Object detection device

Abstract

The object detection device of the present application is provided with: a transceiver (4) that transmits an ultrasonic wave encoded by frequency modulation and receives the ultrasonic wave and outputs a reception signal; a first quadrature detector (61) that generates a complex reception signal by quadrature detection of the reception signal and outputs it; a second quadrature detector (71) that generates a complex reference signal by quadrature detection of a reference signal and outputs it; a correlation filter (62) that performs correlation detection of the complex reception signal and the complex reference signal and outputs a correlation signal; and a code determination unit (8) that determines a code contained in the reception signal based on the correlation signal.

Description

Technical Field

[0001] This disclosure relates to an object detection device. Background Technology

[0002] Regarding obstacle detection using ultrasonic sensors, the following technique has been proposed: encoding by varying the frequency of the transmitted wave, and determining the code based on the correlation output of the received signal obtained through a matched filter and a reference signal (for example, see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 63-249071

[0004] Because the correlation detection between the received signal and the reference signal requires a large amount of computation, the circuit size tends to increase in object detection devices that use such correlation detection. Summary of the Invention

[0005] The purpose of this disclosure is to reduce the amount of computation in object detection devices.

[0006] According to one aspect of this disclosure, an object detection apparatus includes: a transceiver unit that transmits ultrasonic waves encoded by frequency modulation, receives ultrasonic waves, and outputs a received signal; a first quadrature detector unit that generates a complex received signal by quadrature detection of the received signal and outputs it; a second quadrature detector unit that generates a complex reference signal by quadrature detection of a reference signal and outputs it; a correlation filter that performs correlation detection between the complex received signal and the complex reference signal and outputs a correlation signal; and a code determination unit that determines a code contained in the received signal based on the correlation signal.

[0007] In this way, by using orthogonal detection to convert the received signal and the reference signal into complex signals, the correlation can be calculated through vector and matrix operations, thus reducing the computational load of correlation detection.

[0008] Furthermore, the parenthetical reference numerals used to indicate each constituent element, etc., represent an example of the correspondence between the constituent element, etc., and the specific constituent elements, etc., described in the embodiments described later. Attached Figure Description

[0009] Figure 1 This is a block diagram of the object detection device according to the first embodiment.

[0010] Figure 2 yes Figure 1 The block diagram shown is of the quadrature detector section included in the matched filter section.

[0011] Figure 3 yes Figure 1 The block diagram shown is of the quadrature detector included in the reference signal processing unit.

[0012] Figure 4 yes Figure 1 The block diagram of the correlation filter is shown.

[0013] Figure 5 yes Figure 4 The diagram shows the vector rotation section and the addition section.

[0014] Figure 6 It is a diagram representing the phase difference between the complex received signal and the complex reference signal.

[0015] Figure 7 This is a diagram illustrating the vector rotation of a complex received signal.

[0016] Figure 8 It is a graph representing the signal after vector rotation.

[0017] Figure 9 It is a graph representing the sum of signals after vector rotation.

[0018] Figure 10 It is a graph representing the signal after vector rotation.

[0019] Figure 11 It is a graph representing the sum of signals after vector rotation.

[0020] Figure 12 This is a flowchart of the object detection and processing.

[0021] Figure 13 This is a block diagram of the object detection device according to the second embodiment.

[0022] Figure 14 yes Figure 13 The block diagram shown is of the normalization section included in the matched filter section.

[0023] Figure 15 yes Figure 13 The block diagram of the correction section is shown.

[0024] Figure 16 It is a graph showing the relationship between the bandwidth of the probe wave and the signal width.

[0025] Figure 17 This is a graph representing the transceiver sensitivity of the transducer.

[0026] Figure 18 This is a diagram representing the received complex signal before normalization.

[0027] Figure 19 This is a diagram representing the normalized complex received signal.

[0028] Figure 20 This is a graph showing the amplification of the frequency band caused by normalization.

[0029] Figure 21 This is a graph showing the filter output in the comparison example.

[0030] Figure 22 This is a diagram showing the filter output in the second embodiment.

[0031] Figure 23 This is a block diagram of the object detection device according to the third embodiment.

[0032] Figure 24 It is a diagram showing the amplification of the frequency band caused by phase rotation.

[0033] Figure 25 This is a diagram showing the filter output corresponding to the uplink chirp signal.

[0034] Figure 26 This is a diagram showing the filter output corresponding to the downlink chirped signal.

[0035] Figure 27 This is a graph showing the filter output in the comparison example.

[0036] Figure 28 This is a diagram showing the filter output in the third embodiment.

[0037] Figure 29 This is a graph representing the frequency of the probe wave in other implementation methods.

[0038] Figure 30 This is a block diagram of an object detection device according to other embodiments. Detailed Implementation

[0039] Hereinafter, embodiments of the present disclosure will be described based on the accompanying drawings. Furthermore, in the following embodiments, the same or equivalent parts will be referred to by the same reference numerals.

[0040] (First Implementation)

[0041] The first embodiment will be described. Figure 1 The object detection device 1 of this embodiment shown is mounted on a vehicle (not shown) and configured to detect objects B around the vehicle. Hereinafter, the vehicle on which the object detection device 1 is mounted will be referred to as "this vehicle". The vehicle (not shown) is, for example, an automobile.

[0042] The object detection device 1 includes an ultrasonic sensor 2 and a control unit 3 for controlling the operation of the ultrasonic sensor 2. The ultrasonic sensor 2 is configured to detect object B by transmitting a probe wave as an ultrasonic wave and receiving the reflected wave of the probe wave from object B.

[0043] The ultrasonic sensor 2 includes a transceiver unit 4, a drive signal generation unit 5, a matched filter unit 6, a reference signal processing unit 7, and a determination unit 8. The transceiver unit 4 includes a transmitting unit 40A and a receiving unit 40B. The transmitting unit 40A is configured to transmit a detection wave to the outside. The receiving unit 40B is configured to receive ultrasonic waves containing the reflected wave from the detection wave transmitted from the transmitting unit 40A by an object B.

