Ultrasonic transmission control device, ultrasonic transmission device, and underwater detection device

Abstract

To provide an ultrasonic transmission control device capable of increasing the transmission distance of an ultrasonic wave, and to provide an ultrasonic transmission device and underwater detection device.SOLUTION: A signal wave is output to a drive signal generation unit DG1, and others, configured to compare a signal wave and a triangle wave to generate a drive signal consisting of a PWM wave, the signal wave being an exponential chirp signal having a frequency f(t) modulated according to the following formula (1) and formula (2): f(t)=(f0-1)+Kt ...(1), K=(B+C)(1 / tau) ...(2), where f0 represents an initial frequency, K represents a rate of frequency increase, B represents a chirp band width, C represents a constant equal to or less than 1, and tau represents a chirp period.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an ultrasonic transmission control device, an ultrasonic transmitting device that transmits ultrasonic waves under the control of the ultrasonic transmission control device, and an underwater detection device equipped with an ultrasonic transmitting device. [Background technology]

[0002] Underwater detection devices such as scanning sonars installed on ships transmit ultrasonic waves into the water using multiple transducers built into a transducer, and receive the waves reflected by targets. The underwater detection device generates an image of underwater information such as a school of fish based on the received reflected waves, and displays the image on a display device.

[0003] As is well known, the lower the frequency of ultrasonic waves propagating underwater, the less attenuation there is, and therefore the wider the directivity and the longer the transmission distance. A conventional underwater detection device is known that transmits ultrasonic waves modulated into a linear chirp from a transducer to lengthen the low-frequency period of the ultrasonic waves and thereby lengthen the transmission distance of the ultrasonic waves (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-85792 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with a linear chirp, the transmission distance of ultrasound is not very long due to the short period of low frequency.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an ultrasonic transmission control device, an ultrasonic transmitting device, and an underwater detection device that are capable of extending the transmission distance of ultrasonic waves. [Means for solving the problem]

[0007] In order to solve the above problem, the invention described in claim 1 is an ultrasonic transmission control device that inputs a transmission signal generated based on a drive signal consisting of a PWM wave to a transducer and transmits ultrasonic waves from the transducer, comprising a first DDS that generates a signal wave, a second DDS that generates a carrier wave, and a comparator that compares the signal wave with the carrier wave to generate the drive signal, wherein the signal wave is an exponential chirp signal whose frequency f(t) is modulated according to the following formulas (1) and (2). f(t)=(f0-1)+K t ...(1) K=(B+C) (1 / tau) ...(2) (fo: start frequency, K: frequency increase rate, B: chirp bandwidth, C: constant less than or equal to 1, tau: chirp time)

[0008] The invention described in claim 2 is characterized in that, in the ultrasonic transmission control device described in claim 1, it comprises a plurality of drive signal generating units that generate the drive signals corresponding to each of the plurality of transducers, the plurality of drive signal generating units comprising the comparator, a phase control unit that controls the phase of the signal wave input to the comparator, and an amplitude control unit that controls the amplitude of the signal wave input to the comparator, the first DDS, the second DDS, and the plurality of drive signal generating units are mounted on an FPGA, and the phase control unit and the amplitude control unit perform phase control and amplitude control of the signal wave for each operating clock of the FPGA.

[0009] The invention described in claim 3 is an ultrasonic transmission device characterized by comprising an ultrasonic transmission control device described in claim 1 or 2, a plurality of transmission signal generating units that generate transmission signals based on a drive signal input from the ultrasonic transmission control device, and a plurality of transducers that transmit ultrasonic waves based on the transmission signal input from the transmission signal generating units.

