Underwater sensor, and control method and program of underwater sensor

Abstract

To provide an underwater sensor, and a control method and program of the underwater sensor capable of suppressing the separation of an envelope waveform of transmission waves from an ideal envelope waveform.SOLUTION: A fish finder 100 (underwater sensor) includes: a control circuit 101 for outputting control pulses; a transmission circuit 103 for supplying transmission signals corresponding to the control pulses to an ultrasonic vibrator 21; and a transmission current measurement circuit 108 for measuring a transmission current supplied to the ultrasonic vibrator 21. The control circuit 101 acquires a waveform corresponding to an envelope of transmission waves outputted from the ultrasonic vibrator 21 on the basis of a transmission current measured by the transmission current measurement circuit 108, and suppresses a difference between the acquired, actual envelope waveform and an ideal envelope waveform by executing correction of pulse width of control pulses.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an underwater detection device that detects underwater conditions, a control method for the underwater detection device, and a program that causes a control circuit of the underwater detection device to execute a predetermined function. [Background technology]

[0002] Conventionally, underwater detection devices that detect underwater conditions are known. In the underwater detection device, ultrasonic waves (transmission waves) are transmitted from an ultrasonic transducer into the water, and the reflected waves are received by the ultrasonic transducer. Echo data is generated according to the intensity of the received reflected waves, and an echo image is displayed based on the generated echo data.

[0003] In this type of underwater detection device, for example, a process is performed in which the amplitude of a plurality of transmission waves transmitted in one transmission period is modulated while maintaining the frequency of these transmission waves constant. This makes it possible to suppress, for example, the influence of frequency components other than the fundamental wave. Alternatively, for example, a process is performed in which the amplitude of a plurality of transmission waves is modulated while modulating the frequency of these transmission waves. This makes it possible to suppress range side lobes occurring in the received signal.

[0004] The following Patent Document 1 describes weighting the envelope of a burst signal so that it changes according to a function such as a Gaussian function, in order to ensure frequency isolation between signals. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-202362 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, various factors can cause the envelope waveform of the transmission wave to deviate from the ideal envelope waveform. For example, the impedance of the transmission circuit and the ultrasonic transducer usually changes depending on the frequency of the transmission signal. Therefore, when the frequency of the transmission wave is modulated as described above, the envelope waveform of the transmission wave is distorted due to the change in impedance. Even when the frequency of the transmission wave is constant, the envelope waveform of the transmission wave can be distorted due to the response characteristics of the transmission circuit, etc.

[0007] In view of such problems, the present invention aims to provide an underwater detection device, a control method for an underwater detection device, and a program capable of preventing the envelope waveform of a transmitted wave from deviating from an ideal envelope waveform. [Means for solving the problem]

[0008] A first aspect of the present invention relates to an underwater detection device. The underwater detection device according to this aspect includes a control circuit that outputs a control pulse, a transmission circuit that supplies an ultrasonic transducer with a transmission signal corresponding to the control pulse, and a transmission current measurement circuit that measures a transmission current supplied to the ultrasonic transducer. The control circuit acquires a waveform corresponding to the envelope of a transmission wave output from the ultrasonic transducer based on the transmission current measured by the transmission current measurement circuit, and corrects the pulse width of the control pulse to suppress a difference between the acquired actual envelope waveform and an ideal envelope waveform.

[0009] The envelope waveform of the transmission current corresponds to the envelope waveform of the transmission wave that is actually transmitted. Therefore, the actual envelope waveform of the transmission wave can be obtained from the transmission current. According to the underwater detection device of the above aspect, the pulse width of the control pulse is corrected so as to suppress the difference between the actual envelope waveform obtained from the transmission current and the ideal envelope waveform. Therefore, the envelope waveform of the transmission wave transmitted from the ultrasonic transducer can be made closer to the ideal envelope waveform.

[0010] In the underwater detection device of this aspect, the control circuit may be configured to repeatedly perform the correction at least until the difference between the actual envelope waveform and the ideal envelope waveform falls within a predetermined threshold range for each of the control pulses.

[0011] According to this configuration, the difference between the actual envelope waveform and the ideal envelope waveform can be kept within the threshold range for all control pulses, and therefore the deviation between the transmission wave transmitted from the ultrasonic transducer and the ideal envelope waveform can be appropriately suppressed.

[0012] In this configuration, the predetermined threshold range is set so that the purpose of applying an envelope to the transmission wave (suppression of frequency components other than the fundamental wave, suppression of range side lobes, etc.) can be substantially achieved if the difference is included in the threshold range. Therefore, according to the above configuration, the envelope waveform of the corrected transmission wave transmitted from the ultrasonic transducer can be made to approach the ideal envelope waveform to the extent that this purpose can be achieved.

[0013] In this configuration, the control circuit can be configured to correct the pulse width of each of the control pulses by multiplying the difference by a coefficient smaller than 1 and larger than 0 in each correction.

[0014] According to this configuration, the difference is gradually reduced with each correction, and excessive correction in one correction can be prevented, so that the difference can be smoothly converged within the threshold range.

[0015] In the underwater detection device of this aspect, the control circuit may be configured to calculate a moving average of the actual envelope waveform and calculate the difference between the envelope waveform based on the moving average and the ideal envelope waveform.

[0016] According to this configuration, even if a large fluctuation suddenly occurs in the actual envelope waveform, excessive correction due to this fluctuation can be suppressed, and therefore the envelope waveform of the transmission wave transmitted from the ultrasonic transducer can be smoothly brought closer to the ideal envelope waveform.

