, and notifies the driver according to the determination result. Do. For example, in the control unit 4, a detection time is set corresponding to the detection distance. When the threshold determination unit 24 determines that the amplitude is larger than the amplitude threshold within the detection time, and the signal determination unit 11 determines that the received wave is a reflected wave of the exploration wave, the control unit 4 It is determined that an object exists within the detection range.

  The amplitude determination unit 9 and the signal determination unit 11 measure delay times of the signal processing units 6 and 7 and transmit them to the control unit 4. Since the delay time of the filter varies depending on the BW and the Q value, etc., the BPF 18 and the BPF 20 are different from each other. However, the control unit 4 selects information used for the determination according to the difference in the delay time. Can be improved.

  The operation of the object detection device will be described. When the control unit 4 sends a transmission instruction to the signal generation unit 3, the signal generation unit 3 starts generating a pulse signal. The pulse signal generated by the signal generator 3 is converted into an AC signal by the transmission circuit 2, an AC voltage is applied from the transmission circuit 2 to the microphone 1, and an exploration wave is transmitted from the microphone 1. At this time, the signal generation unit 3 generates a pulse signal according to the transmission instruction from the control unit 4 so as to include a frequency pattern representing an ultrasonic identification code. As a result, the exploration wave including the identification code is transmitted from the microphone 1.

  Thereafter, when the control unit 4 issues a reception instruction to the signal processing units 6 and 7, the receiving circuit 5 and the signal processing units 6 and 7 perform amplification, filtering, A / D conversion, and the like on the output signal of the microphone 1. Processing is performed. Then, the amplitude generator 8 and the frequency generator 10 generate an amplitude waveform and a frequency waveform.

  At this time, since the BW of the BPF 18 included in the signal processing unit 6 is set narrow, much noise is removed in the signal processing unit 6 and distortion of the amplitude waveform generated by the amplitude generation unit 8 is suppressed. Further, since the BW of the BPF 20 included in the signal processing unit 7 is set widely, the signal processing unit 7 can suppress the loss of frequency information and can easily detect the code from the frequency waveform generated by the frequency generation unit 10. become.

  When the amplitude generation unit 8 and the frequency generation unit 10 generate waveforms, the amplitude determination unit 9 compares the amplitude of the received wave with the amplitude threshold value, and the signal determination unit 11 identifies the received wave. The control unit 4 determines whether an object exists within the detection range based on the determination results of the amplitude determination unit 9 and the signal determination unit 11, and notifies the driver according to the determination result. The object detection apparatus repeatedly executes such ultrasonic wave transmission / reception processing.

  In such an operation, for example, if a common filter is used for signal processing for generating an amplitude waveform and signal processing for generating a frequency waveform, and this filter has a wide bandwidth, an amplitude waveform is generated from a signal containing a large amount of high-frequency components. And a frequency waveform is generated. In this case, it is easy to detect the identification code from the frequency waveform, but the amplitude waveform is distorted by noise, and a plurality of peaks are detected in a portion larger than the amplitude threshold, which may reduce the code detection accuracy. .

  For example, as shown in FIG. 8, when two peaks are detected in a portion where the amplitude of the received wave is large, a code detection process is performed in each of the portions corresponding to the two amplitude peaks in the frequency waveform. As a result, for example, when a search wave including a downlink chirp signal corresponding to the code “1” is transmitted, a code “0” is received from the received wave including the reflected wave in addition to the downlink chirp signal corresponding to the code “1”. Uplink chirp signals corresponding to may be detected. In the frequency graph of FIG. 8, the alternate long and short dash line indicates a reference waveform corresponding to the downstream chirp signal, and the alternate long and two short dashes line indicates a reference waveform corresponding to the upstream chirp signal.

  On the other hand, when the filter band is narrowed, the distortion of the amplitude waveform is reduced, but it becomes difficult to detect the identification code from the frequency waveform.

  On the other hand, in the present embodiment, separate filters, that is, BPFs 18 and 20 are used for the signal processing for amplitude waveform generation and the signal processing for frequency waveform generation, and the BW of the BPF 18 is narrower than that of the BPF 20. Therefore, distortion of the amplitude waveform due to noise is reduced.

  As a result, as shown in FIG. 9, only one peak is detected in the portion where the amplitude of the received wave is large. For example, when a search wave including a downstream chirp signal corresponding to the code “1” is transmitted, Only the downlink chirp signal corresponding to the code “1” is detected from the received wave. In the frequency graph of FIG. 9, the alternate long and short dash line indicates the reference waveform corresponding to the downstream chirp signal.

  Further, since the band of the BPF 20 is wide, it is easy to detect the identification code from the frequency waveform.