[0044] The transceiver unit 4 includes a transducer 41, a transmitting circuit 42, and a receiving circuit 43. The transmitting unit 40A is composed of the transducer 41 and the transmitting circuit 42. The receiving unit 40B is composed of the transducer 41 and the receiving circuit 43.

[0045] The transducer 41 functions as a transmitter that sends probe waves to the outside and as a receiver that receives reflected waves, and is electrically connected to the transmitting circuit 42 and the receiving circuit 43. That is, the ultrasonic sensor 2 has a so-called transceiver integrated structure.

[0046] Specifically, the transducer 41 is configured as an ultrasonic microphone that incorporates electromechanical energy conversion elements such as piezoelectric elements. The transducer 41 is positioned facing the outer surface of the vehicle so as to transmit probe waves to the outside of the vehicle and receive reflected waves from the outside of the vehicle.

[0047] The transmitting circuit 42 is configured to drive the transducer 41 according to the input drive signal, thereby transmitting a probe wave through the transducer 41. Specifically, the transmitting circuit 42 includes a digital-to-analog conversion circuit, etc. That is, the transmitting circuit 42 is configured to generate a component input signal by performing signal processing such as digital-to-analog conversion on the drive signal output from the drive signal generation unit 5. The component input signal is an AC voltage signal used to drive the transducer 41. Furthermore, the transmitting circuit 42 is configured to generate a probe wave by applying the generated component input signal to the transducer 41 to excite the electromechanical energy conversion element in the transducer 41.

[0048] The receiving circuit 43 is configured to generate a received signal corresponding to the result of the transducer 41 receiving the ultrasonic wave, and output it to the matched filter section 6. Specifically, the receiving circuit 43 includes an amplification circuit and an analog-to-digital conversion circuit. That is, the receiving circuit 43 is configured to generate a received signal containing information related to the amplitude and frequency of the received wave by amplifying and performing analog-to-digital conversion on the element output signal output from the transducer 41. The element output signal is an AC voltage signal generated by the electromechanical energy conversion element provided in the transducer 41 through the reception of the ultrasonic wave.

[0049] As described later, the probe wave contains ultrasonic waves encoded by frequency modulation. The center frequency of the frequency modulation band of the probe wave is set to fc, and the sampling frequency of the receiving circuit 43 is set to at least twice fc. Furthermore, the sampling frequency of the received signal can be the same as or different from the sampling frequency of the driving signal.

[0050] The drive signal generation unit 5 is configured to generate a drive signal and output it to the transmitting circuit 42. The drive signal is used to drive the transducer 41 so that a probe wave is transmitted from the transducer 41.

[0051] The drive signal generation unit 5 generates a drive signal corresponding to the frequency modulation state in the probe wave having a predetermined frequency modulation state. The drive signal generation unit 5 generates a drive signal so that the frequency of the probe wave scans within a range including the resonant frequency of the transducer 41.

[0052] In this embodiment, the defined frequency modulation state includes uplink chirp or downlink chirp. Uplink chirp is a frequency modulation state in which the frequency monotonically increases over time. Downlink chirp is a frequency modulation state in which the frequency monotonically decreases over time.

[0053] The drive signal generation unit 5, the matched filter unit 6, the reference signal processing unit 7, and the determination unit 8 are, for example, composed of a DSP (Digital Signal Processor) programmed with functions such as the generation of the drive signal, orthogonal detection, correlation detection, code determination, and object detection determination described later.

[0054] The matched filter unit 6 processes the received signal and performs correlation detection between the received signal and the reference signal. The matched filter unit 6 includes a quadrature detector unit 61 and a correlation filter 62. The quadrature detector unit 61 performs quadrature detection on the received signal output from the receiving circuit 43 and generates a complex signal, equivalent to the first quadrature detector unit. Figure 2 As shown, the quadrature detector 61 includes a multiplication unit 611, an LPF (low-pass filter) 612, and a downsampling unit 613.

[0055] The multiplication unit 611 multiplies the received signal output from the receiving circuit 43 by sin(2π·fc·t) and cos(2π·fc·t) to generate a complex signal. Here, t is time. The sin(2π·fc·t) and cos(2π·fc·t) signals are input from the drive signal generation unit 5 to the multiplication unit 611. The multiplication unit 611 outputs the generated complex signal to the LPF 612.

[0056] The LPF612 removes high-frequency components from the complex signal output from the multiplication unit 611. The cutoff frequency of the LPF612 is input from the control unit 3 and set according to the bandwidth of the transducer 41 and the scanning frequency band of the drive signal. The complex signal after removing high-frequency components by the LPF612 is input to the downsampling unit 613.

[0057] The downsampling unit 613 downsamples the output signal of the LPF 612. For example, the downsampling unit 613 downsamples the signal sampled at twice the center frequency fc to once the center frequency fc. The downsampled sampling frequency can be set to be lower than once the center frequency fc, based on the cutoff frequency of the LPF 612. Since high-frequency components are removed by the LPF 612, downsampling of the received signal is possible, thereby reducing the computational load of the correlation filter 62 and decreasing the circuit area.

[0058] When the object detection device 1 has multiple transceivers 4 and identifies direct waves that are the same for both the transmitting transceiver 4 on the transmitting side and the receiving transceiver 4 on the receiving side, and indirect waves that are different from each other, it is necessary to perform correlation calculations on both the uplink chirp and the downlink chirp.

[0059] For example, when two transceiver units 4 transmit uplink chirped signals and downlink chirped signals respectively, the correlation between the received signals of each transceiver unit 4 and the two chirped signals is calculated. Then, if the received signal of the transceiver unit 4 that transmitted the uplink chirped signal has a high correlation with the uplink chirped signal, it is determined that the ultrasonic wave received by that transceiver unit 4 is a direct wave; if the correlation with the downlink chirped signal is high, it is determined that the ultrasonic wave is an indirect wave. Similarly, if the received signal of the transceiver unit 4 that transmitted the downlink chirped signal has a high correlation with the downlink chirped signal, it is determined that the ultrasonic wave received by that transceiver unit 4 is a direct wave; if the correlation with the uplink chirped signal is high, it is determined that the ultrasonic wave is an indirect wave.

