Object detection device

Abstract

This object detection device comprises: a transmitting unit for transmitting a transmission wave; a receiving unit for receiving a reception wave generated as a result of the transmission wave being reflected by an object; a constant false alarm rate (CFAR) processing unit for acquiring a difference value between a processing target value, which is a value of a processing target signal corresponding to the reception wave received at a certain detection timing, and a reference value based on a moving average value of the values of a group of reference signals corresponding to the reception wave received in a prescribed period before and after the detection timing; a detection processing unit for generating information relating to the object on the basis of the difference value; and a setting unit for selecting, from among a plurality of said reference values, the reference value matching a detection distance corresponding to the detection timing.

Description

[Technical field]

[0001] The present disclosure relates to an object detection device. [Background technology]

[0002] In vehicle control systems and the like, devices that use a TOF (Time Of Flight) method to detect objects present around a vehicle are used. The TOF method is a technique for calculating the distance from a vehicle to an object based on the difference between the timing at which a transmission wave such as an ultrasonic wave is transmitted and the timing at which a reception wave (reflected wave) generated by the transmission wave being reflected by the object is received. In addition, as a technique for improving the accuracy of object detection using the TOF method, a CFAR (Constant False Alarm Rate) process is known that suppresses the influence of road clutter and the like by subtracting from the value of a certain reception signal the moving average value of the values ​​of reception signals acquired in a predetermined period before and after the reception signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-292597 A Summary of the Invention [Problem to be solved by the invention]

[0004] One of the objectives of the present disclosure is to provide an object detection device capable of detecting an object with high accuracy by using CFAR processing. [Means for solving the problem]

[0005] An object detection device as an example of the present disclosure includes a transmitting unit that transmits a transmitted wave, a receiving unit that receives a received wave generated when the transmitted wave is reflected by an object, a CFAR processing unit that obtains a difference value between a processing target value, which is the value of a processing target signal corresponding to the received wave received at a certain detection timing, and a reference value based on a moving average value of each value of a reference signal group corresponding to the received wave received in a predetermined period before and after the detection timing, a detection processing unit that generates information about the object based on the difference value, and a setting unit that selects a reference value that matches the detection distance corresponding to the detection timing from multiple reference values.

[0006] According to the above configuration, the reference value used in the CFAR processing (the value to be subtracted from the processing target value) can be optimized according to the distance, thereby improving the accuracy of object detection using the CFAR processing.

[0007] The setting unit may set the reference value so that the reference value increases as the detection distance decreases.

[0008] This makes it possible to suppress erroneous detection of objects at close range and failure to detect objects at long range.

[0009] In addition, the setting unit may select a first reference value from the multiple reference values ​​when the detection distance is in a predetermined short-distance range, select a second reference value smaller than the first reference value from the multiple reference values ​​when the detection distance is in a medium-distance range farther than the short-distance range, and select a third reference value smaller than the second reference value from the multiple reference values ​​when the detection distance is in a long-distance range farther than the medium-distance range.

[0010] This makes it possible to set appropriate reference values ​​for each of the short, medium, and long distances.

[0011] In addition, the first reference value may be a maximum average value which is the larger of a first average value which is the average value of each value of a first reference signal group corresponding to a received wave received at a first predetermined time before the detection timing, and a second average value which is the average value of each value of a second reference signal group corresponding to a received wave received at a second predetermined time after the detection timing; the second reference value may be a total average value which is the average value of all reference values ​​including each value of the first reference signal group and each value of the second reference signal group; and the third reference value may be a minimum average value which is the smaller of the first average value and the second average value.

[0012] This allows the reference values ​​for short, medium and long distances to be set using the total average value, the maximum average value and the minimum average value. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a top view showing an example of the appearance of a vehicle equipped with a driving assistance system according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing an example of a hardware configuration of the ECU and the object detection device according to the first embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of a method for calculating distance using the TOF method. [Figure 4] FIG. 4 is a block diagram illustrating an example of a functional configuration of the object detection device according to the embodiment. [Diagram 5] FIG. 5 is a diagram illustrating an example of the CFAR process and the reference value setting process according to the embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of the total average value, the maximum average value, and the minimum average value according to the embodiment. [Figure 7] FIG. 7 is a flowchart illustrating an example of a reference value setting process in the object detection device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The configurations of the embodiments described below and the actions and effects brought about by the configurations are merely examples and are not limited to the contents described below.