  As described above, in this embodiment, separate filters are used for signal processing for amplitude waveform generation and signal processing for frequency waveform generation, and the characteristics of each filter are suitable for amplitude waveform generation and frequency waveform generation, respectively. It is supposed to be. Thereby, the detection accuracy of the peak of amplitude and the code can be improved, and the identification accuracy of the received wave can be improved.

(Other embodiments)
In addition, this invention is not limited to above-described embodiment, In the range described in the claim, it can change suitably.

  For example, the transmission / reception unit may be composed of two microphones 1 for transmitting and receiving ultrasonic waves.

  In the first embodiment, the propagation time is measured using the time when the amplitude becomes larger than the amplitude threshold. However, the propagation time may be measured using the time when the amplitude takes a peak. In this case, if the amplitude waveform is distorted by noise, the measurement accuracy of the propagation time is reduced. However, by reducing the BW of the BPF 18, a decrease in the measurement accuracy of the propagation time can be suppressed.

  The receiving circuit 5 may be a first filter unit and a second filter unit. For example, two receiving circuits 5 may be arranged corresponding to the signal processing units 6 and 7, and each receiving circuit 5 may be a first filter unit and a second filter unit. Further, two BPFs 15 having different characteristics from each other may be arranged in the receiving circuit 5 in correspondence with the signal processing units 6 and 7.

  Moreover, in the said 1st Embodiment, although the characteristic of BPF15,18,20 was set with the input signal from the control part 4, these characteristics may be fixed.

  In the first embodiment, the code is represented using a chirp signal whose frequency changes with time. However, the exploration wave may be modulated by another method to represent the code. For example, amplitude shift modulation that changes the amplitude or phase shift modulation that changes the phase may be used. As the amplitude shift keying, for example, on-off modulation or the like can be used. As the phase shift keying, for example, two-phase shift keying that encodes at phases 0 ° and 180 °, or four-phase shift keying that encodes at 0 °, 90 °, 180 °, and 270 ° is used. Can do. Alternatively, a plurality of frequencies included in the resonance band of the microphone 1 may be selected, and a code may be assigned to each frequency.

  Further, the characteristics of the BPFs 18 and 20 may be set according to a code included in the pulse signal generated by the signal generator 3. The detection accuracy can be improved by setting the characteristics of these filters to a setting suitable for the frequency representing each code.

  Moreover, you may comprise a 1st filter part and a 2nd filter part with LPF or HPF. Further, as shown in FIG. 10, the first filter unit and the second filter unit may be configured by a filter combining LPF and HPF. In FIG. 10, the LPF indicated by a solid line is an LPF constituting the first filter unit, and the LPF indicated by an alternate long and short dash line is an LPF constituting the second filter unit. By increasing the Q values of the LPF and HPF, it is possible to obtain a characteristic that complements the frequency characteristic of the microphone 1 as indicated by a one-dot chain line in FIG. Further, the Q value of only one of LPF and HPF may be increased.

  When combining the LPF and the HPF, the cutoff frequency of only the LPF or only the HPF may be changed between the first filter portion and the second filter portion, or the cutoff frequencies of both the LPF and HPF may be changed. It may be changed. Moreover, you may comprise a 1st filter part and a 2nd filter part combining one or both of LPF and HPF, and BPF. Further, the characteristics of the microphone 1 may be supplemented by a BPF and a notch filter.

  Further, the BPFs 18 and 20 may not have the characteristic of complementing the frequency characteristics of the microphone 1, or only the BPF 20 may have the complementary characteristic.

  In the first embodiment, the control unit 4 selects information used for determination according to the difference in delay time, but the timing at which the determination result or the like is transmitted from the amplitude determination unit 9 or the signal determination unit 11 to the control unit 4 is used. May be adjusted according to the difference in delay time.

  The frequency of the reflected wave is Doppler shifted according to the relative speed of the object with respect to the microphone 1, but the signal determination unit 11 may measure the Doppler shift amount and correct the filter characteristics based on the Doppler shift amount.

For example, the magnitude of the inverse characteristics of the BPFs 18 and 20 may be changed according to the Doppler shift amount. Further, the BW of the BPF 18 may be changed according to the Doppler shift amount. Specifically, BW before correction and BW after correction are set as BW ₀ and BW ₁ , respectively, and Doppler shift amount is set as f _shift , and BW ₁ = BW ₀ + f _shift is set. By changing BW in this way, it is possible to reduce the influence of Doppler shift in amplitude determination. Further, the BW of the BPF 20 may be changed according to the Doppler shift amount.