[0060] Performing multiple correlation calculations in this way increases the computational load and easily increases the circuit size of the object detection device 1. In contrast, by performing downsampling as described above, the computational load is reduced, and the circuit size can be reduced. The output signal of the downsampling unit 613 is input to the correlation filter 62.

[0061] The complex signal output from the downsampling unit 613 is designated as a complex received signal. The complex received signal is composed of N signals sampled by the downsampling unit 613. N is an integer greater than or equal to 2. The N signals constituting the complex received signal are designated as signals S1 to S2 in the order of sampling. N .

[0062] The correlation filter 62 performs correlation detection on the complex received signal generated by the quadrature detector 61 and the reference signals corresponding to the uplink and downlink chirps, respectively, and outputs a correlation signal. The correlation signal output from the correlation filter 62 is input to the determination unit 8. Details about the correlation filter 62 will be described later.

[0063] The reference signal processing unit 7 processes the signal output from the drive signal generation unit 5 and outputs it to the matched filter unit 6. The signal output from the drive signal generation unit 5 to the reference signal processing unit 7 is a signal corresponding to the uplink and downlink chirps of the drive signal input to the transceiver unit 4, and this signal is set as a reference signal for identifying the code of the received signal. Furthermore, the drive signal generation unit 5 outputs the reference signal corresponding to the uplink chirp and the reference signal corresponding to the downlink chirp to the reference signal processing unit 7. In the matched filter unit 6, the reference signal processed by the reference signal processing unit 7 is used for correlation detection. Figure 1 As shown, the reference signal processing unit 7 includes an orthogonal detector 71.

[0064] The quadrature detector 71 performs quadrature detection on the reference signal output from the drive signal generation unit 5 and generates a complex signal, which is equivalent to a second quadrature detector. For example... Figure 3 As shown, the quadrature detector 71 includes a multiplier 711, an LPF 712, and a downsampling unit 713. The multiplier 711, LPF 712, and downsampling unit 713 are configured with the same structure as the multiplier 611, LPF 612, and downsampling unit 613 of the quadrature detector 61.

[0065] That is, the multiplication unit 711 multiplies the reference signal by sin(2π·fc·t) and cos(2π·fc·t) to generate a complex signal, and the LPF712 removes high-frequency components from the complex signal output from the multiplication unit 711. Then, the downsampling unit 713 downsamples the output signal of the LPF712.

[0066] Furthermore, the downsampling unit 713 performs downsampling so that the sampling frequency after downsampling is the same between the received signal and the reference signal. That is, for example, if the input signal is downsampled to 1 times the center frequency fc in the downsampling unit 613, the input signal is also downsampled to 1 times the center frequency fc in the downsampling unit 713. Since the high-frequency components are removed by the LPF 712, the reference signal can be downsampled, thereby reducing the computational load of the correlation filter 62 and reducing the circuit area. The output signal of the downsampling unit 713 is input to the correlation filter 62.

[0067] The complex signal output from the downsampling unit 713 is designated as the complex reference signal. The complex reference signal, like the complex received signal, is composed of N signals. These N signals constituting the complex reference signal are designated as signals S in the order they were sampled. R1 ~S RN In the correlation filter 62, the signals S1 to S2 are processed. N The complex received signal constituted by signal S R1 ~S RN Correlation detection of the complex reference signal.

[0068] like Figure 4 As shown, the correlation filter 62 includes an uplink chirp filter 620A and a downlink chirp filter 620B. The uplink chirp filter 620A performs correlation detection on the uplink chirped signal using a complex received signal and a complex reference signal. The downlink chirp filter 620B performs correlation detection on the downlink chirped signal using a complex received signal and a complex reference signal.

[0069] The uplink chirped filter 620A includes a reference signal holding unit 621, a vector rotation unit 622, an adder unit 623, and an amplitude conversion unit 624.

[0070] The reference signal processing unit 7 inputs a complex reference signal generated by quadrature detection of the reference signal corresponding to the uplink chirp to the uplink chirp filter 620A. The reference signal holding unit 621 holds and outputs the complex reference signal input from the reference signal processing unit 7, and outputs the structure of multiple signals constituting the complex reference signal independently. Specifically, the reference signal holding unit 621 independently outputs the signal S output from the downsampling unit 713. R1 ~S RN .

[0071] The vector rotation unit 622 performs vector rotation on the input signal. For example... Figure 5 As shown, the vector rotation unit 622 includes a matrix conversion unit 625, a received signal holding unit 626, and a multiplication unit 627.

[0072] The matrix conversion unit 625 will take the signal S output from the reference signal holding unit 621 R1 ~S RN Convert to rotation matrix R1~R N Specifically, if signal S R1 Let the phase be θ R1 Then the rotation matrix R1 is generated as shown in the following equation.

[0073] [Formula 1]

[0074]

[0075] Regarding the rotation matrices R2~R N Also using signal S R2 ~S RN phase θ R2 ~θ RN The same process is repeated. The matrix transformation unit 625 will be used in conjunction with the generated rotation matrices R1 to R2. N The corresponding signals are output independently to the multiplication unit 627.

[0076] The receive signal holding unit 626 holds the complex received signal and outputs it to the multiplication unit 627. A complex received signal is input from the quadrature detector 61 to the receive signal holding unit 626, which then stores the input signals S1 to S27. N Each is output independently to the multiplication section 627.

[0077] Multiplication unit 627 converts the rotation matrices R1 to R2 generated by matrix transformation unit 625. N Multiply by signals S1 to S N The vector is used to generate signals ΔS1~ΔS, which take the phase difference between the received signal and the reference signal as the phase. N For example, such as Figure 6 As shown, if signal S1 and signal S R1 Let the phase difference be Δθ1, and the amplitude of signal S1 be r1, then as follows Figure 7 As shown, the phase of signal ΔS1 is Δθ1, and its amplitude is r1. Furthermore, Figure 6 , Figure 7 and the following Figures 8-11 , Figure 18 , Figure 19 Represent the signal S1 on the complex plane. If we set the real part of the signal S1 as I1 and the imaginary part as Q1, and set the real part of the signal ΔS1 as I1' and the imaginary part as Q1', then I1' and Q1' can be obtained by the following formula.