[0015] 1 is a top view showing an example of the appearance of a vehicle 1 equipped with a driving assistance system according to an embodiment. The driving assistance system exemplified below is a system that uses ultrasonic waves to detect objects (other vehicles, road obstacles, people, animals, etc.) present around the vehicle 1, and performs processing to assist the driving of the vehicle 1 based on the detection results.

[0016] As shown in FIG. 1, the driving assistance system includes an ECU (Electronic Control Unit) 100 mounted inside a vehicle 1 having a pair of front wheels 3F and a pair of rear wheels 3R, and object detection devices 201-204 mounted on the exterior of the vehicle 1.

[0017] 1, the object detection devices 201-204 are installed at different positions on the rear end (e.g., rear bumper) of a vehicle body 2 serving as the exterior of a vehicle 1. In this embodiment, the object detection devices 201-204 have the same hardware configuration and functions. Therefore, hereinafter, for simplicity, the object detection devices 201-204 may be collectively referred to as object detection device 200.

[0018] The installation position of the object detection device 200 is not limited to the example shown in Fig. 1. The object detection device 200 may be installed, for example, at the front end portion (e.g., the front bumper) or the side portion of the vehicle body 2. Furthermore, the number of object detection devices 200 is not limited to the example shown in Fig. 1.

[0019] FIG. 2 is a block diagram showing an example of a hardware configuration of the ECU 100 and the object detection device 200 according to the first embodiment.

[0020] The ECU 100 includes an input / output device 110, a storage device 120, and a processor 130.

[0021] The input / output device 110 is an interface that enables transmission and reception of information between the ECU 100 and an external device (such as the object detection device 200). The storage device 120 includes a main storage device such as a read only memory (ROM) or a random access memory (RAM), and / or an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). The processor 130 is an arithmetic processing device including a central processing unit (CPU) that performs various arithmetic processing according to a program stored in the storage device 120. The processor 130 performs various processes (such as processes for realizing automatic driving, alarm output, etc.) based on various information (such as the detection result of the object detection device 200) input from the input / output device 110.

[0022] The object detection device 200 includes a transceiver 210 and a control unit 220 .

[0023] The transceiver 210 has a vibrator 211 such as a piezoelectric element, and realizes transmission and reception of ultrasonic waves by the action of the vibrator 211. Specifically, the transceiver 210 transmits ultrasonic waves generated in response to the vibration of the vibrator 211 as a transmission wave, and receives, as a reception wave, the vibration of the vibrator 211 caused by the ultrasonic waves transmitted as the transmission wave being reflected by an object present outside and returning. In the example shown in Fig. 2, an obstacle O installed on the road surface RS is illustrated as an object that reflects the transmission wave from the transceiver 210.

[0024] 2 illustrates a configuration in which both transmission of the transmission wave and reception of the reception wave are realized by a single transceiver 210 having a single oscillator 211, but the embodiment is not limited to this. For example, a configuration in which the transmission side mechanism and the reception side mechanism are separated, such as a configuration in which a first oscillator for transmitting the transmission wave and a second oscillator for receiving the reception wave are separately provided, may be used.

[0025] The control unit 220 includes an input / output device 221 , a storage device 222 , and a processor 223 .

[0026] The input / output device 221 is an interface that enables transmission and reception of information between the control unit 220 and external devices (ECU 100, transceiver 210, etc.). The storage device 222 includes a main storage device such as a ROM or a RAM, and / or an auxiliary storage device such as an HDD or an SSD. The processor 223 is an arithmetic processing device including a CPU or the like that performs various arithmetic processing according to programs stored in the storage device 333. The processor 223 performs various processes (e.g., generation of information related to an obstacle O, etc.) based on various information input from the input / output device 221 (e.g., detection data of the transceiver 210, etc.).