[0010] The invention described in claim 4 is an underwater detection device mounted on a ship, comprising the ultrasonic transmitting device described in claim 3, a signal processing unit that processes received signals generated by multiple transducers of the ultrasonic transmitting device receiving ultrasonic waves to generate an image signal of a target and display it on a monitor, and an inclination detection unit that detects the inclination of the ship, and a phase control unit of the ultrasonic transmitting device controls the phase of the signal wave in accordance with the amount and direction of inclination of the ship detected by the inclination detection unit. Effect of the Invention

[0011] According to the inventions described in claims 1, 3 and 4, by performing pulse compression on the signal wave using an exponential chirp signal and adding a constant C of 1 or less to the chirp bandwidth B of the exponential chirp signal, the low-frequency period can be made longer than that of a conventional general exponential chirp that does not add the constant C, making it possible to propagate ultrasonic waves farther and detect targets.

[0012] According to the inventions described in claims 2, 3 and 4, a driving signal consisting of a PWM wave is generated on a digital circuit configured by an FPGA, and the phase of the signal wave that is the basis of the driving signal is controlled for each operation clock of the FPGA, so that the phase control of the driving signal can be performed with high resolution. In addition, a window function can be applied by controlling the amplitude of the signal wave that is the basis of the driving signal on a digital circuit configured by an FPGA, so that it is possible to arbitrarily control the envelope of the ultrasonic wave transmitted from the transducer and remove unnecessary wave components. Furthermore, the ratio of analog circuits is reduced, and the configuration of the required analog circuits is simplified, so that costs can be reduced.

[0013] According to the invention described in claim 4, the phase of the signal wave can be controlled for each FPGA operating clock in accordance with the amount and direction of inclination of the ship detected by the inclination detection unit, so that the transmission direction of the ultrasonic wave can be adjusted quickly and with high resolution in accordance with the inclination of the ship. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a schematic configuration of an underwater detection device according to an embodiment of the present invention; [Diagram 2] 2 is a block diagram showing a schematic configuration of an ultrasonic transmission unit shown in FIG. 1. [Diagram 3] 1 is a graph showing the transition of the frequency of a signal wave consisting of an exponential chirp signal. [Figure 4] 1 is a graph showing a power waveform after pulse compression processing of a received signal consisting of an exponential chirp signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the present invention will be described based on the illustrated embodiment.

[0016] 1 to 4 show an embodiment of the present invention, and Fig. 1 is a block diagram showing a schematic configuration of an underwater detection device 1 according to this embodiment. The underwater detection device 1 is, for example, a fish finder mounted on a ship, and comprises a transducer 2, a main body 3, a monitor 4, an operation unit 5, and a tilt detection unit 6.

[0017] The transducer 2 includes multiple transducers TD1, TD2 to TDn and is disposed in water. The transducers TD1, TD2 to TDn are driven by electrical signals (transmission signals) to transmit ultrasonic waves into water, and also receive waves reflected by targets and convert them into electrical signals (reception signals).

[0018] The main body 3 includes a transmit / receive switch 31 connected to the transducer 2, a transmission control unit 32 and a receiver 33 connected to the transmit / receive switch 31, and a signal processor 34 connected to the receiver 33. When transmitting ultrasonic waves, the transmit / receive switch 31 switches the connection so that a transmission signal generated by the transmission control unit 32 is sent from the transmission control unit 32 to the transducer 2. When receiving reflected waves, the transmit / receive switch 31 switches the connection so that a reception signal converted from ultrasonic waves by the transducer 2 is sent from the transducer 2 to the receiver 33.

[0019] The transmission control unit 32 generates a transmission signal based on the conditions set on the monitor 4 and the operation unit 5, and outputs the signal to the transducer 2 via the transmission / reception switching unit 31. The transducer 2 and the transmission control unit 32 constitute an ultrasonic transmission unit (ultrasonic transmission device) 7, which will be described later.

[0020] The receiving unit 33 amplifies the received signal output from the transducer 2 using an analog circuit, performs A / D conversion to generate digital received data, performs pulse compression processing on the received data, and outputs the data to the signal processing unit 34. The signal processing unit 34 processes the received data output from the receiving unit 33 to generate a video signal of the target. Note that the receiving unit 33 may perform pulse compression processing on the received signal, amplify it, and then perform A / D conversion to generate digital received data.

