Object detection device

Abstract

To provide an object detection device which can improve accuracy of object height determination.SOLUTION: An object detection device for detecting an object with transmission / reception of an ultrasonic wave comprises: a transmission unit which transmits an ultrasonic wave according to a transmission signal; a reception unit which receives the ultrasonic wave and outputs a reception signal according to the received ultrasonic wave; an amplitude signal generation unit 63 which generates an amplitude signal of the reception signal; an amplitude feature detection unit 64 which detects an amplitude feature point from the amplitude signal and outputs amplitude feature point information being information about the amplitude feature point; a phase difference signal generation unit 61 which generates a phase difference signal between the reception signal and a reference signal; a phase feature detection unit 62 which detects a phase feature point from the phase difference signal and outputs phase feature point information being information about the phase feature point; a reflection signal detection unit 7 which detects a reflection signal on the basis of the amplitude feature point information and the phase feature point information and outputs reflection signal information being information about the reflection signal; and a height determination unit which determines the height of an object on the basis of the reflection signal information.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Technologies have been proposed that use this type of object detection device to perform automatic parking, etc. In such technologies, in order to improve the accuracy of obstacle detection, it is necessary to determine the height of the detected object from the ground.

[0003] For example, Patent Document 1 proposes a technology for determining the type of obstacle based on the number of peaks in a reflected sonar signal. Specifically, two reflected waves are returned from an obstacle such as a tall wall, and one reflected wave is returned from an obstacle such as a short curb. Therefore, if there are two peaks, the obstacle is determined to be a wall, and if there is one peak, it is determined to be a curb. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5846316 Summary of the Invention [Problem to be solved by the invention]

[0005] However, on uneven road surfaces such as asphalt, the signal-to-noise ratio decreases due to the influence of reflected waves from the road surface. Also, the strength of the reflected waves decreases when the distance between the sonar and the object is long. Therefore, it may not be possible to detect the peak of the reflected signal from a short object at a distance.

[0006] Furthermore, when the sonar is close to an object, the strength of the reflected waves from the base of the object is reduced due to the influence of ultrasonic directionality. As a result, for tall objects nearby, the peak of the reflected signal corresponding to the reflected wave from the base may not be detected, and only one peak may be detected.

[0007] In this way, the method of determining the height of an object based on the number of peaks in the reflected signal may result in an erroneous determination of the height of the object.

[0008] In view of the above, an object of the present invention is to provide an object detection device that can improve the accuracy of determining the height of an object. [Means for solving the problem]

[0009] In order to achieve the above object, the invention of claim 1 provides an object detection device that detects an object by transmitting and receiving ultrasonic waves, comprising: a transmitting unit (40A) that transmits ultrasonic waves according to a transmission signal; a receiving unit (40B) that receives ultrasonic waves and outputs a reception signal according to the received ultrasonic waves; an amplitude signal generating unit (63) that generates an amplitude signal of the reception signal; and an amplitude feature detecting unit (64) that detects amplitude feature points from the amplitude signal and outputs amplitude feature point information that is information related to the amplitude feature points. Calculate the difference between the phase of the received signal and the phase of the reference signal a phase difference signal generating unit (61) that generates a phase difference signal between a received signal and a reference signal; a phase feature detecting unit (62) that detects a phase feature point from the phase difference signal and outputs phase feature point information that is information about the phase feature point; and a phase feature detecting unit (63) that detects a phase feature point based on the amplitude feature point information and the phase feature point information. From the received signal The reflected signal is detected and information about the reflected signal is This information includes the detection result of the reflected signal. The device includes a reflected signal detector (7) that outputs reflected signal information, and a height determiner (8) that determines the height of the object based on the reflected signal information.

[0010] Even when the strength of the reflected wave is low, the phase of the received signal is likely to reflect the characteristics of the reflected wave from an object. Therefore, detecting the reflected signal based on the amplitude feature information and phase feature information improves the accuracy of determining the height of an object.

[0011] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram of an object detection device according to a first embodiment. [Figure 2] FIG. 2 is a block diagram of a received signal processing unit and the like shown in FIG. [Figure 3] FIG. 10 is a diagram illustrating a phase difference signal. [Figure 4] 10A and 10B are diagrams illustrating an amplitude signal and a phase difference signal. [Figure 5] FIG. 10 is a diagram for explaining a method for setting a detection range. [Figure 6] FIG. 10 is a diagram for explaining a method for setting a detection range. [Figure 7] 10 is a flowchart of an object detection process. [Figure 8] FIG. 10 is a diagram showing an expected received signal when a search wave is transmitted to a short object. [Figure 9] FIG. 10 is a diagram showing an expected received signal when a search wave is transmitted to a tall object. [Figure 10] FIG. 10 is a diagram showing the received signal when a search wave is transmitted to a short object at a distance. [Figure 11] FIG. 10 is a diagram showing the received signal when a search wave is transmitted to a nearby tall object. [Figure 12] FIG. 10 is a diagram showing a phase difference signal when a search wave is transmitted to a short object. [Figure 13] FIG. 10 is a diagram showing a phase difference signal when a search wave is transmitted to a tall object. [Figure 14] 10A and 10B are diagrams showing amplitude signals and phase difference signals of a reflected wave returned from a tall object. [Figure 15] 10A and 10B are diagrams showing amplitude signals and phase difference signals of a reflected wave returned from a short object. [Figure 16] 10A and 10B are diagrams showing amplitude signals and phase difference correlation signals of reflected waves returned from a tall object. [Figure 17] 10A and 10B are diagrams showing amplitude signals and phase difference correlation signals of a reflected wave returned from a short object. [Figure 18] 10A and 10B are diagrams illustrating a phase difference signal and a phase difference correlation signal in another embodiment. [Figure 19] FIG. 10 is a diagram for explaining an object determination method according to another embodiment. [Figure 20] FIG. 10 is a diagram illustrating a phase correlation signal in another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, parts that are identical or equivalent to each other will be denoted by the same reference numerals.

