OBJECT DETECTION DEVICE

Abstract

Object detection device (1) comprising: a signal generation unit (20) which generates a drive signal, a transmitting unit (10) which outputs an ultrasonic wave as a search wave in response to the input drive signal, a receiving unit (50) which receives an ultrasonic wave to generate a reception signal, and an evaluation unit (70) which performs an object detection determination based on the received signal, wherein the drive signal has at least two frequencies, the evaluation unit extracts at least two amplitudes corresponding to the at least two frequencies from the received signal and makes a determination based on a relationship between the at least two amplitudes, the assessment unit makes a determination based on a ratio of at least two amplitudes, if the two frequencies are divided by f L and f H are designated, and the two amplitudes corresponding to the two frequencies f L and f H correspond, by A L or A H are designated, and if a directivity of the transmitting unit and the receiving unit with respect to the frequency f L wider than a directivity thereof with respect to the frequency f H is, the evaluation unit determines that an object is not present in a given detection area if A H / A L is smaller than a reference value or if A L / A H greater than a reference value, and if the directivity of the transmitting unit and the receiving unit with respect to the frequency f L narrower than the directivity of it with respect to the frequency f His, the evaluation unit determines that an object is not present in the detection area if A H / A L is greater than a reference value, or if A L / A H is smaller than a reference value.

Description

Technical field

[0001] The present invention relates to an object detection device configured to detect an object by transmitting and receiving ultrasonic waves. State of the art

[0002] A known example of a device of this type can distinguish a low-height obstacle, such as a wheel chock, from a high-height obstacle, such as a wall (see, for example, JP 2010-197351 A). The device described in JP 2010-197351 A comprises a transmitter / receiver, a peak detection unit, a difference calculation unit, and an object determination unit.

[0003] The transmitter / receiver is mounted on the vehicle at a specific height and facing outward. The transmitter / receiver includes a transmitting unit for repeatedly transmitting search waves at predetermined intervals and a receiving unit for receiving reflected waves from the search waves arriving from the direction of the detection area after being reflected by the object to be detected. The peak detection unit detects the peak values ​​of the reflected waves received by the receiving unit of the transmitter / receiver and stores the detected peak values. The difference calculation unit calculates the difference between peak values ​​detected by the peak detection unit as the vehicle moves closer to the object to be detected.

[0004] If the peak difference value calculated by the difference calculation unit is a "negative" value, the object determination unit determines that the type of detected object is "obstacle near the road surface." An "obstacle near the road surface" is an obstacle that exists near the road surface. The object determination unit further determines that the type of detected object is "obstacle of another type (or other obstacles)" if the difference value is a "positive" value. An "obstacle of another type" is an obstacle that exists at a position higher than a position near the road surface.

[0005] According to the device described in JP 2010-197351 A having such a configuration, the transmitting means of the transmitter / receiver transmits search waves at predetermined intervals. The receiving means receives the reflected waves arriving from the direction of the detection area. The peak detection unit detects and stores the peak values ​​of the reflected waves received by the receiving means. The difference calculation unit calculates the differences between peak values ​​that change as the vehicle moves closer to the object to be detected. If the value of the calculated peak value is a "negative" value, the object detection unit determines that the type of detected object is an obstacle near the road surface. On the other hand, if the calculated difference value is a "positive" value, the object determination unit determines that the type of detected object is an obstacle of a different type.

[0006] Furthermore, JP 2014 - 132 220 A discloses a fish finder with a dual-beam unit for generating a wide, low-frequency beam and a narrow, high-frequency beam as transmission signals. These are transmitted with a time interval to prevent interference. The reception signals of the two beams are separated by filters to maintain the respective reception amplitudes.

[0007] From DE 10 2010 015 077 A1 a method for determining a target angle of an object by means of an ultrasonic sensor is known, wherein the target angle is an angle between a connecting line running through the ultrasonic sensor and the object and a reference line running through the ultrasonic sensor, wherein a first signal with a first radiation characteristic and a second signal with a second radiation characteristic are emitted by the ultrasonic sensor, are reflected by the object and are received, and with which the target angle is determined.

[0008] DE 10 2015 111 264 A1 discloses a method for detecting an object in the surrounding area of ​​a motor vehicle, in which a first ultrasonic signal with a first directional characteristic and a second signal with a second radiation characteristic are emitted by an ultrasonic sensor, reflected by the object, and received, and the position of the object is determined using their amplitudes. Summary of the Invention

[0009] It is desirable for this type of device to have further improved accuracy in discriminating objects. For example, assume in particular that the object detection device is mounted on a vehicle. In this case, an object such as a wall with a relatively large projection height from the road surface is likely to come into contact with the vehicle body. Consequently, such an object must be appropriately detected as an obstacle. On the other hand, an obstacle such as a wheel chock whose projection height from the road surface is sufficiently small is unlikely to come into contact with the vehicle body. Consequently, such an object is essentially not judged as an obstacle. The same applies to objects such as beams that protrude only slightly from the ceiling.Consequently, in the case of a vehicle-mounted object detection device, it is necessary to accurately distinguish objects that are likely to come into contact with the vehicle and are thus likely to be obstacles from other objects.

[0010] The present invention was made with the foregoing in mind. That is, the present invention provides an object detection device capable of improving the accuracy of object detection. This is achieved by the subject matter of independent claim 1. Further developments are disclosed in the subclaims.

[0011] An object detection device includes: a signal generation unit that generates a drive signal; a transmission unit that transmits an ultrasonic wave as a search wave in response to the input drive signal; a reception unit that receives an ultrasonic wave to generate a received signal; and an evaluation unit that performs an object detection determination based on the received signal. According to one aspect of the present invention, the drive signal has at least two frequencies. The evaluation unit extracts at least two amplitudes corresponding to the at least two frequencies from the received signal and performs a determination based on a relationship between the at least two amplitudes.

[0012] The directivity of an ultrasonic wave changes with frequency. Consequently, the amplitudes of reception signals of reflected waves from an object corresponding to the at least two different ultrasonic waves having different directivity change depending on the positional relationship between the object and the directivity range corresponding to the directivity. For example, there may be an object that is present within the directivity range of an ultrasonic wave having wide directivity but outside the directivity range of an ultrasonic wave having narrow directivity. In this case, there is a large difference in the amplitude of the reception signal between the reflected wave of the ultrasonic wave having wide directivity and the reflected wave of the ultrasonic wave having narrow directivity.On the other hand, the object may be present in a zone where the directivity range of the ultrasonic wave with a wide directivity and the directivity range of the ultrasonic wave with a narrow directivity overlap. In this case, there is no significant difference in the amplitude of the received signal between the reflected wave of the ultrasonic wave with a wide directivity and the reflected wave of the ultrasonic wave with a narrow directivity.

[0013] Thus, the object detection device according to the present invention transmits an ultrasonic wave having at least two frequencies as a search wave, extracts the amplitude for each frequency from the received signal, and performs an object detection determination based on the relationship between the at least two amplitudes. Specifically, the evaluation unit compares the at least two extracted amplitudes. This makes it possible to perform an object detection determination with high accuracy. In particular, this makes it possible to distinguish between obstacle objects and other objects with good accuracy. For example, objects likely to come into contact with the vehicle body can be distinguished from other objects.In addition, by performing object detection determination based on the amplitudes of the received signals corresponding to two or more frequencies, the influence of amplitude level changes due to atmospheric fluctuations and the like can be reduced. Thus, according to such a configuration, it is possible to improve the accuracy of object detection compared to the prior art.