[0021] The monitor 4 displays on a display screen an image corresponding to the video signal output from the signal processing unit 34. The user can check the underwater conditions around the ship (such as the schools of fish and the condition of the seabed) by looking at the display screen. The monitor 4 also displays a setting screen for the underwater detection device 1. While checking this setting screen, the user can operate the input keys of the operation unit 5 to perform various settings such as the ultrasonic transmission frequency.

[0022] The tilt detection unit 6 is, for example, a gyro sensor, which detects the amount of tilt and the direction of tilt of the ship with respect to the horizontal plane, and outputs the detection values ​​to the transmission control unit 32.

[0023] Fig. 2 is a block diagram showing a schematic configuration of the ultrasonic transmission unit 7. As described above, the ultrasonic transmission unit 7 is composed of the transducer 2 and the transmission control unit 32. That is, the ultrasonic transmission unit 7 shown in Fig. 2 is composed of the transducer 2 and the transmission control unit 32 connected by the transmission / reception switching unit 31.

[0024] The transmission control unit 32 constituting the ultrasonic transmission unit 7 includes an FPGA 321 corresponding to the ultrasonic transmission control device of the present invention, and a plurality of transmission signal generating units TG1, TG2 to TGn. The plurality of transmission signal generating units TG1, TG2 to TGn are connected between the FPGA 321 and each of the transducers TD1, TD2 to TDn of the ultrasonic transmitter / receiver 2.

[0025] The FPGA 321 includes a signal wave DDS (first DDS) 3211, a triangular wave DDS (second DDS) 3212, and a plurality of drive signal generators DG1, DG2 to DGn. A plurality of ultrasonic transmission channels are configured by the drive signal generators DG1, DG2 to DGn, the corresponding transmission wave signal generators TG1, TG2 to TGn, and the corresponding transducers TD1, TD2 to TDn.

[0026] The triangular wave DDS 3212 generates a triangular wave (carrier wave) having a predetermined amplitude and frequency. Note that, in addition to the triangular wave, a sawtooth wave or the like may be used as the carrier wave.

[0027] The signal wave DDS3211 generates a signal wave having a predetermined amplitude and frequency. As shown in FIG. 3, the signal wave generated by the signal wave DDS3211 is an exponential chirp signal whose frequency increases exponentially. More specifically, the signal wave has a frequency f(t) modulated according to the following formulas (1) and (2). In the formulas below, f0 indicates the start frequency, K indicates the frequency increase rate, B indicates the chirp bandwidth, C indicates a constant equal to or less than 1, and tau indicates the chirp time. The general formula for calculating a chirp signal is "f(t)=f0+K t " but when t=0, k t =1, and the initial frequency is f0+1Hz, so in the following formula (1), it is "f0-1". f(t)=(f0-1)+K t ...(1) K=(B+C) (1 / tau) ...(2)

[0028] In the above formula (2), when calculating the frequency increase rate K, a constant C is added to the chirp bandwidth B, so that the low-frequency period is longer than that of the linear chirp (two-dot chain line in the figure) and the general exponential chirp (dashed line in the figure) shown in FIG. 3. As is well known, the lower the frequency, the less attenuation there is in the propagation of ultrasonic waves in water, so the directionality is wider and the transmission distance is longer. Therefore, by making the signal wave the above-mentioned exponential chirp signal, it is possible to transmit ultrasonic waves farther and detect targets. The constant C can be selected as any value equal to or less than 1 according to the desired transmission distance, and the larger the constant C, the longer the transmission distance of ultrasonic waves can be.

[0029] 4 shows a power waveform obtained by pulse compression processing of the received ultrasonic signal transmitted based on the signal wave consisting of the exponential chirp signal by the receiving unit 33. This power waveform has a wider beam width than the conventional linear chirp, but the occurrence of side lobes can be reduced. Note that the power waveform obtained by pulse compression processing of the received signal when the center frequency of the signal wave is 22.5 kHz is shown, but a power waveform with a similar tendency can be obtained even when the center frequency is, for example, 17.5 kHz or 20.0 kHz.