[0014] (First embodiment) A first embodiment will be described. An object detection device 1 of this embodiment shown in Fig. 1 is mounted on a vehicle (not shown) and configured to detect an object B around the vehicle. The vehicle on which the object detection device 1 is mounted will be referred to as "host vehicle" hereinafter. The vehicle (not shown) is, for example, an automobile.

[0015] The object detection device 1 detects objects by transmitting and receiving ultrasonic waves, and includes an ultrasonic sensor 2 and a control unit 3 that controls the operation of the ultrasonic sensor 2. The ultrasonic sensor 2 is configured to detect object B by transmitting a search wave, which is an ultrasonic wave, and receiving the search wave reflected by object B.

[0016] The ultrasonic sensor 2 includes a transmitter / receiver 4, a transmission signal generator 5, a reception signal processor 6, a reflected signal detector 7, and a determination unit 8.

[0017] The transceiver 4 has a transmitter 40A and a receiver 40B. The transmitter 40A is configured to be able to transmit a probe wave to the outside. The receiver 40B is configured to be able to receive ultrasonic waves, including the probe wave transmitted from the transmitter 40A and reflected by the object B.

[0018] The transmitting / receiving unit 4 includes a transducer 41, a transmitting circuit 42, and a receiving circuit 43. The transmitting unit 40A is made up of the transducer 41 and the transmitting circuit 42. The receiving unit 40B is made up of the transducer 41 and the receiving circuit 43.

[0019] The transducer 41 functions as a transmitter that transmits a search wave to the outside and as a receiver that receives a reflected wave, and is electrically connected to a transmission circuit 42 and a reception circuit 43. In other words, the ultrasonic sensor 2 has a so-called integrated transmission and reception configuration.

[0020] Specifically, the transducer 41 is configured as an ultrasonic microphone incorporating an electromechanical energy conversion element such as a piezoelectric element, etc. The transducer 41 is disposed at a position facing the outer surface of the vehicle so as to be able to transmit a search wave to the outside of the vehicle and receive a reflected wave from the outside of the vehicle.

[0021] The transmission circuit 42 is configured to drive the transducer 41 based on the input transmission signal, thereby causing the transducer 41 to emit a search wave. Specifically, the transmission circuit 42 has a digital / analog conversion circuit and the like. That is, the transmission circuit 42 is configured to generate an element input signal by performing signal processing such as digital / analog conversion on the transmission signal output from the transmission signal generation unit 5. The element input signal is an AC voltage signal for driving the transducer 41. The transmission circuit 42 is configured to apply the generated element input signal to the transducer 41 to excite the electromechanical energy conversion element in the transducer 41, thereby generating a search wave.

[0022] The receiving circuit 43 is configured to generate a receiving signal corresponding to the result of receiving the ultrasonic waves by the transducer 41 and output the signal to the receiving signal processing unit 6. Specifically, the receiving circuit 43 has an amplifier circuit, an analog / digital conversion circuit, etc. That is, the receiving circuit 43 is configured to perform signal processing such as amplification and analog / digital conversion on the element output signal output by the transducer 41 to generate a receiving signal including information about the amplitude and frequency of the received wave. The element output signal is an AC voltage signal generated by an electromechanical energy conversion element provided in the transducer 41 in response to the reception of the ultrasonic waves.

[0023] The transmission signal generation unit 5 is configured to generate a transmission signal and output it to the transmission circuit 42. The transmission signal is a signal that drives the transducer 41 to emit a search wave from the transducer 41. The transmission signal generation unit 5 of this embodiment generates an unmodulated transmission signal with a constant frequency.

[0024] The received signal processing unit 6 processes the received signal and generates a signal used for detecting the reflected signal in the reflected signal detection unit 7. As shown in FIG. 2, the received signal processing unit 6 includes a phase difference signal generation unit 61, a phase feature detection unit 62, an amplitude signal generation unit 63, and an amplitude feature detection unit 64.

[0025] The phase difference signal generator 61 generates a phase difference signal between the received signal output by the receiver circuit 43 and a reference signal. Specifically, a reference signal corresponding to the transmitted signal is input to the phase difference signal generator 61, which calculates the difference between the phase of the received signal and the phase of the reference signal and outputs the signal generated as a result as a phase difference signal to the phase feature detector 62. The reference signal is a burst-like signal with the same frequency as the transmitted signal.

[0026] The phase feature detection unit 62 detects phase feature points from the phase difference signal output by the phase difference signal generation unit 61, and outputs phase feature point information that is information relating to the phase feature points.

[0027] Specifically, the phase feature detector 62 sets a detection range for the phase feature points based on the transmission signal. This detection range is, for example, a time range between the time when the generation of the transmission signal starts and a time after a predetermined time has elapsed since that time.

[0028] The phase feature detection unit 62 then detects, from the phase difference signal in the set detection range, a portion where the phase difference is flat, i.e., a continuous section where the amount of change in the phase difference value is within a predetermined range. When the length of the section is equal to or longer than a determination time set based on the length of the transmission signal, the phase feature detection unit 62 determines the central sample of the section as a phase feature point and outputs information about the phase feature point to the reflected signal detection unit 7 as phase feature point information.

[0029] Whether the length of the interval is equal to or greater than the determination time may be determined by determining whether the difference between the start time and end time of the interval is equal to or greater than a predetermined time, or by determining whether the number of samples in the interval is equal to or greater than a predetermined number. The phase feature point information includes, for example, the start time, end time, and center time of the interval, the length of the time range, and the value of the phase difference.

[0030] For example, in the phase difference signal shown in Fig. 3, the phase difference is flat at two points surrounded by dashed lines. When multiple sections where the phase difference is flat are detected in this way, the phase feature detection unit 62 detects the sample at the center of the longest section as the phase feature point.