[0017] In the underwater detection device of this embodiment, the ideal envelope waveform is a window function waveform that determines the transmission power of the ultrasonic transducer, and the control circuit normalizes the envelope waveform obtained from the transmission current so that it can be compared with the window function waveform to calculate the actual envelope waveform, and calculates the difference between the calculated actual envelope waveform and the window function waveform.

[0018] According to this configuration, the ideal envelope waveform can be set simply and accurately, and the difference between the actual envelope waveform and the ideal envelope waveform can be calculated accurately by normalizing the envelope waveform obtained from the transmission current. Therefore, the transmission wave transmitted from the ultrasonic transducer can be brought close to the ideal envelope waveform with high accuracy by simple processing.

[0019] In the underwater detection device of this aspect, the control circuit may be configured to output a plurality of the control pulses at regular intervals during the transmission period of the transmission wave.

[0020] In this configuration, the above-mentioned correction process is performed, so that the transmission wave transmitted from the ultrasonic transducer can be made to approach an ideal envelope waveform, thereby making it possible to appropriately suppress frequency components other than the fundamental wave.

[0021] Alternatively, the control circuit may be configured to output a plurality of frequency-modulated control pulses during a transmission period of the transmission wave.

[0022] In this configuration, the above-mentioned correction process is performed to make the transmission wave sent from the ultrasonic transducer closer to an ideal envelope waveform, thereby appropriately suppressing the occurrence of range side lobes in the received signal.

[0023] A second aspect of the present invention relates to a control method for an underwater detection device including a transmission circuit that supplies a transmission signal corresponding to a control pulse to an ultrasonic transducer, and a transmission current measurement circuit that measures a transmission current supplied to the ultrasonic transducer. The control method according to this aspect obtains a waveform corresponding to the envelope of a transmission wave output from the ultrasonic transducer based on the transmission current measured by the transmission current measurement circuit, and corrects the pulse width of the control pulse to suppress a difference between the obtained actual envelope waveform and an ideal envelope waveform.

[0024] According to the control method of this aspect, the same effects as those of the first aspect can be achieved.

[0025] A third aspect of the present invention relates to a program for causing a control circuit of an underwater detection device, the control circuit including a control circuit for outputting a control pulse, a transmission circuit for supplying a transmission signal corresponding to the control pulse to an ultrasonic transducer, and a transmission current measurement circuit for measuring a transmission current supplied to the ultrasonic transducer, to execute predetermined functions. The program according to this aspect causes the control circuit to execute a function of acquiring a waveform corresponding to the envelope of a transmission wave output from the ultrasonic transducer based on the transmission current measured by the transmission current measurement circuit, and a function of suppressing a difference between the acquired actual envelope waveform and an ideal envelope waveform by executing a correction of the pulse width of the control pulse.

[0026] According to the program of this aspect, the same effects as those of the first aspect can be achieved. Effect of the Invention

[0027] As described above, according to the present invention, it is possible to provide an underwater detection device, a control method for an underwater detection device, and a program that can prevent the envelope waveform of a transmitted wave from deviating from an ideal envelope waveform.

[0028] The effects and significance of the present invention will become clearer from the following description of the embodiment. However, the embodiment described below is merely an example of how the present invention can be put into practice, and the present invention is not limited to the embodiment described below. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a diagram showing a usage pattern of a fish detector according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a fish detector according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing a configuration of a transmission circuit according to an embodiment. [Figure 4] FIG. 4 is a graph showing a schematic relationship between the waveform (ideal waveform) of a window function and the pulse width of a control pulse according to the embodiment. [Diagram 5] FIG. 5 is a flow chart illustrating a process for correcting the pulse width of a control pulse according to an embodiment. [Figure 6] 6(a) and 6(b) are graphs illustrating example waveforms obtained in corresponding steps of the flowchart of FIG. 5 according to an embodiment. [Figure 7] 7(a) and 7(b) are graphs illustrating example waveforms obtained in corresponding steps of the flowchart of FIG. 5, according to an embodiment. [Figure 8] 8(a) and 8(b) are graphs illustrating example waveforms obtained in corresponding steps of the flowchart of FIG. 5 according to an embodiment. [Figure 9] 9(a) and 9(b) are graphs illustrating example waveforms obtained in corresponding steps of the flowchart of FIG. 5 according to an embodiment. [Figure 10] 10(a) and 10(b) are graphs illustrating example waveforms obtained in corresponding steps of the flowchart of FIG. 5 according to an embodiment. [Figure 11] Fig. 11(a) is a graph showing an example of a waveform of data after normalization processing acquired by processing for the next wave transmission period when correction is performed in the corresponding step of the flowchart in Fig. 5 according to an embodiment. Fig. 11(b) is a graph showing a waveform of data after normalization processing acquired by the correction processing in Fig. 5 according to an embodiment, a waveform of data after normalization processing before correction, and an ideal envelope waveform (waveform of a window function). [Figure 12] Figures 12(a) and 12(b) are graphs showing the waveform of the data after normalization processing obtained by the correction processing of Figure 5, the waveform of the data after normalization processing before correction, and an ideal envelope waveform (window function waveform) for each embodiment of a constant frequency transmission wave (CW wave) and a frequency modulated transmission wave (FM wave), respectively. [Figure 13] FIG. 13 is a graph showing a verification result obtained by an experiment verifying the effect of the correction process of FIG. 5 when a transmission wave (CW wave) with a constant frequency according to the embodiment is transmitted. [Figure 14] FIG. 14 is a graph showing a verification result obtained by an experiment verifying the effect of the correction process in FIG. 5 when a frequency-modulated transmission wave (FM wave) according to the embodiment is transmitted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, a fish detector is shown as an example of an underwater detector.

