JP2019066383A - Object detector - Google Patents

Abstract

To provide an object detector with which it is possible to determine with high accuracy whether or not a received wave is a reflected wave of a survey wave.SOLUTION: Provided is an object detector, mounted in a vehicle, for detecting an object outside of the vehicle, comprising: a signal generation unit 3 for generating an AC signal whose frequency changes in a prescribed pattern with the time; transmission units 1, 2 for transmitting, upon input of the AC signal, a survey wave of the frequency that corresponds to the frequency of the AC signal; reception units 1, 5, designed to receive a reflected wave of the survey wave, for outputting a signal that corresponds to the amplitude of the received wave; and a frequency determination unit 11 for determining, on the basis of whether or not a signal whose frequency changes in a prescribed pattern is included in the output signals of the reception units 1, 5, whether or not the received wave is a reflected wave of the survey wave. The frequency determination unit 11 makes determination using a signal whose frequency changes the same way as the prescribed pattern and a signal preceding it among the output signals of the reception units 1, 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an object detection device.

  For an object detection device mounted on a vehicle that detects an obstacle, the frequency of the ultrasonic wave that is the survey wave is changed with time, the frequency of the received wave and the survey wave is compared, and other vehicles traveling around are A technique has been proposed to avoid interference with the ultrasonic waves to be transmitted (see, for example, Patent Document 1).

European Patent No. 2373434

  As a device for transmitting and receiving ultrasonic waves, for example, a microphone provided with a piezoelectric element can be used. That is, an AC signal is input to the microphone, and the piezoelectric element is vibrated to transmit an ultrasonic wave, and the amplitude, frequency, etc. of the ultrasonic wave are detected based on the output signal of the piezoelectric element when the microphone receives the ultrasonic wave. can do. Then, by changing the frequency of the AC signal input to the microphone, it is possible to change the frequency of the ultrasonic wave used as the search wave.

  The inventors of the present invention, when using such a microphone, the change width of the frequency of the search wave, and the change width of the frequency of the reception wave detected when the microphone receives the reflected wave of the search wave, It has been found that it is smaller than the change width of the frequency of the input AC signal. This is considered to be due to the narrowness of the band of the microphone and the low followability.

  If the frequency change width of the detectable receive wave is small, the frequency of the receive wave is simply compared with the frequency of the AC signal to determine whether the receive wave is a reflected wave of the search wave or not. It will be difficult.

  An object of the present invention is to provide an object detection device capable of highly accurately determining whether a received wave is a reflected wave of a search wave.

  In order to achieve the above object, the invention according to claim 1 is an object detection device mounted on a vehicle for detecting an object outside the vehicle, which generates an alternating current signal whose frequency changes in a predetermined pattern with time. A signal generation unit (3), a transmission unit (1, 2) for transmitting a probe wave of a frequency according to the frequency of the AC signal by receiving an AC signal, and a reflected wave of the probe wave Receiver, which outputs a signal corresponding to the amplitude of the received wave, and whether or not the output signal of the receiver includes a signal whose frequency changes in a predetermined pattern. And a frequency determination unit (11) that determines whether or not the reception wave is a reflection wave of the search wave, and the frequency determination unit changes the frequency of the output signal of the reception unit in the same manner as the predetermined pattern. Signal and the signal before the signal We perform constant.

  The present inventors change the frequency of the AC signal in a predetermined pattern, so that the frequency of the reflected wave changes in the opposite direction to the predetermined pattern before changing in the predetermined pattern, or We found that it changed more slowly than the pattern of.

  Therefore, as described above, by using the signal whose frequency changes in a predetermined pattern and the signal before this signal, it is possible to determine with high accuracy whether the received wave is a reflected wave of the search wave or not. become.

  In addition, the code | symbol in the parenthesis of each said means shows an example of the correspondence with the specific means as described in embodiment mentioned later.

It is a block diagram of the object detection apparatus concerning 1st Embodiment. It is a figure which shows the frequency of an uplink chirp signal. It is a figure which shows the frequency of a downstream chirp signal. It is a figure which shows the detection method of the reflected wave received time in 1st Embodiment. It is a figure which shows the amplitude and frequency of a received wave containing an upstream chirp signal. It is a figure which shows the amplitude and frequency of a received wave containing a downlink chirp signal. It is a figure which shows the method to compare a received wave and a reference wave using a frequency offset. It is a figure which shows the code | symbol determination method in 1st Embodiment. It is a figure which shows the frequency determination area in a comparative example. It is a figure which shows the method to compare a received wave and a reference wave using frequency magnification. It is a figure which shows the detection method of the reflected wave received time in 2nd Embodiment. It is a figure which shows the frequency of the pulse signal containing the uplink chirp signal in 3rd Embodiment. It is a figure which shows the frequency of the pulse signal containing the downstream chirp signal in 3rd Embodiment. It is a figure which shows the amplitude and frequency of a received wave containing the upstream chirp signal in 3rd Embodiment. It is a figure which shows the amplitude and frequency of a received wave containing the downstream chirp signal in 3rd Embodiment. It is a figure which shows the frequency of the pulse signal in the modification of 3rd Embodiment. It is a figure which shows the frequency of the pulse signal in 4th Embodiment. It is a figure which shows the frequency of the pulse signal in the 1st modification of 4th Embodiment. It is a figure which shows the frequency of the pulse signal in the 2nd modification of 4th Embodiment. It is a figure which shows the frequency of the pulse signal in the 3rd modification of 4th Embodiment. It is a figure which shows the frequency of the pulse signal in the 4th modification of 4th Embodiment. It is a figure which shows the frequency of the pulse signal in the 5th modification of 4th Embodiment. It is a figure which shows the frequency of the pulse signal in the 6th modification of 4th Embodiment.

  Hereinafter, an embodiment of the present invention will be described based on the drawings. In the following embodiments, parts that are the same as or equivalent to each other will be described with the same reference numerals.

First Embodiment
The first embodiment will be described. The object detection device according to the present embodiment is a so-called ultrasonic sonar device, which 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 pulse generation unit 3, and a control unit 4. Further, the object detection apparatus includes a reception circuit 5, a signal processing unit 6, an amplitude generation unit 7, an amplitude determination unit 8, a distance determination unit 9, a frequency generation unit 10, a frequency determination unit 11, and a reference wave. A storage unit 12 and a relative speed determination unit 13 are provided. The control unit 4 and the signal processing unit 6 are constituted by a known microcomputer provided with a CPU, a ROM, a RAM, an I / O and the like, and execute processing such as various operations according to a program stored in the ROM.

  The microphone 1 is disposed facing the outer surface of the vehicle, and transmits an ultrasonic wave, which is a search wave for detecting an object, toward the outside of the vehicle. Specifically, the microphone 1 includes a not-shown piezoelectric element having a configuration in which a piezoelectric film is disposed between two electrodes facing each other. The two electrodes are connected to the transmission circuit 2, and an AC voltage is applied from the transmission circuit 2 to deform the piezoelectric film, whereby ultrasonic waves are transmitted from the microphone 1 to the outside of the vehicle.

  The transmitter circuit 2 D / A converts the input signal and outputs a voltage generated thereby. The transmission circuit 2 is connected to a pulse generation unit 3 for generating a pulse signal, and the transmission circuit 2 D / A converts the pulse signal input from the pulse generation unit 3 and generates an alternating voltage generated thereby The voltage is applied to the microphone 1.

  As described above, the microphone 1 and the transmission circuit 2 transmit a probe wave of a frequency according to the frequency of the pulse signal by inputting the pulse signal as the AC signal generated by the pulse generation unit 3. It corresponds to a transmitter. Also, the pulse generation unit 3 corresponds to a signal generation unit.

  The pulse generation unit 3 generates a pulse signal including a chirp signal whose frequency changes in a predetermined pattern with time in accordance with a transmission instruction from the control unit 4. Thereby, a search wave including a chirp signal whose frequency changes with time is transmitted from the microphone 1. Furthermore, a plurality of patterns of probe waves including different types of chirp signals are transmitted from the microphone 1, and the pattern of probe waves is determined by the transmission instruction issued from the controller 4 to the pulse generator 3. .

  Specifically, when an instruction to transmit a first pattern is issued from the control unit 4 to the pulse generation unit 3, the pulse generation unit 3 generates a pulse signal whose frequency monotonously increases with the passage of time as shown in FIG. Do. As a result, the first search wave including the upstream chirp signal whose frequency increases with the passage of time is transmitted from the microphone 1.

  In addition, when the control unit 4 instructs the pulse generation unit 3 to transmit a second pattern, the pulse generation unit 3 generates a pulse signal whose frequency monotonically decreases with the passage of time as shown in FIG. As a result, a second search wave including a downward chirp signal whose frequency decreases with the passage of time is transmitted from the microphone 1.

When the resonance frequency of the microphone 1 is f ₀ , the pulse generation unit 3 starts sweeping the frequency of the pulse signal from a frequency different from the resonance frequency f ₀ . Specifically, the pulse generation unit 3 sweeps the frequency of the pulse signal between a frequency lower than the resonance frequency f ₀ and a high frequency. The frequency of the pulse signal generated by the pulse generation unit 3 may change continuously or may change discretely.

  The microphone 1 is configured to transmit an ultrasonic wave, receive an ultrasonic wave, and output a voltage according to the sound pressure of the received ultrasonic wave. Specifically, the two electrodes of the piezoelectric element included in the microphone 1 are also connected to the receiving circuit 5, and the voltage between the two electrodes when the piezoelectric film is deformed by receiving the ultrasonic wave is received by the receiving circuit 5. It is supposed to be input to The receiving circuit 5 A / D converts the voltage input from the microphone 1 and outputs a signal generated thereby. As described above, the microphone 1 and the receiving circuit 5 are configured to receive an ultrasonic wave and output a signal according to the amplitude of the received ultrasonic wave, and correspond to a receiving unit.

  The signal processing unit 6 detects the frequency and amplitude of the received wave by orthogonal demodulation using the signal generated by the receiving circuit 5 by A / D conversion.

Specifically, the signal processing unit 6, the _{^{A r = (I 2 + Q}} 2) 1/2 the amplitude of the received wave as _{A r} to calculate the _{A r.} Further, the signal processing unit 6 calculates P by P = a tan (Q / I), assuming that the phase of the received wave is P, sets the frequency of the received wave to _fr, and the frequency of the pulse signal generated by the pulse generation unit 3 As f _p , f _r is calculated by f _r = 1 / (2π) · dP / dt + f _p .

Here, I is the magnitude of the signal obtained by removing the component having a frequency of 2f ₀ or more after multiplying the output signal of the receiving circuit 5 by sin 2πf ₀ t. Also, Q is the magnitude of the signal obtained by removing the component having a frequency of 2f ₀ or more after multiplying the output signal of the receiving circuit 5 by cos 2πf ₀ t. Also, t is time.