[0031] The amplitude signal generator 63 generates an amplitude signal of the received signal output by the receiving circuit 43. For example, the amplitude signal generator 63 generates the amplitude signal by using the strength of the received signal as the amplitude. Alternatively, the amplitude signal generator 63 performs quadrature detection on the received signal and generates the amplitude signal by using the amplitude of the complex signal generated thereby as the amplitude of the received signal. Alternatively, the amplitude signal generator 63 generates the amplitude signal by calculating the correlation between the received signal and a reference signal set based on the transmitted signal. When the amplitude signal is generated by such correlation calculation, the signal width of the amplitude signal is reduced due to the effect of pulse compression, improving the S / N ratio and improving the detection accuracy of the reflected signal. The amplitude signal generator 63 outputs the generated amplitude signal to the amplitude feature detector 64.

[0032] The amplitude feature detection unit 64 detects amplitude feature points from the amplitude signal output by the amplitude signal generation unit 63, and outputs amplitude feature point information that is information relating to the amplitude feature points.

[0033] For example, the amplitude feature detector 64 sets a detection range for amplitude feature points in the same way as the phase feature detector 62, detects peaks in this detection range that are equal to or greater than a threshold value of the amplitude signal, and sets these peaks as amplitude feature points.

[0034] The amplitude feature detection unit 64 then generates amplitude feature information based on the detected amplitude feature and outputs it to the reflected signal detection unit 7. The amplitude feature information includes, for example, one or more of the peak value of the amplitude signal, the time of the peak, the width of the section where the signal value is equal to or greater than the threshold, the area of ​​the section, and the number of peaks. The area of ​​the section is the area of ​​the part of the graph of the amplitude signal where the amplitude is equal to or greater than the threshold.

[0035] The reflected signal detection unit 7 detects the reflected signal based on the amplitude feature point information and the phase feature point information, and outputs reflected signal information that is information related to the reflected signal. As shown in Fig. 2, the reflected signal detection unit 7 includes a first reflected signal detection unit 71 and a second reflected signal detection unit 72.

[0036] The first reflected signal detector 71 detects a first reflected signal, which is one of the reflected signals. When the first reflected signal detector 71 detects the first reflected signal, the second reflected signal detector 72 detects a second reflected signal, which is a reflected signal different from the first reflected signal.

[0037] The reflected signal detection unit 7 performs detection processing for at least one reflected signal based on both amplitude feature point information and phase feature point information. In this embodiment, the first reflected signal detection unit 71 performs detection processing for the first reflected signal based on both the amplitude feature point information and the phase feature point information. The second reflected signal detection unit 72 performs detection processing for the second reflected signal based on the phase feature point information of the amplitude feature point information and the phase feature point information.

[0038] Specifically, the first reflected signal detection unit 71 sets a time range based on the peak time of an amplitude feature point included in the amplitude feature point information, and if a phase feature point is included in this time range, detects the received signal corresponding to this amplitude feature point and phase feature point as the first reflected signal.

[0039] For example, when the amplitude signal and phase difference signal shown in FIG. 4 are generated, the received signal at time t1 where the amplitude peaks above the threshold and the phase difference is flat is determined to be the first reflected signal.

[0040] When the first reflected signal detector 71 detects the first reflected signal, the second reflected signal detector 72 sets the detection range of the second reflected signal using the first reflected signal as a reference as follows.

[0041] First, let us consider the case where the first reflected signal corresponds to a wave reflected from the front or top of the object. In this case, the second reflected signal is considered to correspond to a wave reflected from the base of the object.

[0042] Therefore, the time difference between the first reflected signal and the second reflected signal corresponds to the difference between the distance between the ultrasonic sensor 2 and the front or upper end of the object, and the distance between the ultrasonic sensor 2 and the base of the object. This time difference is greatest when the height of the object is higher than the mounting height of the ultrasonic sensor 2 and the first reflected signal corresponds to the wave reflected from the front of the object.

[0043] Therefore, the time difference in this case is calculated, and the time obtained by adding the calculated time difference to the reception time of the first reflected signal is set as the end time of the detection range of the second reflected signal.

[0044] Specifically, as shown in FIG. 5, the height of the ultrasonic sensor 2 from the ground is defined as h1, the distance between the ultrasonic sensor 2 and the object estimated based on the first reflected signal is defined as L1, and the distance between the ultrasonic sensor 2 and the base of the object is defined as L2. The second reflected signal detection unit 72 then calculates L2=√(h1 2 +L1 2 ) to estimate the distance L2.

[0045] The distance L1 is calculated, for example, by the TOF method based on the time from transmission of the search wave to reception of the first reflected signal and the speed of sound. TOF stands for Time of Flight. The second reflected signal detection unit 72 then calculates the time difference corresponding to the distance L2-L1 and sets the end time of the detection range of the second reflected signal.

[0046] Next, let us consider the case where the first reflected signal corresponds to a wave reflected from the base of the object. In this case, the second reflected signal is considered to correspond to a wave reflected from the front or top of the object.

[0047] The time difference between the first reflected signal and the second reflected signal is greatest when the height of the object is higher than the mounting height of the ultrasonic sensor 2 and the second reflected signal corresponds to a wave reflected from the front of the object. Therefore, the time difference in this case is calculated, and the time obtained by subtracting the calculated time difference from the reception time of the first reflected signal is set to the start time of the detection range of the second reflected signal.

[0048] Specifically, the second reflected signal detection unit 72 calculates L1=√(L2 2 -h1 2 ) to estimate the distance L1. The distance L2 is calculated, for example, by the TOF method. The second reflected signal detection unit 72 then calculates the time difference corresponding to the distance L2-L1, and sets the start time of the detection range of the second reflected signal.

[0049] When there is a phase feature point within the set detection range where the phase difference value is different from the phase difference value of the first reflected signal by a predetermined value or more, the second reflected signal detection unit 72 determines the received signal corresponding to this phase feature point as the second reflected signal. Note that when there are multiple phase feature points within the detection range, the second reflected signal detection unit 72 detects the phase feature point with the longest section where the phase difference is flat from the multiple phase feature points, and determines the received signal corresponding to this phase feature point as the second reflected signal.