[0030] Next, a description will be given of the drive signal generation units DG1, DG2 to DGn of the FPGA 321. Since the drive signal generation units DG1, DG2 to DGn have the same configuration, the following will describe the drive signal generation unit DG1, and a detailed description of the drive signal generation units DG2 to DGn will be omitted.

[0031] The drive signal generating unit DG1 includes a comparator 35, multipliers 36 and 37, an amplitude control unit 38, and a phase control unit 39. The comparator 35 generates a drive signal consisting of a PWM wave by comparing the signal wave output from the signal wave DDS3211 with the triangular wave output from the triangular wave DDS3212. That is, the drive signal generating unit DG1 generates a drive signal consisting of a PWM wave by a so-called triangular wave comparison method.

[0032] The triangular wave is input to the comparator 35 after its frequency is multiplied by N (for example, 12) by a frequency multiplier circuit (not shown) provided in the FPGA 321. In the triangular wave comparison method, the pulse width of the PWM wave can be controlled to be narrower by increasing the frequency of the triangular wave, so that the envelope of the ultrasonic wave transmitted from the transducer TD1 or the like can be controlled more finely. The multiplication factor of the triangular wave can be set to any value according to the response speed of the transmission signal generating unit TG1, which is an analog circuit, and the larger the multiplication factor, the narrower the pulse width of the PWM wave can be.

[0033] The amplitude control unit 38 controls the amplitude of the signal wave via the multiplier 36. That is, the amplitude control unit 38 controls the amplitude of the signal wave to control the pulse width of the drive signal, thereby multiplying it by a window function to arbitrarily control the envelope of the ultrasonic wave and remove unnecessary wave components.

[0034] The phase control unit 39 controls the phase of the signal wave via the multiplier 36. More specifically, the phase control unit 39 controls the time offset, which is the input timing to the comparator 35, so that a delay occurs in the phase of the signal wave according to the detection value output from the tilt detection unit 6. As a result, a delay occurs in each drive signal output from the drive signal generation units DG1, DG2 to DGn according to the rocking of the ship, so that even if the ship rocks, the directivity of the ultrasonic waves can be controlled to always transmit ultrasonic waves in a fixed direction.

[0035] The amplitude control section 38 and the phase control section 39 perform amplitude control and phase control of the signal wave for each operation clock of the FPGA 321. This makes it possible to perform amplitude control and phase control of the drive signal with high resolution.

[0036] Although not shown in detail, the transmission signal generating units TG1, TG2 to TGn are configured, for example, by a push-pull type switching circuit with a low-pass filter connected to the output stage. The transmission signal generating units TG1, TG2 to TGn generate transmission signals based on the drive signals consisting of PWM waves output from the drive signal generating units DG1, DG2 to DGn, and output them to the transducers TD1, TD2 to TDn. Each transducer TD1, TD2 to TDn generates ultrasonic waves by being driven based on the transmission signal.

[0037] In the figure, the waveforms and envelopes of the ultrasonic waves transmitted from each transducer TD1, TD2 to TDn are shown on the right side of the transducer 2. As can be seen from these ultrasonic waveforms, delays occur in the ultrasonic waves transmitted from each transducer TD1, TD2 to TDn according to the rocking of the ship. In addition, by arbitrarily controlling the multiplication factor of the triangular wave and the amplitude of the signal wave, the envelope is controlled so that a slope is generated at the rise and fall, and unnecessary wave components are removed.

[0038] As described above, according to the underwater detection device 1 of this embodiment, pulse compression is performed on the signal wave using an exponential chirp signal, and by adding a constant C of 1 or less to the chirp bandwidth B of the exponential chirp signal, the low-frequency period can be made longer than in conventional general exponential chirps that do not add constant C, making it possible to propagate ultrasonic waves further and detect targets.