[0027] The object detection device 200 according to this embodiment detects the distance to an object (such as an obstacle O) by a technique known as the TOF method. As described in detail below, the TOF method is a technique for calculating the distance to an object based on the difference between the timing at which a transmission wave is transmitted (more specifically, the transmission starts) and the timing at which a reception wave is received (more specifically, the reception starts).

[0028] Fig. 3 is a diagram showing an example of a method for calculating distance using the TOF method. Fig. 3 illustrates an envelope L11 (echo information) showing a change over time in the intensity (signal level) of ultrasonic waves transmitted and received by the transceiver 210. In the graph shown in Fig. 3, the horizontal axis corresponds to time (TOF), and the vertical axis corresponds to the intensity of ultrasonic waves transmitted and received by the transceiver 210 (the magnitude of vibration of the transducer 211).

[0029] The envelope curve L11 indicates a change over time in the strength indicating the magnitude of vibration of the oscillator 211. From the envelope curve L11 illustrated in Fig. 3, it can be seen that the oscillator 211 is driven to vibrate for a period of time Ta from timing t0, and the transmission of the transmission wave is completed at timing t1, and then the vibration of the oscillator 211 due to inertia continues while attenuating for a period of time Tb until timing t2. Therefore, in the graph shown in Fig. 3, the period of time Tb corresponds to the so-called reverberation time.

[0030] The envelope L11 reaches a peak at a time t4 when the vibration of the vibrator 211 is equal to or greater than the detection threshold Th, which is a time Tp after the time t0 when the transmission of the transmission wave starts. The detection threshold Th is a value set to distinguish whether the vibration of the vibrator 211 is caused by the reception of a reflected wave from an obstacle O (another vehicle, a structure, a pedestrian, etc.) or the reception of a reflected wave from an object other than the obstacle O (for example, a road surface RS, etc.). Note that although the detection threshold Th is shown here as a constant value, the detection threshold Th may be a variable value that changes depending on the situation. Vibrations having a peak equal to or greater than the detection threshold Th can be considered to be caused by the reception of a reflected wave from the obstacle O.

[0031] The envelope curve L11 in this example shows that the vibration of the transducer 211 attenuates after timing t4. Therefore, timing t4 corresponds to the timing at which reception of the reflected wave from the obstacle O is completed, in other words, the timing at which the transmission wave last transmitted at timing t1 returns as a reflected wave.

[0032] In addition, in the envelope L11, timing t3 as the start point of the peak at timing t4 corresponds to the timing at which reception of the reflected wave from the obstacle O begins, in other words, the timing at which the transmission wave first transmitted at timing t0 returns as a reflected wave. Therefore, the time ΔT between timing t3 and timing t4 is equal to the time Ta as the transmission time of the transmission wave.

[0033] From the above, in order to use TOF to find the distance from the source of ultrasonic transmission / reception to the obstacle O, it is necessary to find the time Tf between the timing t0 when the transmission of the transmitted wave begins and the timing t3 when the reflected wave begins to be received. This time Tf can be found by subtracting the time ΔT, which is equal to the time Ta as the transmission time of the transmitted wave, from the time Tp, which is the difference between the timing t0 and the timing t4 when the intensity of the reflected wave reaches a peak by exceeding the detection threshold Th.

[0034] The time t0 when the transmission wave starts can be easily identified as the time when the object detection device 200 starts operating, and the time Ta as the transmission time of the transmission wave is determined in advance by settings, etc. Therefore, by identifying the time t4 when the intensity of the reflected wave reaches a peak and becomes equal to or greater than the detection threshold value Th, the distance from the transmission source to the obstacle O can be obtained.