[0050] For example, when the detection range for the second reflected signal is set as shown in FIG. 4, the received signal corresponding to the phase feature point at time t2 is detected as the second reflected signal.

[0051] The reflected signal detector 7 outputs reflected signal information including the detection results of the first and second reflected signals by the first reflected signal detector 71 and the second reflected signal detector 72 to the determiner 8 .

[0052] The determination unit 8 performs object detection determination, object height determination, object distance calculation, etc. based on the reflected signal information output from the reflected signal detection unit 7. The determination unit 8 corresponds to a height determination unit.

[0053] Specifically, when the first reflected signal detection unit 71 detects the first reflected signal, the determination unit 8 determines that a detection target object is present within the detection range of the ultrasonic sensor 2. On the other hand, when the first reflected signal detection unit 71 does not detect the first reflected signal, the determination unit 8 determines that a detection target object is not present within the detection range. When it is determined that an object is present, the determination unit 8 determines the height of the object as follows.

[0054] When the second reflected signal detector 72 detects the second reflected signal, the determiner 8 calculates the estimated height of the detected object.

[0055] First, of the first and second reflected signals, the one received first corresponds to the reflected wave from the front or top end of the object, and the one received later corresponds to the reflected wave from the base of the object.

[0056] Then, the reception time of the reflected signal received later is set as the reception time of the reflected wave from the base, and the distance L2 between the ultrasonic sensor 2 and the base of the object is calculated based on the time from the transmission time of the search wave to the reception time of the reflected wave and the speed of sound. As shown in Figure 6, if the horizontal distance between the ultrasonic sensor 2 and the base of the object is L3, the distance L3 is calculated as follows: L3 = √(L2 2 -h1 2 ) can be calculated by

[0057] Next, the height of the object is calculated using the height h1 of the ultrasonic sensor 2 and the distance L3. That is, the reception time of the first reflected signal is set to the same as the reception time of the second reflected signal, and the distance L1 is calculated based on this reception time and the speed of sound. The height h2 of the object is then calculated as h2 = h1 - √(L1 2 -L3 2 ) As shown in FIG. 5, when the upper end of the object is located higher than the mounting height of the ultrasonic sensor 2, the height of the front part of the object is calculated as the height h2 of the object.

[0058] After calculating the estimated height in this manner, the determination unit 8 compares the calculated estimated height with a threshold value to determine whether the object is a tall object or a short object. A tall object is, for example, an object whose height from the road surface is greater than a predetermined value and which may come into contact with the vehicle body. A short object is, for example, an object whose height from the road surface is less than a predetermined value and which is unlikely to come into contact with the vehicle body.

[0059] If the estimated height is greater than the threshold, the determination unit 8 determines that the detected object is a tall object. On the other hand, if the reflected signal detection unit 7 detects only the first reflected signal of the first and second reflected signals and does not detect the second reflected signal, or if the calculated estimated height is equal to or less than the threshold, the determination unit 8 determines that the detected object is a short object.

[0060] The object detection determination result, height determination result, calculation result of distance L3 to the object, etc., by the determination unit 8 are transmitted to the control unit 3.

[0061] The transmission signal generator 5, reception signal processor 6, reflected signal detector 7, and determination unit 8 are configured with DSPs programmed with functions such as transmission signal generation, phase difference signal generation, amplitude signal generation, phase feature detection, amplitude feature detection, reflected signal detection, object detection determination, object height determination, estimated height calculation, distance calculation, etc. DSP is an abbreviation for Digital Signal Processor.

[0062] The control unit 3 is connected to the ultrasonic sensor 2 via an in-vehicle communication line so as to be able to communicate information with the ultrasonic sensor 2, and is configured to control the transmission and reception operations of the ultrasonic sensor 2. The control unit 3 is provided as a so-called sonar ECU, and is equipped with an in-vehicle microcomputer having a CPU, ROM, RAM, non-volatile rewritable memory, etc. (not shown). ECU is an abbreviation for Electronic Control Unit. Examples of non-volatile rewritable memory include EEPROM and flash ROM. EEPROM is an abbreviation for Electronically Erasable and Programmable Read Only Memory.

[0063] As described above, the object detection determination result, height determination result, calculation result of the distance to the object, etc. are transmitted from the determination unit 8 to the control unit 3. These determination results are used for processing such as warning of an obstacle and automatic parking.

[0064] The operation of the object detection device 1 will now be described. The object detection device 1 repeatedly executes an object detection process including the process shown in Fig. 7. In the object detection process, the control unit 3 issues a transmission instruction to the transmission signal generation unit 5, and the transducer 41 transmits a search wave based on the transmission signal generated by the transmission signal generation unit 5. Then, when reception of an ultrasonic signal by the transmission / reception unit 4 is detected, the object detection device 1 executes the process shown in Fig. 7.

[0065] First, in step S101, the received signal is processed in the received signal processing unit 6. That is, the phase difference signal generation unit 61 generates a phase difference signal between the received signal output from the transmitting / receiving unit 4 and a reference signal, and the phase feature detection unit 62 detects phase feature points from the phase difference signal and outputs phase feature point information to the reflected signal detection unit 7. Also, the amplitude signal generation unit 63 generates an amplitude signal of the received signal, and the amplitude feature detection unit 64 detects amplitude feature points from the amplitude signal and outputs amplitude feature point information to the reflected signal detection unit 7.

[0066] In the following step S102, the first reflected signal detection unit 71 detects the first reflected signal based on the phase feature point information and the amplitude feature point information. In the following step S103, the determination unit 8 determines whether the first reflected signal detection unit 71 has detected the first reflected signal.

[0067] If it is determined that the first reflected signal is detected, the process proceeds to step S104. On the other hand, if it is determined that the first reflected signal is not detected, the process proceeds to step S105, where the determination unit 8 determines that the object to be detected does not exist, and the process ends.

[0068] In step S104, the second reflected signal detection unit 72 sets the detection range of the second reflected signal based on the detection result of the first reflected signal by the first reflected signal detection unit 71. That is, as described above, the second reflected signal detection unit 72 calculates the time range in which the second reflected signal is likely to be received from the reception time of the first reflected signal, and sets this as the detection range of the second reflected signal.

[0069] In the following step S106, the second reflected signal detection unit 72 detects a second reflected signal. That is, the second reflected signal detection unit 72 detects a reflected signal different from the first reflected signal based on the phase feature point information within the detection range set in step S104, and sets the detected signal as the second reflected signal.

[0070] In the following step S107, the determination unit 8 determines whether or not the second reflected signal has been detected by the second reflected signal detection unit 72. If it is determined that the second reflected signal has been detected, the process proceeds to step S108, and the determination unit 8 calculates the estimated height of the object by the method described above.

[0071] In the following step S109, the determination unit 8 determines whether the estimated height calculated in step S108 is greater than a threshold value. If it is determined that the estimated height is greater than the threshold value, the process proceeds to step S110, where the determination unit 8 determines that the detected object is a tall object, and the process ends.

[0072] If it is determined in step S107 that the second reflected signal has not been detected, or if it is determined in step S109 that the estimated height is equal to or less than the threshold, the process proceeds to step S111. Then, the determination unit 8 determines that the detected object is a short object, and the process ends.

[0073] When the process shown in FIG. 7 is completed, the determination unit 8 transmits to the control unit 3 the object detection determination result, the height determination result, the calculation result of the distance to the object, and the like.

[0074] The effects of this embodiment will be described below. One possible method for determining the height of an object is to determine the height of the object based on the number of peaks in the amplitude signal.

[0075] For example, when a reflected wave from a short object is received, an amplitude signal such as that shown in Figure 8 is expected. That is, a reflected wave from the top end and a reflected wave from the base are returned, but since the reflected wave from the top end has low intensity, the amplitude signal will have one peak above the threshold.

[0076] Furthermore, when a reflected wave is received from an object that is taller than the mounting height of the ultrasonic sensor 2, an amplitude signal such as that shown in Fig. 9 is expected. That is, high-intensity reflected waves are returned from the front and base of the object, resulting in two peaks above the threshold.

[0077] Therefore, it seems possible to determine that an object is short when the number of peaks in the amplitude signal is one, and that an object is tall when the number of peaks in the amplitude signal is two.

[0078] However, in reality, on uneven road surfaces such as asphalt, the signal-to-noise ratio decreases due to the influence of reflected waves from the road surface. Furthermore, the strength of the reflected waves decreases when the distance between the ultrasonic sensor 2 and an object is long. Therefore, for a short object located far away, the amplitude signal may not exceed the threshold, and a peak may not be detected, as shown in Figure 10.

[0079] Furthermore, when the distance between the ultrasonic sensor 2 and an object is short, the intensity of the reflected wave from the base of the object is reduced due to the influence of ultrasonic directionality. As a result, for a tall object nearby, the peak corresponding to the reflected wave from the base may not be detected, and only one peak may be detected, as shown in Figure 11. As such, the method of determining the height of an object based on the number of peaks in the amplitude signal may result in an erroneous determination of the height of the object.

[0080] Furthermore, in automatic parking, etc., it is necessary to distinguish between an object that is too tall to come into contact with the vehicle body and a step or the like that is unlikely to come into contact with the vehicle body. However, the determination method based on the number of peaks in the amplitude signal can only determine whether the object is higher than the mounting height of the ultrasonic sensor 2.

[0081] In contrast to this, in this embodiment, reflected signals are detected based on amplitude feature point information and phase feature point information, and the height of the object is determined based on the number of reflected signals.

[0082] The amplitude of the received signal corresponds to the sum of the intensities of all reflected waves returned from a wide azimuth range centered on the ultrasonic sensor 2. Meanwhile, the phase of the received signal corresponds to the phase of the reflected wave with the strongest intensity in this azimuth range. Therefore, even if the signal-to-noise ratio of the amplitude signal is low, the phase of the received signal is likely to show the characteristics of the reflected wave from the object. Furthermore, for the wave reflected from the object of the search wave transmitted from the transmitter 40A, the phase difference between the received signal and the reference signal is almost constant.

[0083] Therefore, for waves reflected from a short object, the difference in propagation distance between the waves reflected from the top end and the base of the object is small, so the area with a constant phase difference is one area surrounded by a dashed line, and one reflected signal is detected, as shown in Figure 12. For waves reflected from a tall object, the difference in propagation distance between the waves reflected from the front or top end of the object and the base is large, so the area with a constant phase difference is two areas surrounded by dashed lines, and two reflected signals are detected, as shown in Figure 13.

[0084] In this way, by calculating the phase difference between the received signal and the reference signal, detecting phase feature points from the phase difference signal, and using the phase feature point information in addition to the amplitude feature point information, it becomes possible to detect low-intensity reflected waves from the top end of a low-profile object in the distance or the base of a nearby object, etc., thereby improving the accuracy of height determination.

[0085] Furthermore, since it is possible to detect reflected waves with low intensity, it is possible to make a more detailed height determination for objects that are lower than the mounting height of the ultrasonic sensor 2. For example, it is possible to distinguish between an object that is too tall to come into contact with the vehicle body and a step or the like that is unlikely to come into contact with the vehicle body.

[0086] 14 and 15 show the object detection results obtained by the method of this embodiment when probe waves are transmitted to a tall object and a short object, respectively. A tall object here is an object that is about the same height as the mounting height of the ultrasonic sensor 2 and that is tall enough to come into contact with the bumper of the vehicle. A short object here is an object that is tall enough not to come into contact with the bumper of the vehicle.

[0087] As shown in Figure 14, for a tall object, the amplitude signal corresponding to the reflected wave from the base of the object peaks above the threshold, and the phase difference signal remains constant for a long period of time, so the received signal corresponding to this reflected wave was detected as the first reflected signal.