[0031] FIG. 1 is a diagram showing a usage pattern of a fish finder.

[0032] In this embodiment, a transducer 2 is installed on the bottom of a ship 1, and a transmission beam 3 (ultrasonic waves) is transmitted from the transducer 2 underwater. The transmission beam 3 is shaped like a cone with a small apex angle and is transmitted in pulses in the vertically downward direction. The transmission beam 3 is reflected by the water bottom 4 and a school of fish 5, and the reflected waves (echoes) are received by the transducer 2. The received signal of the reflected wave based on a single transmission of the transmission beam 3 generates echo data in which the signal strength (echo intensity) of the received signal is distributed over the detection range in the water depth direction.

[0033] By accumulating echo data for a predetermined time, an echo image is generated that shows the distribution of signal intensity (echo intensity) in the water depth direction. The echo image includes the intensity distribution of the echoes from each target. The generated underwater echo image is displayed on a display unit installed in the wheelhouse of the ship 1 or the like. This allows the user to confirm targets (such as the bottom 4 and schools of fish 5) that exist underwater.

[0034] FIG. 2 is a block diagram showing the configuration of the fish detector 100. As shown in FIG.

[0035] The fish finder 100 includes, in addition to the transmitter / receiver 2 shown in Figure 1, a control circuit 101, a memory 102, a transmission circuit 103, a reception circuit 104, a switching circuit 105, an input unit 106, a display unit 107, and a transmission current measuring circuit 108.

[0036] The control circuit 101, memory 102, transmission circuit 103, reception circuit 104, switching circuit 105, input unit 106, display unit 107 and transmission current measuring circuit 108 are installed in the wheelhouse or the like of the ship 1. The configuration except for the transducer 2 may be unitized in a single housing, or some of the components such as the display unit 107 may be separate. The switching circuit 105 is communicatively connected to the transducer 2 by a signal cable.

[0037] The transducer 2 includes a transmitting element used for transmitting ultrasonic waves and a receiving element used for receiving ultrasonic waves. In this embodiment, the transmitting element and the receiving element of the transducer 2 are configured by one ultrasonic transducer 21.

[0038] The transmission circuit 103 generates a transmission signal for driving the ultrasonic transducer 21 from a control signal (control pulse) of a predetermined frequency input from the control circuit 101, and outputs the generated transmission signal to the ultrasonic transducer 21 of the transmitter / receiver 2 via the switching circuit 105.

[0039] The ultrasonic transducer 21 transmits an ultrasonic transmission wave (transmission beam 3) into water based on the input transmission signal. The ultrasonic transducer 21 also receives a reflected wave of the transmitted transmission wave, and outputs a reception signal having a magnitude according to the intensity of the reflected wave to the reception circuit 104 via the switching circuit 105. The switching circuit 105 switches between transmitting and receiving signals to the ultrasonic transducer 21.

[0040] The receiving circuit 104 includes a filter that extracts the frequency components of the transmitted waves from the received signal from the ultrasonic transducer 21, and an amplifier circuit that amplifies the received signal. The receiving circuit 104 generates echo data indicating the echo intensity for each depth based on the received signal of the frequency components extracted by the filter.

[0041] Specifically, the receiving circuit 104 generates echo data that associates the elapsed time from the timing of transmitting the transmission wave (transmission beam 3) with the intensity of the reflected wave, and outputs the generated echo data to the control circuit 101.

[0042] Here, the time elapsed from the timing of transmission of the transmitted wave corresponds to the depth. Note that the strength of the reflected wave attenuates as the depth increases. Therefore, the receiving circuit 104 corrects the strength of the reflected wave, which attenuates according to the elapsed time, so as to eliminate this attenuation, and outputs the corrected echo data to the control circuit 101.

[0043] The control circuit 101 is composed of an arithmetic processing circuit such as a CPU, and an integrated circuit such as an FPGA. The memory 102 is composed of a ROM, a RAM, a hard disk, etc. Various programs and information are stored in the memory 102. These programs include a program that causes the control circuit 101 (computer) to execute a function of processing echo data to generate an image, and a function of correcting the pulse width of a control signal (control pulse). The memory 102 is also used as a work area during processing by the control circuit 101. The control circuit 101 controls each part according to the programs stored in the memory 102.

[0044] The input unit 106 is composed of input means such as a mouse and a keyboard, and accepts input from a user. The input unit 106 may be a touch panel integrated with the display unit 107. The display unit 107 is composed of a display device such as a CRT monitor or a liquid crystal panel, and displays an image generated by the control circuit 101. As described above, the display unit 107 displays an echo image generated based on the echo data.

[0045] The transmission current measuring circuit 108 measures the transmission current supplied from the transmission circuit 103 to the transducer 2 (ultrasonic transducer 21). The configuration of the transmission current measuring circuit 108 is similar to that of a transmission current measuring circuit used to measure the transmission current of a power supply circuit or the like. The parameters (resistance value, etc.) of each element of the transmission current measuring circuit 108 are adjusted so as to match the magnitude of the transmission current that may be expected to be supplied to the transducer 2 (ultrasonic transducer 21). The measurement results of the transmission current measuring circuit 108 are input to the control circuit 101 at any time. As described below, the control circuit 101 corrects the pulse width of the control pulse based on the measurement results of the input transmission current.

[0046] The control circuit 101 acquires echo data in which depth and echo intensity are associated with each other for each transmission of a transmission wave (transmission beam 3). The control circuit 101 generates an echo image based on one frame of continuously acquired echo data, and displays the image on the display unit 107. The echo image is sometimes called an echogram.

[0047] An echo image is an image in which echo intensity is distributed in a coordinate region with two axes of depth and time. In an echo image, each pixel is colored or shaded in a gradation according to the signal intensity of the reflected wave. A user such as a fisherman can grasp the position and range of a school of fish in the water by referring to the echo image displayed on the display unit 107.

[0048] FIG. 3 is a diagram showing a configuration of the transmission circuit 103. As shown in FIG.

[0049] The transmission circuit 103 includes a FET driver 201, FETs 202 and 203 (field effect transistors), and an amplifier circuit 204. The two FETs 202 and 203 are connected in series between a power supply voltage Vdd and ground. The amplifier circuit 204 is connected between the two FETs 202 and 203.

[0050] The control circuit 101 outputs control pulses S01 and S02 for driving the FETs 202 and 203 to the FET driver 201. Here, the control pulses S01 and S02 are voltage pulse signals with a fixed period, and are out of phase with each other by a half period. The FET driver 201 outputs first voltage signals S11 and S12, which are respectively amplified from the input control pulses S01 and S02, to the gates of the FETs 202 and 203. This causes the FETs 202 and 203 to be alternately turned on at a predetermined period. The frequency of the first voltage signals S11 and S12 is the same as the frequency of the control pulses S01 and S02. Therefore, the operating frequency of the FETs 202 and 203 is also the same as the frequency of the control pulses S01 and S02.

[0051] When the upper FET 202 is turned on, a second voltage signal S21 having the power supply voltage Vdd at a high level is supplied to the amplifier circuit 204. The frequency of the second voltage signal S21 is the same as the frequency of the control pulse S01.

[0052] The amplifier circuit 204 includes a voltage conversion circuit such as a transformer. The amplifier circuit 204 boosts or lowers the second voltage signal S21 to generate a transmission signal of a predetermined frequency, and supplies the generated transmission signal to the ultrasonic transducer 21. This causes the ultrasonic transducer 21 to transmit ultrasonic waves.

[0053] When the upper FET 202 is turned on, a second voltage signal S22 is guided to ground from the amplifier circuit 204. The second voltage signal S22 is a voltage signal that remains in a transformer or the like in the amplifier circuit 204 when a transmission signal is generated. In this way, when the FETs 202 and 203 are turned on alternately by the first voltage signals S11 and S12, a transmission signal of a predetermined frequency is supplied to the ultrasonic transducer 21, and an ultrasonic transmission wave is transmitted from the ultrasonic transducer 21.

[0054] The transmission wave sent from the ultrasonic transducer 21 becomes an AC waveform that oscillates at the same frequency as the control pulse S01 due to the action of the amplifier circuit 204 and the equivalent circuit of the ultrasonic transducer 21. At this time, the transmission current flowing through the ultrasonic transducer 21 also oscillates with a similar AC waveform. Therefore, in the configuration of FIG. 2, the control circuit 101 can grasp the actual amplitude state of the transmission wave from the transmission current measured by the transmission current measuring circuit 108.

[0055] In this embodiment, the pulse width of the control pulse S01 is adjusted so that the envelope waveform of the transmission wave (transmission power) transmitted in one transmission period becomes a waveform according to a predetermined window function. As the window function, for example, a Hamming window or a Gaussian window can be used. However, the window function is not limited to these windows. The window function can be appropriately changed depending on the purpose.

[0056] FIG. 4 is a graph showing a schematic relationship between the waveform (ideal waveform) of the window function and the pulse width of the control pulse S01.

[0057] FIG. 4 shows the window function and control pulses in one transmission period. For convenience, 24 control pulses S01 are shown, but the actual number of control pulses S01 is several levels greater. In FIG. 4, the maximum value of the window function indicated by the dashed line is 1. The amplitude (voltage) of the control pulse S01 is constant. The pulse width of the control pulse S01 increases toward the center of the window function period. In this way, by adjusting the pulse width of the control pulse S01 according to the window function, the transmission wave is transmitted with a transmission power according to the window function.

[0058] However, in the above-mentioned configuration, the envelope waveform of the transmission wave may deviate from the ideal envelope waveform. For example, when the frequency of the transmission wave is constant because the frequency of the control pulse S01 is constant as described above, the envelope waveform of the transmission wave may be distorted depending on the response characteristics of the circuitry constituting the transmission circuit 103.

[0059] 3, if the pulse width of the control pulse S01 is small, the control pulse S01 will go low before the outputs of the FET driver 201 and the FET 202 fully rise, causing the envelope waveform of the transmission wave to deviate from the ideal envelope waveform.

[0060] Furthermore, the impedance of the transmission circuit 103 and the ultrasonic transducer 21 changes depending on the frequency of the transmission signal. Therefore, when the frequency of the transmission wave is modulated by modulating the frequency of the control pulse S01, these impedances change depending on the modulated frequency. This causes distortion in the envelope waveform of the transmission wave due to the change in impedance. As a result, the envelope waveform of the transmission wave deviates from the ideal envelope waveform.

[0061] Therefore, in this embodiment, a correction for suppressing such a deviation is performed in the control circuit 101.

[0062] As described above, the transmission current flowing through the ultrasonic transducer 21 oscillates with the same AC waveform as the transmission wave. Therefore, the actual envelope waveform of the transmission wave can be obtained from the transmission current measured by the transmission current measuring circuit 108. The control circuit 101 obtains the actual envelope waveform of the transmission wave from the measurement result of the transmission current by the transmission current measuring circuit 108, and corrects the pulse width of the control pulse S01 so as to suppress the difference between the obtained actual envelope waveform and the ideal envelope waveform. This process will be described below.

[0063] Fig. 5 is a flowchart showing a process for correcting the pulse width of the control pulse S01. Fig. 6(a) to Fig. 11(a) are graphs showing examples of waveforms acquired in corresponding steps of the flowchart in Fig. 5. In Fig. 6(a) to Fig. 11(a), the step numbers of the corresponding steps are added.

[0064] The process of Fig. 5 is performed, for example, when the fish finder device 100 is started up. However, the timing of performing the process of Fig. 5 is not limited to this, and for example, the process of Fig. 5 may be performed at regular intervals during the operation of the fish finder device 100 after starting up the fish finder device 100.

[0065] In the correction process, the control circuit 101 first obtains the measurement result of the transmission current in one wave transmission period from the transmission current measurement circuit 108 (S101). An example of the measurement result of the transmission current is shown in Fig. 6(a). For convenience, Fig. 6(a) shows the transmission current in a range slightly wider than the wave transmission period.

[0066] The waveform in Fig. 6(a) is obtained by measuring, with an oscilloscope, the transmission current supplied to the ultrasonic transducer 21. Fig. 6(b) and subsequent figures show the results of processing the measurement results with predetermined numerical calculation software.

[0067] The control circuit 101 performs A / D conversion on the transmission current during one wave transmission period at a predetermined sampling cycle, and acquires digital data corresponding to the peak value at each sampling timing (S102). An example of the acquired digital data is shown in Fig. 6(b). In Fig. 6(b), the start time of the wave transmission period is set to zero, so the waveform of the digital data is shifted slightly to the left compared to Fig. 6(a).

[0068] The control circuit 101 executes mixer processing on the acquired digital data (S103). This processing reduces the digital data to baseband. The mixer processing calculates real and imaginary digital data. An example of real and imaginary data when the mixer processing is applied to the digital data of FIG. 6(b) is shown in FIG. 7(a) and (b), respectively.

[0069] The control circuit 101 applies low-pass filter processing according to the baseband to the real and imaginary data obtained by the mixer processing (S104). As a result, real and imaginary data from which noise components have been removed are obtained. An example of the real and imaginary data that has been subjected to low-pass filter processing is shown in Figures 8(a) and 8(b), respectively.

[0070] The control circuit 101 multiplies the real and imaginary data that have been subjected to the low-pass filter processing at each sampling timing to calculate the absolute value of these data (S105). This allows acquisition of waveform data that correlates with the window function in Fig. 4. An example of this data is shown in Fig. 9(a).

[0071] The control circuit 101 calculates a moving average of the calculated absolute values ​​for each sampling timing (S106). That is, the absolute values ​​of each sampling timing are averaged for the current wave transmission period up to a predetermined number of previous wave transmission periods to calculate the moving average. The number of wave transmission periods to which the moving average is applied is set in consideration of the variation in the absolute values. If the variation in the absolute values ​​is small, the moving average process (S106) may be omitted. An example of data obtained by the moving average is shown in FIG. 9(b).

[0072] The control circuit 101 normalizes the data obtained by the moving average so that the peak of the data coincides with the peak of the window function waveform in Fig. 4 (S107). Here, since the peak value of the window function waveform is 1, normalization is performed so that the peak of the data obtained by the moving average becomes 1. This makes it possible to compare the waveform based on the normalized data with the window function waveform. An example of data that has been normalized is shown in Fig. 10(a).

[0073] The control circuit 101 calculates the difference between the normalized data (actual envelope waveform) and the window function waveform, which is the ideal envelope waveform, for each sampling timing corresponding to the output of the control pulse S01 (S108). The window function waveform, which is the ideal envelope waveform, is stored in advance in the memory 102 of FIG. 2. The difference is calculated by subtracting the data value of the actual envelope waveform from the data value of the ideal envelope waveform. An example of the difference data is shown in FIG. 10(b).

[0074] The control circuit 101 judges whether or not all the timing differences are within a threshold range (S109). Here, the threshold range is set to a boundary range within which the purpose of applying an envelope to a transmission wave (suppression of frequency components other than the fundamental wave, suppression of range side lobes, etc.) can be substantially achieved if the differences are included in the range.

[0075] If all the differences are within the threshold range (S109: YES), the control circuit 101 ends the process of Fig. 5. On the other hand, if any of the differences are not within the threshold range (S109: NO), the control circuit 101 corrects the pulse width of the corresponding control pulse S01 so as to suppress each difference (S110), and returns the process to step S101. As a result, the process from step S101 onwards is performed in the next wave transmission period by the control pulse S01 with the corrected pulse width.

[0076] In the correction process of step S110, the control circuit 101 corrects the pulse width of each control pulse S01 so as to eliminate the difference in value obtained by multiplying each difference by a coefficient (for example, 0.5) smaller than 1 and larger than 0. This prevents the pulse width from being excessively corrected in the current correction, and the difference is gradually reduced by the next and subsequent corrections.