[0035] FIG. 4 is a block diagram showing an example of a functional configuration of the object detection device 200 according to the embodiment. The object detection device 200 according to the embodiment includes a transmission unit 411, a transmission control unit 412, a reception unit 421, a preprocessing unit 422, a CFAR processing unit 423, a setting unit 424, and a detection processing unit 425. These functional components 411, 412, 421 to 425 can be realized by, for example, cooperation of hardware components of the object detection device 200 as illustrated in FIG. 2 and software components such as programs. In the example shown in FIG. 4, the configuration of the transmission side and the configuration of the reception side are separated, but such an illustrated form is merely for convenience of explanation. In this embodiment, as described above, both the transmission of the transmission wave and the reception of the reception wave are realized by a single transceiver 210 having a single transducer 211. However, as described above, a configuration in which the configuration of the transmission side and the configuration of the reception side are separated can also be applied.

[0036] The transmitting unit 411 transmits a transmission wave to the outside by vibrating the above-mentioned vibrator 211. In addition to the vibrator 211, the transmitting unit 411 can be configured using, for example, a circuit that generates a carrier wave, a circuit that generates a pulse signal corresponding to identification information to be added to the carrier wave, a multiplier that modulates the carrier wave according to the pulse signal, an amplifier that amplifies the transmission signal output from the multiplier, and the like.

[0037] The transmission control unit 412 controls the transmission of the transmission wave. The transmission control unit 412 controls, for example, the transmission time, transmission interval, intensity, wavelength, frequency, etc. of the transmission wave. The transmission control unit 412 may adjust the transmission of the transmission wave based on, for example, the object detection result, the state of the road surface RS, the speed of the vehicle 1, etc.

[0038] The receiving unit 421 receives a received wave (reflected wave) generated when the transmission wave transmitted from the transmitting unit 411 is reflected by an object. The receiving unit 421 can be configured using, in addition to the transducer 211, for example, an AD converter or the like.

[0039] The preprocessing unit 422 performs preprocessing to generate echo information (e.g., an envelope as shown in FIG. 3) that indicates a change over time in the intensity of the received wave. The preprocessing may include, for example, an amplification process that amplifies a received signal corresponding to the received wave, a filter process that reduces noise contained in the amplified received signal, and a correlation process that obtains a correlation value that indicates the similarity between a transmission signal and a received signal.

[0040] The CFAR processing unit 423 executes CFAR processing on the echo information generated by the pre-processing unit 422. The CFAR processing unit 423 acquires a difference value between a processing target value, which is a value of a processing target signal corresponding to a received wave received at a certain detection timing, and a reference value based on a moving average value of each value of a reference signal group corresponding to a received wave received in a predetermined period before and after the detection timing. The CFAR processing unit 423 according to this embodiment performs CA-CFAR (Cell Averaging Constant False Alarm Rate) processing, GO-CFAR (Greatest Of Constant False Alarm Rate) processing, and SO-CFAR (Smallest Of Constant False Alarm Rate) processing as CFAR processing. The CA-CFAR processing is processing in which the average value (total average value) of all reference values ​​including each value of a first reference signal group corresponding to a received wave received in a first predetermined period before the detection timing and each value of a second reference signal group corresponding to a received wave received in a second predetermined period after the detection timing is used as a reference value. GO-CFAR processing is processing in which the larger of the first average value, which is the average value of each value of the first reference signal group, and the second average value, which is the average value of each value of the second reference signal group (maximum average value), is used as a reference value.SO-CFAR processing is processing in which the smaller of the first average value and the second average value (minimum average value) is used as a reference value.

[0041] The setting unit 424 executes a reference value setting process to select a reference value to be used in the CFAR process from a plurality of preset reference values ​​based on the detection distance corresponding to the detection timing. The setting unit 424 according to the present embodiment sets (selects) the reference value so that the closer the detection distance is, the larger the reference value in the CFAR process becomes. A specific example of the reference value setting process will be described later.

[0042] The detection processing unit 425 generates information about the object based on the difference value acquired by the CFAR processing unit 423. For example, the detection processing unit 425 generates information indicating the presence or absence of an object (obstacle O), the distance to the object, etc., based on the TOF when the difference value exceeds a predetermined threshold (for example, a detection threshold Th illustrated in FIG. 3).

