Fish school detection device

Abstract

To provide a fish finder that can shorten a distance of the dead zone while improving detection performance.SOLUTION: A fish finder includes: first control means 21a that transmits an ultrasonic beam TB from a vibrator 16 at a fixed first frequency f0 for a first time T1 and controls the reflected wave to be received by the vibrator 16; and second control means 21b that, after the control by the first control means 21a, transmits the ultrasonic beam TB from the vibrator 16 while changing the frequency between a second frequency f2 and a third frequency f3 over a second time T2 longer than the first time T1 and controls the reflected wave to be received by the vibrator 16.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a fish school detecting device that displays a detection image based on a reception signal obtained by receiving a reflected wave of ultrasonic waves transmitted underwater.

Background Art

[0002] A fish school detecting device is known as a device that detects an object to be detected such as a fish school in water by transmitting and receiving ultrasonic waves (for example, Patent Document 1). The fish school detecting device is configured to transmit (irradiate) a thin beam-shaped ultrasonic wave toward the water or the bottom of the water from a vibrator disposed, for example, on the bottom of a ship, and the vibrator receives the reflected wave of the beam-shaped ultrasonic wave. The fish school detecting device forms a detection image indicating the presence position and the reflection intensity (level) of an object that has reflected the ultrasonic wave based on the reception signal obtained by the vibrator receiving the reflected wave, and displays it on a display device.

[0003] In order to improve the detection performance and increase the reflection intensity (level) from the object to be detected, it is necessary to increase the power (sound pressure) of the ultrasonic wave transmitted from the vibrator. As one method, increasing the amplitude of the ultrasonic wave can be mentioned, but there is a limit to the voltage that the vibrator can withstand. Therefore, a method of increasing the power of the ultrasonic wave by increasing the time (pulse length) of the ultrasonic wave transmitted from the vibrator is known.

[0004] By the way, as a method of transmitting ultrasonic waves from a vibrator, a pulse method has been conventionally known. The pulse method is a method of transmitting ultrasonic waves at a fixed frequency for a predetermined time (predetermined pulse length). In the pulse method, when the predetermined time is set to a long time in order to increase the power of the ultrasonic wave to be transmitted, the length (time) of the reflected wave reflected from the object to be detected also becomes long. Therefore, when a plurality of objects to be detected are approaching, the reflected waves reflected from each of them are mixed, and it becomes difficult to separate and display each object to be detected. Therefore, there are cases where it becomes difficult for the user of the fish school detecting device to accurately distinguish the object to be detected.

[0005] On the other hand, as another method of transmitting ultrasonic waves from a vibrator, there is a chirp method. The chirp method is a method of transmitting ultrasonic waves for a predetermined time while changing the frequency so that the frequency gradually increases or the frequency gradually decreases. Since the chirp method changes the frequency over time, a certain length is required as the predetermined time. Conversely, by making the predetermined time long, the power of the ultrasonic wave can be increased. Furthermore, since the frequency of the chirp method changes gradually, by setting the predetermined time to be long, even if the reflected waves from adjacent detection targets are mixed, the detection targets can be separated from the temporal deviation of the reflected frequencies.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in general fish school detection devices, many perform ultrasonic wave transmission and reception with a single vibrator. Even if ultrasonic waves are transmitted from the vibrator by the chirp method for a long time so as to accurately detect adjacent detection targets while increasing the reflection intensity from the detection targets, the following problems occur. That is, while the ultrasonic wave is being transmitted, the reflected wave from the detection target cannot be received at the vibrator. Therefore, a predetermined distance from the position where the vibrator is attached becomes a dead zone of the detection target, and it becomes impossible to detect the detection target. And, there is a problem that the longer the ultrasonic wave transmission time, the longer this dead zone becomes.

[0008] The present invention has been made to solve the above problems, and an object thereof is to provide a fish school detection device that can shorten the distance of the dead zone while improving the detection performance.

Means for Solving the Problems

[0009] To achieve this object, the fish school detecting device according to claim 1 includes a vibrator capable of transmitting ultrasonic waves into water and receiving reflected waves thereof, a forming means for forming a detection image based on a reception signal generated when the vibrator receives the reflected waves of the ultrasonic waves transmitted by the vibrator, a display means for displaying the detection image formed by the forming means, a first control means for transmitting the ultrasonic waves from the vibrator at a fixed first frequency for a first time, controlling the vibrator to receive the reflected waves of the ultrasonic waves, and ending the reception by the vibrator without waiting for the reflected waves of the ultrasonic waves from all of the set detection ranges, and a second control means for, after the control by the first control means, transmitting the ultrasonic waves from the vibrator while changing the frequency between a second frequency and a third frequency over a second time longer than the first time without waiting for the reflected waves of the ultrasonic waves from all of the detection ranges by the ultrasonic waves transmitted from the vibrator by the first control means, and controlling the vibrator to receive the reflected waves of the ultrasonic waves. , the forming means synthesizes the received signal generated by the oscillator under the control of the first control means and the received signal generated by the oscillator under the control of the second control means to form one of the detection images. At a position corresponding to the first depth, the received signal generated by the oscillator under the control of the first control means is more strongly reflected than the received signal generated by the oscillator under the control of the second control means. At a position corresponding to a second depth deeper than the first depth, the received signal generated by the oscillator under the control of the second control means is more strongly reflected than at the time of the position corresponding to the first depth, and the detection image is formed. It is provided with.