[0014] The reference numerals in parentheses attached to the components or the like merely represent examples of correspondence between the components or the like and the specific components described with reference to the present embodiments. Accordingly, the present invention is not limited to the above reference numerals. Short description of the characters Fig. 1 shows the configuration of an object detection device according to the first embodiment. Fig. Figure 2 is a diagram showing the directivity of a transmitter / receiver. Fig. Figure 3 is a diagram showing the directivity of a transmitter / receiver. Fig. Figure 4 is a diagram to explain the relationship between the position of an object and its vertical orientation angle. Fig. Figure 5 shows graphs of the amplitude and frequency of a drive shaft. Fig. Figure 6 is a diagram showing the range of search waves. Fig. Figure 7 is a diagram showing the amplitudes of reflected waves when a search wave was transmitted with a wide directivity. Fig. Figure 8 is a diagram showing the amplitudes of reflected waves when a search wave was transmitted with a narrow directivity. Fig. Figure 9 is a diagram showing the relationship between the horizontal distance from the transmitter / receiver and the vertical orientation angle. Fig. Figure 10 is a graph showing the relationship between the horizontal distance from the transmitter / receiver and the amplitude ratio. Fig. 11 is a diagram showing the reference value for determining and the detection range. Fig. 12 is a flowchart of the reception processing. Fig. Figure 13 is a diagram for explaining the analysis section and the amplitude extraction method. Fig. Figure 14 is a graph showing the relationship between the linear distance from the transmitter / receiver and the attenuation of an amplitude level. Fig. 15 is a diagram showing the difference of an amplitude level difference when the frequency difference is small. Fig. Figure 16 is a diagram showing the difference of an amplitude level when the frequency difference is large. Fig. Figure 17 is a diagram showing frequency characteristics of a transmitter / receiver. Fig. Figure 18 is a diagram showing the frequency characteristics of a transmitter / receiver. Fig. Figure 19 is a graph showing the relationship between the linear distance from the transmitter / receiver to the object and the amplitude ratio. Fig. 20 shows the detection range according to the second embodiment. Fig. 21 shows the configuration of an object detection device according to the third embodiment. Fig. Figure 22 is a graph showing the temperature characteristics of a transmitter / receiver. Fig. Figure 23 is a graph showing the relationship between temperature and amplitude ratio. Fig. Figure 24 is a graph showing a change in distance attenuation with temperature. Fig. 25 is a diagram showing the configuration of a frequency separation unit and a signal evaluation unit according to the fourth embodiment. Fig. 26 shows the configuration of an object detection apparatus according to the fifth embodiment. Fig. Figure 27 is a graph showing the result of an FFT analysis. Fig. Figure 28 is a graph showing the result of FFT analysis when a Doppler shift is present. Fig. 29 shows the configuration of an object detection device according to the sixth embodiment. Fig. 30 is a diagram for explaining how the analysis section is set according to the sixth embodiment. Fig. 31 shows the configuration of an object detection device according to another embodiment. Fig. 32 is a diagram showing the drive signal according to another embodiment. Fig. 33 is a diagram showing the drive signal according to another embodiment. Fig. 34 is a diagram showing the drive signal according to the other embodiment. Fig. 35 is a diagram showing the drive signal according to another embodiment. Fig. 36 is a graph showing the result of FFT analysis in the case where the drive signal of Fig. 35 is used. Fig. 37 is a diagram showing the drive signal according to another embodiment. Fig. 38 is a diagram showing the drive signal according to another embodiment. Fig. 39 is a diagram showing the drive signal according to another embodiment. Fig. 40 is a graph showing the result of FFT analysis in the case where the drive signal of Fig. 39 is used. Fig. 41 is a diagram showing the drive signal according to another embodiment. Fig. 42 is a graph showing the result of FFT analysis in the case where the drive signal of Fig. 41 is used. Fig. Figure 43 is a diagram showing the propagation paths of search waves reflected by a wall. Fig. Figure 44 is a diagram showing the amplitude of the reflected wave when two overlapping reflected waves are received. Fig. Figure 45 is a diagram showing the amplitude of the received wave when two reflected waves are received with an interval between them. Fig. Figure 46 is a graph showing how the propagation distance changes depending on the path. Description of the embodiments

[0015] Embodiments of the present invention will be described below with reference to the figures. In the present embodiments, parts of one embodiment that are the same as or equivalent to parts of another embodiment are assigned the same reference numerals. (First embodiment)

[0016] The first embodiment will be described. An object detection device 1 according to this embodiment has, as shown in Fig. 1, a transmitting unit 10, a signal generating unit 20, a transceiver 30, a control unit 40, a receiving unit 50, a frequency separating unit 60, and a signal evaluating unit 70. The object detecting device 1 is an ultrasonic sonar device mounted on a vehicle to detect an object outside the vehicle.

[0017] The transmitting unit 10 transmits ultrasonic waves as search waves. Output signals from the signal generating unit 20 are input to the transmitting unit 10, and the transmitting unit 10 transmits search waves according to the drive signals input from the signal generating unit 20. The drive signal is an electrical signal for driving the transmitter / receiver 30 and has a frequency corresponding to the frequency of the search wave.

[0018] The signal generation unit 20 generates, in particular, a pulse signal having a frequency in the ultrasonic band as a drive signal. The transmitting unit 10 has, as shown in Fig. 1, a transmitter / receiver 30 and a transmission circuit 11. A drive signal generated by the signal generation unit 20 is input to the transmission circuit 11. The transmission circuit 11 processes the input drive signal, including, for example, stepping up the voltage, and outputs the signal generated thereby. The output signal of the transmission circuit 11 is input to the transmitter / receiver 30. The transmitter / receiver 30 then transmits a search wave toward the outside of the vehicle in response to the input signal. The transmitter / receiver 30 includes, for example, a microphone provided with an electromechanical conversion element (for example, a piezoelectric element) driven by a drive signal.

[0019] The signal generation unit 20 receives transmission instructions, drive signal setting information, and the like from the control unit 40. The control unit 40, the distance determination unit 70, and the like are configured by a known microcomputer including, for example, a CPU, ROM, RAM, I / O, and the like, and execute processing such as various calculations according to programs stored in the ROM or the like. "ROM or the like" includes a rewritable non-volatile memory such as EEPROM. ROM and RAM are non-transitory tangible storage media.

[0020] The receiving unit 50 receives ultrasonic waves and generates received signals according to the sound pressure of the received waves. The received signals generated by the receiving unit 50 are processed by the frequency separation unit 60 and then input to the signal evaluation unit 70 to be used in the object detection processing performed by the signal evaluation unit 70.

[0021] Specifically, the receiving unit 50 includes a transmitter / receiver 30 and a receiving circuit 51. The transmitter / receiver 30 outputs a voltage corresponding to the sound pressure of the received wave, and the receiving circuit 51 generates and outputs a received signal by processing the output voltage of the transmitter / receiver 30, including, for example, amplifying the output voltage. The received signal generated by the receiving circuit 51 is input to the frequency separation unit 60. The frequency separation unit 60 processes the received signal, for example, applying a filter thereto, and outputs the resulting signal. The signal evaluation unit 70 is configured to determine whether an object has been detected based on the received signal. The determination result of the signal evaluation unit 70 is transmitted to the control unit 40.

[0022] According to the object detection device 1 with such a configuration, for example, the object detection processing is performed as follows. When a transmission instruction is output from the control unit 40 to the signal generation unit 20, the signal generation unit 20 generates a drive signal, and the transmission unit 10 transmits a search wave according to the drive signal. When the search wave is reflected by an object outside the vehicle, the reception unit 50 receives the reflected wave and generates a received signal. The signal evaluation unit 70 detects an object based on the received signal, measures the distance to the object based on the time from the transmission of the search wave to the reception of the reflected wave, that is, the TOF, and transmits the detection result and the like to the control unit 40. TOF is an abbreviation for Time of Flight.

[0023] With such a method for detecting an object based on TOF, it is difficult to determine the position of the object because only the linear distance between the object that reflected the search wave and the vehicle is measured. For example, it is difficult to determine whether the detected object is an obstacle, such as a wall, that will collide with the vehicle body, or an object, such as a small hill, that is unlikely to collide with the vehicle. In this regard, the developers involved in the present invention focused on the relationship between the frequency and directivity of ultrasonic waves and developed a configuration that enables discrimination between obstacle objects and other objects.