[0043] Fig. 5 is a diagram showing an example of CFAR processing and reference value setting processing according to the embodiment. In Fig. 5, a processing target signal 501, a first reference signal group 502, and a second reference signal group 503 are illustrated. The processing target signal 501 is a received signal corresponding to a received wave received at a certain detection timing. The first reference signal group 502 is a received signal group corresponding to a received wave received in a first predetermined period before the detection timing corresponding to the processing target signal 501. The second reference signal group 503 is a received signal group corresponding to a received wave received in a second predetermined period after the detection timing corresponding to the processing target signal 501.

[0044] As shown in FIG. 5, the CFAR processing unit 423 calculates a first average value, which is the average value of each value in the first reference signal group 502, a second average value, which is the average value of each value in the second reference signal group 503, and a total average value, which is the average value of all reference values ​​including each value in the first reference signal group 502 and each value in the second reference signal group 503.

[0045] The setting unit 424 compares the first average value with the second average value, and outputs the larger one as the maximum average value, and the smaller one as the minimum average value. The setting unit 424 also selects an average value that matches the distance (detection distance) corresponding to the detection timing corresponding to the processing target signal 501 from among the total average value, the maximum average value, and the minimum average value, and sets the selected average value as a reference value. Specifically, the setting unit 424 sets the maximum average value as the reference value when the detection distance is in a predetermined short distance range, sets the total average value as the reference value when the detection distance is in a predetermined medium distance range farther than the short distance range, and sets the minimum average value as the reference value when the detection distance is in a predetermined long distance range farther than the medium distance range. Then, the CFAR processing unit 423 calculates a difference value by subtracting the reference value set by the setting unit 424 from the processing target value. The detection processing unit 425 generates a measurement result indicating the distance to the obstacle O, etc., based on a comparison result between the difference value calculated as above and a threshold value (for example, the detection threshold value Th illustrated in FIG. 3).

[0046] The specific values ​​of the short, medium, and long distance ranges are not particularly limited, but may be set, for example, as a short distance range less than 2 m, a medium distance range between 2 m and 4 m, and a long distance range greater than 4 m.

[0047] Fig. 6 is a diagram showing an example of the total average value, the maximum average value, and the minimum average value according to the embodiment. In Fig. 6, the relationship between an envelope curve L700 showing the change over time of the signal level (strength) of the received wave, a total average value line L701 showing the change over time of the total average value, a maximum average value line L702 showing the change over time of the maximum average value, and a minimum average value line L703 showing the change over time of the minimum average value is illustrated. As shown in Fig. 6, the maximum average value is greater than the total average value, and the minimum average value is smaller than the total average value. By using these three average values ​​having a magnitude relationship, the reference value in the CFAR process can be appropriately set according to the detection distance.

[0048] 7 is a flowchart showing an example of a reference value setting process in the object detection device 200 according to the embodiment. When the transmitting unit 411 transmits a transmission wave and the receiving unit 421 receives a reception wave (S101), the CFAR processing unit 423 acquires a processing target value (see FIG. 5) which is a value of the processing target signal 501 from the echo information generated by the pre-processing unit 422 (S102). After that, the CFAR processing unit 423 calculates a total average value, a first average value, and a second average value (S103), and the setting unit 424 determines the larger of the first average value and the second average value as the maximum average value, and determines the smaller of the first average value and the second average value as the minimum average value (S104).

[0049] Thereafter, the setting unit 424 determines whether the detection distance is within the short distance range (S105), and if the detection distance is within the short distance range (S105: Yes), sets the reference value to the maximum average value (S106). If the detection distance is not within the short distance range (S105: No), the setting unit 424 determines whether the detection distance is within the medium distance range (S107). If the detection distance is within the medium distance range (S107: Yes), the setting unit 424 sets the reference value to the total average value (S108). If the detection distance is not within the medium distance range (S107: No), the setting unit 424 determines whether the detection distance is within the long distance range (S109). If the detection distance is within the long distance range (S109: Yes), the setting unit 424 sets the reference value to the minimum average value (S110). If the detection distance is not within the long distance range (S109: No), the setting unit 424 sets the reference value to a predetermined default value (S111). A difference value is calculated by CFAR processing using the reference value thus set, and information about the object (obstacle O, etc.) is generated based on the difference value.