[0078] [Equation 2]

[0079]

[0080] Similarly, if signals S2 to S... N and signal S R1 ~S RN The phase difference is set as Δθ2~Δθ N Signals S2 to S N The amplitude is set to r2~r N Then the signal ΔS2~ΔS N The phase is Δθ2~Δθ N The amplitude is r2~r N According to signals S2 to S... N The real part I2~I NImaginary part Q2~Q N Rotation matrices R2~R N Calculate the signal ΔS2~ΔS N The real part I2'~I N '、Imaginary part Q2'~Q N The multiplication unit 627 will convert signals ΔS1 to ΔS... N Each is output independently to the addition section 623.

[0081] like Figure 5 As shown, the adder 623 includes an addition signal generation unit 628 and an averaging unit 629, and the signals ΔS1 to ΔS2 output from the multiplication unit 627 are... N The input signal is fed to the summing signal generation unit 628. The summing signal generation unit 628 sums the input signals, thereby performing correlation detection between the received signal and the reference signal.

[0082] If the signal ΔS1~ΔS N When added together, the amplitude increases when the correlation between the received signal and the reference signal is high, and decreases when the correlation is low. For example, as... Figure 7 , Figure 8 As shown, if the phases Δθ1 and Δθ2 of signals ΔS1 and ΔS2 are aligned, then as follows Figure 9 As shown, the amplitude is increased by adding signal ΔS1 to signal ΔS2. On the other hand, as... Figure 10 As shown, if the phase Δθ2 of signal ΔS2 is significantly different from the phase Δθ1 of signal ΔS1, then as... Figure 11 As shown, the amplitude is reduced by adding the signal ΔS1 to the signal ΔS2.

[0083] Thus, if the signal ΔS1~ΔS N The amplitude of the complex signal generated by addition represents the degree of correlation between the received signal and the reference signal. The addition signal generation unit 628 transmits the sum of the signals ΔS1 to ΔS... N The complex signal generated by the summation of the two signals is output to the averaging section 629.

[0084] The averaging unit 629 averages the amplitude of the output signal from the summing signal generation unit 628 by dividing it by N. The complex signal after averaging by the averaging unit 629 is then output to the amplitude conversion unit 624.

[0085] Furthermore, in the addition section 623, only signals ΔS1 to ΔS can be added. N The signals within a range defined by specified conditions are added together. For example, since the signal-to-noise ratio (S / N) of the components at both ends of the frequency band in the received signal is low, the code determination accuracy is improved by setting the addition range to exclude the corresponding portions from the reference signal.

[0086] The amplitude conversion unit 624 converts the complex signal input from the averaging unit 629 into an amplitude signal. Specifically, the amplitude conversion unit 624 calculates the absolute value based on the real and imaginary parts of the complex signal and outputs this absolute value as the amplitude. The amplitude signal generated by the amplitude conversion unit 624 is output to the determination unit 8 as a correlation signal.

[0087] like Figure 4 As shown, the downlink chirped filter 620B, like the uplink chirped filter 620A, includes a reference signal holding unit 621, a vector rotation unit 622, an adder 623, and an amplitude conversion unit 624. The reference signal holding unit 621 to the amplitude conversion unit 624 of the downlink chirped filter 620B have the same structure as those of the uplink chirped filter 620A. However, in the downlink chirped filter 620B, a complex reference signal generated by orthogonal detection of a reference signal corresponding to the downlink chirp is input from the reference signal processing unit 7 to the reference signal holding unit 621, and correlation detection is performed between the complex received signal and the complex reference signal. Then, the amplitude signal generated by the amplitude conversion unit 624 is output to the determination unit 8 as a correlation signal.

[0088] The determination unit 8 determines the code contained in the received signal based on the correlation signal output by the matched filter unit 6, which is equivalent to a code determination unit. Furthermore, the determination unit 8 performs object detection determination based on the received signal and the code determination result. The determination unit 8 calculates the peak value of the uplink chirp correlation signal and the peak value of the downlink chirp correlation signal based on the correlation outputs of the uplink chirp filter 620A and the downlink chirp filter 620B. Then, the determination unit 8 compares them and determines that the received signal contains the code with the larger value, thus performing object detection determination. The determination unit 8 sends the object detection determination result to the control unit 3.

[0089] The control unit 3 is connected to the ultrasonic sensor 2 via an onboard communication line for information communication, thereby controlling the transmission and reception operations of the ultrasonic sensor 2. The control unit 3 is configured as a sonar ECU, equipped with an onboard microcomputer containing a CPU, ROM, RAM, and non-volatile physical memory (not shown). ECU is an abbreviation for Electronic Control Unit. Non-volatile physical memory includes, for example, EEPROM and flash ROM. EEPROM is an abbreviation for Electrically Erasable and Programmable Read Only Memory. ROM, RAM, etc., are non-volatile physical storage media.

[0090] The operation of the object detection device 1 will be explained. The object detection device 1 repeatedly performs actions including... Figure 12 The object detection process shown is as follows. In this process, firstly, the control unit 3 sends a transmission instruction to the drive signal generation unit 5, and a probe wave is transmitted from the transducer 41 based on the drive signal generated by the drive signal generation unit 5. Then, if the reception of the ultrasonic signal from the transceiver unit 4 is detected, the object detection device 1 executes... Figure 12 The process shown is for detecting objects.

[0091] First, in step S101, the quadrature detector 61 performs quadrature detection on the received signal output from the transceiver unit 4 and generates a complex received signal, which is then output to the correlation filter 62. Additionally, the quadrature detector 71 performs quadrature detection on the reference signals corresponding to the uplink and downlink chirps output from the drive signal generation unit 5 and generates complex reference signals, which are then output to the correlation filter 62.

[0092] In the next step S102, the correlation filter 62 performs correlation detection between the complex received signal output from the quadrature detector 61 and the complex reference signal corresponding to the uplink chirp, and outputs the correlation signal to the determination unit 8. Additionally, the correlation filter 62 performs correlation detection between the complex received signal and the complex reference signal corresponding to the downlink chirp, and outputs the correlation signal to the determination unit 8.