[0010] The fish school detecting device according to claim 2 is the fish school detecting device according to claim 1, wherein a third time for receiving a reflected wave by the control of the first control means is set to a time sufficient for receiving a reflected wave from a depth at which it is difficult to receive a reflected wave of the ultrasonic wave due to the ultrasonic wave being transmitted over the second time by the control of the second control means. Transmitted under the control of the second control means It is set to a time sufficient for receiving a reflected wave from a depth at which it is difficult to receive a reflected wave of the ultrasonic wave.

[0011] The fish school detecting device according to claim 3 is the fish school detecting device according to claim 2, wherein the third time is set to a time shorter than a fourth time for receiving a reflected wave by the control of the second control means.

[0012] The fish school detecting device according to claim 4 is the fish school detecting device according to any one of claims 1 to 3, wherein the first frequency is set outside the range of the second frequency to the third frequency.

[0013] The fish school detecting device according to claim 5 is the fish school detecting device according to claim 4, wherein the second frequency is set to a frequency higher than the second frequency and the third frequency.

[0014] The fish school detecting device according to claim 6 is the fish school detecting device according to claim 4 or 5, wherein the first frequency is set such that the reception sensitivity of the ultrasonic wave at the first frequency in the vibrator is lower than the reception sensitivity of the ultrasonic wave in the vibrator in the range from the second frequency to the third frequency.

Advantages of the Invention

[0016] According to the fish school detection device described in claim 1, first, under the control of the first control means, ultrasonic waves are transmitted from the vibrator at a fixed first frequency for a first time, and the reflected waves of the ultrasonic waves are received by the vibrator. At this time, the reception by the vibrator is terminated without waiting for the reflected waves of the ultrasonic waves from the entire set detection range. Next, after the control by the first control means, without waiting for the reflected waves from the entire detection range by the ultrasonic waves transmitted from the vibrator by the first control means, under the control of the second control means, the ultrasonic waves are transmitted from the vibrator while changing the frequency between a second frequency and a third frequency over a second time longer than the first time, and the reflected waves of the ultrasonic waves are received by the vibrator. Then, based on the reception signals generated when the vibrator receives these reflected waves, a detection image is formed by the forming means and displayed on the display means. Since the ultrasonic waves are transmitted for a second time longer than the first time under the control of the second control means, the intensity of the reflected waves can be increased. Also, since the ultrasonic waves are transmitted while the frequency is changing, even if the detection target is close, each detection target can be separated and displayed. Thus, the detection performance can be improved. On the other hand, in the transmission and reception of ultrasonic waves under the control of the first control means, since the ultrasonic waves are transmitted from the vibrator for only a first time shorter than the second time, the period during which the reflected waves cannot be received by the vibrator can be shortened. Therefore, the dead zone can be shortened. Also, since the transmission time of the ultrasonic waves transmitted by the first control means is short, even if the detection target is close, the mixing of the reflected waves from these detection targets can be suppressed, so each detection target can be separated and displayed. Furthermore, after the control by the first control means, without waiting for the reflected waves from the entire detection range by the ultrasonic waves transmitted from the vibrator by the first control means, the transmission of the ultrasonic waves under the control of the second control means and the reception of the reflected waves of the ultrasonic waves are performed, so the detection time related to the detection range can be shortened. Therefore, there is an effect that the distance of the dead zone can be shortened while improving the detection performance. In addition, the received signal generated by the oscillator under the control of the first control means and the received signal generated by the oscillator under the control of the second control means are synthesized by the forming means to form one detection image. At this time, at a position corresponding to a first depth with a shallow depth, the detection image is formed by more strongly reflecting the received signal generated by the oscillator under the control of the first control means than the received signal generated by the oscillator under the control of the second control means. On the other hand, at a position corresponding to a second depth with a deep depth, the detection image is formed by more strongly reflecting the received signal generated by the oscillator under the control of the second control means than at the time of the position corresponding to the first depth. As a result, there is an effect that a detection image with high detection performance and a short insensitive zone distance can be displayed on the display means.

[0017] According to the fish school detection device described in claim 2, in addition to the effects achieved by the fish school detection device described in claim 1, the following effects are achieved. That is, the third time for receiving the reflected wave under the control of the first control means is set to a time sufficient for receiving the reflected wave from a depth where it is difficult to receive the reflected wave of the ultrasonic wave when the ultrasonic wave is transmitted over the second time under the control of the second control means. Therefore, under the control of the second control means, the detection of the detection target in the dead zone where the transmission time of the ultrasonic wave is long and the distance is long can be surely performed by the transmission and reception of the ultrasonic wave under the control of the first control means, excluding the dead zone under the control of the first control means. Transmitted under the control of the second control means The third time for receiving the reflected wave under the control of the first control means is set to a time sufficient for receiving the reflected wave from a depth where it is difficult to receive the reflected wave of the ultrasonic wave when the ultrasonic wave is transmitted over the second time under the control of the second control means. Therefore, under the control of the second control means, the detection of the detection target in the dead zone where the transmission time of the ultrasonic wave is long and the distance is long can be surely performed by the transmission and reception of the ultrasonic wave under the control of the first control means, excluding the dead zone under the control of the first control means.