[0077] FIG. 11(a) shows the waveform of the normalized data obtained by processing for the next transmission period when this correction is applied (the waveform corresponding to FIG. 10(a)). This waveform is obtained when the correction of step S110 is performed with the coefficient set to 0.5. FIG. 11(b) shows the waveform of the normalized data obtained by this correction, the waveform of the normalized data before correction, and the ideal envelope waveform (window function waveform). As shown in FIG. 11(b), the waveform of the corrected data is much closer to the ideal envelope waveform (window function waveform) than the waveform of the data before correction.

[0078] In addition, in the correction process of step S110, if there is no risk of excessive correction being performed even if the difference is used as is, the pulse width of each control pulse S01 may be corrected so that the difference itself is eliminated without multiplying the difference by a coefficient.

[0079] In this manner, the control circuit 101 repeatedly executes the processes of steps S101 to S109 and S110 until all the differences are within the threshold range (S109: NO). When all the differences are thus determined to be within the threshold range (S109: YES), the control circuit 101 ends the process of FIG.

[0080] 12(a) is a graph showing the waveform of the normalized data obtained when corrections are made until all the differences are within the threshold range, the waveform of the normalized data before these corrections are made, and an ideal envelope waveform (waveform of a window function). Here, no frequency modulation is applied to the transmission wave.

[0081] As shown in Fig. 12(a), the waveform of the data after these corrections is substantially overlapped with the ideal envelope waveform (waveform of the window function). Therefore, by outputting the control pulse S01 with the corrected pulse width, it is possible to transmit the transmission wave to the ultrasonic transducer 21 with an envelope waveform according to the window function. Therefore, the influence of frequency components other than the fundamental wave can be suppressed.

[0082] FIG. 12(b) is a graph showing the waveform of the data after normalization processing obtained by the correction processing of FIG. 5 when the transmission wave is further frequency modulated, the waveform of the data after normalization processing when this correction processing is not performed, and an ideal envelope waveform (waveform of the window function).

[0083] As described above, the frequency modulation of the transmission wave is performed by frequency modulating a plurality of control pulses S01 included in one transmission period, that is, by changing the time interval between adjacent control pulses S01. The receiving circuit 104 includes a matched filter for extracting a signal corresponding to the frequency modulation of the transmission wave from the received signal. The configuration of the receiving circuit 104 that processes the received signal based on the frequency-modulated transmission wave is well known, so a detailed description thereof will be omitted here.

[0084] In this transmission mode, the pulse widths of multiple control pulses S01 included in one transmission period are initially set so that the envelope waveform of the transmission wave becomes a waveform according to a predetermined window function. Then, the pulse width of each control pulse S01 is corrected by the correction process of Fig. 5. This results in a waveform of data after normalization processing, as shown by the dotted line in Fig. 12(b).

[0085] As shown in Fig. 12(b), the waveform of the normalized data obtained when the correction process of Fig. 5 is performed is slightly different from the ideal envelope waveform (waveform of the window function), but is almost the same. Therefore, by outputting the control pulse S01 with the corrected pulse width, it is possible to transmit a transmission wave to the ultrasonic transducer 21 with an envelope waveform according to the window function. Therefore, the range side lobe can be appropriately suppressed from the waveform of the data obtained by applying a matched filter to the received signal.

[0086] FIG. 13 is a graph showing the experimental verification results of the effect of the correction process in FIG. 5 when a transmission wave (CW wave) with a constant frequency is transmitted.

[0087] In this experiment, a transmission wave (ultrasonic wave) was sent from the ultrasonic transducer 21 into the water tank, and the pulse width of the control pulse S01 was corrected by the correction process of Fig. 5. The reflected wave when the transmission wave was sent into the water tank by the corrected control pulse S01 was received by a microphone to obtain a received signal. Then, a fast Fourier transform (FFT) was applied to the envelope of the fundamental wave component of the received signal to obtain a spectral waveform.

[0088] The dotted waveform in Fig. 13 indicates the spectral waveform based on the corrected transmission wave. For comparison, Fig. 13 also shows an ideal spectral waveform (solid line) and a spectral waveform (dashed line) obtained in a similar experiment when the correction process of Fig. 5 was not performed.

[0089] As shown in Fig. 13, in the frequency band of -5kHz to +5kHz, the spectrum waveform based on the corrected transmission wave was substantially overlapped with the ideal spectrum waveform. Moreover, in this frequency band, the deviation in amplitude level of the spectrum waveform based on the corrected transmission wave from the ideal spectrum waveform was improved by about 10dB compared to the case where the correction process was not performed.

[0090] In addition, in the frequency band outside ±5 kHz, the spectrum waveform based on the corrected transmitted wave deviates from the ideal spectrum waveform. However, this is because the experiment was conducted in a water tank, and reverberation (harmonic components) caused by the tank was picked up by the microphone.

[0091] From the above experimental results, it was confirmed that the correction process in FIG. 5 has an effect (suppression of frequency components other than the fundamental wave) when the transmitted wave is a CW wave with a constant frequency.

[0092] FIG. 14 is a graph showing the results of an experiment verifying the effect of the correction process in FIG. 5 when a frequency-modulated transmission wave (FM wave) is transmitted.

[0093] In this experiment, the ultrasonic transducer 21 also sent a transmission wave (ultrasound) into the water tank, and the pulse width of the control pulse S01 was corrected by the correction process of Fig. 5. The reflected wave when the transmission wave was sent into the water tank by the corrected control pulse S01 was received by a microphone to obtain a received signal. Then, the waveform of the amplitude level of the signal obtained by applying a matched filter to the received signal was obtained.