[0088] In the detection range set based on this first reflected signal, the phase difference signal corresponding to the reflected wave from the upper end of the object is constant, so the received signal corresponding to this reflected wave is detected as the second reflected signal. Furthermore, since the estimated height calculated based on the two reflected signals is greater than the threshold, the detected object is determined to be a tall object.

[0089] As shown in Figure 15, for a short object, the amplitude signal corresponding to the reflected wave from the base of the object peaks above the threshold and the phase difference signal is constant, so the received signal corresponding to this reflected wave was detected as the first reflected signal.

[0090] However, since there was no area with a constant phase difference signal within the detection range set based on this first reflected signal, the second reflected signal was not detected. As only one reflected signal was detected, it was determined that the detected object was a short object.

[0091] As described above, in this embodiment, the phase difference between the received signal and the reference signal corresponding to the transmitted signal is calculated, a phase feature point is detected from the phase difference signal, and a reflected signal is detected based on the amplitude feature point information and the phase feature point information. This makes it possible to detect a reflected wave with low intensity, thereby improving the accuracy of determining the height of an object.

[0092] Furthermore, according to the above embodiment, the following effects can be obtained.

[0093] (1) The phase feature detection unit 62 detects, from the phase difference signal, a continuous section in which the amount of change in the phase difference value is within a predetermined range, and when the length of the section is equal to or longer than a determination time set based on the length of the transmission signal, outputs information about the section as phase feature point information. In this way, by detecting phase feature points from portions where the phase difference signal is flat, the detection of phase feature points becomes easier and the amount of calculation can be reduced.

[0094] (2) The reflected signal detector 7 performs detection processing for at least one reflected signal based on both amplitude feature information and phase feature information. Due to phase characteristics, there are often multiple regions where the phase difference is constant. By using an amplitude signal with a high S / N ratio in addition to the phase difference signal, it is possible to accurately detect reflected signals corresponding to reflected waves from the front, top, and base of an object, thereby improving the accuracy of height determination.

[0095] (3) When one reflected signal is detected, the reflected signal detector 7 sets the detection range for another reflected signal based on the detected reflected signal. In this way, by setting the detection range for the second reflected signal based on the first reflected signal, the amount of calculation is reduced and detection of the second reflected signal becomes easier.

[0096] (Second embodiment) The second embodiment will be described. This embodiment is different from the first embodiment in that the method of detecting the reflected signal is changed, but the other points are the same as the first embodiment, so only the points that are different from the first embodiment will be described.

[0097] In this embodiment, the transmission signal is a modulated signal whose phase or frequency changes over time. For example, the transmission signal generator 5 generates a transmission signal corresponding to a frequency modulation state of a probe wave having a predetermined frequency modulation state. The transmission signal generator 5 generates the transmission signal so that the frequency of the probe wave is swept within a range including the resonant frequency of the transducer 41.

[0098] The predetermined frequency modulation state may be an up-chirp or a down-chirp. An up-chirp is a frequency modulation state in which the frequency monotonically increases over time. A down-chirp is a frequency modulation state in which the frequency monotonically decreases over time.

[0099] The probe signal is coded by frequency modulation of the transmitted signal. For example, an up-chirp indicates a "1" and a down-chirp indicates a "0." This code is used to identify the received signal.

[0100] The phase difference signal generator 61 generates a second phase difference signal based on the transmission signal by adding a phase difference signal between the received signal and the reference signal as a first phase difference signal. The reference signal in this embodiment is, for example, a burst-like signal having the same frequency as the average or center frequency of the transmission signal. The second phase difference signal is the phase difference signal between the transmission signal and the reference signal. The phase difference signal generator 61 then generates a phase difference correlation signal between the first phase difference signal and the second phase difference signal. The phase difference correlation signal is generated, for example, by cross-correlation between the first phase difference signal and the second phase difference signal. The phase difference signal generator 61 outputs the generated phase difference correlation signal to the phase feature detector 62.

[0101] When the phase difference correlation signal is generated in this manner, the phase difference correlation signal reaches a peak at the time when the first phase difference signal has the same shape as the second phase difference signal.

[0102] The phase feature detection unit 62 detects an interval from the phase difference correlation signal where the signal value is equal to or greater than a predetermined value, and outputs information about the interval as phase feature point information. Specifically, the phase feature detection unit 62 detects a portion where the phase difference correlation signal peaks at a value equal to or greater than a threshold, and sets the sample at this peak as a phase feature point. The phase feature point information output by the phase feature detection unit 62 includes, for example, one or more of the peak value of the phase difference correlation signal, the time of the peak, the width of the interval where the signal value is equal to or greater than a predetermined value, the area of ​​the interval, and the number of peaks.

[0103] The first reflected signal detection unit 71 detects the first reflected signal using the condition that the signs of the transmitted signal and the received signal match, in addition to the conditions used in the first embodiment. That is, the first reflected signal detection unit 71 sets a time range based on the peak time of an amplitude feature point included in the amplitude feature point information, and when a phase feature point is included in this time range, determines whether the signs of the received signal corresponding to this amplitude feature point and phase feature point match those of the transmitted signal.

[0104] In the code determination, the first reflected signal detector 71 extracts a frequency signal from the received signal and determines whether the code corresponding to this frequency signal matches the code of the transmitted signal. The frequency signal is extracted, for example, by FFT, where FFT stands for Fast Fourier Transform. If the codes of the received signal and the transmitted signal match, the first reflected signal detector 71 detects the received signal as a first reflected signal.

[0105] When a phase feature point different from that of the first reflected signal is found within a detection range set using the first reflected signal as a reference, the second reflected signal detector 72 determines the received signal corresponding to this phase feature point as the second reflected signal. When the second reflected signal detector 72 detects the second reflected signal, the determiner 8 estimates the height of the object based on the time when the phase difference correlation signal reaches its peak.

[0106] 16 and 17 show the object detection results obtained by the method of this embodiment when probe waves are transmitted to a tall object and a short object, respectively. A tall object here is an object that is about the same height as the mounting height of the ultrasonic sensor 2 and that is tall enough to come into contact with the bumper of the vehicle. A short object here is an object that is tall enough not to come into contact with the bumper of the vehicle.