[0018] According to the fish school detection device described in claim 3, in addition to the effects achieved by the fish school detection device described in claim 2, the following effects are achieved. That is, in the control of the first control means, since it is not necessary to wait for the reflected wave from the entire detection range, the third time for receiving the reflected wave under the control of the first control means is set to a shorter time than the fourth time for receiving the reflected wave under the control of the second control means. Therefore, there is an effect that the detection time related to the detection range can be shortened as compared with the case of simply transmitting and receiving the ultrasonic wave in two methods.

[0019] According to the fish school detection device described in claim 4, in addition to the effects achieved by the fish school detection device described in any one of claims 1 to 3, the following effects are achieved. That is, since the first frequency of the ultrasonic wave transmitted under the control of the first control means is set outside the range from the second frequency to the third frequency of the ultrasonic wave transmitted under the control of the second control means, when receiving the reflected wave with the vibrator in the control of the second control means, there is an effect that it is possible to suppress the reflected wave of the ultrasonic wave transmitted under the control of the first control means from being superimposed and displayed as noise.

[0020] According to the fish school detection device described in claim 5, in addition to the effects achieved by the fish school detection device described in claim 4, the following effects are achieved. That is, the first frequency of the ultrasonic wave transmitted under the control of the first control means is set to a frequency higher than the second frequency and the third frequency of the ultrasonic waves transmitted under the control of the second control means. When the frequency of the ultrasonic wave is high, the number of times the reflected wave received inside the vibrator is reflected within the same time increases. Since the ultrasonic wave has a large energy loss at the reflecting surface, the amount of energy attenuation per unit time increases. Here, in the receiving circuit of the vibrator, generally a protection circuit is provided in the first stage, and while the voltage generated by the vibrator receiving the reflected wave exceeds a safe level voltage, it is prevented from propagating to the subsequent circuit by that protection circuit, and that period also becomes a dead zone. By setting the first frequency to a high frequency, the energy of the reflected wave received by the vibrator attenuates quickly, so the voltage generated by the reception also attenuates early, and thus there is an effect that the period of the dead zone due to the operation of the protection circuit can be shortened.

[0021] According to the fish school detection device described in claim 6, in addition to the effects achieved by the fish school detection device described in claim 4 or 5, the following effects are achieved. That is, the first frequency is set so that the reception sensitivity of the ultrasonic wave of the first frequency transmitted under the control of the first control means in the vibrator is lower than the reception sensitivity of the ultrasonic wave in the vibrator within the range from the second frequency to the third frequency transmitted under the control of the second control means. In the control of the first control means, since the reflected wave from the detection range with a shallow depth that becomes a dead zone by the control of the second control means is received, it functions effectively even if the reception sensitivity of the vibrator is low. Therefore, as the vibrator to be used, there is an effect that a narrow one with a high reception sensitivity region including at least the second frequency to the third frequency can be used. Also, since the reception sensitivity of the first frequency in the vibrator is low, the voltage obtained by the reception is low, and thus there is an effect that the period of the dead zone due to the operation of the above-described protection circuit can be shortened.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings. Note that all of the embodiments described below show preferred specific examples of the present invention. Therefore, the numerical values, shapes, materials, components, arrangement positions of the components, connection forms, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. Therefore, among the components in the following embodiments, the components not described in the independent claims indicating the most general concept of the present invention are described as arbitrary components. Also, in each figure, substantially the same configuration is denoted by the same reference numeral, and duplicate explanations are omitted or simplified.

[0025] First, with reference to FIGS. 1 and 2, the schematic configuration of a fish school detection device 12 according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram schematically showing the configuration of the fish school detection device 12, and FIG. 2 is a schematic diagram showing from the side the state when detection in water is performed by a ship 11 on which the fish school detection device 12 is mounted.

[0026] As shown in FIGS. 1 and 2, the fish school detection device 12 is mounted on the ship 11 and detects a detection target object G such as a fish school in the water directly below or around the ship 11. The fish school detection device 12 includes a main body 13, an operation button 14 provided on the main body 13 for receiving an input from a user, a display device 15 integrally formed with the main body 13, and a vibrator 16 for transmitting and receiving an ultrasonic beam TB.

[0027] The vibrator 16 is fixed to the bottom or the stern of the ship 11 and is electrically connected to the main body 13 by a cable. The vibrator 16 transmits (irradiates) a thin beam-shaped ultrasonic beam TB in one direction (for example, directly downward of the ship 11) by a signal transmitted from the transmission circuit 30 (see FIG. 3) of the main body 13. Further, the vibrator 16 receives a reflected wave of the ultrasonic beam TB reflected from a detection target object G or the bottom of the water such as the seabed, the lake bottom, the river bottom, or the pond bottom, and transmits a received signal obtained by the reception to the reception circuit 31 (see FIG. 3) of the main body 13.

[0028] Here, a vibrator 16 having the best characteristics at the frequency of the ultrasonic beam TB transmitted by the chirp method (in this embodiment, 130 to 220 kHz), which will be described later, is used. In other words, the frequency of the ultrasonic beam TB in the chirp method is set to a frequency at which the reception sensitivity of the vibrator 16 is high. On the other hand, the frequency of the ultrasonic beam TB transmitted by the pulse method (in this embodiment, 240 kHz), which will be described later, is set to a frequency at which the reception sensitivity of the vibrator 16 is low.

[0029] The main body 13 of the fish school detection device 12 is arranged, for example, in the steering room of the ship 11. Based on the received signal obtained when the vibrator 16 receives the reflected wave of the ultrasonic beam TB, a detection image is formed, and the detection result in the water is shown to the user by displaying this detection image on the display device 15.

[0030] Next, with reference to FIG. 3, the functional configuration of the fish school detection device 12 will be described. FIG. 3 is a block diagram showing the functional configuration of the fish school detection device 12. The fish school detection device 12 has a control device 20 inside the main body 13. The control device 20 controls the operation of the fish school detection device 12, and is configured to include at least a CPU (Central Processing Unit) as an arithmetic processing device (not shown), a ROM (Read Only Memory) or / and a flash memory which are non-volatile memories, and a RAM (Random Access Memory) which is a volatile memory.

[0031] Based on program data, fixed value data, etc. stored in the ROM or / and flash memory, the CPU temporarily stores various data in the RAM, and controls the operation of the fish school detection device 12 while reading the data. By the operation of this CPU, the control device 20 functions as an ultrasonic control means 21 and a forming means 24. Also, by its operation, the CPU causes the RAM to function as a pulse reception buffer 22 and a chirp reception buffer 23.

[0032] In addition to being connected to the above-described operation button 14 and display device 15, the control device 20 is connected to a transmission circuit 30 and a reception circuit 31 provided inside the main body 13, and the vibrator 16 is controlled by the control device 20 via the transmission circuit 30 and the reception circuit 31.

[0033] Based on an input from the user by the operation button 14 (for example, the detection range (detection depth) of the detection target G, etc.), the ultrasonic control means 21 controls the vibrator 16 via the transmission circuit 30 and the reception circuit 31 so as to transmit and receive an ultrasonic beam TB under predetermined conditions from the vibrator 16.

[0034] Here, in the fish school detection device 12 of the present embodiment, in one detection, the ultrasonic beam TB is controlled to be sequentially transmitted and received in two methods. That is, the ultrasonic control means 21 has a first control means 21a and a second control means 21b. First, the first control means 21a transmits and receives the ultrasonic beam TB in a pulse method, and then the second control means 21b controls the vibrator 16 to transmit and receive the ultrasonic beam TB in a chirp method.

[0035] Here, with reference to FIG. 4, the ultrasonic beam TB in the pulse method and the ultrasonic beam TB in the chirp method will be described. FIG. 4(a) is a diagram schematically showing the waveform of the ultrasonic beam TB transmitted in the pulse method, and FIG. 4(b) is a diagram schematically showing the waveform of the ultrasonic beam TB transmitted in the chirp method. Note that in FIGS. 4(a) and (b), the scales of the time axis (horizontal axis) and the intensity axis (vertical axis) of the waveforms are made different from each other in order to clearly show the characteristics of the ultrasonic beam TB of each method.

[0036] As shown in FIG. 4(a), the ultrasonic beam TB in the pulse method has its frequency fixed at the first frequency f1 and is transmitted through the transmission circuit 30 to control the vibrator 16 so as to be transmitted for the first time T1. In the first control means 21a according to the present embodiment, 240 kHz is set as the first frequency f1, and 100 microseconds is set as the first time T1. Then, after transmitting the ultrasonic beam TB in such a pulse method, the first control means 21a controls the receiving circuit 31 to receive the reflected wave from the detection object G with the vibrator 16 for the third time (10 milliseconds in the present embodiment).

[0037] That is, in the ultrasonic beam TB in the pulse method, the range up to 7.5 cm (= speed of sound 1500 m / s × 100 microseconds ÷ 2 (round trip of the ultrasonic beam TB)) from the vibrator 16 becomes the dead zone due to the transmission of the ultrasonic beam TB, and the detection object G is detected in the range of approximately 7.5 cm to 7.5 m (= 1500 m / s × 10 milliseconds ÷ 2) from the vibrator 16.

[0038] On the other hand, as shown in Fig. 4(b), the chirp-type ultrasonic beam TB is transmitted through the transmission circuit 30 so that the frequency gradually increases between the second frequency f2 and the third frequency f3 and is transmitted for the second time period T2. In the second control means 21b according to the present embodiment, 130 kHz is set as the second frequency f2, 220 kHz is set as the third frequency f3, and 5 milliseconds is set as the second time period T2.

[0039] Then, after transmitting such a chirp-type ultrasonic beam TB, the second control means 21b controls the receiving circuit 31 so that the reflected wave from the detection target G is received by the vibrator 16 for the fourth time period. This fourth time period is set according to the detection range (detection depth) set by the user operating the operation button 14.

[0040] That is, in the chirp-type ultrasonic beam TB, the range up to a distance of 3.75 m (= 1500 m / s × 5 milliseconds ÷ 2) from the vibrator 16 becomes a dead zone due to the transmission of the ultrasonic beam TB, and the detection target G is detected in the range from approximately 3.75 m from the vibrator 16 to the detection depth set by the user.

[0041] Note that the fish school detection device 12 according to the present embodiment is configured such that the detection range (detection depth) set by the user is set to a depth deeper than the maximum depth of 7.5 m that can be detected under the control of the first control means 21a.

[0042] However, it is of course possible to configure the detection range (detection depth) set by the user to be shallower than the maximum depth of 7.5 m that can be detected under the control of the first control means 21a. In this case, when the detection range (detection depth) set by the user is shallower than the maximum depth of 7.5 m that can be detected under the control of the first control means 21a, the detection of the detection target G may be performed only by the control of the first control means 21a, that is, by using only the pulse-type ultrasonic beam TB.

[0043] Also, in FIG. 4(b), the chirp-type ultrasonic beam TB whose frequency gradually increases between the second frequency f2 and the third frequency f3 was described. However, as the chirp-type ultrasonic beam TB, one whose frequency gradually decreases between the third frequency f3 and the second frequency f2 may be adopted.

[0044] The transmission circuit 30 is a circuit that drives and controls the vibrator 16 so as to transmit the ultrasonic beam TB.

[0045] For example, when the transmission circuit 30 is instructed from the first control means 21a on the pulse mode as the transmission mode, 240 kHz as the transmission frequency, 100 microseconds as the transmission time, and other transmission conditions (for example, amplitude, etc.), while following these conditions, the vibrator 16 is driven and controlled so as to transmit the pulse-type ultrasonic beam TB with a frequency of 240 kHz for 100 microseconds.

[0046] Also, when the transmission circuit 30 is instructed from the second control means 21b on the chirp mode as the transmission mode, 130 to 220 kHz as the transmission frequency, 5 milliseconds as the transmission time, and other transmission conditions, while following these conditions, the vibrator 16 is driven and controlled so as to transmit the chirp-type ultrasonic beam TB whose frequency gradually increases between 130 kHz and 220 kHz for 5 milliseconds.

[0047] The receiving circuit 31 is a circuit that receives a received signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB from the vibrator 16 and transmits it to the control device 20. When viewed from the vibrator 16, a protection circuit (not shown) is provided at the first stage of the receiving circuit 31. While the voltage of the received signal generated when the vibrator 16 receives the reflected wave exceeds a safe level voltage, it is prevented from propagating to the subsequent circuits by that protection circuit, protecting the entire control device 20. That is, the period during which the received signal does not propagate to the public institution's circuit due to the operation of the protection circuit also becomes a dead zone. The received signal that has propagated through the protection circuit is amplified by an amplification circuit (not shown) provided in the receiving circuit, converted into a digital signal by an AD conversion circuit (not shown) also provided in the receiving circuit, and transmitted to the control device 20.

[0048] After the transmission of the ultrasonic beam TB from the vibrator 16 is completed under the control of the transmission circuit 30, the receiving circuit 31 transmits a received signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB to the control device 20 at the time instructed by the first control means 21a or the second control means 21b.

[0049] That is, when the ultrasonic beam TB of the pulse method is transmitted from the vibrator 16 by the first control means 21a, a received signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB within 10 milliseconds after the transmission is received by the receiving circuit 31 and transmitted to the control device 20.

[0050] Also, when the ultrasonic beam TB of the chirp method is transmitted from the vibrator 16 by the second control means 21b, a received signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB is received by the receiving circuit 31 and transmitted to the control device 20 at a time set according to the detection range (detection depth) set by the user operating the operation button 14 after the transmission.

[0051] The pulse reception buffer 22 is a memory that stores, for each depth, the intensity of the reflected wave from each depth calculated based on the reception signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB in pulse mode. When the control device 20 receives the reception signal from the vibrator 16 via the reception circuit 31 based on the control of the first control means 21a, it calculates the intensity of the reflected wave from each depth based on the reception signal, and stores the calculated intensity in the pulse reception buffer 22 for each depth.

[0052] The chirp reception buffer 23 is a memory that stores, for each depth, the intensity of the reflected wave from each depth calculated based on the reception signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB in chirp mode. When the control device 20 receives the reception signal from the vibrator 16 via the reception circuit 31 based on the control of the first control means 21a, it calculates the intensity of the reflected wave from each depth based on the reception signal, and stores the calculated intensity in the chirp reception buffer 23 for each depth.

[0053] The forming means 24 forms a detection image to be displayed on the display device 15 based on the reception signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB. In the present embodiment, the intensity of the reflected wave from each depth obtained by transmitting and receiving the ultrasonic beam TB in pulse mode (hereinafter referred to as "pulse-side intensity") stored in the pulse reception buffer 22 and the intensity of the reflected wave from each depth obtained by transmitting and receiving the ultrasonic beam TB in chirp mode (hereinafter referred to as "chirp-side intensity") stored in the chirp reception buffer 23 are combined to form a detection image.

[0054] The combining process is performed, for example, by alpha-blending the pulse-side intensity P1(d) and the chirp-side intensity P2(d) at the depth d for each depth according to the following formula (1).

[0055] P(d)=α(d)×P1(d)+(1-α(d))×P2(d) ···(1) Here, P(d) is the intensity of the reflected wave after synthesis at depth d. α(d) is an α value defined by a value between 0 and 1 for each depth d.

[0056] For the depth d located in the dead zone in the chirp-type ultrasonic beam TB transmitted and received under the control of the second control means 21b, "1" is set for the α value. That is, for the depth d located in the dead zone, the pulse-side intensity P1(d) remains as the intensity P(d) of the reflected wave at that depth d. In this embodiment, since the chirp-type ultrasonic beam TB is transmitted from the vibrator 16 for 5 milliseconds, as described above, the distance of 3.75 m from the vibrator 16 is the dead zone.

[0057] On the other hand, for a deep depth d at which the reflected wave of the pulse-type ultrasonic beam TB cannot be received due to the reception time (third time) set by the control of the first control means 21a, the α value is set to "0", and the chirp-side intensity P2(d) remains as the intensity P(d) of the reflected wave at that depth d. In this embodiment, since the reception time (third time) of the reflected wave of the pulse-type ultrasonic beam TB is 10 milliseconds, the α value is set to "0" for a depth d of 7.5 m or more from the vibrator 16.

[0058] Then, from the deepest depth d1 (3.75 m) of the dead zone in the chirp-type ultrasonic beam TB to the deepest depth d2 (7.5 m) at which the reflected wave of the pulse-type ultrasonic beam TB is received, the reflected wave is received by both methods. Therefore, the α(d) which is the α value corresponding to each depth d is determined by the following equation (2).

[0059] α(d) = (d2 - d) / (d2 - d1) ··· (2) Thus, by determining the α value α(d) at the depth d from the deepest depth d1 (3.75 m) of the dead zone in the chirp-type ultrasonic beam TB to the deepest depth d2 (7.5 m) at which the reflected wave of the pulse-type ultrasonic beam TB is received by Equation (2), it becomes possible to smoothly connect the detection image formed based on the reflected wave of the pulse-type ultrasonic beam TB of a different method and the detection image formed based on the reflected wave of the chirp-type ultrasonic beam TB, and it is possible to suppress the display of streaks due to the difference in methods in the detection image.

[0060] Next, with reference to FIG. 5, the fish school detection process executed by the control device 20 will be described. FIG. 5 is a flowchart showing the fish school detection process. The fish school detection process is started after the initial settings of each device constituting the fish school detection device 12 are performed when the power of the fish school detection device 12 is turned on, and is continuously executed until the power of the fish school detection device 12 is turned off.

[0061] When starting the fish school detection process, the control device 20 first executes a pulse mode transmission / reception process (S1). The control device 20 that executes this pulse mode transmission / reception process functions as the first control means 21a of the fish school detection device 12.

[0062] In this pulse mode transmission / reception process, the transmission circuit 30 is instructed as follows: the transmission mode is the pulse mode, the transmission frequency is 240 kHz, the transmission time is 100 microseconds, and other transmission conditions (for example, amplitude, etc.). Based on this instruction, the transmission circuit 30 drives the vibrator 16, and a pulse-type ultrasonic beam TB with a frequency of 240 kHz is transmitted for 100 microseconds.

[0063] Also, in the pulse mode transmission and reception process, after the transmission of the ultrasonic beam TB in pulse mode by the vibrator 16 is completed, the receiving circuit 31 is instructed to set 10 milliseconds as the reception time of the reflected wave of the ultrasonic beam TB. As a result, the receiving circuit 31 receives, from the vibrator 16, the received signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB for 10 milliseconds, and transmits the received signal to the control device 20. Then, based on the received signal transmitted from the receiving circuit 31, the pulse mode transmission and reception process calculates the intensity of the reflected wave from each depth, and stores the calculated intensity in the pulse reception buffer 22 for each depth.

[0064] Next, the control device 20 executes the chirp mode transmission and reception process (S2). The control device 20 that executes this chirp mode transmission and reception process functions as the second control means 21b of the fish finder 12.

[0065] In this chirp mode transmission and reception process, the transmission circuit 30 is instructed to use the chirp mode as the transmission mode, 130 to 220 kHz as the transmission frequency, 5 milliseconds as the transmission time, and other transmission conditions (such as amplitude, etc.). Based on this instruction, when the transmission circuit 30 drives the vibrator 16, a chirp ultrasonic beam TB with a gradually increasing frequency between 130 kHz and 220 kHz is transmitted for 5 milliseconds.

[0066] Also, in the chirp mode transmission and reception process, after the transmission of the chirp ultrasonic beam TB by the vibrator 16 is completed, the receiving circuit 31 is instructed to set a time corresponding to the detection range (detection depth) set by the user operating the operation button 14 as the reception time of the reflected wave of the ultrasonic beam TB. As a result, the receiving circuit 31 receives, from the vibrator 16, the received signal generated when the vibrator 16 receives the reflected wave of the ultrasonic beam TB for the set time, and transmits the received signal to the control device 20. Then, based on the received signal transmitted from the receiving circuit 31, the chirp mode transmission and reception process calculates the intensity of the reflected wave from each depth, and stores the calculated intensity in the chirp reception buffer 23 for each depth.

[0067] Next, the control device 20 executes a synthesis process (S3). The control device 20 that executes this synthesis process functions as the forming means 24 of the fish school detection device 12.

[0068] As described above, in the synthesis process, for each depth, the pulse-side intensity P1(d) stored in the pulse reception buffer 22 at the depth d and the chirp-side intensity P2(d) stored in the chirp reception buffer 23 are alpha-blended using the formula (1) to form a detection image.