[0050] With the above-described configuration, the closer the detection distance is, the higher the reference value in the CFAR processing is set, so that the difference value calculated by the CFAR processing is prevented from becoming an excessively large value. This reduces the possibility of erroneous detection of an obstacle O in a short distance. Also, the farther the detection distance is, the lower the reference value is set, so that the difference value is prevented from becoming an excessively small value. This reduces the possibility of missing detection of an obstacle O in a long distance.

[0051] As described above, the object detection device 200 according to this embodiment can appropriately set the reference value used in the CFAR process in accordance with the detection distance, thereby enabling highly accurate object detection using the CFAR process.

[0052] The program for causing a computer (processor 223, 130 in the above embodiment) to execute the processes for realizing the above-mentioned functions may be stored in an installable or executable file format on a computer-readable storage medium such as a CD-ROM, CD-R, memory card, DVD (Digital Versatile Disk), or flexible disk (FD) and provided as a computer program product. The program may also be stored on a computer connected to a network such as the Internet and provided by downloading it via the network. The program may also be provided or distributed via a network such as the Internet.

[0053] Although the embodiment of the present disclosure has been described above, the above-described embodiment is merely an example and is not intended to limit the scope of the invention. The above-described novel embodiment can be implemented in various forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. The above-described embodiment is included in the scope and gist of the invention, and is included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0054] 1...vehicle, 2...vehicle body, 3F...front wheel, 3R...rear wheel, 100...ECU, 110...input / output device, 120...storage device, 130...processor, 200, 201 to 204...object detection device, 210...transmitter / receiver, 211...transmitter, 220...control unit, 221...input / output device, 222...storage device, 223...processor, 411...transmitter, 412...transmission control unit, 421...receiver, 422...pre-processing unit, 423...CFAR processing unit, 424...setting unit, 425...detection processing unit, 501...signal to be processed, 502...first reference signal group, 503...second reference signal group, L11, L700...envelope curve, L701...total average value line, L702...maximum average value line, L703...minimum average value line, Th...detection threshold

Claims

1. A transmitting unit that transmits a transmission wave; a receiving unit that receives a received wave generated by the transmission wave being reflected by an object; a CFAR processing unit that acquires a difference between a processing target value, which is a value of a processing target signal corresponding to the received wave received at a certain detection timing, and a reference value based on a moving average value of each value of a reference signal group corresponding to the received wave received during a predetermined period before and after the detection timing; a detection processing unit that generates information about the object based on the difference value; a setting unit that selects the reference value that matches the detection distance corresponding to the detection timing from a plurality of preset reference values; Equipped with the setting unit sets the reference value so that the reference value becomes larger as the detection distance becomes shorter. Object detection device.

2. the setting unit selects a first reference value from the plurality of reference values ​​when the detection distance is in a predetermined short distance range, selects a second reference value smaller than the first reference value from the plurality of reference values ​​when the detection distance is in a medium distance range farther than the short distance range, and selects a third reference value smaller than the second reference value from the plurality of reference values ​​when the detection distance is in a long distance range farther than the medium distance range. The object detection device according to claim 1 .

3. the first reference value is a maximum average value that is the larger of a first average value that is an average value of each of a first reference signal group corresponding to the received wave received at a first predetermined time before the detection timing and a second average value that is an average value of each of a second reference signal group corresponding to the received wave received at a second predetermined time after the detection timing, the second reference value is a total average value that is an average value of all reference values ​​including each value of the first reference signal group and each value of the second reference signal group; The third reference value is a minimum average value that is a smaller value of the first average value and the second average value. The object detection device according to claim 2 .

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