[0107] As shown in Figure 16, for a tall object, the amplitude signal corresponding to the reflected wave from the base of the object peaks above the threshold, and the phase difference correlation signal also peaks above the threshold, so the received signal corresponding to this reflected wave was detected as the first reflected signal.

[0108] In the detection range set based on this first reflected signal, the phase difference correlation signal corresponding to the reflected wave from the upper end of the object peaks above the threshold, and therefore the received signal corresponding to this reflected wave is detected as the second reflected signal. Furthermore, since the estimated height calculated based on the two reflected signals is greater than the threshold, the detected object is determined to be tall.

[0109] As shown in Figure 17, for a short object, the amplitude signal corresponding to the reflected wave from the base of the object peaks above the threshold, and the phase difference correlation signal also peaks above the threshold, so the received signal corresponding to this reflected wave was detected as the first reflected signal.

[0110] On the other hand, within the detection range set based on this first reflected signal, there is no region where the phase difference correlation signal has a peak above the threshold, so the second reflected signal was not detected. As only one reflected signal was detected, it was determined that the detected object was a short object.

[0111] This embodiment has the same configuration and operation as the first embodiment, and can therefore obtain the same effects as the first embodiment.

[0112] Furthermore, according to the above embodiment, the following effects can be obtained.

[0113] (1) The phase difference signal generator 61 generates a second phase difference signal based on the transmitted signal by adding a phase difference signal between the received signal and the reference signal as a first phase difference signal, and generates a phase difference correlation signal between the first phase difference signal and the second phase difference signal. The phase feature detector 62 then detects a section where the phase difference correlation signal is equal to or greater than a predetermined value, and outputs information about the section as phase feature point information.

[0114] This improves the signal-to-noise ratio and height determination accuracy, and also makes it possible to check the phase correlation with high accuracy not only when the transmitted signal is an unmodulated signal, but also when it is a modulated signal whose phase or frequency changes over time.

[0115] (2) The phase feature detection unit 62 detects phase feature points based on the peaks of the phase difference correlation signal. By using the peaks of the phase difference correlation signal as a reference, the accuracy of determining the height of an object, calculating the estimated height, and calculating the distance to the object is improved.

[0116] (Other embodiments) The present invention is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the claims. Furthermore, in each of the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where they are particularly clearly stated as essential or where they are clearly considered essential in principle.

[0117] The transducer 41 constituting the transmitting section 40A and the transducer 41 constituting the receiving section 40B may be provided as separate bodies.

[0118] In the second embodiment, the transmission signal may be an unmodulated signal, in which case the phase difference correlation signal will reach a peak at the time when the first phase difference signal becomes flat, as shown in FIG.

[0119] When generating an amplitude signal by correlation calculation, the received signal may be subjected to amplitude doubling processing to widen the frequency band before correlation calculation, which can improve detection performance even when a narrow-band microphone is used.

[0120] In the first embodiment, the reception time used to calculate the estimated height of an object or the distance to the object may be the time corresponding to a phase feature point or the time corresponding to the first sample in the section where the phase difference is flat. For example, when determining the reception time of a reflected wave based on an amplitude signal, the peak time of the amplitude signal is used as the reception time because the rising edge of the amplitude signal is buried in noise and difficult to detect. In contrast, by using the reception time of the first sample in that section as the reception time of the reflected wave, the reception start time of the reflected wave, which is difficult to detect from the amplitude signal, can be used as the reception time. This improves the accuracy of estimating the height of an object.

[0121] In the detection range set based on the transmission signal, a sample at a time when the amplitude signal becomes equal to or greater than a threshold may be set as an amplitude feature point. In this case, for example, the detection range of the first reflected signal is set based on the time when the amplitude becomes equal to or greater than the threshold.

[0122] In each of the above embodiments, the detection range of the second reflected signal is set based on the first reflected signal, but the second reflected signal may be detected in the same range as the first reflected signal.

[0123] The first reflected signal may be detected based on only one of the amplitude feature point information and the phase feature point information. In this case, the second reflected signal may be detected based on either the amplitude feature point information or the phase feature point information that was not used to detect the first reflected signal, or the second reflected signal may be detected based on both the amplitude feature point information and the phase feature point information.

[0124] When there is a phase feature point corresponding to the amplitude feature point, the first reflected signal detection unit 71 may detect the first reflected signal by further taking the following condition into consideration. That is, the first reflected signal detection unit 71 may compare the amplitude feature amount included in the amplitude feature point information with a predetermined value, compare the phase feature amount included in the phase feature point information with a predetermined value, and detect the reflected signal based on the comparison results of the amplitude feature amount and the comparison results of the phase feature amount. The amplitude feature amount is, for example, an amplitude peak value or the width of a section where the amplitude is equal to or greater than a threshold. The phase feature amount is, for example, the width of a section where the phase difference is flat or a correlation peak value.

[0125] The height of an object may be determined based only on the number of detected reflected signals without using the estimated height of the object. That is, if the second reflected signal is detected, the object may be determined to be tall, and if the second reflected signal is not detected and only the first reflected signal is detected, the object may be determined to be short.

[0126] If the amplitude signal is greater than a predetermined threshold, the object may be determined to be a tall wall.

[0127] The strength of the reflected wave from the top of an object varies depending on the height of the object. Therefore, when two reflected signals are detected, the height of the object may be determined based on the amplitude of the reflected signals. For example, if the difference between the amplitude of the first reflected signal and the amplitude of the second reflected signal or the ratio of the two amplitudes is greater than a predetermined value, the object may be more likely to be determined to be short.

[0128] In the first embodiment, if a region where the phase difference is constant continues for a predetermined time or longer, it may be determined that two reflected signals are included in that region.

[0129] In the second embodiment, if the phase difference correlation signal remains above the threshold for a predetermined period of time or longer, or if two or more peaks are observed in one region where the signal is above the threshold, it may be determined that two reflected signals are included in the region where the signal is above the threshold.