[0093] In the next step S103, the determination unit 8 determines whether the peak value of the correlation signal of the uplink chirp output from the correlation filter 62 is greater than the peak value of the correlation signal of the downlink chirp. If it is determined that the peak value of the correlation signal of the uplink chirp is greater than the peak value of the correlation signal of the downlink chirp, then in step S104, the determination unit 8 stores the code determination result that the received wave contains uplink chirp, and performs object detection determination based on the result. If it is determined that the peak value of the correlation signal of the uplink chirp is less than or equal to the peak value of the correlation signal of the downlink chirp, then in step S105, the determination unit 8 stores the code determination result that the received wave contains downlink chirp, and performs object detection determination based on the result.

[0094] For example, the determination unit 8 calculates the distance to the object based on the time from the transmission of the detection wave to the amplitude of the received signal with the same code as the transmitted signal reaching a predetermined value, and sends the calculation result to the control unit 3. Then, the control unit 3 determines whether the probability of collision with the object is high based on the distance calculation result and the vehicle's speed, etc. Based on the determination result, avoidance control and braking control are performed. After steps S104 and S105, the object detection device 1 ends the processing.

[0095] The effects of this embodiment will be explained. As described above, in this embodiment, the received signal and the reference signal are converted into complex signals by orthogonal detection, and the code contained in the received signal is determined by correlation detection between the complex received signal and the complex reference signal. In this way, by converting the received signal and the reference signal into complex signals, correlation calculation and downsampling based on vector and matrix operations can be performed, which can reduce the computational load of the correlation filter 62 and reduce the circuit area.

[0096] (Second Implementation)

[0097] The second embodiment will be described. This embodiment adds a structure for normalizing complex signals compared to the first embodiment. All other aspects are the same as the first embodiment, so only the parts that are different from the first embodiment will be described.

[0098] like Figure 13 As shown, the matched filter unit 6 of this embodiment includes, in addition to the quadrature detector unit 61 and the correlation filter 62, a normalization unit 63 and a correction unit 64. Furthermore, the reference signal processing unit 7 includes, in addition to the quadrature detector unit 71, a normalization unit 72. The drive signal generation unit 5, the matched filter unit 6, the reference signal processing unit 7, and the determination unit 8 are, for example, composed of a DSP programmed with the aforementioned functions of drive signal generation, quadrature detection, correlation detection, code determination, object detection determination, normalization, delay correction, and amplitude correction (described later).

[0099] Normalization unit 63 normalizes the complex received signal output from quadrature detector 61 to keep the amplitude constant, which is equivalent to a second normalization unit. For example... Figure 14 As shown, the normalization unit 63 includes an amplitude conversion unit 631, a moving average filter 632, and a vector normalization unit 633. The complex received signal output from the quadrature detector 61 is input to the amplitude conversion unit 631 and the vector normalization unit 633.

[0100] The amplitude conversion unit 631 converts the complex received signal output from the quadrature detector 61 into an amplitude. N According to the real part I1~I N Imaginary part Q1~Q N Calculate the amplitude r1~r N That is, the amplitude r1 is r1 = √(I1) 2 +Q1 2 Regarding the amplitude r2~r N The same calculation is performed. The amplitude calculation result from the amplitude conversion unit 631 is input to the moving average filter 632 and the vector normalization unit 633.

[0101] Moving average filter 632 calculates amplitude r1~r N The moving average value is used to generate the envelope of the amplitude of the complex received signal. The setting of the moving average filter 632 is input from the control unit 3. The envelope of the amplitude generated by the moving average filter 632 is output to the correction unit 64 and the determination unit 8. In addition, the normalization unit 63 of this embodiment includes the moving average filter 632, but the normalization unit 63 may also include an LPF instead of the moving average filter 632. Alternatively, the normalization unit 63 may not include the moving average filter 632, and the output of the amplitude conversion unit 631 may be directly output to the correction unit 64 and the determination unit 8.

[0102] The vector normalization unit 633 normalizes the amplitudes r1 to r2 input from the amplitude conversion unit 631. N The complex received signal input from the quadrature detector 61 is normalized in amplitude while maintaining phase, thus converting it into a unit vector. Specifically, the vector normalization unit 633 divides the complex received signal by the original amplitude. That is, signals S1 to S2... N The real part I1~I N Convert to I1 / r1~I N / r N Imaginary part Q1~Q N Convert to Q1 / r1~Q N / r N .

[0103] In this embodiment, the normalized signals S1 to S2 are thus... N The input is fed to the correlation filter 62. Then, in the multiplication section 627 of the vector rotation section 622, I1 / r1~I N / r N Q1 / r1~Q N / r N To replace I1~I N Q1~Q N Perform the operations shown in equation 2.

[0104] Furthermore, this embodiment describes the case where the amplitude of the complex received signal is normalized to 1, but the amplitude of the complex received signal can also be adjusted to a different value. Additionally, as described later, this embodiment normalizes the complex reference signal to 1, but the amplitude of the complex reference signal can also be adjusted to a different value.

[0105] Thus, in this embodiment, the normalization unit 63 normalizes the complex received signal. Then, the normalized complex received signal is input to the correlation filter 62 for correlation detection with the complex reference signal. The correlation filter 62 in this embodiment outputs the correlation signal to the correction unit 64.

[0106] Normalization unit 72 normalizes the complex reference signal output from quadrature detector 71 to keep the amplitude constant, essentially functioning as a first normalization unit. Normalization unit 72 has the same structure as the amplitude conversion unit 631 and vector normalization unit 633 of normalization unit 63. Normalization by normalization unit 72 results in a complex reference signal with an amplitude of 1 being output to correlation filter 62. Specifically, normalized signal S corresponding to the uplink chirp is input from normalization unit 72 to the uplink chirp filter 620A of correlation filter 62. R1 ~S RN Additionally, the normalized signal S corresponding to the downlink chirp is input from the normalization unit 72 to the downlink chirp filter 620B. R1 ~S RN In the uplink chirped filter 620A and the downlink chirped filter 620B, correlation detection is performed between the normalized complex received signal and the normalized complex reference signal, and the correlation signal is output.