[0024] First, the relationship between frequency and directivity of search waves is described. For example, the transmitter / receiver 30 has, as shown in Fig. 2 or Fig. 3, components such as a microphone that have a directivity characteristic such that the amplitude level of the search wave is reduced as the vertical orientation angle and the horizontal orientation angle increase. In Fig. 2 and Fig. 3, the dashed line represents the amplitude level when the orientation is 0°. In Fig. 4, "road surface protrusion" refers to a protrusion, such as a wheel chock, whose height from the surface of a path is sufficiently small. Furthermore, "ceiling protrusion" refers to a protrusion whose height from the ceiling is sufficiently small, such as a beam that projects only slightly downward from the ceiling of a path. Therefore, it is not necessary to detect or record these objects as "obstacles" that may collide with the vehicle body.

[0025] The vertical orientation angle is, as in Fig. 4, is defined by an angle between the horizontal plane passing through the transmitter / receiver 30 and a straight line connecting the transmitter / receiver 30 to the object. The vertical orientation angle of an object that reflects the reflected wave from the front of the transmitter / receiver 30, for example, an object such as a wall in front of the transmitter / receiver 30, is 0°. The vertical orientation angle of a protrusion on the road surface at a height different from that of the transmitter / receiver 30 and the vertical orientation angle of a protrusion, such as a beam, below the ceiling of a passage, are greater than 0°.

[0026] The amplitude level of a search wave traveling from the transmitter / receiver 30 toward a different height from that of the transmitter / receiver 30 is smaller than that of a search wave traveling in a direction parallel to the horizontal plane. Consequently, the amplitude level of the reflected wave from an object located in front of the transmitter / receiver 30 is smaller than the amplitude level of the reflected wave from an object located at a different height from that of the transmitter / receiver 30.

[0027] It is known that the directivity characteristic changes depending on the size of the transmitting area of ​​the transmitter / receiver 30, the wavelength of the transmitted wave, the vibration mode of the transmitting area, and the like. That is, when the size of the transmitting area is constant, the directivity can be changed by changing the frequency of the transmitted signal. Generally, when the vibration modes are the same, the narrower the directivity, the higher the frequency. The vibration modes are often the same when the frequency difference is small. Conversely, when the frequency difference is large, the vibration mode may change. In this case, the relationship between the frequency (high-low) and the width of the directivity (narrow-wide) may be inverted.

[0028] Depending on the configuration of the transmitter / receiver 30, for example, as shown in Fig. 2, in particular the directivity of a frequency f L, which is lower than a frequency f H is, further than the directivity of the frequency f H . Depending on the configuration of the transmitter / receiver 30, for example, as shown in Fig. 3, the directivity of the frequency f L is narrower than the directivity of the frequency f H .

[0029] The larger the vertical orientation angle, the greater the directivity difference due to the frequency difference, and the smaller the vertical orientation angle, the smaller the directivity difference due to the frequency difference. That is, the larger the vertical orientation angle of the object, the greater the amplitude level difference of the reflected waves due to the frequency difference, and the smaller the vertical orientation angle of the object, the smaller the amplitude level difference of the reflected waves due to the frequency difference.

[0030] In the case of the vehicle-mounted object detection device 1 implemented by mounting a sonar on the vehicle, the device is configured so that the vertical directivity becomes narrow and the horizontal directivity becomes wide. In this case, as shown in the Fig. 2 and Fig. 3, the difference of directivity due to the difference of frequency in the vertical direction, the difference in the horizontal direction is small.

[0031] Next, a configuration that enables discrimination between obstacle objects and other objects will be described. The signal generation unit 20 of this embodiment generates drive signals with at least two frequencies. The signal generation unit 20 generates intermittently, for example, as shown in Fig. 5, a signal with a frequency f H and a signal with a frequency f L .

[0032] The frequency separation unit 60 of the present embodiment further comprises, as shown in Fig. 1, BPFs 61a and 61b and amplitude generation units 62a and 62b. BPF refers to a bandpass filter. BPFs 61a and 61b pass signals in a predetermined frequency band and block signals in other frequency bands. The bands of BPFs 61a and 61b are determined by input signals from control unit 40, and the center frequencies of the passband of BPFs 61a and 61b are f L or f H Of the reception signals generated by the receiver circuit 51, those that have passed through the BPFs 61a and 61b are input to the amplitude generation units 62a and 62b.

[0033] The amplitude generation units 62a and 62b calculate the amplitude values ​​of the input signals. For example, any of the following values ​​can be used as the amplitude value: the zero-to-peak measurement value of the input signal, the peak-to-peak measurement value of the input signal, the RMS value of the input signal, the envelope value of the input signal, or the average energy value of the input signal.

[0034] In this way, two amplitudes corresponding to the two frequencies f L and f H are extracted from the received signal. In the following, the amplitudes corresponding to the frequencies f L and f H correspond to A L or A H designated.

[0035] The signal evaluation unit 70 of the present embodiment evaluates the object detection based on the relationship between the amplitude A L and the amplitude A Hwhich are extracted by the frequency separation unit 60. The signal evaluation unit 70 determines, for example, in particular based on the comparison between the amplitude A L and the amplitude A Hwhether the detected object is present within a predetermined detection area. The "predetermined detection area" is a zone with a specific height and width centered on the directional axis of the transmitter / receiver 30. The "directional axis" is a straight line that substantially coincides with the points where the maximum search wave intensity is obtained while changing the linear distance from the transmitter / receiver 30. The "directional axis" typically substantially coincides with the center axis of the transmitter / receiver 30. The "predetermined height and width" may change depending on the linear distance of the transmitter / receiver 30. The cross-sectional area of ​​the "predetermined detection area" in a virtual plane orthogonal to the directional axis is typically circular.

[0036] As clarified by the above description, according to the configuration of the present embodiment, the manner in which the difference between the amplitude levels of the reception signals of the reflected waves occurs changes depending on the difference between the frequencies of the search waves, which changes depending on the vertical orientation angle of the object. When the transmitter / receiver 30 Fig. 2, the zone in which the search wave can sufficiently reach an object changes, as shown in Fig. 6, due to the difference in directivity caused by the difference in frequency. In Fig. 6, the zone R1 represents the zone in which a search wave with a low frequency f L and with a wide directivity can sufficiently reach an object. Zone R2 represents the zone in which a search wave with a high frequency f Hand with a narrow directivity, it can sufficiently reach an object. That is, search waves with a wide directivity can sufficiently reach the road surface and the ceiling of the passage in addition to a wall or the like in front of the transmitter / receiver 30. On the other hand, search waves with a narrow directivity can reach a wall or the like in front of the transmitter / receiver 30, but not the road surface or the ceiling of the passage.

[0037] If, therefore, as in Fig. 7, the search wave is transmitted with a wide directivity, there is no large difference between the amplitude of the reflected wave from a wall in front of the transmitter / receiver 30 and the amplitude of the reflected wave from an object such as a protrusion on the road surface. On the other hand, if a search wave with a narrow directivity, as shown in Fig. 8, there is a large difference between the amplitude of the reflected wave from a wall in front of the transmitter / receiver 30 and the amplitude of the reflected wave from an object such as a protrusion on the road surface. Specifically, the amplitude of the reflected wave from a protrusion on the road surface is much larger than that of the reflected wave from a wall in front of the transmitter / receiver 30.

[0038] The signal evaluation unit 70 of this embodiment uses this to determine whether the detected object is present within a predetermined detection range. In particular, the signal evaluation unit 70 has, as shown in Fig. 1, an amplitude ratio evaluation unit 71 and the signal determination unit 70 makes this determination based on the ratio of the amplitude A L and the amplitude A H .

[0039] For example, the amplitude ratio evaluation unit 71 calculates Ar = A H / A L as the amplitude ratio and makes a determination as follows. That is, for example, as in Fig. 2, assume that the transmitter / receiver 30 has a characteristic such that the directivity of a wave at a frequency f L further than the directivity of a wave at frequency f H In this case, the amplitude ratio evaluation unit 71 determines that the object is present in the detection area when the amplitude ratio Ar is greater than or equal to a predetermined reference value. The amplitude ratio evaluation unit 71 determines that the object is not present in the detection area when the amplitude ratio Ar is less than the reference value.

[0040] Furthermore, as in Fig. 3, it is now assumed that the transmitter / receiver 30 has such a characteristic that the directivity of a wave with the frequency f L narrower than the directivity of a wave at frequency f H In this case, the amplitude ratio evaluation unit 71 determines that the object is present in the detection area when the amplitude ratio Ar is equal to or less than the reference value. The amplitude ratio evaluation unit 71 determines that the object is not present in the detection area when the amplitude ratio Ar is less than the reference value.

[0041] The amplitude ratio evaluation unit 71 can Ar = A L / A H as the amplitude ratio and make a determination as follows. That is, if the transmitter / receiver 30 receives the Fig. 2, the amplitude ratio evaluation unit 71 determines that the object is present in the detection area if the amplitude ratio Ar is less than or equal to the reference value. The amplitude ratio evaluation unit 71 determines that the object is not present in the detection area if the amplitude ratio Ar is greater than the reference value. In contrast, when the transmitter / receiver 30 has the characteristics shown in Fig. 3, the amplitude ratio evaluation unit 71 determines that the object is present in the detection area when the amplitude ratio Ar is greater than or equal to the reference value. The amplitude ratio evaluation unit 71 determines that the object is not present in the detection area when the amplitude ratio Ar is less than the reference value.

[0042] It should be noted that it is also possible to use AR = K × log(A H / A L ) = K × log(AH ) - K × log(A L ) as the amplitude ratio. The amplitude ratio AR can also be referred to as the logarithmic amplitude ratio AR. The constant K is typically 20. When the constant K is 20, the logarithmic amplitude ratio AR can also be referred to as a decibel difference. This means that the "amplitude ratio" is not limited to the arithmetic division between two amplitudes, but is a concept that includes the decibel difference.

[0043] Fig. Figure 10 shows the relationship between the horizontal distance from the transmitter / receiver 30 and the amplitude ratio for both the wall and the protrusion on the road surface. In the graph, the dashed line represents the theoretical value (i.e., the calculated value) when the detected object is the wall, and the short and long dashes represent the theoretical value when the detected object is the protrusion on the road surface.

[0044] As in Fig. 9, the vertical orientation angles of a road surface projection and a ceiling projection increase as the horizontal distance from the transmitter / receiver 30 decreases. Consequently, as shown in Fig. 10, the amplitude ratio of a reflected wave from a wall in front of the transmitter / receiver 30 is substantially constant regardless of the horizontal distance from the transmitter / receiver 30. In contrast, the amplitude ratio of the reflected wave from the road surface or the like decreases as the horizontal distance from the transmitter / receiver 30 decreases.

[0045] For example, as in Fig. 11, assume that the reference value with which the amplitude ratio Ar is compared is set to decrease as the linear distance from the transmitter / receiver 30 decreases. Note that the linear distance L from the transmitter / receiver 30 to the object is obtained by L = c × TOF / 2, where c is the speed of sound. When the transmitter / receiver 30 detects the Fig. has two shown characteristics, it is determined that the object is present in the detection range when the amplitude ratio Ar, that is A H / A L is greater than or equal to a predetermined reference value. On the other hand, it is determined that the object is not present in the detection range when the amplitude ratio Ar is less than the reference value.

[0046] In Fig. 11, the dashed line shows the amplitude ratio at A H = A L . The echo zone, which is shown in Fig. 11, is a zone in which the echo of the transmitter / receiver 30 caused by sending search waves is detected. When the linear distance measured by the TOF is less than a predetermined value, the signal evaluation unit 70 determines that the received signal is generated by echo and does not perform object detection determination.

[0047] In the present embodiment, the reception processing described in Fig. 12, by such a configuration, it is possible to distinguish between objects that become obstacles and other objects. This makes it possible to avoid performing unnecessary actions, for example, a collision avoidance action.

[0048] That is, when the amplitude of the received signal generated by the receiving unit 50 exceeds a predetermined amplitude threshold, the received signal is split into frequency components corresponding to the two frequencies f L and f H are divided by the frequency separation unit 60 in step S1. The respective amplitudes A L and A H the frequency components corresponding to the two separated frequencies f L and f H are extracted.

[0049] By selecting a specific period as the analysis period, the frequency separation unit 60 extracts the amplitudes A L and A H from the received signal present in the analysis period, and the signal evaluation unit 70 makes a determination. As in Fig. 13, the analysis period is set based on, for example, the time at which the amplitude of the received signal exceeds the amplitude threshold. The analysis period may also be set based on the time at which the peak amplitude of the received signal is obtained or the time at which a rise of the received signal begins. Further, the analysis period may be a fixed duration from the reference time or a fixed duration before and after the reference time. By selecting a specific time point, such as the time at which a rise of the received signal begins, as the reference time of the analysis period instead of the amplitude of the received signal, the accuracy of the determination can be further improved.

[0050] As in Fig. 13, in the frequency separation unit 60, the amplitude generation unit 62a extracts the amplitude A L , which corresponds to the frequency f Lfrom the part of the amplitude waveform of the received signal that has passed through the BPF 61a present in the analysis period. Similarly, the amplitude generation unit 62b extracts the amplitude A H , which corresponds to the frequency f H corresponds to that part of the amplitude waveform of the received signal that has passed the BPF 61b and is present in the analysis period.

[0051] After step S1, in step S2, the amplitude ratio Ar is calculated by the amplitude ratio evaluation unit 71. Then, in step S3, as described above, the amplitude ratio Ar is compared with a reference value. If it is determined from the comparison between the amplitude ratio Ar and the reference value that the object is present in the detection area, in step S4, the signal evaluation unit 70 compares the amplitudes A L and A Hextracted in step S1 with an amplitude threshold. If the signal evaluation unit 70 determines that the amplitudes A L and A H are greater than or equal to the amplitude threshold, the signal evaluation unit 70 transmits the reflected wave information to the control unit 40 in step S5 and terminates the reception processing. The transmitted reflected wave information may include, for example, the pattern of frequencies present in the reflected wave, the TOF, and the threshold. Based on the transmitted reflected wave information, the control unit 40 initiates one or more actions, such as a collision avoidance action.

[0052] If it is determined in step S3 that the object is outside the detection range, or if it is determined in step S4 that the amplitudes A L and A Hare smaller than the amplitude threshold, the detection processing is terminated without performing step S5. That is, if it is determined that the object is outside the detection range based on the comparison result between the amplitude ratio Ar and the reference value or the comparison result between the amplitude of the received signal and the amplitude threshold, the reception processing is terminated without executing a collision avoidance action or the like.

[0053] As described above, the object detection device 1 according to the present embodiment transmits search waves at two frequencies, extracts the amplitude for each frequency from the received signal, and makes an object detection determination based on the relationship between the extracted two amplitudes. Specifically, the signal evaluation unit 70 compares, for example, at least two extracted amplitudes. This makes it possible to distinguish objects likely to come into contact with the vehicle body from other objects.

[0054] The amplitude of ultrasonic waves fluctuates as they propagate through the air, being affected by atmospheric fluctuations caused by wind, uneven temperature distribution, and the like. The amount of this amplitude variation acts similarly on ultrasonic waves that have propagated along the same propagation path at the same time. On the other hand, the period from the start of the transmission of two ultrasonic waves with different frequencies to the end of the reception of the reflected waves from the same object is much shorter than the rate of change of an atmospheric fluctuation. Consequently, it can be assumed that the two ultrasonic waves with different frequencies were transmitted at essentially the same timing with respect to the rate of change of an atmospheric fluctuation. The same applies to the reception of reflected waves.Consequently, the amount of amplitude variation in the reflected wave will be essentially the same for ultrasonic waves of two frequencies emitted at essentially the same timing and reflected from the same object. Thus, the influence of atmospheric fluctuation can be eliminated by using the amplitude ratio of the reflected waves of two frequencies.

[0055] Next, the above qualitative description is verified using theoretical equations. The sound pressure level p [Pa] at a distance r [m] is represented by the following equation (1). In equation (1), E 0 the energy density [J / m 3 ], if no attenuation is present. c is the speed of sound [m / s] in the medium in which the ultrasonic wave propagates. ρ is the density of the medium [kg / m 3]. D(θ) represents the directional gain. θ represents the orientation angle. The orientation angle θ is the angle formed by the directional axis and a virtual straight line connecting the object and the transmitter / receiver 30. β represents the attenuation constant. [Equation 1] p2=E0ρc2D(θ)4πr2e(−2βr)

[0056] E 0 = p 0 2 / (ρc 2 ), where p 0 represents the sound pressure at a distance r = 0. The damping constant β changes with frequency.

[0057] The sound pressure of a reflected wave, which is an ultrasonic wave reflected by an object with a reflectance R at a distance r, is represented by the following equation (2). For ease of explanation, equation (2) assumes that the directional gain is the same for transmission and reception. [Equation 2] p2=E0ρc2D(θ)4πr2e(−2βr)⋅R⋅D(θ)4πr2e(−2βr)=E0ρc2⋅R⋅(D(θ)4πr2)2e(−4βr)

[0058] In the case of a frequency f L Equation (2) is transformed into equation (3) and in the case of frequency f H equation (2) is transformed into equation (4). [Equation 3] pL2=E0Lρc2⋅R⋅(DL(θ)4πr2)2e(−4βLr) [Equation 4] pH2=E0Hρc2⋅R⋅(DH(θ)4πr2)2e(−4βHr)

[0059] In an actual environment where the device is used, the values ​​of ρ and c change over time as the temperature and humidity change. However, as described above, it can be assumed that search waves with two frequencies f L and f H are transmitted and received by the same object detection device 1 at the same timing. Consequently, it can be assumed that r, ρ, c, and R in the above equations (3) and (4) are equal.

[0060] Therefore, r, ρ, c, and R vanish by dividing the right-hand part of equation (3) by the right-hand part of equation (4). That is, the following equation (5) can be obtained from equations (3) and (4). Furthermore, the following equation (6) can be obtained from equation (5). [Equation 5] pL2pH2=E0LE0H(DL(θ)DH(θ))2e4r(−βL+βH) [Equation 6] pLpH=E0LE0HDL(θ)DH(θ)e2r(−βL+βH)

[0061] If the microphone sensitivity, i.e. the sensitivity of the transmitter / receiver 30 by M r [V / Pa], the amplitude, i.e. the received voltage V r by the product of the microphone sensitivity M r and the sound pressure p. This means V r = M r p. Accordingly, the following equation (7) can be obtained. [Equation 7] VrLVrH=MrLPLMrHpH=MrLMrHE0LE0HDL(θ)DH(θ)e2r(−βL+βH)=MrLMrHp0Lp0HDL(θ)DH(θ)e2r(−βL+βH)

[0062] In equation (7) p 0L the emitted sound pressure of the ultrasonic wave with frequency f L , and p 0H is the external sound pressure of the ultrasonic wave with frequency f H . As described above, in equation (7), which represents the ratio of the receiving voltages, p 0L / p 0H , M rL / M rH , D L (θ) / D H (θ), and exp{2r(-β L + β H )} left. p 0L / p 0H is referred to as an emitted sound pressure ratio. M rL / M rH is called the microphone sensitivity ratio. D L (θ) / D H (θ) is called the directional gain ratio. exp{2r(-β L + β H )} is called a frequency damping ratio.

[0063] The emitted sound pressure ratio and the microphone sensitivity ratio are determined once when the structure and frequencies of the object detection device 1 are determined. Consequently, it is possible to eliminate the influence of the emitted sound pressure and the microphone sensitivity in Equation (7) by calculating the emitted sound pressure ratio and the microphone sensitivity ratio based on measurements obtained under standard conditions.

[0064] The frequency damping ratio represents the difference in the amount of attenuation due to a difference in frequency. The frequency damping ratio can be ignored if the frequency difference is small. That is, the frequency damping ratio is 1. On the other hand, if the frequency difference is not small enough to ignore the frequency damping ratio, a correction value can be calculated by actual measurement or theoretically. If the correction value is represented by k, the following equation (8) can be obtained from equation (7). [Equation 8] DL(θ)DH(θ)=kVLVH

[0065] In this way, the accuracy of evaluation of objects of a method in which two amplitudes corresponding to two frequencies are compared can be improved by reducing the influence of changes in the amplitude level due to atmospheric fluctuations and the like.

[0066] Fig. Figure 14 shows the relationship between the linear distance from the transmitter / receiver 30 and the attenuation of the amplitude level. In the figure, "f L “ the amplitude, i.e. the reception voltage V rL at frequency f L may H “ represents the amplitude, ie the receiving voltage V rH at frequency f H As in Fig. As shown in Figure 14, the greater the distance to the object, the greater the attenuation of the amplitude of the reflected wave, and further, the higher the frequency, the greater the attenuation. According to a method using the amplitude ratio as in the present embodiment, the influence of the amount of attenuation due to distance can be reduced, and thus the accuracy of object evaluation can be improved.

[0067] The difference in the amount of attenuation generated according to the distance and the difference in frequency can also be theoretically derived from the frequencies. The signal evaluation unit 70 can correct the reference value for comparing the amplitudes using the theoretically obtained attenuation difference according to the linear distance to the object calculated from the TOF. This makes it possible to improve the evaluation accuracy even when the frequency difference and thus the attenuation difference is large. The signal evaluation unit 70 can also improve the evaluation accuracy by comparing the two amplitudes after they have been corrected according to the linear distance. Distance attenuation characteristics, such as those described in Fig. 14 can be obtained by actual measurements or by using theoretical equations, and the amount of correction of the reference value or amplitude can be determined based on the obtained distance attenuation characteristics.

[0068] It should be noted that, as in the Fig. 15 and Fig. 16, the greater the difference between the frequencies f L and f H is, the greater the difference in directivity. Accordingly, the difference between the amplitude levels of the reflected waves also increases, and the accuracy of determining whether an object is present in the detection area is improved. However, if the frequencies f L and f Hare not present in the resonance band of the transmitter / receiver 30, the amplitudes and reception sensitivity of the search waves decrease, causing the long-distance detection performance to deteriorate. Consequently, to improve the evaluation accuracy or prevent the detection performance from deteriorating, it is recommended to set one of the two frequencies higher than the resonance frequency and the other lower than the resonance frequency. More preferably, the upper and lower limits of the resonance band of the transmitter / receiver 30 are defined as f H or f L selected.

[0069] For example, if the resonance frequency of the transmitter / receiver is 30 f 0 and the range of the center frequency f 0 ±3%, the resonance band is preferably the center frequency +3% equal to f H and the center frequency -3% is equal to f L .

[0070] Furthermore, if the search waves with the frequencies f H and f L as in the present embodiment, if the interval between the two search waves is long, there tends to be a difference in the amount of variation due to atmospheric fluctuation and the like between the amplitudes A H and A L present. Consequently, the interval between two search waves is preferably small.