The amplitude generation unit 7 generates an envelope waveform of the amplitude _Ar based on the amplitude _Ar calculated by the signal processing unit 6. The amplitude determination unit 8 determines, based on the waveform generated by the amplitude generation unit 7, whether or not the amplitude _Ar is equal to or greater than a predetermined threshold value at each sampled time.

  The distance determination unit 9 calculates the distance to an object outside the vehicle reflecting the survey wave based on the time from the transmission of the survey wave by the microphone 1 to the reception of the reflected wave, and the calculated distance is equal to or less than a predetermined value It is determined whether or not In this embodiment, as shown in FIG. 4, the time when the amplitude of the received wave becomes equal to or more than the threshold value is taken as the received time. Then, the distance determination unit 9 calculates the distance d from d = c · T / 2, where T is the time from the time the microphone 1 transmits the search wave to the reception time, and the distance to the object is d.

The frequency generation unit 10 generates a waveform of the frequency f _r based on the frequency f _r calculated by the signal processing unit 6.

  The frequency determination unit 11 detects whether the ultrasonic wave received by the microphone 1 is transmitted by the microphone 1 based on whether the output signal of the reception circuit 5 includes a signal that changes in a pattern specified by the control unit 4. It is determined whether or not the wave is a reflected wave.

  Specifically, the frequency determination unit 11 detects a chirp signal included in the ultrasonic wave received by the microphone 1 based on the waveform generated by the frequency generation unit 10. When the microphone 1 transmits the first search wave, the frequency determination unit 11 determines that the reception wave is a reflection wave of the search wave transmitted from the microphone 1 when the detected chirp signal is an upstream chirp signal. Determine that there is. When the microphone 1 transmits the second search wave, the frequency determination unit 11 determines that the reception wave is a reflection wave of the search wave transmitted from the microphone 1 when the detected chirp signal is a downlink chirp signal. Determine that there is.

  Even if the frequency of the pulse signal is changed as shown in FIG. 2 and FIG. 3, the change width of the frequency of the search wave and the frequency of the reception wave detected when the microphone 1 receives the reflected wave of the search wave. The change width of is smaller than the change width of the frequency of the pulse signal. This is considered to be due to the narrowness of the resonance band of the microphone 1 and the low followability.

  Then, the frequency of the received wave changes in the opposite direction to the frequency of the chirp signal or changes more slowly than the frequency of the chirp signal before changing similarly to the chirp signal included in the pulse signal. . This is because the microphone 1 slightly vibrates around the resonance frequency when the AC voltage starts to be applied from the transmission circuit 2, and it takes time until the microphone 1 vibrates at the frequency of the pulse signal. It is believed that there is.

  For example, when the microphone 1 transmits a first search wave including an upstream chirp signal, as shown in FIG. 5, the frequency monotonously increases more slowly than the pulse signal before the upstream chirp signal which changes similarly to the pulse signal. Signal appears. Alternatively, a signal with monotonically decreasing frequency appears before an upstream chirp signal that changes in the same manner as the pulse signal.

  When the microphone 1 transmits the second search wave including the downstream chirp signal, as shown in FIG. 6, a signal whose frequency monotonically increases appears before the downstream chirp signal which changes in the same manner as the pulse signal. Alternatively, a signal whose frequency monotonically decreases more slowly than the pulse signal appears before the downstream chirp signal, which changes in the same manner as the pulse signal.

  Therefore, in the present embodiment, the reception wave is determined using the chirp signal included in the reception wave and the portion in front of the chirp signal. Specifically, the reference wave storage unit 12 stores, for each chirp signal, a chirp signal and a reference wave corresponding to the previous portion of the chirp signal. Then, the frequency determination unit 11 determines the chirp signal included in the received wave by comparing the waveform transmitted from the frequency generation unit 10 with the waveform of the reference wave stored in the reference wave storage unit 12.

  As the waveform of the reference wave corresponding to the upstream chirp signal, for example, a waveform in which the frequency increases at the same change rate as the pulse signal after the frequency increases more slowly than the pulse signal generated by the pulse generation unit 3 is used. Also, for example, after the frequency decreases, a waveform in which the frequency increases at the same change rate as the pulse signal is used.

  As the waveform of the reference wave corresponding to the downstream chirp signal, for example, a waveform whose frequency decreases at the same change rate as the pulse signal after the frequency decreases more slowly than the pulse signal generated by the pulse generation unit 3 is used. Also, for example, after the frequency is increased, a waveform whose frequency decreases at the same change rate as the pulse signal is used.

  When the coincidence between the waveform generated by the frequency generation unit 10 and the reference wave becomes equal to or higher than a predetermined reference value, the frequency determination unit 11 determines that the received wave contains a chirp signal. Further, the frequency determination unit 11 obtains the coincidence between the reference wave for the upstream chirp signal and the reference wave for the downstream chirp signal, and the chirp signal having the higher degree of coincidence is included in the reception wave. It is determined that Thus, a chirp signal is detected from the received wave.

  That is, when the coincidence between the reference wave for uplink chirp signal and the reception wave is higher than the coincidence between the reference wave for downlink chirp signal and the reception wave, it is determined that the reception wave includes uplink chirp signal Do. At this time, the reference wave for the upstream chirp signal corresponds to the first reference wave, and the reference wave for the downstream chirp signal corresponds to the second reference wave.

  In addition, when the degree of coincidence between the reference wave for downlink chirp signal and the reception wave is higher than the degree of coincidence between the reference wave for uplink chirp signal and the reception wave, it is determined that the downlink chirp signal is included in the reception wave. Do. At this time, the reference wave for the downstream chirp signal corresponds to the first reference wave, and the reference wave for the upstream chirp signal corresponds to the second reference wave.