[0107] The correction unit 64 corrects the amplitude, etc., of the correlation signal output from the correlation filter 62. For example... Figure 15 As shown, the correction unit 64 includes delay correction units 641 and 642, and multiplication units 643 and 644. The delay correction units 641 and 642 delay the phase of the amplitude signal output from the normalization unit 63, corresponding to the phase delay of the output signals of the uplink chirped filter 620A and the downlink chirped filter 620B. The amplitude signal generated by the moving average filter 632 of the normalization unit 63 is input to the delay correction units 641 and 642, and the delayed-corrected amplitude signals are output to the multiplication units 643 and 644, respectively.

[0108] Multiplication units 643 and 644 multiply the amplitudes of the correlation signals output from the uplink chirped filter 620A and downlink chirped filter 620B of the correlation filter 62 by the amplitudes before normalization, thus restoring them to their original values. Therefore, in the determination unit 8, code determination and object detection determination can be performed by comparing the original amplitude with a predetermined threshold. The amplitude signal, transformed to its original value by multiplication units 643 and 644, is output to the determination unit 8.

[0109] In the object detection processing of this embodiment, Figure 12In step S101, after the quadrature detector 61 converts the received signal into a complex signal, the normalization unit 63 normalizes the complex received signal output from the quadrature detector 61 to make its amplitude 1. Additionally, the normalization unit 72 normalizes the complex reference signal output from the quadrature detector 71 to make its amplitude 1. Then, in step S102, the correlation filter 62 performs correlation detection between the normalized complex received signal and the normalized complex reference signal. In step S103, the determination unit 8 performs code determination based on the result of this correlation detection.

[0110] The effects of this implementation method will be explained. For example... Figure 16 As shown, the output signal width of the correlation filter 62 is inversely proportional to the bandwidth of the received signal; the wider the bandwidth, the shorter the output signal width. Furthermore, Figure 16 The dotted line represents the signal width measured by the inventor by varying the bandwidth, and the dashed line is an approximate curve of the measurement result.

[0111] In obstacles with complex shapes, due to the presence of multiple reflection points, it is desirable to shorten the signal width of the filter output to achieve higher code determination accuracy. However, as... Figure 17 As shown, the microphone used as a transducer in the vehicle sensor has a narrow-band frequency characteristic. That is, when such a microphone is used in transducer 41, if the resonant frequency of transducer 41 is set to f0, the transmit and receive sensitivity is high near the resonant frequency f0, but the transmit and receive sensitivity decreases at frequencies far from the resonant frequency f0.

[0112] Therefore, for example, if a chirped signal is sent such that fc = f0, the component at the center frequency fc becomes larger, but the component at frequencies far from the center frequency fc becomes smaller, and only the components near the center frequency fc in the overall frequency band can be fully utilized.

[0113] Specifically, if the signals S1 to S2 that constitute the complex received signals are... N Let the signal corresponding to the resonant frequency f0 in the signal be S. A Let the signal corresponding to the frequency far from the resonant frequency f0 be S. B Then signal S A S B The amplitude, for example, Figure 18 shown. That is, the signal S A The amplitude is greater than 1, signal S B The amplitude is smaller than 1.

[0114] like Figure 16 As shown, due to the hardware limitations of such microphones, it is difficult to shorten the signal width of the filter output to the desired value. This raises concerns about incorrect code determination when detecting obstacles with complex shapes, such as vehicles and fences. Furthermore, as... Figure 18 As shown, if signals S1~S N If the difference in amplitude caused by the frequency is large, there is a concern that the correlation detection result may be pulled towards the amplitude near the resonance frequency f0, resulting in misjudgment of the code.

[0115] In contrast, in this embodiment, before correlation detection, the complex received signal output by the quadrature detector 61 is normalized by the normalization unit 63. That is, as shown in the figure... Figure 19 As shown, signals S1 to S2 N The amplitude was adjusted to 1. Furthermore, in Figure 19 Only signals S1 to S2 are shown in the diagram. N Signal S in A S B Therefore, the influence of the microphone's frequency characteristics is reduced, such as Figure 20 As shown, the bandwidth of the received signal widens, while the signal width after correlation detection shortens. Furthermore, it can suppress false code interpretations.

[0116] also, Figure 20 This is a graph showing the frequency band changes caused by normalization. Figure 20 In the diagram, the dashed line represents the amplitude of the complex received signal generated by the quadrature detector 61, and the solid line represents the amplitude of the complex received signal normalized by the normalization unit 63. Figure 20 In the middle, f LPF It is the cutoff frequency of LPF612.

[0117] In this way, by normalizing the received signal whose amplitude is deviated due to the frequency characteristics of the transducer 41 by the normalization unit 63, the influence of the microphone's frequency characteristics is reduced.

[0118] For example, if a probe wave is sent to a complex-shaped object such as a fence, multiple reflected waves will be returned. In this case, if correlation detection is performed without normalizing the complex received signals, then... Figure 21 As shown, the peak value of the correlation output is reduced compared to the amplitude signal of the original probe wave, which is represented by the dotted line. Furthermore, if the threshold for reflected wave detection is set as shown by the dashed line, for example, the signal width increases, resulting in reduced resolution due to interference from the reflected wave.

[0119] In contrast, if normalization of the complex received signal is performed, then as follows: Figure 22 As shown, the reduction in the peak value of the correlation output is suppressed, and the signal width is shortened, thus suppressing the resolution reduction caused by the interference of reflected waves.

[0120] As explained above, in this embodiment, the influence of the frequency characteristics of the transducer 41 is reduced by normalizing the complex received signal before correlation detection. This suppresses the reduction of the peak value of the correlation output and shortens the signal width, thus improving resolution. Furthermore, code determination accuracy is improved. Additionally, by normalizing the amplitude of the complex signal to 1, the calculation can be simplified using known formulas. Furthermore, by normalizing the complex reference signal before correlation detection, the influence of the frequency characteristics of the transducer 41 is further reduced. Moreover, by normalizing the complex reference signal, it can be treated as a trigonometric function, thus facilitating the conversion to a rotation matrix and further reducing computational load.