[0071] In addition, the one of the two-frequency search waves with the smaller amplitude is a bottleneck in determining long-distance detection performance. Consequently, it is preferable to set the two frequencies so that the amplitude of the reflected waves from an object in front of the transmitter / receiver 30 is the same for the frequencies f L and f H , as in Fig. 17 is shown.

[0072] For example, it is preferable to generate drive signals in such a way that the amplitude levels of search waves corresponding to the frequencies f L and f H correspond, are the same in the zone in front of the transmitter / receiver 30, or the amplitude levels of the reflected waves from an object located in front of the transmitter / receiver 30 are the same. It should be noted that the sentence "the amplitude levels are the same" does not only mean that the amplitude levels are completely the same, but also includes cases where the amplitude levels are substantially the same.

[0073] If the amplitude levels of the reflected waves from an object located in front of the transmitter / receiver 30 are different, for example, if the amplitude ratio given by AR = 20log(A H / A L) is not 0, the amplitude ratio obtained from the measurement result can be corrected based on this amplitude ratio AR. Alternatively, the reference value used to evaluate the amplitude ratio can be offset by an amount equal to the amplitude ratio AR.

[0074] Furthermore, since an ultrasonic wave with a high frequency f H a greater distance attenuation than the ultrasonic wave with a low frequency f L In the case of long-distance detection, the frequencies f L and f H be chosen so that the amplitude of a search wave at the frequency f H greater than the amplitude of a search wave at frequency f H , as in Fig. 18 is shown.

[0075] If the performance of an assessment of the height of the object is prioritized, the frequencies f L and fH preferably chosen to maximize the difference in directivity. However, since the long-distance detection performance deteriorates when the frequencies f L and f H are not present in the resonance band of the transmitter / receiver 30, in this case the frequencies f L and f H also preferably selected so that they are present in the resonance band of the transmitter / receiver 30.

[0076] The object detection device 1 of the present embodiment uses drive signals with at least two frequencies that have different directivity due to the difference in frequency. The object detection device 1 of the present embodiment extracts at least two amplitudes corresponding to the at least two frequencies and performs object detection determination based on the relationship between the extracted at least two amplitudes. This makes it possible to distinguish between obstacle objects and other objects with good accuracy. In addition, the influence of changes in amplitude level due to atmospheric fluctuation and the like can be reduced by performing object detection determination based on the amplitudes of the reception signals corresponding to the two or more frequencies.Consequently, according to such a configuration, it is possible to perform object detection determination more accurately than with the known techniques. (Second embodiment)

[0077] The second embodiment will be described. In this embodiment, the method for evaluating the object is changed from the first embodiment, and other features are the same as those in the first embodiment. Therefore, only the differences from the first embodiment will be described.

[0078] The signal evaluation unit 70 according to the present embodiment sets the detection range based on the height at which the transmitter / receiver 30 is arranged and evaluates an object as follows. That is, the signal evaluation unit 70 is provided with a map showing the relationship between the amplitude ratio and the linear distance from the transmitter / receiver 30 to the object, such as that shown in Fig. 19. It should be noted that in Fig. 19 the transmitter / receiver 30 is provided at a height of 0.5 m and for a reflected wave from an object at a height of 0.5 m, r = 1 and R = 0.

[0079] The relationship between the amplitude ratio and the linear distance can be obtained, for example, through actual measurement. Based on the amplitude ratio evaluated by the amplitude ratio evaluation unit 71 and the linear distance L calculated by the TOF, the signal evaluation unit 70 determines the height h. 0 of the object from the Fig. Map shown in 19.

[0080] As in Fig. As shown in Figure 20, the detection range is determined based on the height h S in which the transmitter / receiver 30 is arranged. The signal evaluation unit 70 compares the height h 0 with height h d , which is the lower limit of the detection range, and if h 0 ≥ h d is determined that the object is present in the detection area and if h 0 < h dis determined that the object is outside the detection range.

[0081] The effects of the first embodiment are provided in the same manner by the present embodiment which evaluates objects in such a manner. (Third embodiment)

[0082] The third embodiment will be described. In the present embodiment, a temperature measurement unit is added to the first embodiment, and other features are the same as those in the first embodiment. Thus, only differences from the first embodiment will be described.

[0083] As in Fig. 21, the object detection device 1 of this embodiment includes a temperature measuring unit 80. The temperature measuring unit 80 is arranged to measure the ambient temperature, and the ambient temperature measured by the temperature measuring unit 80 is transmitted to the signal evaluation unit 70 via the control unit 40. The signal evaluation unit 70 then corrects the reference value with which the amplitudes A L and A H are compared according to the ambient temperature. Alternatively, the signal evaluation unit 70 performs the comparison after the amplitudes A L and A H corrected according to the ambient temperature.

[0084] The resonant frequency and a resonant band of the transmitter / receiver 30 change depending on the temperature. For example, as in Fig. 22, the lower the temperature, the higher the resonance frequency, and the higher the temperature, the lower the resonance frequency. Since the amplitude ratio changes according to such changes in the characteristics as shown in Fig. 23, the accuracy of the evaluation of objects may deteriorate.

[0085] For example, by correcting the reference value according to the ambient temperature, the influence of temperature change can be reduced and the accuracy of object evaluation can be improved.

[0086] It should be noted that although the amplitude of a reflected wave is attenuated due to distance, as described in connection with the first embodiment, this distance attenuation changes not only with the frequency of the search wave but also with the temperature, as in Fig. As shown in Fig. 24, the amount of variation of distance attenuation due to temperature change differs depending on the frequency. In a configuration provided with a temperature measuring unit 80 as in the present embodiment, the determination accuracy can be improved by correcting the distance attenuation difference between reflected waves based on the frequency difference on the basis of the ambient temperature. (Fourth Embodiment)

[0087] The fourth embodiment is described. In the present embodiment, the configuration of the frequency separation unit 60 is changed with respect to the first embodiment, and the other features are the same as those in the first embodiment. Accordingly, only the differences from the first embodiment are described.

[0088] As in Fig. As shown in Fig. 25, the frequency separation unit 60 according to the present embodiment includes four BPFs in addition to the BPFs 61a and 61b. These four BPFs are referred to as BPFs 61c, 61d, 61e, and 61f.

[0089] In the present embodiment, the signal evaluation unit 70 includes a Doppler shift detection unit 72. The Doppler shift detection unit 72 estimates the range of the Doppler shift amount of the reflected wave with respect to the search wave based on information such as the position history of the detected object, the frequency analysis result of the received signal, and the vehicle speed. The bands of the BPFs 61c to 61f are set taking into account the estimated range of the Doppler shift amount.

[0090] If the range of the Doppler shift quantity is particularly defined by ± f SHIFT As shown, the center frequency of the band of the BPF 61c is around f SHIFTlower than that of the BPF 61a, and the center frequency of the band of the BPF 61d is around f SHIFT higher than that of the BPF 61a. Furthermore, the center frequency of the band of the BPF 61e is around f SHIFT lower than that of the BPF 61b, and the center frequency of the band of the BPF 61f is around f SHIFT higher than that of the BPF 61b.

[0091] Similarly to the amplitude generation units 62a and 62b, amplitude generation units 62c, 62d, 62e, and 62f are provided for the BPFs 61c to 61f, and the amplitude generation units 62c to 62f extract amplitudes from the received signals that have passed through the BPFs 61c to 61f. The amplitude ratio evaluation unit 71 selects two of the amplitudes extracted by the amplitude generation units 62a to 62f based on the current estimation of the Doppler shift amount and calculates the amplitude ratio.

[0092] With such a configuration, it is possible to suppress a reduction in detection accuracy based on the influence of the Doppler shift of the reflected wave with respect to the search wave.

[0093] It should be noted that although additional BPFs are added to the frequency separation unit 60 in the present embodiment, the Doppler effect may be taken into account by other means.