[0069] After the synthesis process, the control device 20 displays the detection image formed based on the synthesis process on the display device 15 (S4), and returns to the process of S1. Then, the control device 20 repeatedly executes the processes of S1 to S4.

[0070] By executing this fish school detection process, the control device 20 exhibits the following operational effects.

[0071] (A) Under the control of the second control means 21b, the chirp-type ultrasonic beam TB is transmitted over a second time T2 (5 milliseconds), which is longer than the first time T1 (100 microseconds) during which the pulse-type ultrasonic beam TB is transmitted. Therefore, the intensity (level) of the reflected wave can be increased. Also, in the chirp method, since the ultrasonic beam TB is transmitted while the frequency changes, even if the transmission time of the ultrasonic beam TB is increased and the reflected waves from adjacent detection objects G are mixed, each detection object G can be separated and displayed based on the temporal shift of the reflected frequencies. Thus, the detection performance can be improved.

[0072] On the other hand, in the transmission and reception of the pulse-type ultrasonic beam TB under the control of the first control means 21a, the oscillator 16 transmits for only the first time T1 (100 microseconds), which is shorter than the second time T2 during which the chirp-type ultrasonic beam TB is transmitted. Therefore, the period during which the reflected wave cannot be received by the oscillator 16 can be shortened. Thus, the insensitive zone where the detection object G cannot be detected can be shortened to 7.5 cm.

[0073] In addition, since the transmission time of the pulsed ultrasonic beam TB is short, even if the detection target object G is in the vicinity, it is possible to suppress the mixing of the reflected waves from these detection target objects G, so each detection target object G can be separated and displayed.

[0074] From the above, the fish school detection device 12 can shorten the distance of the dead zone while improving the detection performance.

[0075] (A) The second time T2 during which the chirp-type ultrasonic beam TB is transmitted under the control of the second control means 21b is set to 5 milliseconds, while the third time for receiving the reflected wave of the pulsed ultrasonic beam TB under the control of the first control means 21a is set to 10 milliseconds. That is, the third time for receiving the reflected wave of the pulsed ultrasonic beam TB under the control of the first control means 21a is set to a time sufficient to receive the reflected wave from a depth at which it is difficult to receive the reflected wave due to the long transmission time of the ultrasonic beam TB transmitted over the second time T2 by the control of the second control means 21b. Therefore, due to the control of the second control means 21b, the detection of the detection target object G in the dead zone where the distance is long due to the long transmission time of the ultrasonic beam TB can be surely performed by the transmission and reception of the ultrasonic beam TB under the control of the first control means 21a, excluding the dead zone under the control of the first control means 21a.

[0076] (C) In the control of the first control means 21a, without waiting for the reflected waves from all the detection ranges (detection depths) set by the user operating the operation button 14, the third time (10 milliseconds) for receiving the reflected wave under the control of the first control means 21a is set to a shorter time than the fourth time (time corresponding to the search range (search depth > 7.5 m) set by the user > 10 milliseconds) for receiving the reflected wave under the control of the second control means 21b. Therefore, compared with the case of simply transmitting and receiving the ultrasonic beam TB in two modes, the detection time related to the detection range can be shortened.

[0077] (E) The first frequency f1 (240 kHz) of the pulsed ultrasonic beam TB transmitted under the control of the first control means 21a is set outside the range from the second frequency f2 (130 kHz) to the third frequency f3 (220 kHz) of the chirped ultrasonic beam TB transmitted under the control of the second control means 21b. Thereby, when the reflected wave is received by the vibrator 16 under the control of the second control means 21b, it is possible to suppress the reflected wave of the ultrasonic beam TB transmitted under the control of the first control means 21a from being superimposed and displayed as noise.

[0078] (O) The first frequency f1 (240 kHz) of the pulsed ultrasonic beam TB transmitted under the control of the first control means 21a is set to a frequency higher than the second frequency f2 (130 kHz) and the third frequency f3 (220 kHz) of the chirped ultrasonic beam TB transmitted under the control of the second control means 21b. When the frequency of the ultrasonic beam TB is high, the number of times the reflected wave received inside the vibrator 16 is reflected increases within the same time. Since the ultrasonic beam TB has a large energy loss at the reflecting surface, the amount of energy attenuation per unit time increases. Here, a protection circuit is provided in the receiving circuit 31 of the vibrator 16 so that the voltage generated when the vibrator 16 receives the reflected wave does not propagate to the subsequent circuit by that protection circuit while exceeding a safe level voltage, and that period also becomes a dead zone. By setting the first frequency f1 to a high frequency, the energy of the reflected wave received by the vibrator 16 attenuates quickly, so the voltage generated by the reception also attenuates early, and there is an effect that the period of the dead zone due to the operation of the protection circuit can be shortened.

[0079] The first frequency f1 is set such that the reception sensitivity of the transducer 16 of the pulsed ultrasonic beam TB of the first frequency f1 (240 kHz) transmitted under the control of the first control means 21a is lower than the reception sensitivity of the transducer 16 of the chirp ultrasonic beam TB in the range from the second frequency f2 (130 kHz) to the third frequency f3 (220 kHz) transmitted under the control of the second control means 21b. In the control of the first control means 21a, since the reflected wave from the detection range with a shallow depth that becomes the dead zone under the control of the second control means 21b is received, it functions effectively even if the reception sensitivity of the transducer 16 is low. Therefore, as the transducer 16 to be used, one with a high reception sensitivity region that is narrow and includes at least the second frequency f2 to the third frequency f3 can be used. Further, since the reception sensitivity of the first frequency f1 in the transducer 16 is low, the voltage obtained by reception becomes low, so there is an effect that the period of the dead zone due to the operation of the protection circuit provided in the reception circuit 31 can also be shortened.