[0121] (Third Implementation)

[0122] The third embodiment will be described. This embodiment adds a structure for rotating the phase of the complex signal compared to the second embodiment. All other aspects are the same as the second embodiment, so only the parts that are different from the second embodiment will be described.

[0123] The object detection device 1 of this embodiment has a structure that further amplifies the frequency band of the received signal through phase rotation. Specifically, as shown in the figure... Figure 23 As shown, the matched filter unit 6, in addition to the quadrature detector unit 61, correlation filter 62, normalization unit 63, and correction unit 64, also includes a phase rotation unit 65. Similarly, the reference signal processing unit 7, in addition to the quadrature detector unit 71 and normalization unit 72, also includes a phase rotation unit 73. The drive signal generation unit 5, matched filter unit 6, reference signal processing unit 7, and determination unit 8 are, for example, composed of a DSP programmed with the aforementioned functions of drive signal generation, quadrature detection, normalization, correlation detection, delay correction, amplitude correction, code determination, object detection determination, and phase rotation (described later).

[0124] The phase rotation unit 65 rotates the phase of the complex received signal, which is equivalent to the first phase rotation unit. The complex received signal normalized by the normalization unit 63 is input to the phase rotation unit 65, and the complex received signal after phase rotation by the phase rotation unit 65 is output to the correlation filter 62.

[0125] Specifically, the phase rotation unit 65 processes the input signal as follows: The real part of the normalized complex received signal is set as I', the imaginary part as Q', and the phase as θ, using I' = cosθ, Q' = sinθ, and cos²θ = 1 - 2sinθ. 2 Given θ, sin2θ = 2sinθcosθ, calculate cos2θ and sin2θ based on I' and Q'. Then, output the real and imaginary parts of the new complex received signal as cos2θ and sin2θ, respectively.

[0126] Phase rotation unit 73 rotates the phase of the complex reference signal, essentially functioning as a second phase rotation unit. The complex reference signal, normalized by normalization unit 72, is input to phase rotation unit 73, and the phase-rotated complex reference signal is output to correlation filter 62. Phase rotation is performed in phase rotation unit 73 in the same manner as in phase rotation unit 65. Correlation filter 62 performs correlation detection between the phase-rotated complex received signal and the phase-rotated complex reference signal, and outputs a correlation signal.

[0127] Figure 24 This is a graph showing the change in frequency band caused by phase rotation. In Figure 24 In the diagram, the dashed line represents the amplitude of the complex received signal after normalization by the normalization unit 63, and the solid line represents the amplitude of the complex received signal after phase rotation by the phase rotation unit 65. As explained in the second embodiment, the bandwidth is widened due to normalization, however... Figure 24 As shown, the apparent bandwidth is further widened due to phase rotation.

[0128] The phase rotation amount is an integer multiple, such as 2 times as described above, but other multiples can also be used for phase rotation. For example, in phase rotation units 65 and 73, two 2-fold phase rotations can be performed, and the output phase can be rotated 4 times to make cos4θ = 1 - 2sinθ. 2 The signal is 2θ, sin4θ=2sin2θcos2θ.

[0129] Alternatively, the phase rotation amount can be varied under specified conditions. For example, although a higher magnification results in a wider bandwidth after phase rotation, the Doppler shift has a significant impact. Therefore, the magnification can be lower than the specified value when traveling straight at higher speeds, and higher than the specified value when reversing at lower speeds.

[0130] In the object detection processing of this embodiment, Figure 12 In step S101, the quadrature detector 61 converts the received signal into a complex signal. After the normalization unit 63 normalizes the complex received signal, the phase rotation unit 65 rotates the phase of the normalized complex received signal. Additionally, after the normalization unit 72 normalizes the complex reference signal output from the quadrature detector 71, the phase rotation unit 73 rotates the phase of the normalized complex reference signal. Then, in step S102, the correlation filter 62 performs correlation detection between the phase-rotated complex received signal and the phase-rotated complex reference signal. In step S103, the determination unit 8 performs code determination based on the result of this correlation detection.

[0131] The effects of this implementation method will be explained. Figure 25 , Figure 26 This diagram illustrates the results of an experiment conducted by the inventors, showing the output of the correlation filter 62 when a probe wave is sent to a rod with a diameter of 60 mm. Furthermore, in this experiment, a chirped signal with a frequency modulation range narrower than that of the chirped signal contained in the probe wave was used as a reference signal. Specifically, the lower limit of the frequency modulation range of the probe wave was set to f1, and the upper limit to f2; the lower limit of the frequency modulation range of the reference signal was set to f3, and the upper limit to f4; and f1 to f4 were set to f1 < f3 < f4 < f2.

[0132] Figure 25 This diagram shows the output of the uplink chirp filter 620A when transmitting a probe wave containing an uplink chirp signal. Figure 26 This is a diagram showing the output of the downlink chirped filter 620B when transmitting a probe wave containing a downlink chirped signal. Figure 25 , Figure 26 In the diagram, solid lines represent the correlation output with phase rotation, dashed lines represent the correlation output without phase rotation, and dashed lines represent the threshold for reflected wave detection. For example... Figure 25 , Figure 26 As shown, by rotating the phase, the signal width of the output signal of the correlation filter 62 becomes shorter.

[0133] Figure 27 , Figure 28 This represents the output of the correlation filter 62 when a probe wave containing a downlink chirped signal is sent to the mesh fence. Figure 27 This is an example of the output signal of the correlation filter 62 without phase rotation. Figure 28 This is an example of the output signal of the correlation filter 62 in the case of phase rotation. Figure 27 , Figure 28 In the diagram, the solid line represents the output signal of the downlink chirped filter 620B, and the dotted-dash line represents the output signal of the uplink chirped filter 620A.

[0134] exist Figure 27 In the above, the peak output of the uplink chirp filter 620A is larger than the peak output of the downlink chirp filter 620B, thus mistakenly identifying the received signal as containing an uplink chirp signal. On the other hand, in Figure 28 In the middle, the output peak value of the downlink chirp filter 620B is larger than the output peak value of the uplink chirp filter 620A, so it is correctly determined that the received signal contains a downlink chirp signal.