[0094] For example, a reception signal may not only be input to frequency separation unit 60 but also may be stored in a buffer (not shown), and when a Doppler shift of the output signals from frequency separation unit 60 is detected, the center frequencies of the bands of BPFs 61a and 61b are shifted by the Doppler shift amount f SHIFT shifted. Then, the received signal in the buffer is processed by the frequency separation unit 60.

[0095] It is also possible to calculate the Doppler shift quantity f SHIFT from information such as the vehicle speed before transmitting the search wave, and to estimate the center frequencies of the bands of the BPF 61a and 61b by the previously estimated Doppler shift amount f SHIFT to change. (Fifth embodiment)

[0096] The fifth embodiment will be described. In the present embodiment, the configuration of the frequency separation unit 60 is changed from the first embodiment, and the other features are the same as those in the first embodiment. Therefore, only the differences from the first embodiment will be described.

[0097] As in Fig. As shown in Figure 26, the frequency separation unit 60 of the present embodiment includes an FFT circuit 63. FFT is an abbreviation for Fast Fourier Transformation. The FFT circuit 63 performs FFT analysis on the received signal generated by the receiving circuit 51 and extracts the amplitudes A L and A H of the components corresponding to the frequencies f L and f H from the received signal. As the time window for the FFT analysis, an analysis period determined as in the first embodiment is used. The FFT circuit 63 outputs the amplitudes A L and A H extracted by the FFT analysis to the signal evaluation unit 70.

[0098] The effects according to the first embodiment are similarly achieved by the present embodiment, which uses the amplitudes A L and A Hextracted by an FFT analysis.

[0099] It should be noted that in the present embodiment, when there is no Doppler shift, the amplitude for each frequency is calculated by FFT analysis as shown in Fig. 27. For example, when the vehicle approaches the object and the frequency of the reflected wave increases, as shown in Fig. 28, the amplitude of the reflected wave corresponding to the frequency f L , as the frequency approaches the center of the band of the transmitter / receiver 30. On the other hand, the amplitude of the reflected wave corresponding to the frequency f H because the frequency moves away from the center of the band of the transmitter / receiver 30. In Fig. 28 are f L ' and f H ' the frequencies f L and f H , to which the Doppler shift is added.

[0100] It is possible to suppress a decrease in the evaluation accuracy due to the influence of the Doppler shift by detecting the amount of Doppler shift based on such changes in the amplitudes and frequency characteristics of the transmitter / receiver 30 and correcting the reference value with which the amplitude ratio or amplitude is compared based on the Doppler shift.

[0101] In some cases, Doppler shift generation can be predicted before starting measurement based on the vehicle speed, the number of times a Doppler shift has been acquired in the history of measured values ​​for a predetermined number of predetermined measurement cycles, and the like. In such cases, the attenuation of the amplitude of the reflected wave can be suppressed by correcting the frequency of the drive signal according to the amount of Doppler shift. As a result, it is possible to prevent a decrease in evaluation accuracy and also prevent deterioration in long-distance detection performance.

[0102] It should be noted that if the time window of an FFT analysis is represented by Tw, the frequency step size f Step equal to f Step = 1 / T W In a case of a correction of the frequency according to the Doppler shift, it is preferable to use T Wto be determined so that f Step is sufficiently small with respect to the frequency accuracy to be corrected. (Sixth Embodiment)

[0103] The sixth embodiment will be described. This embodiment differs from the first embodiment in that a configuration for discriminating reflected waves is added, and other parts are the same as those in the first embodiment. Therefore, only differences from the first embodiment will be described.

[0104] As in Fig. 29, the object detection device 1 according to the present embodiment includes a BPF 90, and a received signal generated by the receiving circuit 51 is input to the frequency separation unit 60 and the BPF 90.

[0105] The signal evaluation unit 70 includes an amplitude evaluation unit 73 and a frequency evaluation unit 74 in addition to the amplitude ratio evaluation unit 71. The received signal that has passed through the BPF 90 is input to the amplitude evaluation unit 73 and the frequency evaluation unit 74. The amplitude evaluation unit 73 and the frequency evaluation unit 74 are configured to distinguish the reflected waves from search waves transmitted by the transmitter / receiver 30 from ultrasonic waves transmitted from other vehicles or the like by comparing the drive signals and reception signals.

[0106] The amplitude evaluation unit 73 determines whether the amplitude of the received signal is greater than or equal to a predetermined threshold. If the amplitude evaluation unit 73 determines that the amplitude of the received signal is greater than or equal to the threshold, the frequency evaluation unit 74 identifies the received wave based on the frequency of the received signal.

[0107] Specifically, the frequency evaluation unit 74 mixes the drive signal and the received signal, extracts phase difference information from the received signal, calculates the frequency of the received wave based on the frequency of the drive signal and the extracted phase difference information, and generates a frequency waveform. The frequency evaluation unit 74 then calculates the residual sum of squares of the generated frequency waveform and the frequency waveform of the drive signal. If the calculated residual sum of squares is less than a predetermined threshold, it is determined that the received wave is a reflected wave of a search wave transmitted from the transmitter / receiver 30. On the other hand, if the calculated residual sum of squares is equal to or greater than the threshold, the frequency evaluation unit 74 determines that the received wave is not a reflected wave of a search wave transmitted from the transmitter / receiver 30.

[0108] The signal evaluation unit 70 performs an object detection determination when the frequency evaluation unit 74 determines that the received wave is a reflected wave of a search wave. Performing the detection determination after identifying the received wave in this way further increases the accuracy of object detection.

[0109] In the case where the frequencies of the drive signal and the receive signal are compared, as in Fig. 30 shows, the analysis period can be set based on the time at which the same frequency pattern as the drive signal is detected by the received signal. It should be noted that in Fig. 30 the same pattern as the drive signal is detected in the part surrounded by a dashed line, and the analysis period is set as a specific duration centered on the time at which this pattern was detected. By setting the analysis period in this way, the accuracy of object determination is increased. (Other embodiments)

[0110] It should be noted that the present invention is not limited to the embodiments described above and can be appropriately modified. In addition, the above embodiments are not irrelevant to each other, and they can be appropriately combined unless the combination is clearly impossible. Needless to say, the elements constituting the embodiments are not necessarily essential unless it is specifically stated that they are essential or is obviously essential. In addition, when a numerical value such as the number, value, quantity, or range of a component or components in any of the embodiments described above is mentioned, it is not limited to the specific number or value unless explicitly stated or obviously limited to the specific number or value in general, etc.When the shape, a positional relationship, or the like of a component or components or the like of any of the embodiments is mentioned, it is not limited to the shape, a positional relationship, or the like unless explicitly stated otherwise or limited to the specific shape, positional relationship, or the like in general.

[0111] For example, as in Fig. 31, the object detection device 1 may include a transmitter 31 and a receiver 32, and the transmitter 31 and the transmitting circuit 11 may form the transmitting unit 10, and the receiver 32 and the receiving circuit 51 may form the receiving unit 50.

[0112] Furthermore, drive signals different from those of the first embodiment may be used. For example, as shown in Fig. As shown in Figure 34, the signal generation unit may generate a drive signal such that a signal having a frequency f H and a signal with a frequency f L are continuously present. A drive signal with frequency f H can be generated first or a drive signal with frequency f L can be generated first. Furthermore, the drive signals can be generated with frequencies f H and f L be generated alternately, or a drive signal at one of the frequencies can be generated twice or more successively. Additionally, the signal length can be different for each frequency.

[0113] If drive signals, as in Fig. 32, the drive signals can be generated with two frequencies, as shown in Fig. 33, continuously generated or, as shown in Fig. 34, are generated intermittently.

[0114] For example, as in Fig. As shown in Figure 35, a drive signal can be generated to have a chirp signal that sweeps or runs from a certain frequency to another frequency. In this case, the result of an FFT analysis is, for example, Fig. 36 shown. Although Fig. 35 shows a down-chirp signal whose frequency decreases over time, an up-chirp signal whose frequency increases over time can also be used. When chip signals are used, they can sweep from either the upper or lower limit of the band of the transmitter / receiver 30 to the other, and these two frequencies can be set as the frequencies used in the determination. This increases the difference in directivity, which improves the accuracy of object determination. It should be noted that if a reduction in the amplitude of the search waves can be tolerated, frequencies outside the band of the transmitter / receiver 30 can be changed. Although the frequencies in Fig. 35 change linearly, the frequencies can also change non-linearly.

[0115] As another example, as in Fig. 37, a drive signal can be generated in which an up-chirp signal and a down-chirp signal occur alternately or continuously. Alternatively, as shown in Fig. As shown in Figure 38, one of the two chirp signals may be generated an interval before the other chirp signal is generated. The up-chirp signal and the down-chirp signal may be generated alternately, or one of them may be generated twice or more successively.

[0116] If the transmitter / receiver 30 follows the input signal well and has a wide bandwidth, signals containing wideband frequency components, for example, white noise signals or pulse signals, as in the Fig. 39 to 44 are used as the drive signals. It is also possible to use a white noise signal or a pulse signal with the drive signal shown in the Fig. 5 and 32 to 38. Furthermore, the drive signal may be a signal in which two frequencies are mixed so as to interfere with each other.

[0117] In the first to seventh embodiments and in the examples shown in the Fig. 32 to 34, the drive signal may be generated by combining three or more frequencies, and amplitudes corresponding to the three or more frequencies may be extracted from the received signal and compared. As in the early examples, the drive signal may be generated either continuously or intermittently when three or more frequencies are used. It is also possible to extract the amplitudes corresponding to the three or more frequencies from the received signal in the examples shown in the Fig. 35 to 42, to extract and compare.

[0118] It should be noted that in order to reduce the influence of amplitude variation due to environmental factors such as atmospheric fluctuations, it is advantageous to generate drive signals continuously. On the other hand, when a search wave is directed toward an object such as a wall, as in Fig. 43, a reflected wave is generated from the part of the wall directed toward the transmitter / receiver 30 and a reflected wave from its bottom part. If the signal length of the drive signals, as shown in Fig. 44, two reflected waves may overlap each other and the detection accuracy may be deteriorated. By intermittently generating drive signals and reducing the signal length, the two reflected waves are Fig. 45, so that the reduction in the determination accuracy due to the overlap of the reflected waves is suppressed. It should be noted that, as shown in Fig. As shown in Figure 46, the closer the horizontal distance from the transmitter / receiver 30, the greater the differences between the propagation distances of the two reflected waves. Likewise, the higher the altitude at which the transmitter / receiver 30 is arranged, the greater the difference in propagation distance. Accordingly, it is also possible to prevent overlap of the reflected waves by arranging the transmitter / receiver 30 at a higher position.

[0119] Furthermore, in the fourth and fifth embodiments, the frequencies of the drive signals, the frequency components used in object detection determination, and the reference value used for amplitude comparison are determined based on the Doppler shift amount. However, they may also be determined based on the speed of the transmitting unit 10.

[0120] The control unit 40 is not limited to a well-known microcomputer provided with a CPU, ROM, RAM, I / O, and the like. That is, the control unit 40 may comprise a digital circuit configured to enable the operations described above; for example, it may comprise an ASIC or a gate array. ASIC is an abbreviation for Application Specific Integrated Circuit. The same applies to the signal evaluation unit 70 and other components.

[0121] The signal evaluation unit 70 is not limited to a unit that determines whether the detected object is present within a specific detection range. For example, the signal evaluation unit 70 may be adapted to determine the vertical orientation angle of the detected object. Alternatively, the signal evaluation unit 70 may determine the vertical orientation angle of the detected object and may also determine whether the object is present within a specific detection range.

[0122] Each of the functional configurations and methods described above may be implemented by a dedicated computer provided by configuring a processor and a memory programmed to perform one or more functions embodied by computer programs. Alternatively, each of the functional configurations and methods described above may be implemented by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, each of the functional configurations and methods described above may be implemented by one or more dedicated computers configured by combining a processor and a memory programmed to perform one or more functions with a processor formed by one or more hardware logic circuits.Furthermore, the computer program may be stored in a computer-readable non-transitory tangible storage medium as instructions to be executed by the computer.

Claims

[1] Object detection device (1) comprising: a signal generation unit (20) which generates a drive signal, a transmitting unit (10) which outputs an ultrasonic wave as a search wave in response to the input drive signal, a receiving unit (50) which receives an ultrasonic wave to generate a reception signal, and an evaluation unit (70) which performs an object detection determination based on the received signal, wherein the drive signal has at least two frequencies, the evaluation unit extracts at least two amplitudes corresponding to the at least two frequencies from the received signal and makes a determination based on a relationship between the at least two amplitudes, the assessment unit makes a determination based on a ratio of at least two amplitudes, if the two frequencies are divided by f L and f H are designated, and the two amplitudes corresponding to the two frequencies f L and f H correspond, by A L or A H are designated, and if a directivity of the transmitting unit and the receiving unit with respect to the frequency f L wider than a directivity thereof with respect to the frequency f H is, the evaluation unit determines that an object is not present in a given detection area if A H / A L is smaller than a reference value or if A L / A H greater than a reference value, and if the directivity of the transmitting unit and the receiving unit with respect to the frequency f L narrower than the directivity of it with respect to the frequency f His, the evaluation unit determines that an object is not present in the detection area if A H / A L is greater than a reference value, or if A L / A H is smaller than a reference value. [2] The object detection device according to claim 1, wherein the signal generating unit generates the drive signal intermittently. [3] The object detection device according to claim 1 or 2, wherein the signal generation unit generates the drive signal so that signals having the at least two frequencies are continuously present therein. [4] The object detection device according to any one of claims 1 to 3, wherein the relationship between the at least two amplitudes is a relationship obtained based on an amplitude ratio obtained from the at least two amplitudes. [5] The object detection device according to any one of claims 1 to 4, wherein the evaluation unit extracts amplitudes of components corresponding to the two frequencies from a part of the reception signal present in a predetermined time range, and the time range is set based on a time point at which a pattern present in the drive signal is detected from the reception signal. [6] The object detection device according to any one of claims 1 to 5, wherein the evaluation unit corrects a reference value used for amplitude comparison according to a distance to an object calculated from a propagation time of the ultrasonic wave, or compares the two amplitudes after correcting the two amplitudes according to the distance. [7] The object detection device according to any one of claims 1 to 6, wherein the evaluation unit corrects a reference value used for a comparison of the two amplitudes according to an ambient temperature, or compares the two amplitudes after the two amplitudes are corrected according to the ambient temperature. [8] The object detecting device according to any one of claims 1 to 7, wherein the evaluation unit sets a frequency of the drive signal, a frequency component used for determination, or a reference value used for amplitude comparison based on a speed of the transmission unit or a Doppler shift amount of a received wave for the search wave. [9] An object detection device according to any one of claims 1 to 8, wherein when a resonance frequency of the transmitting unit and the receiving unit is determined by f 0is designated, one of the two frequencies higher than the resonance frequency f 0 and the other lower than the resonance frequency f 0 is. [10] The object detection device according to any one of claims 1 to 9, wherein the evaluation unit extracts amplitudes of components corresponding to the two frequencies from a part of the reception signal present in a predetermined time range, and the time range is set based on a time point at which an amplitude of the reception signal exceeds a predetermined amplitude threshold, a time point at which a peak amplitude of the reception signal is obtained, or a time point at which a rise of the reception signal starts. [11] The object detecting device according to any one of claims 1 to 10, wherein the signal generating unit generates the drive signal such that amplitude levels of search waves corresponding to the two frequencies are the same in a zone in front of the transmitting unit, or amplitude levels of reflected waves from an object located in front of the transmitting unit are the same.

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