[0080] (C) The forming means (synthesis process) 24 strongly reflects the reception signal generated by the reception of the transducer 16 under the control of the first control means 21a rather than the reception signal generated by the reception of the transducer 16 under the control of the second control means 21b at a shallow depth, for example, at the position of the first depth, to form a detection image. On the other hand, the forming means (synthesis process) 24 strongly reflects the reception signal generated by the reception of the transducer 16 under the control of the second control means 21b rather than the reception signal generated by the reception of the transducer 16 under the control of the first control means 21a at the position of the second depth deeper than the first depth, to form a detection image. Thereby, a detection image with high detection performance and a short dead zone distance can be displayed on the display means.

[0081] The present invention has been described based on the embodiments. However, the present invention is not limited to the above embodiments at all, and it can be easily inferred that various improvements and modifications are possible without departing from the spirit of the present invention. For example, each embodiment may be configured by modifying the embodiment by adding a part or a plurality of parts of the configuration of another embodiment to the embodiment or replacing a part or a plurality of parts of the configuration of the embodiment. Further, the numerical values given in the above embodiments are merely examples, and it is of course possible to adopt other numerical values.

[0082] In the above embodiment, the case where the first frequency f1 of the pulsed ultrasonic beam TB transmitted under the control of the first control means 21a is set to a frequency higher than the second frequency f2 and the third frequency f3 of the chirped ultrasonic beam TB transmitted under the control of the second control means 21b has been described. However, even if the first frequency f1 is set to a frequency lower than the second frequency f2 and the third frequency f3, it goes without saying that it is sufficient if there is no practical problem in the extension of the dead zone based on the operation of the protection circuit due to the lower frequency.

[0083] In the above embodiment, the case where the present invention is applied to a fish school detection device that transmits the ultrasonic beam TB fixed in one direction (directly below the ship 11) in water, receives the reflected wave, and performs detection in water has been described. However, the present invention is not necessarily limited to this. For example, the present invention may be applied to a sonar-type fish school detection device that performs detection in water over a predetermined range while changing the transmission direction of the ultrasonic beam TB transmitted in one direction.

Explanation of Reference Numerals

[0084] 12 Fish school detection device 15 Display device (display means) 16 Vibrator 21 Ultrasonic control means 21a First control means 21b Second control means 24 Forming means f1 First frequency f2 Second frequency f3 Third frequency T1 First time T2 Second time

Claims

1. A vibrator capable of transmitting ultrasonic waves into water and receiving the reflected waves thereof, a forming means for forming a detection image based on a reception signal generated when the vibrator receives a reflected wave of the ultrasonic wave transmitted by the vibrator, a display means for displaying the detection image formed by the forming means, a first control means for transmitting the ultrasonic wave from the vibrator at a fixed first frequency for a first time, controlling the vibrator to receive the reflected wave of the ultrasonic wave, and ending the reception by the vibrator without waiting for the reflected waves of the ultrasonic wave from all the set detection ranges, after the control by the first control means, without waiting for the reflected waves from all the detection ranges by the ultrasonic wave transmitted from the vibrator by the first control means, transmitting the ultrasonic wave from the vibrator while changing the frequency between a second frequency and a third frequency over a second time longer than the first time, and controlling the vibrator to receive the reflected wave of the ultrasonic wave, and the forming means synthesizes a reception signal generated when the vibrator receives by the control of the first control means and a reception signal generated when the vibrator receives by the control of the second control means to form one detection image, and at a position corresponding to a first depth, reflects more strongly the reception signal generated when the vibrator receives by the control of the first control means than the reception signal generated when the vibrator receives by the control of the second control means, and at a position corresponding to a second depth deeper than the first depth, reflects more strongly the reception signal generated when the vibrator receives by the control of the second control means than when at the position corresponding to the first depth, to form the detection image. A fish school detection device characterized by this.

2. The third time for receiving the reflected wave by the control of the first control means is set to a time sufficient for receiving the reflected wave from a depth at which it is difficult to receive the reflected wave of the ultrasonic wave transmitted by the control of the second control means when the ultrasonic wave is transmitted over the second time by the control of the second control means. The fish school detection device according to Claim 1, characterized by this.

3. The fish school detection device according to Claim 2, characterized in that the third time is set to a time shorter than a fourth time for receiving the reflected wave by the control of the second control means.

4. The fish school detection device according to any one of claims 1 to 3, wherein the first frequency is set outside the range from the second frequency to the third frequency.

5. The fish school detection device according to claim 4, wherein the first frequency is set to a frequency higher than the second frequency and the third frequency.

6. The fish school detection device according to claim 4 or 5, wherein the first frequency is set such that the reception sensitivity of the ultrasonic wave at the vibrator of the first frequency is lower than the reception sensitivity of the ultrasonic wave at the vibrator within the range from the second frequency to the third frequency.

Images