[0135] While there is a concern about misjudgment without phase rotation, as mentioned above, phase rotation can mitigate this risk. Figure 28As shown, the passivation of the output signals of the uplink chirped filter 620A and the downlink chirped filter 620B is reduced, resulting in fewer false positives. In experiments conducted by the inventors, the code recognition rate when sending probe waves to the mesh fence was increased from 88% to 95% by adding phase rotation processing.

[0136] As explained above, in this embodiment, the signal width is further shortened by rotating the phase of the complex signal, thus improving the code determination accuracy. Furthermore, since the complex received signal and the complex reference signal are normalized before phase rotation, the phase rotation process can be performed using a double-angle formula as described above, reducing the computational load of phase rotation.

[0137] (Other implementation methods)

[0138] Furthermore, the present invention is not limited to the above-described embodiments and appropriate modifications can be made. Moreover, in the above-described embodiments, it is self-evident that, except for cases specifically expressed as necessary or cases clearly considered necessary in principle, the elements constituting the embodiments are not essential.

[0139] For example, such as Figure 29 As shown, the probe wave and reference signal can also be composed of a frequency component lower than the resonant frequency f0 of transducer 41 and a frequency component higher than the resonant frequency. In this way, by using a probe wave with a frequency different from the resonant frequency f0 of transducer 41, the influence of the frequency characteristics of transducer 41 is reduced, and the robustness of the object detection device 1 is improved. Furthermore, in Figure 29 In this process, the frequency of the probe wave is modulated from a frequency lower than the resonant frequency f0 to a frequency higher than the resonant frequency f0, but it can also be modulated from a frequency higher than the resonant frequency f0 to a frequency lower than the resonant frequency f0.

[0140] Furthermore, in the second embodiment described above, both the complex received signal and the complex reference signal are normalized. However, it is also possible to normalize only the complex reference signal without normalizing the complex received signal.

[0141] Furthermore, in the third embodiment described above, correlation detection can also be performed after restoring the normalized and phase-rotated complex received signal to its original amplitude. For example, as... Figure 30As shown, the matched filter unit 6 includes an amplitude multiplication unit 66. The complex received signal, after phase rotation by the phase rotation unit 65, and the amplitude calculated by the normalization unit 63 are input to the amplitude multiplication unit 66. Then, the amplitude multiplication unit 66 multiplies the complex received signal by the amplitude before normalization, restores the amplitude of the complex received signal, and outputs the amplitude-restored complex received signal to the correlation filter 62. In this case, amplitude correction by the correction unit 64 is not required. Similarly, correlation detection can be performed after restoring the normalized complex reference signal to its original amplitude.

[0142] Alternatively, phase rotation units 65 and 73 can be added to the first embodiment to perform phase rotation of the complex received signals and complex reference signals output by the quadrature detectors 61 and 71.

[0143] The drive signal generation unit, matched filter unit, reference signal processing unit, determination unit, control unit, and methods described in this disclosure can also be implemented using a dedicated computer, which is provided by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the drive signal generation unit, matched filter unit, reference signal processing unit, determination unit, control unit, and methods described in this disclosure can also be implemented using a dedicated computer, which is provided by configuring a processor using one or more dedicated hardware logic circuits. Alternatively, the drive signal generation unit, matched filter unit, reference signal processing unit, determination unit, control unit, and methods described in this disclosure can also be implemented using one or more dedicated computers, which are configured by combining a processor and memory programmed to perform one or more functions and a processor containing one or more hardware logic circuits. Furthermore, the computer program can also be stored as instructions executable by a computer on a computer-readable non-volatile tangible recording medium.

Claims

1. An object detection device, wherein, have: The transceiver unit transmits ultrasonic waves encoded by frequency modulation and receives ultrasonic waves and outputs the received signal. The first quadrature detector generates and outputs a complex received signal by orthogonal detecting the received signal. The second orthogonal detector generates a complex reference signal and outputs it through orthogonal detection of the reference signal; A correlation filter is used to detect the correlation between the complex received signal and the complex reference signal and output a correlation signal; and The code determination unit determines the code contained in the received signal based on the aforementioned correlation signal.

2. The object detection device according to claim 1, wherein, have: The first normalization part normalizes the complex reference signal to keep the amplitude constant. The aforementioned correlation filter performs correlation detection on the aforementioned complex received signal and the aforementioned complex reference signal normalized by the aforementioned first normalization unit.

3. The object detection device according to claim 2, wherein, have: The second normalization unit normalizes the complex received signal to keep the amplitude constant. The aforementioned correlation filter performs correlation detection on the complex received signal normalized by the second normalization unit and the complex reference signal normalized by the first normalization unit.

4. The object detection device according to claim 3, wherein, have: The correction unit corrects the aforementioned correlation signal. The second normalization unit normalizes the complex received signal by dividing it by the original amplitude. The aforementioned correction unit corrects the correlation signal by multiplying it by the amplitude of the complex received signal before normalization. The code determination unit determines the code contained in the received signal based on the correlation signal corrected by the correction unit.

5. The object detection device according to any one of claims 1 to 4, wherein, have: The first phase rotating section rotates the phase of the aforementioned complex received signals; and The second phase rotation unit rotates the phase of the aforementioned complex reference signal. The aforementioned correlation filter performs correlation detection on the complex received signal after phase rotation by the first phase rotation unit and the complex reference signal after phase rotation by the second phase rotation unit.

6. The object detection device according to claim 5, wherein, The aforementioned first phase rotation unit rotates the phase of the normalized complex received signal.

7. The object detection device according to claim 5 or 6, wherein, The second phase rotation unit rotates the phase of the normalized complex reference signal.

8. The object detection device according to any one of claims 5 to 7, wherein, The aforementioned first phase rotation unit and the aforementioned second phase rotation unit change the phase rotation amount under specified conditions.

9. The object detection device according to any one of claims 1 to 8, wherein, The first orthogonal detector described above downsamples and outputs the complex received signal. The second orthogonal detector downsamples and outputs the complex reference signal.

10. The object detection device according to any one of claims 1 to 9, wherein, The frequency of the ultrasonic wave transmitted from the transceiver unit and the frequency of the reference signal are set to frequencies different from the resonant frequency of the transceiver unit.

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