[0130] A predetermined value may be added to the phase difference used to detect the reflected signal. For example, the phase difference used to detect the reflected signal may be offset in consideration of the Doppler shift that occurs when an object moves.

[0131] The detection range of the reflected signal and the number of consecutive samples that serve as the detection criterion for the reflected signal may be changed depending on the distance to be detected.

[0132] The reflected signal detection unit 7 may be configured to detect three or more reflected signals. Objects with complex shapes may return three or more reflected waves. For example, when a search wave is transmitted toward a stepped object as shown in FIG. 19, three reflected signals are detected as shown in FIG. 20. Therefore, if multiple reflected signals other than the first reflected signal are detected within a detection range set based on the first reflected signal, the shape of the object may be estimated based on the detection results. For example, data on reflected signals relating to objects that may exist in a parking lot may be stored in the determination unit 8. If three or more reflected signals are detected during automatic parking, the detection results may be compared with the stored data to estimate the shape of the object. Furthermore, the detection criteria for reflected signals may be broadened to take into account the influence of the object's shape.

[0133] The transmit signal generator, receive signal processor, reflected signal detector, determiner, controller, etc., and their methods described herein may be implemented by a special-purpose computer configured with a processor and memory programmed to execute one or more functions embodied in a computer program. Alternatively, the transmit signal generator, receive signal processor, reflected signal detector, determiner, controller, etc., and their methods described herein may be implemented by a special-purpose computer configured with a processor configured with one or more dedicated hardware logic circuits. Alternatively, the transmit signal generator, receive signal processor, reflected signal detector, determiner, controller, etc., and their methods described herein may be implemented by one or more special-purpose computers configured with a processor and memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory tangible recording medium. [Explanation of symbols]

[0134] 40A Transmitter 40B Receiver 61 Phase difference signal generation section 62 Topological feature detection unit 63 Amplitude signal generation section 64 Amplitude feature detector 7 Reflection signal detector 8 Judgment section

Claims

1. An object detection device that detects an object by transmitting and receiving ultrasonic waves, a transmitting unit (40A) that transmits an ultrasonic wave in response to a transmission signal; a receiving unit (40B) that receives ultrasonic waves and outputs a reception signal corresponding to the received ultrasonic waves; an amplitude signal generator (63) that generates an amplitude signal of the received signal; an amplitude feature detection unit (64) that detects amplitude feature points from the amplitude signal and outputs amplitude feature point information that is information about the amplitude feature points; a phase difference signal generating unit (61) that calculates a difference between the phase of the received signal and the phase of a reference signal and generates a phase difference signal between the received signal and the reference signal; a phase feature detection unit (62) that detects a phase feature point from the phase difference signal and outputs phase feature point information that is information about the phase feature point; a reflected signal detection unit (7) that detects a reflected signal from the received signal based on the amplitude feature point information and the phase feature point information, and outputs reflected signal information that is information about the reflected signal and includes a detection result of the reflected signal; and a height determination unit (8) that determines the height of an object based on the reflected signal information.

2. An object detection device as described in Claim 1, wherein the reflected signal is the received signal corresponding to the amplitude feature point or the phase feature point.

3. The topological feature detection unit detecting a continuous section in which a change in the phase difference value is within a predetermined range from the phase difference signal; 3. The object detection device according to claim 1, wherein when the length of the section is equal to or longer than a determination time set based on the length of the transmission signal, information of the section is output as the phase feature point information.

4. The phase difference signal generation unit the phase difference signal as a first phase difference signal, generating a second phase difference signal based on the transmission signal in addition to the first phase difference signal; generating a phase difference correlation signal between the first phase difference signal and the second phase difference signal; The topological feature detection unit detecting an interval in which the phase difference correlation signal is equal to or greater than a predetermined value; 3. The object detection device according to claim 1, wherein information on the section is output as the topological feature point information.

5. An object detection device as described in Claim 4, wherein the phase difference correlation signal is generated by cross-correlation between the first phase difference signal and the second phase difference signal.

6. The object detection device according to claim 4 , wherein the phase feature detection unit detects the phase feature points based on peaks of the phase difference correlation signal.

7. 7. The object detection device according to claim 4, wherein the phase feature point information includes one or more of a peak value of the phase difference correlation signal, a peak time, a width of a section where the signal value is equal to or greater than a predetermined value, an area of ​​the section, and a number of peaks.

8. 8. The object detection device according to claim 4, wherein the transmission signal is a modulated signal whose phase or frequency changes over time.

9. 9. The object detection device according to claim 1, wherein the reflected signal detection unit performs detection processing for at least one of the reflected signals based on both the amplitude feature point information and the phase feature point information.

10. 10. The object detection device according to claim 1, wherein when one of the reflected signals is detected, the reflected signal detection unit sets a detection range for another reflected signal based on the detected reflected signal.

11. The reflected signal detection unit comparing the amplitude feature amount included in the amplitude feature point information with a predetermined value; comparing the topological feature amount included in the topological feature point information with a predetermined value; 11. The object detection device according to claim 1, wherein the reflected signal is detected based on a comparison result for the amplitude feature amount and a comparison result for the phase feature amount.

12. 12. The object detection device according to claim 1, wherein the amplitude feature point information includes one or more of the peak value of the amplitude signal, the peak time, the width of the section where the signal value is equal to or greater than a predetermined value, the area of ​​the section, and the number of peaks.

13. 13. The object detection device according to claim 1, wherein the height determination unit determines the height of the object based on the number of the detected reflected signals.

14. When a plurality of the reflected signals are detected, 14. The object detection device according to claim 1, wherein the height determination unit determines the height of the object based on a time difference between the two reflected signals.

15. When a plurality of the reflected signals are detected, The object detection device according to claim 1 , wherein the height determination unit determines the height of the object based on the amplitudes of the two reflected signals.

16. 16. The object detection device according to claim 1, wherein the amplitude signal is a signal generated by calculating a correlation between the received signal and a reference signal set based on the transmitted signal.

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