[0094] In Fig. 14, the dotted waveform indicates the waveform of the amplitude level based on the corrected transmission wave. For comparison, Fig. 14 also shows an ideal waveform (solid line) and a waveform (dashed line) obtained in a similar experiment when the correction process of Fig. 5 was not performed.

[0095] In Fig. 14, the time range (around 2.4 to 2.8 msec) where the ideal waveform is near the peak corresponds to the time range where the reflected wave from the bottom of the water is received. In the experimental results of Fig. 14, in the time range immediately preceding that, around 2.2 to 2.4 msec, the range side lobes that appeared in the waveform when the correction process was performed were improved by about 10 dB compared to when the correction process was not performed. Therefore, it was confirmed that when the correction process of Fig. 5 was performed, it was possible to suppress the appearance of a virtual image due to the range side lobe in front of the bottom of the water in the echo image displayed on the display unit 107 of Fig. 2.

[0096] In the experimental results shown in Fig. 14, there are some bumps in the waveform when the correction process is performed at around 2 msec and 3.2 msec. However, this is also due to the fact that the experiment was performed in a water tank (experimental environment), just like in the case of Fig. 13.

[0097] From the above experimental results, it was confirmed that the correction process in FIG. 5 was effective (suppression of range side lobes) even when the transmitted wave was a frequency-modulated FM wave.

[0098] <Effects of the embodiment> According to this embodiment, the following effects are achieved.

[0099] As shown in FIG. 5, the control circuit 101 acquires a waveform corresponding to the envelope of the transmission wave output from the ultrasonic transducer 21 based on the transmission current measured by the transmission current measuring circuit 108 (S101 to S107), calculates the difference between the acquired actual envelope waveform and an ideal envelope waveform (window function waveform) (S108), and corrects the pulse width of the control pulse S01 so as to suppress the calculated difference (S110).

[0100] As described above, the envelope waveform of the transmission current corresponds to the envelope waveform of the transmission wave that is actually transmitted. Therefore, a waveform corresponding to the actual envelope of the transmission wave can be obtained from the transmission current. According to the process of FIG. 5, the pulse width of the control pulse S01 is corrected so that the difference between the actual envelope waveform obtained from the transmission current and the ideal envelope waveform is suppressed. Therefore, as shown in FIG. 11(b) and FIG. 12(a) and (b), the envelope waveform of the transmission wave transmitted from the ultrasonic transducer 21 can be made closer to the ideal envelope waveform.

[0101] As shown in FIG. 5, control circuit 101 repeatedly performs correction (S110) at least until the difference between the actual envelope waveform and the ideal envelope waveform falls within a predetermined threshold range for each control pulse S01 (S109).

[0102] 12(a) and 12(b), the difference between the actual envelope waveform and the ideal envelope waveform can be kept within the threshold range for all control pulses S01. Therefore, the deviation between the transmission wave transmitted from the ultrasonic transducer 21 and the ideal envelope waveform can be appropriately suppressed.

[0103] Here, as described above, the threshold range (S109) is set to a boundary range within which the purpose of applying an envelope to the transmission wave (suppression of frequency components other than the fundamental wave, suppression of range side lobes, etc.) can be substantially achieved if the difference is included in that range. Therefore, according to the process of Fig. 5, the envelope waveform of the corrected transmission wave transmitted from the ultrasonic transducer 21 can be made to approach the ideal envelope waveform to the extent that this purpose can be achieved.

[0104] As described with reference to FIG. 5, in each correction (S110), the control circuit 101 corrects the pulse width of each control pulse S01 so as to eliminate the deviation in the value obtained by multiplying the difference by a coefficient (for example, 0.5) that is smaller than 1 and larger than 0.

[0105] This allows the difference to be gradually reduced with each correction (S110), and can prevent excessive correction from being performed in one correction (S110). Therefore, the difference can be smoothly converged to within the threshold range.

[0106] As described with reference to FIG. 5, control circuit 101 calculates a moving average of the actual envelope waveform (S106), and calculates the difference between the envelope waveform based on the moving average and the ideal envelope waveform (S107, S108).

[0107] According to this configuration, even if a large fluctuation suddenly occurs in the actual envelope waveform, excessive correction (S110) due to this fluctuation can be suppressed. Therefore, the envelope waveform of the transmission wave transmitted from the ultrasonic transducer 21 can be smoothly brought closer to the ideal envelope waveform.

[0108] As shown in FIG. 4, the ideal envelope waveform is the waveform of a window function that defines the transmission power of the ultrasonic transducer 21. In the processing of FIG. 5, the control circuit 101 normalizes the envelope waveform acquired from the transmission current so as to be comparable with the waveform of the window function to calculate an actual envelope waveform (S107), and calculates the difference between the calculated actual envelope waveform and the waveform of the window function (S108).

[0109] According to this configuration, the ideal envelope waveform can be set simply and accurately, and the difference between the actual envelope waveform and the ideal envelope waveform can be calculated accurately by normalizing the envelope waveform obtained from the transmission current. Therefore, the transmission wave transmitted from the ultrasonic transducer 21 can be made to approach the ideal envelope waveform with high accuracy by simple processing.

[0110] As shown in FIG. 4, the control circuit 101 outputs a plurality of control pulses S01 at regular intervals during the transmission period of the transmission wave.