In the present embodiment, the frequency determination unit 11 obtains the degree of coincidence using the offset of the frequency. FIG. 7 shows that for the upstream chirp signal, the frequency of the reference wave is R (t), the frequency offset is Δf, and the frequency R (t) of the reference wave is approximated to the frequency f _r (t) of the reception wave using Δf. Then, a method of evaluating the correlation between R (t) + Δf and f _r (t) to obtain the degree of coincidence is shown.

  Assuming that the number of samples is N and the standard deviation is σ, the error sum of squares E is as shown in Formula 1.

  The error sum of squares E is minimized when Equation 2 holds, and Δf at this time is given by Equation 3.

  The degree of coincidence M can be obtained by substituting this Δf into the equation 1 and substituting the error sum of squares E obtained thereby into the equation 4.

  Also for the downlink chirp signal, the matching degree M can be similarly obtained using the reference wave for the downlink chirp signal.

  Then, the frequency determination unit 11 compares the degree of coincidence M for the upstream chirp signal with the degree of coincidence M for the downstream chirp signal, and determines that the chirp signal with the higher degree of coincidence M is included in the received wave. . For example, when the microphone 1 transmits the first search wave, as shown in FIG. 8, the coincidence between the received wave and the reference wave for the upstream chirp signal corresponds to that for the received wave and the downstream chirp signal. Higher than the degree of coincidence, and an upstream chirp signal is detected.

  The degree of coincidence M may be compared with a predetermined threshold, and if the degree of coincidence M is higher than the threshold, it may be determined that the chirp signal is included in the received wave. That is, it is determined that the uplink chirp signal is included in the reception wave when the coincidence M for the uplink chirp signal is higher than the threshold, and the downlink chirp signal when the coincidence M for the downlink chirp signal is higher than the threshold May be determined to be included in the received wave.

  In the present embodiment, the peak values of the coincidence degree M of the chirp signals are compared. That is, when the difference between the frequencies of the reference wave and the reception wave has a local minimum on the time axis, it is determined that the chirp signal having the smaller minimum local value is included in the reception wave.

Thus, after offsetting R (t) so that the difference between R (t) and f _r (t) becomes smaller, frequency determination unit 11 reduces the difference between R (t) + Δf and f _r (t). Evaluate the correlation. Then, when the frequency of the received wave changes in the same manner as the frequency of the reference wave, the frequency determination unit 11 determines that the ultrasonic wave received by the microphone 1 is a reflected wave of the survey wave transmitted by the microphone 1 Do.

  The determination result of the frequency determination unit 11 is transmitted to the distance determination unit 9. The distance determination unit 9 calculates and calculates the distance to the object only when it is determined by the frequency determination unit 11 that the ultrasonic wave received by the microphone 1 is a reflection of the probe wave transmitted by the microphone 1. It is determined whether the calculated distance is equal to or less than a predetermined threshold. The determination result of the distance determination unit 9 is transmitted to an ECU (not shown), and when the distance determination unit 9 determines that the distance to the object is equal to or less than a predetermined value, the driver Notification to the user, automatic braking, etc. are performed.

The offset Δf calculated by the frequency determination unit 11 according to Equation 3 is transmitted to the relative speed determination unit 13. The relative velocity determination unit 13 calculates the relative velocity of the object to determine whether the object is approaching the vehicle, and the relative velocity Δv of the object is calculated by Equation 5. Here, the sound velocity is c, and the resonance frequency f ₀ of the microphone 1 is used as the reference frequency. Note that another frequency may be used as the reference frequency. For example, the central frequency of the sweep of the pulse signal may be used as the reference frequency.

  When Δv is larger than 0, the relative speed determination unit 13 determines that the object is approaching the vehicle. Specifically, the relative velocity determination unit 13 periodically calculates the relative velocity according to Formula 5, and the frequency determination unit 11 calculates the relative velocity at the time when the coincidence degree M reaches the peak with the relative velocity of the object. presume. When the object approaches the vehicle, the Doppler shift causes the frequency of the received wave to be higher than the frequency of the reference wave, and a frequency change similar to the frequency change of the reference wave is detected. The value is stored.

  The reference wave storage unit 12 may correct the waveform of the stored reference wave in accordance with the velocity and acceleration of the vehicle and the determination result of the relative velocity determination unit 13. For example, in the reference wave storage unit 12, a plurality of reference waves corresponding to the relative velocity of the object are stored for each chirp signal. Then, the reference wave storage unit 12 selects a reference wave according to the relative speed assumed from the speed of the vehicle, and transmits the reference wave to the frequency determination unit 11.

  The operation of the object detection device will be described. In the object detection device, when the control unit 4 sends a transmission instruction to the pulse generation unit 3, the pulse generation unit 3 starts generation of a pulse signal. The pulse signal generated by the pulse generation unit 3 is D / A converted by the transmission circuit 2. When an alternating voltage is applied from the transmission circuit 2 to the microphone 1, an ultrasonic wave, which is an exploration wave, is transmitted from the microphone 1. At this time, the pulse generation unit 3 changes the frequency of the pulse signal to be generated with time according to the transmission instruction from the control unit 4. Thereby, the first search wave or the second search wave is transmitted from the microphone 1.

  When the search wave is reflected by an object outside the vehicle and the microphone 1 receives the reflection wave of the search wave, the voltage between the two electrodes of the piezoelectric element included in the microphone 1 changes. This voltage is input to the receiving circuit 5, and the receiving circuit 5 A / D converts the input voltage. Then, the signal processing unit 6 detects the frequency and the amplitude of the received wave by orthogonal demodulation using the signal generated by the receiving circuit 5 by A / D conversion.

  The amplitude generation unit 7 generates an envelope waveform of amplitude based on the amplitude detected by the signal processing unit 6. The amplitude determination unit 8 determines whether the amplitude of the received wave is equal to or greater than a predetermined threshold value based on the waveform generated by the amplitude generation unit 7, and transmits the determination result to the distance determination unit 9.

  Further, the frequency generation unit 10 generates a waveform of a frequency based on the frequency detected by the signal processing unit 6. The frequency determination unit 11 compares the waveform generated by the frequency generation unit 10 with the waveform of the reference wave stored in the reference wave storage unit 12 to obtain the degree of coincidence, and detects a chirp signal included in the received wave.

  Then, when the microphone 1 transmits the first search wave and the upstream chirp signal is detected from the reception wave, the frequency determination unit 11 determines that the reception wave is a reflection wave of the search wave. Further, when the microphone 1 transmits the second search wave and the downstream chirp signal is detected from the reception wave, the frequency determination unit 11 determines that the reception wave is a reflection wave of the search wave.

  The ultrasonic waves received by the microphone 1 may include, for example, ultrasonic waves transmitted by another vehicle, in addition to the reflected wave of the probe wave transmitted by the microphone 1. On the other hand, the frequency of the search wave is characterized in this way, and changes in the frequency of the reception wave and the search wave are compared, and it is determined whether the reception wave is a reflected wave of the search wave transmitted from the microphone 1 By determining, interference can be avoided and detection accuracy of an object can be improved.

  If it is determined by the frequency determination unit 11 that the received wave is a reflected wave of the survey wave, the distance determination unit 9 determines the distance to an object outside the vehicle reflecting the survey wave based on the determination result of the amplitude determination unit 8. calculate. Then, when the distance determination unit 9 determines that the distance to the object is equal to or less than a predetermined value, a monitor, a buzzer, or the like (not shown) notifies the driver that the object is at a distance closer than the predetermined distance. Ru.

  The effects of this embodiment will be described. The change width of the frequency of the received wave is smaller than the change width of the frequency of the pulse signal due to the narrowness of the band of the microphone 1 and the low tracking performance. Then, when the frequency change width of the detectable reception wave is small, it becomes difficult to determine with high accuracy whether the reception wave is a reflection wave of the search wave.

  On the other hand, in the present embodiment, before the frequency of the received wave changes in the same manner as the pulse signal, the above-mentioned waveform is used by utilizing the characteristic that the frequency of the received wave changes inversely to the pulse signal or more slowly than the pulse signal. The chirp signal is detected by comparing the reference wave and the received wave. Therefore, even when the change width of the frequency is small, the determination of the received wave is easy, and the determination accuracy is improved.

  Further, as a method of determining a received wave different from the present embodiment, for example, the following method can be considered. First, a change in frequency until a predetermined time passes from the amplitude peak of the reflected wave is extracted, and the frequency is linearly approximated within this time. Then, based on the slope of the straight line, the signal is classified into an upstream chirp signal, a downstream chirp signal, and other signals, and it is determined whether or not it matches the chirp signal of the search wave.

  However, if the amplitude of the received wave decreases because the distance to the object is long, the detection accuracy of the peak of the amplitude decreases, and the range of time used for the determination may be erroneous and may not be determined correctly. For example, when the microphone 1 transmits the first search wave, as shown in FIG. 9, since the upstream chirp signal appears before the detected peak and the frequency of the reception wave decreases after the peak, the reception wave There is a possibility that it may be misjudged that the downlink chirp signal is included in.

  On the other hand, in the present embodiment, the peak of the degree of coincidence is obtained by comparison between the reference wave of the waveform described above and the received wave. Therefore, it is possible to suppress an erroneous determination due to a decrease in the amplitude of the received wave.

  Also, if the determination is performed only in the portion where the frequency changes as in the pulse signal, sweeping the frequency of the pulse signal only in the resonance band of the microphone 1 to increase the amplitude of the received wave increases the sweep time. Need to increase the number of samples. Then, the determination of the received wave becomes difficult due to the expansion of the calculation scale and the overlapping of the signals.

  On the other hand, in the present embodiment, since the determination is also performed using the change in frequency before the appearance of the chirp signal, the characteristic of the chirp signal can be captured with a small number of samples. Therefore, the reception wave can be determined in a short time.

  Further, in the ultrasonic sensor, the frequency of the received wave changes due to the Doppler shift, but as shown in FIG. 7, in the present embodiment in which the coincidence is determined by the method considering the Doppler shift, the object moves at a speed different from that of the vehicle. Even if it does, it becomes possible to judge the reception wave.

In the present embodiment, the degree of coincidence is determined using the frequency offset, but the degree of coincidence may be determined using the magnification of the frequency. That is, as shown in FIG. 10, assuming that the frequency magnification is k and using k to approximate the frequency R (t) of the reference wave to the frequency f _r (t) of the received wave, k · R (t) and f _The degree of coincidence may be determined by evaluating the correlation of _r (t).

  Specifically, the error sum of squares E is expressed by Equation 6, and when the error sum of squares E is minimized, that is, when the expression 7 is satisfied, the frequency magnification k is represented by Expression 8. Then, the degree of coincidence M can be obtained by substituting the error sum of squares E obtained by substituting the equation 8 into the equation 6 into the equation 4. Further, the relative velocity Δv is as shown in Formula 9.

Second Embodiment
The second embodiment will be described. The present embodiment is the same as the first embodiment except that the method of detecting the reflected wave reception time is changed from the first embodiment, and therefore, only the parts different from the first embodiment will be described. Do.

  The distance determination unit 9 according to the present embodiment uses the time that is a predetermined time before the time when the matching degree M becomes the peak value as the receiving time. Then, the distance determination unit 9 detects the distance d based on d = c · T / 2, where T is the time from the time when the microphone 1 transmits the search wave to the time of reception. Let said predetermined time be ΔT. The time ΔT is set, for example, for each individual object detection device, and is stored in the distance determination unit 9. The distance determination unit 9 corresponds to a time storage unit.

  For example, as shown in FIG. 11, the time ΔT places an object at a predetermined distance from the microphone 1 and transmits a search wave, and when the microphone 1 receives a reflected wave from this object, the distance between the electrodes of the microphone 1 It is the time from the rise of the voltage to the coincidence M taking a peak value.

  The time ΔT is set for each of the upstream chirp signal and the downstream chirp signal, and is stored in the distance determination unit 9.

  If the degree of coincidence is calculated using only the part corresponding to the chirp signal in the received wave and the change in frequency due to the change in relative velocity also calculated, the peak of the degree of coincidence is less clear. Therefore, when detecting the receiving time based on the time when the matching degree takes the peak value as in the present embodiment, the detection accuracy decreases.

  On the other hand, by calculating the degree of coincidence using the portion in front of the chirp signal, the peak of the degree of coincidence becomes easy to be clear, so that the detection accuracy of the receiving time is improved.

  In addition, even if the amplitude of the reflected wave changes, the time from the start of reception of the reflected wave to the peak of the degree of coincidence hardly changes. Therefore, compared to the method of detecting the reception time by comparing the amplitude with a threshold, It is possible to suppress a decrease in detection accuracy of the reception time due to a change in wave amplitude. Therefore, it is possible to suppress the decrease in the detection accuracy of the distance to the object.

Third Embodiment
A third embodiment will be described. The present embodiment is the same as the first embodiment except that the frequency of the pulse signal is changed with respect to the first embodiment, and only the parts different from the first embodiment will be described.

  As shown in FIG. 12 and FIG. 13, before sweeping the frequency of the pulse signal, the pulse generation unit 3 of the present embodiment generates a pulse signal of a constant frequency and inputs the pulse signal to the transmission circuit 2. That is, when transmitting the first search wave, the frequency of the pulse signal is made constant for a predetermined time and then increases with the passage of time, and when transmitting the second search wave, the frequency of the pulse signal is After being fixed for a predetermined time, it decreases with the passage of time. As a result, after an alternating voltage of a constant frequency is input for a predetermined time, an alternating voltage whose frequency changes with time is input to the microphone 1.

  When the search wave is transmitted in this way, the sound pressure immediately after the start of reception of the reflected wave tends to be large, and the detection of the chirp signal becomes easy.

  Also, when the microphone 1 transmits the first search wave, in the waveform of the frequency of the reception wave, the increase in the frequency of the portion before the appearance of the upstream chirp signal tends to be gradual, and as shown in FIG. The frequency tends to decrease before the upstream chirp signal. In addition, when the microphone 1 transmits the second search wave, in the waveform of the frequency of the reception wave, the decrease in the frequency of the portion before the appearance of the downstream chirp signal tends to be gradual, and as shown in FIG. The frequency is likely to increase before the down-chirp signal. Therefore, detection of the chirp signal is further facilitated.

The frequency at the start of generation of the pulse signal may be different from the frequency at the start of the sweep. For example, as shown in FIG. 16, after generating a pulse signal at a constant frequency close to the resonance frequency f ₀ , the pulse signal is generated from a low frequency away from the resonance frequency f ₀ to a frequency higher than the resonance frequency f ₀ . The frequency may be swept.

However, as shown in FIG. 12, after the pulse signal is generated at a low frequency away from the resonance frequency f _0, if sweeping is started from this frequency to generate an upstream chirp signal, the frequency of the The increase tends to be gradual and the frequency is likely to decrease. Also, as shown in FIG. 13, after generating a pulse signal at a high frequency away from the resonance frequency f _0, if sweeping is started from this frequency to generate a down chirp signal, the frequency of the frequency immediately after the reception of the reflected wave is started. The decrease is likely to be gradual and the frequency is likely to increase. Therefore, in order to facilitate detection of the chirp signal, it is preferable to use pulse signals as shown in FIGS. 12 and 13.

Fourth Embodiment
A fourth embodiment will be described. The present embodiment is the same as the third embodiment except that the configuration of the pulse signal is changed with respect to the third embodiment, and only the parts different from the third embodiment will be described.

  The pulse generation unit 3 of the present embodiment simultaneously generates two pulse signals and inputs the two pulse signals to the transmission circuit 2 as shown in FIG. In FIG. 17 and FIGS. 18 to 23 described later, the frequency of one pulse signal is indicated by a solid line, and the frequency of the other pulse signal is indicated by an alternate long and short dash line.

  Here, each pulse signal is composed of a pulse signal of a constant frequency and an upstream chirp signal and a downstream chirp signal generated thereafter. Then, the time from the start of generation of the pulse signal to the start of sweeping of the frequency, that is, the length of time during which the frequency is constant is made equal between the two pulse signals. Also, the length of time from the start of the frequency sweep to the end of the sweep is equalized by the two pulse signals.

  Further, the frequency at the end of the sweep of the pulse signal including the upstream chirp signal is higher than the frequency at the start of generation of the pulse signal including the downstream chirp signal. Further, the frequency at the end of the sweep of the pulse signal including the downlink chirp signal is lower than the frequency at the start of generation of the pulse signal including the uplink chirp signal.

  Also in this embodiment in which two pulse signals are combined and generated as described above, detection of a chirp signal is facilitated as in the third embodiment.

  Note that, as shown in FIG. 18, the time from the start of generation of the pulse signal to the start of sweep of the frequency may be different between the two pulse signals.

  Further, as shown in FIG. 19, after the frequency of the pulse signal changes at a predetermined change rate, the absolute value may change at a change rate larger than the predetermined change rate. Further, as shown in FIG. 19, the frequency at the end of the sweep of the pulse signal including the uplink chirp signal may be lower than the frequency at the start of generation of the pulse signal including the downlink chirp signal. Also, the frequency at the end of the sweep of the pulse signal including the downstream chirp signal may be higher than the frequency at the start of generation of the pulse signal including the upstream chirp signal.

  Further, as shown in FIG. 20, the frequency at the end of the sweep of the pulse signal including the upstream chirp signal may be equal to the frequency at the start of generation of the pulse signal including the downstream chirp signal.

  Further, as shown in FIG. 21, the frequency at the end of the sweep of the pulse signal including the downstream chirp signal may be equal to the frequency at the start of generation of the pulse signal including the upstream chirp signal.

  Further, as shown in FIG. 22, the length of time from the increase of the absolute value of the rate of change of frequency to the end of the sweep may be different between the two pulse signals.

  Also, as shown in FIG. 23, two pulse signals may both include the upstream chirp signal. Also, the two pulse signals may both include the downstream chirp signal.

(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, in the first embodiment, the pulse generation unit 3 may generate only one of a pulse signal including an upstream chirp signal and a pulse signal including a downstream chirp signal.

  Further, the object detection apparatus may include two microphones 1, one microphone 1 and the transmission circuit 2 may constitute a transmission unit, and the other microphone 1 and the reception circuit 5 may constitute a reception unit.

  In addition, the object detection device may be provided with a plurality of microphones 1 as a transmission unit. In this case, by making the waveform of the reference wave stored in the reference wave storage unit 12 correspond to the characteristic of each microphone 1, individual variation of the microphone 1 can be reduced. In the second embodiment, the object detection apparatus may include a plurality of microphones 1 and the time ΔT stored in the distance determination unit 9 for each of the microphones 1 may be set.

  Also, the search wave may not be an ultrasonic wave. For example, an electromagnetic wave may be used as a search wave. Even in the case where the search wave is not an ultrasonic wave, and the transmitter and the receiver are configured by devices other than the microphone, if the above-described feature appears in the frequency of the received wave, as in the first embodiment. The determination accuracy of the received wave can be improved.

  In addition, the reference wave storage unit 12 stores a plurality of reference waves for each chirp signal, and the frequency determination unit 11 performs the determination using a reference wave selected from the plurality of reference waves according to the outside air temperature and humidity. You may Further, the change pattern of the frequency of the pulse signal generated by the pulse generation unit 3 may be changed according to the outside air temperature and the humidity.

  Also, the determination by the frequency determination unit 11 may be performed only when the amplitude detected by the signal processing unit 6 is equal to or greater than a predetermined value. In addition, when the peak of the degree of coincidence is larger than a predetermined value, that is, when the difference between the frequencies of the reference wave and the received wave is smaller than a predetermined value, it is assumed that the received wave is a reflected wave of the search wave by the frequency determination unit 11 It may be determined. When the frequency difference between the first reference wave and the reception wave is smaller than the difference between the frequency of the second reference wave and the reception wave and smaller than a predetermined value, the frequency judgment unit 11 It may be determined that it is a reflected wave.

1 microphone 2 transmission circuit 3 pulse generation unit 5 reception circuit 11 frequency determination unit

Claims (27)

An object detection device mounted on a vehicle for detecting an object outside the vehicle, comprising:
A signal generation unit (3) that generates an alternating current signal whose frequency changes in a predetermined pattern with time;
A transmitting unit (1, 2) for transmitting a search wave of a frequency according to the frequency of the AC signal by inputting the AC signal;
A receiver (1, 5) for receiving a reflected wave of the survey wave, and outputting a signal according to the amplitude of the received wave;
A frequency determination unit that determines whether or not the received wave is a reflected wave of the exploration wave based on whether or not the output signal of the reception unit includes a signal whose frequency changes in the predetermined pattern ( 11) and
The object detection device, wherein the frequency determination unit performs determination using a signal whose frequency changes in the same manner as the predetermined pattern among output signals of the reception unit, and a signal before the signal.   The object detection apparatus according to claim 1, wherein the alternating current signal has a frequency that monotonously increases with time.   The object detection apparatus according to claim 2, wherein when the reception wave is a reflection wave of the search wave, a frequency of the reception wave monotonously decreases as time passes, and then monotonously increases like the AC signal.   The object detection apparatus according to claim 1, wherein the alternating current signal has a frequency that monotonously decreases with time.   The object detection apparatus according to claim 4, wherein when the reception wave is a reflection wave of the search wave, the frequency of the reception wave monotonously increases with the passage of time and then decreases monotonously in the same manner as the AC signal.   The object detection apparatus according to any one of claims 1 to 5, wherein the frequency of the alternating current signal changes continuously or discretely.   The object detection apparatus according to any one of claims 1 to 6, wherein the search wave is an ultrasonic wave.   The object detection device according to any one of claims 1 to 7, wherein the frequency of the alternating current signal starts changing from a frequency different from the resonant frequency of the transmission unit.   The frequency of the alternating current signal starts changing after being kept constant for a predetermined time, or changes at a predetermined change rate, and then changes at a change rate whose absolute value is larger than the predetermined change rate. The object detection apparatus according to any one of to 8. A reference wave storage unit (12) for storing a reference wave including a waveform whose frequency changes in the predetermined pattern;
The object detection according to any one of claims 1 to 9, wherein the frequency determination unit makes the determination by comparing the frequency of the reference wave stored in the reference wave storage unit with the frequency of the reception wave. apparatus. A plurality of the transmission units,
The object detection device according to claim 10, wherein the reference wave storage unit stores, for each of the plurality of transmission units, a reference wave including a waveform whose frequency changes in the predetermined pattern. The reference wave storage unit stores a plurality of the reference waves,
The object detection device according to claim 10, wherein the frequency determination unit performs the determination using a reference wave selected from a plurality of the reference waves according to the outside air temperature or the humidity. The reference wave storage unit stores a plurality of the reference waves,
The object detection device according to claim 10, wherein the frequency determination unit performs the determination using a reference wave selected from a plurality of the reference waves according to a velocity or an acceleration of the vehicle.   The object detection according to any one of claims 10 to 13, wherein the frequency determination unit compares the correlation between the received wave and the reference wave using an error in frequency of the received wave and the reference wave. apparatus.   The frequency determination unit offsets the reference wave in the frequency direction so as to reduce a difference in frequency axis between the received wave and the reference wave, and then an error in frequency of the received wave and the reference wave The object detection apparatus according to claim 14, wherein the correlation between the received wave and the reference wave is compared using   A relative velocity detection unit (13) for detecting the relative velocity of the object based on the offset amount when the reference wave is offset in the frequency direction so that the difference between the received wave and the reference wave on the frequency axis becomes small. The object detection apparatus according to claim 15, comprising:   The frequency determining unit may multiply the reference wave in the frequency direction by a predetermined magnification so as to reduce a difference in frequency axis between the received wave and the reference wave, and then the received wave and the reference wave. The object detection apparatus according to claim 14, wherein the correlation between the received wave and the reference wave is compared using an error in frequency of.   18. The object detection device according to claim 17, further comprising: a relative velocity detection unit (13) configured to detect a relative velocity of the object from the predetermined magnification.   When the frequency difference between the received wave and the reference wave has a local minimum value on a time axis, the frequency determination unit determines that the predetermined pattern has a frequency in an output signal of the reception unit based on the frequency difference. The object detection apparatus according to any one of claims 10 to 18, wherein it is determined whether or not a signal that changes at is included. Taking the reference wave as a first reference wave,
The reference wave storage unit stores a second reference wave including a waveform whose frequency changes at a change rate different from that of the predetermined pattern,
When the frequency difference between the received wave and the first reference wave is smaller than the frequency difference between the received wave and the second reference wave, the frequency determining unit determines that the frequency of the output signal of the receiving unit is equal to The object detection device according to any one of claims 10 to 19, wherein it is determined that the signal changing in the predetermined pattern is included.   The frequency determination unit determines that the output signal of the reception unit includes a signal whose frequency changes in the predetermined pattern when the difference in frequency between the received wave and the reference wave is smaller than a predetermined value. The object detection apparatus according to any one of claims 10 to 19, which determines. Taking the reference wave as a first reference wave,
The reference wave storage unit stores a second reference wave including a waveform whose frequency changes at a change rate different from that of the predetermined pattern,
When the frequency difference between the received wave and the first reference wave is smaller than the frequency difference between the received wave and the second reference wave, and the frequency determination unit is smaller than a predetermined value, The object detection device according to any one of claims 10 to 19, wherein it is determined that the output signal of the reception unit includes a signal whose frequency changes in the predetermined pattern.   The frequency determination unit determines whether or not the output signal of the reception unit includes a signal whose frequency changes in the predetermined pattern when the amplitude of the received wave is equal to or greater than a predetermined value. 22. An object detection apparatus according to any one of 22 to 22. A distance detection unit (9) that detects a distance to an object that has reflected the exploration wave based on the time from the transmission unit transmitting the exploration wave to the reception unit receiving a reflected wave of the exploration wave Equipped with
The distance detection unit is configured to use the object as the time when the reception unit receives the reflected wave of the survey wave, a time before the time when the degree of coincidence between the received wave and the reference wave takes a peak, and the reception unit receives the reflected wave of the survey wave. The object detection apparatus according to any one of claims 10 to 23, which detects a distance of. A time storage unit (9) for storing a time from the rising of the output signal of the receiving unit to the peak of the coincidence;
The distance calculation unit is configured to receive the time when the reception unit is a time which is traced back by the time stored in the time storage unit from the time when the degree of coincidence between the received wave and the reference wave takes a peak. The object detection device according to claim 24, detecting a distance to the object as a time when a reflected wave is received. A plurality of the receiving units,
26. The object detection device according to claim 25, wherein the time storage unit stores, for each of the plurality of reception units, a time from the rising of the output signal to the peak of the coincidence.   The object detection device according to any one of claims 1 to 26, wherein the predetermined pattern is corrected according to the outside air temperature or humidity.

Images