Further, the center frequency of the BPF 18 may be changed according to the Doppler shift amount. Specifically, the center frequency before correction of the BPF 18 is fc ₀ , the center frequency after correction is fc ₁ , and fc ₁ = fc ₀ + f _shift . Thereby, attenuation of the amplitude waveform due to the difference between the frequency of the received wave and the band of the BPF 18 can be suppressed, and the measurement accuracy of the amplitude of the received wave can be improved. Further, the center frequency of the BPF 20 may be changed according to the Doppler shift amount. Moreover, you may correct | amend both BW and center frequency of BPF18,20.

  The timing for changing the characteristics of the BPFs 18 and 20 according to the Doppler shift amount is, for example, immediately after the signal determination unit 11 determines that the received wave is a reflected wave of the exploration wave. Further, this timing may be from when the control unit 4 determines whether or not an object is present within the detection range until the next exploration wave is transmitted.

  As the Doppler shift amount serving as a reference for the correction amount of the filter characteristic, the latest measured value at that time may be used, or an average value of a plurality of Doppler shift amounts measured in the past may be used. Further, the relative speed of the object with respect to the vehicle may be calculated based on the history of a plurality of distance information measured in the past, the measurement cycle, the vehicle speed, and the like, and the Doppler shift amount may be estimated based on the relative speed.

  In addition, when the base noise is measured by the amplitude determining unit 9 or the signal determining unit 11 and the base noise is larger than the predetermined noise threshold, the BW of the BPFs 18 and 20 is made narrower than when the base noise is equal to or lower than the noise threshold, or , The complementary characteristics may be weakened. Moreover, you may change both BW and complementary characteristics of BPF18 and 20. Further, the frequency of the base noise may be detected by the frequency generator 8 and the BW of the BPFs 18 and 20 may be narrowed in a direction to avoid this frequency. Thereby, the removal rate of noise becomes high, and it can suppress the fall of the determination precision of the amplitude determination part 9 grade | etc., By noise.

  For example, the noise threshold is set according to the level of the base noise measured by monitoring the output signal of the microphone 1 before the start of the object detection process. Further, for example, the signal determination unit 11 monitors the degree of coincidence between the frequency waveform of the received wave and the frequency pattern representing the ultrasonic identification code, and according to the level of the base noise when the degree of coincidence is a predetermined value or less. A noise threshold may be set.

DESCRIPTION OF SYMBOLS 1 Microphone 5 Reception circuit 6 Signal processing part 7 Signal processing part 10 Amplitude determination part 11 Signal determination part

Claims (11)

An object detection device that is mounted on a vehicle and detects an object outside the vehicle,
A transmission / reception unit (1) for transmitting an ultrasonic wave including a code for identification with an ultrasonic wave transmitted from another device as an exploration wave, receiving the ultrasonic wave and outputting a signal corresponding to the received wave;
A first filter unit (5, 6) and a second filter unit (5, 7) for filtering the output signal of the transmission / reception unit;
An amplitude determination unit (10) for detecting a reflected wave based on amplitude information included in an output signal of the first filter unit;
A signal determination unit (11) for determining whether the received wave is a reflected wave of the exploration wave based on code information included in the output signal of the second filter unit;
The first filter unit and the second filter unit are object detection devices having different characteristics.   The object detection device according to claim 1, wherein the first filter unit has a narrower bandwidth than the second filter unit.   The object detection device according to claim 1, wherein the amplitude determination unit or the signal determination unit corrects a difference in delay time caused by a difference in characteristics between the first filter unit and the second filter unit.   4. The bandwidth according to claim 1, wherein a bandwidth of one or both of the first filter unit and the second filter unit is changed based on a Doppler shift amount of a reflected wave with respect to a search wave. 5. Object detection device.   5. The center frequency of one or both of the first filter unit and the second filter unit is changed based on the Doppler shift amount of the reflected wave with respect to the exploration wave. Object detection device.   The object detection device according to claim 4, wherein the Doppler shift amount is estimated based on a relative speed of the object with respect to the vehicle.   When a noise larger than a predetermined value is measured, one or both of the first filter unit and the second filter unit have a narrower bandwidth than before the noise is measured. 6. The object detection device according to any one of 6. The second filter unit has a characteristic that complements the frequency characteristic of the transmission / reception unit,
The object detection device according to claim 1, wherein the first filter unit has a characteristic that complements a frequency characteristic of the transmission / reception unit weaker than that of the second filter unit.   The object detection device according to claim 8, wherein the magnitude of the complementary characteristic of either one or both of the first filter unit and the second filter unit is changed based on a Doppler shift amount of the reflected wave with respect to the exploration wave.   The object detection device according to claim 9, wherein the Doppler shift amount is estimated based on a relative speed of the object with respect to the vehicle.   9. When a noise larger than a predetermined value is measured, one or both of the first filter unit and the second filter unit have a complementary characteristic weaker than before noise is measured. The object detection device according to any one of 10.

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