[0111] In this transmission mode, by performing the correction process of Fig. 5, the envelope waveform of the transmission wave transmitted from the ultrasonic transducer 21 can be made to approach an ideal envelope waveform as shown in Fig. 12(a). Therefore, as shown in Fig. 13, frequency components other than the fundamental wave can be appropriately suppressed.

[0112] Alternatively, the control circuit 101 may be configured to output a plurality of frequency-modulated control pulses S01 during the transmission period of the transmission wave.

[0113] Even in this transmission mode, the correction process of Fig. 5 is performed, so that the transmission wave transmitted from the ultrasonic transducer 21 can be made to approach an ideal envelope waveform, as shown in Fig. 12(b). Therefore, as shown in Fig. 14, the occurrence of range side lobes in the received signal can be appropriately suppressed.

[0114] <Example of change> The present invention is not limited to the above-described embodiment, and various modifications of the embodiment of the present invention are possible in addition to the above-described configuration.

[0115] For example, in the process of Fig. 5, the correction process was terminated when the difference fell within the threshold range (S109), but the process of step S109 may be omitted and the correction process may be continued during operation of the fish finder device 100. In this case, the process proceeds from step S108 to step S110, and the process of Fig. 5 ends in response to the operation of the fish finder device 100 being stopped.

[0116] Furthermore, the coefficient applied in the correction in step S110 does not necessarily have to be uniform; for example, the coefficient may vary depending on the magnitude of the difference.

[0117] In the above embodiment, the waveform of the window function is used as the ideal envelope waveform for calculating the difference, but another waveform having a correlation with the envelope waveform of the transmission wave may be used as the ideal envelope waveform. For example, the envelope waveform of the transmission current obtained when the window function is properly applied may be set as the ideal waveform. In this case, step S107 is omitted from the process of FIG. 5, and in step S108, the difference between the actual envelope waveform of the transmission current (the waveform in FIG. 9(b)) and the ideal envelope waveform of the transmission current is calculated.

[0118] In the above embodiment, an example is shown in which the present invention is applied to the fish detector 100 mounted on the ship 1, but the application of the present invention is not limited to this. For example, the present invention may be applied to a fish detector installed in a fixed net, or to an underwater detection device other than a fish detector, such as a scanning sonar.

[0119] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the claims. [Explanation of symbols]

[0120] 21 Ultrasonic transducer 100 Fish finder (underwater finder) 101 Control circuit 103 Transmitting circuit 108 Transmitting current measuring circuit S01 Control pulse

Claims

1. A control circuit that outputs a control pulse; a transmission circuit that supplies a transmission signal corresponding to the control pulse to an ultrasonic transducer; A transmission current measuring circuit for measuring a transmission current supplied to the ultrasonic transducer, The control circuit includes: A waveform corresponding to an envelope of a transmission wave output from the ultrasonic transducer is obtained based on the transmission current measured by the transmission current measuring circuit; by correcting a pulse width of the control pulse, the difference between the acquired actual envelope waveform and an ideal envelope waveform is suppressed. An underwater detection device characterized by:

2. 2. The underwater detection device according to claim 1, the control circuit repeatedly performs the correction at least until the difference between the actual envelope waveform and the ideal envelope waveform falls within a predetermined threshold range for each of the control pulses. An underwater detection device characterized by:

3. 3. The underwater detection device according to claim 2, the control circuit corrects the pulse width of each of the control pulses by multiplying the difference by a coefficient smaller than 1 and larger than 0 in each correction. An underwater detection device characterized by:

4. 2. The underwater detection device according to claim 1, the control circuit calculates a moving average of the actual envelope waveform, and calculates the difference between the envelope waveform based on the moving average and the ideal envelope waveform. An underwater detection device characterized by:

5. 2. The underwater detection device according to claim 1, The ideal envelope waveform is a waveform of a window function that defines the transmission power of the ultrasonic transducer, the control circuit normalizes the envelope waveform acquired from the transmission current so as to be comparable to the waveform of the window function to calculate the actual envelope waveform, and calculates the difference between the calculated actual envelope waveform and the waveform of the window function. An underwater detection device characterized by:

6. 2. The underwater detection device according to claim 1, The control circuit outputs a plurality of the control pulses at a constant cycle during a transmission period of the transmission wave. An underwater detection device characterized by:

7. 2. The underwater detection device according to claim 1, The control circuit outputs a plurality of frequency-modulated control pulses during a transmission period of the transmission wave. An underwater detection device characterized by:

8. A control method for an underwater detection device including a transmission circuit that supplies a transmission signal corresponding to a control pulse to an ultrasonic transducer, and a transmission current measurement circuit that measures a transmission current supplied to the ultrasonic transducer, comprising: A waveform corresponding to an envelope of a transmission wave output from the ultrasonic transducer is obtained based on the transmission current measured by the transmission current measuring circuit; by correcting a pulse width of the control pulse, the difference between the acquired actual envelope waveform and an ideal envelope waveform is suppressed. A method for controlling an underwater detection device.

9. A control circuit for an underwater detection device, comprising: a control circuit for outputting a control pulse; a transmission circuit for supplying a transmission signal corresponding to the control pulse to an ultrasonic transducer; and a transmission current measurement circuit for measuring a transmission current supplied to the ultrasonic transducer. A function of acquiring a waveform corresponding to an envelope of a transmission wave output from the ultrasonic transducer based on the transmission current measured by the transmission current measuring circuit; A program for executing a function of suppressing a difference between the acquired actual envelope waveform and an ideal envelope waveform by executing correction of the pulse width of the control pulse.

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