[0039] Moreover, according to the underwater detection device 1 of this embodiment, a drive signal consisting of a PWM wave is generated on a digital circuit configured by the FPGA 321, and the phase of the signal wave on which the drive signal is based is controlled for each operation clock of the FPGA 321, so that the phase control of the drive signal can be performed with high resolution. Also, since a window function can be applied by controlling the amplitude of the signal wave on which the drive signal is based on the digital circuit configured by the FPGA 321, it is possible to arbitrarily control the envelope of the ultrasonic waves transmitted from the transducers TD1, TD2 to TDn to remove unnecessary wave components. Furthermore, the ratio of analog circuits is reduced, and the configuration of the required analog circuits is simplified, so that costs can be reduced.

[0040] Furthermore, according to the underwater detection device 1 of this embodiment, the phase of the signal wave can be controlled for each operating clock of the FPGA 321 according to the amount and direction of inclination of the ship detected by the inclination detection unit 6, so that the transmission direction of the ultrasonic wave can be adjusted quickly and with high resolution according to the inclination of the ship.

[0041] Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes and the like within the scope of the gist of the present invention, they are included in the present invention.

[0042] 1 Underwater detection device 2 Transmitter / Receiver 3 Main body 31 Transmission / reception switching unit 32 Transmission control section 321 FPGA (Ultrasonic transmission control device) 3211 Signal wave DDS 3212 Triangle wave DDS 33 Receiving section 34 Signal Processing Section 35 Comparator 36, 37 Multiplier 38 Amplitude control section 39 Phase control section 4 Monitors 5 Control section 6 Tilt detection section 7 Ultrasonic transmission unit (ultrasonic transmission device) DG1~DGn drive signal generator TG1~TGn Transmission signal generation section TD1~TDn transducer

Claims

1. An ultrasonic transmission control device that inputs a transmission signal generated based on a drive signal consisting of a PWM wave to a transducer and transmits ultrasonic waves from the transducer, A first DDS that generates a signal wave; a second DDS for generating a carrier wave; a comparator that compares the signal wave with the carrier wave to generate the drive signal; Equipped with The signal wave is an exponential chirp signal whose frequency f(t) is modulated according to the following Equations (1) and (2):

4. An ultrasonic transmission control device comprising: f(t)=(f0-1)+K t ・・・・・・(1) K=(B+C) (1 / tau) ・・・・・・・・(2) (fo: start frequency, K: frequency increase rate, B: chirp bandwidth, C: constant less than or equal to 1, tau: chirp time)

2. a plurality of drive signal generating units that generate the drive signals corresponding to the plurality of transducers, the plurality of drive signal generating units each include the comparator, a phase control unit that controls a phase of the signal wave input to the comparator, and an amplitude control unit that controls an amplitude of the signal wave input to the comparator; the first DDS, the second DDS, and the plurality of drive signal generating units are mounted on an FPGA; the phase control unit and the amplitude control unit perform phase control and amplitude control of the signal wave for each operation clock of the FPGA; 2. The ultrasonic transmission control device according to claim 1,

3. The ultrasonic transmission control device according to claim 1 or 2, a plurality of transmission signal generating units that generate transmission signals based on the drive signal input from the ultrasonic transmission control device; a plurality of transducers that transmit ultrasonic waves based on the transmission signal input from the transmission signal generating unit; An ultrasonic transmitting device comprising:

4. An underwater detection device mounted on a ship, comprising: The ultrasonic transmitting device according to claim 3 , a signal processing unit that processes a reception signal generated by the plurality of transducers of the ultrasonic transmission device receiving ultrasonic waves to generate a video signal of a target and display the video signal on a monitor; An inclination detection unit that detects the inclination of the ship; Equipped with a phase control unit of the ultrasonic transmitting device that controls a phase of the signal wave in accordance with the amount and direction of inclination of the ship detected by the inclination detection unit; An underwater detection device characterized by: