Liquid surface vibration detection sensor, liquid surface vibration detection unit, liquid surface vibration monitoring device, and liquid surface vibration monitoring method

Abstract

To provide a liquid surface vibration detection sensor and a liquid surface vibration detection unit for detecting vibrations of a liquid surface, and a liquid surface vibration monitoring device and a liquid surface vibration monitoring method for monitoring the status of targets such as aquaculture fish activity and aquaculture facilities on the basis of the detected vibrations.SOLUTION: The liquid surface vibration monitoring device includes: a liquid surface vibration detection sensor 10 that vertically irradiates a liquid surface 80 at predetermined intervals with elliptically polarized light 61, and focuses reflected light 62 slightly offset from the center of a light-receiving element 13 to output an electrical signal corresponding to the intensity of the reflected light 61 as a vibration signal of the liquid surface; and a liquid surface vibration detection unit 20 that controls the liquid surface vibration detection sensor 10 to continuously activate a light source 11 at a fixed cycle, and continuously outputs the vibration signal output from the light-receiving element 13 as a vibration waveform detection signal. The liquid surface vibration monitoring device analyzes the detection signal and monitors the status of the target via liquid surface vibrations by comparing the vibration waveform and vibration pattern of the liquid surface 80 with a threshold or a predetermined pattern obtained in advance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a liquid surface vibration detection sensor and a liquid surface vibration detection unit that detect the fluctuation or vibration of a liquid surface, and also to a liquid surface vibration monitoring device (system) and a liquid surface vibration monitoring method that use this liquid surface vibration detection unit to monitor various conditions reflected in the vibration of the liquid surface. As a specific example, it is useful to apply the present invention as a monitoring device (system) and a monitoring method for monitoring and managing land-based fish farming using aquariums. [Background technology]

[0002] We investigated the prior art for technology that detects and actively utilizes vibrations on the liquid surface. However, we were unable to find any prior art that actively utilizes vibration signals from the liquid surface to monitor anything other than the liquid in question. The monitoring technology of the present invention, which monitors various monitoring targets based on the swaying of the liquid surface, can be used in a variety of industrial fields, but in the following explanation, the background art and embodiments of the present invention will be described using an example in which the present invention is applied to the management of tanks and facilities in land-based fish farming, which is one of the fields currently most applicable and is one of the useful applications of the liquid surface vibration unit of the present invention. However, this does not mean that the scope of application of the present invention is limited to land-based aquaculture and fish farming.

[0003] In recent years, aquaculture has become an important industry in the fishing industry from the perspective of ensuring a stable supply of food and protecting resources. Currently, aquaculture is mainly carried out in the ocean, but issues such as water temperature control due to global warming and marine pollution caused by the feeding involved in aquaculture have become problems, and land-based aquaculture businesses are attracting attention. Although land-based aquaculture technology still has various problems, it is expected that research will continue in the future with the aim of fully land-based aquaculture, and stable land-based aquaculture technology will be established.

[0004] In land-based aquaculture, it is necessary to constantly monitor the growth and activity of fish and whether the aquaculture equipment is operating normally, and to appropriately control and manage the aquaculture conditions. For example, a method has been disclosed in which, in order to monitor the water quality of the aquarium, the fish in the aquarium are photographed using video and the activity of the fish is analyzed from the video images.

[0005] However, in actual land-based aquaculture, there is no established aquaculture monitoring technology, and the majority of the monitoring and management of the fish condition is currently done manually. Specifically, manual management is carried out by people periodically patrolling the tanks and visually checking for any abnormalities.

[0006] Conventional techniques for detecting swaying of the water surface include those using a flow meter floating on the water surface, an accelerometer, a Doppler vibrometer, etc. However, while there are many conventional techniques for measuring liquid level or water level using flow (see, for example, Patent Documents 1 and 2), there are no techniques for measuring or detecting vibrations of the liquid surface. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 01-187417 [Patent Document 2] Japanese Patent Application Publication No. 2018-197728 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, there are still many challenges to overcome before land-based fish farming technology can be put to practical use. For example, the method of managing fish in tanks by taking videos and analyzing the images mentioned above requires analyzing the images of the video footage of the fish's condition in the water, which takes time. Furthermore, because the ecology of farmed fish during land-based farming is not well understood, it is still difficult to accurately analyze the condition of the fish using image analysis alone.

[0009] On the other hand, manual monitoring and management, which involves periodically patrolling the tanks and visually checking for abnormalities, makes it difficult to detect abnormal conditions early, and by the time an abnormality becomes apparent, it is likely to be too late. Furthermore, when people walk around the tanks to patrol, the vibrations and human shadows are stressful for the farmed fish. Therefore, from the perspectives of labor saving and reducing stress on the fish, quiet and accurate monitoring without human intervention is desirable.

[0010] Currently, a variety of different sensors and devices, such as temperature sensors, water quality sensors, and devices for monitoring equipment operation status and intrusion, are used for various purposes, such as managing aquaculture equipment and water quality, monitoring aquaculture areas, and studying fish ecology, and not only is the introduction of these multiple sensors and devices costly, but operation and management are also complicated. Therefore, there is a need for sensors and detection devices that have a simple structure and can accurately monitor equipment status, fish behavior, etc., simultaneously.

[0011] Therefore, the inventors of the present invention focused on the vibration of the liquid surface and developed a sensor that can accurately detect and output the vibration of the liquid surface, and by analyzing the vibration state of the liquid surface, it is possible to monitor the desired monitoring target that is the cause of the vibration. By using this liquid surface vibration sensor that can accurately detect minute vibrations of the liquid surface, it has become possible to monitor the desired monitoring target via the vibration of the liquid surface in industries that use liquid as an essential medium or in technical fields that manage the liquid itself. For example, by monitoring the vibration state of the water surface of an aquarium using the output of a liquid surface vibration detection unit that uses a liquid surface vibration detection sensor, it is possible to monitor the condition of farmed fish growing and moving in the water inside the aquarium, and the operating status of the management equipment (water quality control equipment, oxygen concentration maintenance equipment, etc.) to determine whether it is operating normally.

[0012] In order to detect fluctuations in the liquid surface, such as the water surface, devices that measure the distance to the water surface, such as a flow meter floating on the water surface, have difficulty detecting minute fluctuations or vibrations in the liquid surface, and are therefore not suitable for detecting small water surface vibrations, such as in land-based aquaculture.Furthermore, speedometers and Doppler vibrometers are not suitable for cases where the liquid surface vibrates slowly or has a large amplitude.

[0013] As is clear from the above explanation, the object of this invention is to provide a liquid surface vibration detection sensor, a liquid surface vibration detection unit, a liquid surface vibration monitoring device (system), and a liquid surface vibration monitoring method that can be used in various industries that use liquid, such as the monitoring and management of fish farming, or the ecological research of plants and animals using water and the development of farming techniques. Another object of this invention is to provide a liquid surface vibration monitoring device and an underwater condition monitoring method that use this liquid surface vibration detection unit to measure the fluctuations of the liquid surface, thereby monitoring the activity state of the monitored object and outputting a warning or other monitoring signal as necessary. [Means for solving the problem]

[0014] In order to achieve the above object, the liquid surface vibration detection sensor according to the first aspect of the present invention is characterized by comprising a light source that emits laser light of a wavelength in the near-infrared region, an optical system that irradiates the liquid surface with elliptically polarized light that is emitted from the light source, receives the reflected light of the emitted light from the liquid surface, and branches it, and a light receiving element that receives the reflected light from the optical system and outputs an electrical signal according to the amount of light received.

[0015] When this elliptically polarized light is irradiated vertically onto the liquid surface, the liquid surface vibrates by more than a predetermined amount, and when the wavefront of the irradiated light vibrates by more than the angular deviation of the elliptically polarized light, there occurs a moment when the reflected light from the liquid surface becomes a peak signal, just like when the irradiated light is circularly polarized. Therefore, by making the irradiated light elliptically polarized, this peak can be detected, making it easier to detect the vibrations on the water surface.

[0016] In the liquid surface vibration detection sensor according to a second aspect of the present invention, the optical system converts laser light from the light source into parallel light using a collimating lens, and then transmits only either S-polarized or P-polarized light through a polarizing beam splitter (PBS) 15. The S-polarized or P-polarized light transmitted through the polarizing beam splitter 15 is then irradiated onto a quarter-wave plate at an angle shifted by 2 to 10% from its specified angle, and then transmitted through the quarter-wave plate to become elliptically polarized transmitted light. This elliptically polarized transmitted light is used as illumination light and irradiated perpendicularly onto the liquid surface. By irradiating the liquid surface with elliptically polarized illumination light at an angle shifted by 2 to 10% in this manner, it is possible to increase the detection sensitivity for minute vibrations on the liquid surface. Furthermore, by adjusting the angle shifted from the elliptically polarized light according to the desired vibration, it is possible to increase the detection sensitivity according to the magnitude of the liquid surface vibration.

[0017] A liquid surface vibration detection sensor according to a third aspect of the present invention is characterized in that, in the liquid surface vibration detection sensor of the first or second aspect, the reflected light from the liquid surface is received by the quarter wave plate, then branched by the PBS, and the branched reflected light is condensed by a condenser lens so as to be focused at a position shifted from the center position of the light receiving element. By shifting the position slightly from the center of the light receiving element, it is possible to further increase the sensitivity to detecting minute vibrations on the liquid surface.

[0018] A liquid surface vibration detection unit according to a first aspect of the present invention is characterized by comprising a liquid surface vibration sensor according to any one of the first to third aspects, a drive unit that drives the light source of the liquid surface vibration detection sensor, a light emission control unit that controls the drive timing of the drive unit, and a unit control unit that controls each of the above units and processes and outputs an output signal from the liquid surface vibration detection sensor. The light emission control unit controls the drive unit to drive the light source 11 at regular intervals, and outputs a series of vibrations on the liquid surface as a vibration waveform of a continuous electrical signal. The light emission control unit pulse-drives the light source with a pulse width of 1 to 10 μsec, and it is desirable that the period of the drive pulse be at least twice the maximum frequency of the vibration to be detected.

[0019] By continuously driving the liquid surface vibration sensor at a constant cycle and detecting the vibration state of the liquid surface at a constant cycle for a fixed period, it is possible to output a continuous electrical signal vibration waveform representing the vibration state of the liquid surface. This makes it possible to extract the vibration waveform pattern of the liquid surface vibration from the output waveform of the liquid surface vibration detection unit. It is desirable that the light emission control unit pulse-drives the light source with a pulse width of 1 to 10 μsec, and the cycle of the drive pulse is at least twice the maximum frequency of the vibration to be detected. Furthermore, instead of using the liquid surface vibration sensor of the first aspect, it is also possible to obtain an electrical signal representing the liquid surface vibration using the liquid surface vibration sensor of the second or third aspect. This makes it possible to further increase the vibration detection sensitivity.

[0020] The liquid surface vibration monitoring device according to the first aspect of the present invention is characterized by comprising a liquid surface vibration detection unit according to the first aspect, a signal analysis unit that analyzes the continuous detection signals output from the liquid surface vibration detection unit, the liquid surface vibration detection unit, and a monitoring control unit that controls the signal analysis unit and executes predetermined corresponding processing according to the analysis results of the signal analysis unit.

[0021] The signal analysis unit acquires the detection signal output from the liquid surface vibration sensor at a constant cycle and for a constant period, compares the acquired detection signal with a predetermined threshold value or a pre-stored vibration waveform signal, and / or analyzes the vibration waveform signal consisting of the acquired series of detection signals to detect the state of the object to be monitored.

[0022] The signal analysis unit may analyze the vibration of the liquid surface by, for example, calculating the spectrum of the vibration waveform signal by fast Fourier transform processing of the stored vibration waveform signal. In this way, by comparing the magnitude of the liquid surface vibration signal and the vibration pattern signal with a threshold value or analyzing the characteristics of the signal pattern, it is possible to detect the cause of the vibration of the liquid surface.

[0023] A liquid surface vibration measurement method according to a first aspect of the present invention is characterized by comprising the steps of: irradiating a parallel, elliptically polarized laser beam having a wavelength in the near-infrared region perpendicularly to the liquid surface at a constant period; collecting the reflected light from the liquid surface and converting it into an electrical signal using a light-receiving element; storing the vibration waveform of the electrical signal representing the liquid surface vibration output from the light-receiving element for a predetermined period; analyzing the event that caused the liquid surface vibration from the stored vibration waveform; and outputting the analysis results.

[0024] According to this vibration monitoring method, the vibration state of the liquid surface over a predetermined period of time is converted into an electrical signal, and the vibration waveform of the electrical signal representing the vibration state of the liquid surface is analyzed, thereby making it possible to monitor various events that affect the vibration of the liquid surface. [Effects of the Invention]

[0025] The movements of the farmed fish and the operating status of the equipment that are the subject of monitoring are accompanied by physical movements and vibrations, and therefore appear as vibrations on the surface of the liquid (water surface) in the tank. If the object of monitoring involves some kind of physical movement, changes in the movement of the monitored object will appear as changes in the vibrations of the liquid, not only in fish farming, but also in any equipment that operates using liquid as an essential medium or that manages liquid. By capturing the temporal or instantaneous characteristics of the vibrations on the surface of the liquid (water surface), which reflect these various conditions, it is possible to indirectly grasp various conditions, such as the state of the water, whether the equipment is operating correctly, and abnormal conditions due to external factors.

[0026] The liquid surface vibration detection sensor of the present invention can provide a highly sensitive liquid vibration sensor that can detect minute vibrations on the liquid surface by irradiating a parallel beam of elliptically polarized light vertically onto the liquid surface. Furthermore, by using a liquid surface vibration detection unit that uses this liquid surface vibration detection sensor, it is possible to obtain a continuous vibration waveform as an electrical signal by continuously driving the liquid surface vibration detection sensor at a fixed cycle for a fixed period of time. This makes it possible to perform pattern analysis of the vibration waveform and various spectrum analyses, and it is possible to provide a liquid vibration monitoring device and liquid vibration monitoring method that can analyze the cause of the liquid surface vibration from the liquid surface vibration and monitor the desired target. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram showing a schematic configuration of a liquid surface vibration detection sensor according to the present invention; [Figure 2] FIG. 4 is a schematic diagram illustrating the focusing position of a reflected light beam relative to a light receiving element. [Figure 3] 4 is a diagram showing the relationship between the light-converging position on the light-receiving surface and the profile of the received reflected light beam. [Figure 4] FIG. 4 is a vibration waveform diagram showing an example of a vibration signal obtained by collecting and recording the output from a liquid surface vibration detection sensor for a certain period of time. [Figure 5] 5 is a graph showing the results of fast Fourier transform processing of the vibration waveform of FIG. 4. [Figure 6] FIG. 1 is a functional block diagram showing an embodiment of a liquid surface vibration detection unit using a liquid surface vibration detection sensor. [Figure 7] 3 is a waveform diagram showing a light emitting pulse, a pulse width, a light emitting period, and a signal input to an AD input. [Figure 8] 1 is a functional block diagram of the basic configuration of a liquid surface vibration monitoring device 30 using a liquid surface vibration detection unit according to the present invention. [Figure 9] FIG. 10 is a vibration waveform diagram showing an example of a vibration waveform when a fish is swimming, detected by the liquid surface vibration detection unit. [Figure 10] 10 is a graph showing a spectrum obtained by subjecting the waveform of 512 points in the vibration waveform of FIG. 9 to fast Fourier transform (FFT). [Figure 11]Vibration waveform diagram when an impact is applied to the water surface. [Figure 12] 12 is a graph showing a spectrum obtained by subjecting the vibration waveform of FIG. 11 to fast Fourier transform (FFT). [Figure 13] Graph showing the spectrum of overlapping impulsive vibrations and fish activity. [Figure 14] A graph showing the spectrum when standing waves occur on the water surface. [Figure 15] Graph showing the spectrum of a vibration signal generated through a floor surface. [Figure 16] 10 is a flowchart showing an example of a liquid surface vibration monitoring device (system) that performs analysis using vibration moving average values, clusters the results of spectrum analysis, and performs analysis processing using interval integration. DETAILED DESCRIPTION OF THE INVENTION

[0028] A liquid surface vibration detection sensor, a liquid surface vibration detection device unit, a liquid surface vibration monitoring device, and a liquid surface inspection monitoring method will be described with reference to the drawings. The liquid surface vibration detection sensor of the present invention optically measures the swaying and vibration state of the liquid surface to be monitored and outputs it as an electrical signal. By using this liquid surface vibration detection sensor, it is possible to obtain an electrical signal that reflects even the slightest vibration state of the liquid surface, and a series of vibration waveforms can be obtained by the liquid surface vibration detection unit.

[0029] The liquid surface vibration monitoring device then analyzes the vibration waveform of the acquired electrical signal that represents the vibration state of the liquid surface, thereby making it possible to monitor the state of the object to be managed that caused the vibration and the state of various facilities. This makes it possible to monitor the vibration state of the liquid surface without human intervention, and if it detects that a situation that requires action has occurred, to notify the user that a predetermined response action is required.

[0030] As mentioned above, the application of the present invention is not limited to fish farming, but can be used in any industrial field where water, equipment, or external factors affect water surface vibrations. However, in the following explanation, in order to clearly explain specific monitoring situations and their effects, an example in which the liquid surface vibration detection sensor unit of the present invention is used to manage fish farming in a land-based aquarium or aquaculture pond will be described as an embodiment of the present invention. In the following explanation, the explanation is based on fish farming, and the term "water surface" will be used where appropriate instead of "liquid surface."

[0031] In land-based aquaculture, a specific type of fish is farmed in tanks according to the size of the tank, with the highest possible efficiency. The size of the tank and the number of fish farmed vary depending on the type, size, and growth conditions of the fish. Although there are exceptions, generally, farmed fish of the same species undergoing the same growth period are farmed in the same tank.

[0032] In fish farming, water quality monitoring, growth monitoring, and abnormality monitoring are carried out while feeding the fish regularly. There are no clear definitions for water quality monitoring, fish growth monitoring, and abnormality monitoring, but in this specification, they are used to roughly mean the following. Water quality monitoring involves monitoring the dirt in the tank, water temperature, water oxygen concentration, etc. at specified time intervals or continuously. Growth monitoring involves monitoring the growth status and behavior of the fish for abnormalities, and monitors growth status, activity status, and abnormal behavior.

[0033] Anomaly monitoring involves monitoring abnormalities in facility equipment and abnormal conditions caused by external factors. For example, this includes monitoring the status of facility equipment such as water circulators, water quality regulators, and air conditioners, as well as monitoring external factors such as the throwing of foreign objects and the intrusion of wild animals or suspicious people. Abnormal behavior of fish may also be monitored.

[0034] Among these monitoring activities, the liquid surface vibration detection sensor of the present invention is primarily suited to unmanned automatic status monitoring and abnormality monitoring. If the farmed fish are healthy, they will move about in the tank in roughly the same manner, causing the water surface in the tank to vibrate in a roughly constant pattern. This vibration pattern will vary depending on the size of the farmed fish, the size, shape, type, and material of the equipment, the amount of water, the filtration equipment and other various equipment, and the operating status of these equipment, among other factors.

[0035] However, if the period of the vibration pattern is set to a relatively long period, such as several seconds or several tens of seconds, it becomes possible to obtain a consistent vibration pattern. Also, since the vibration pattern of the water surface is common within a certain range for each type of aquarium depending on the shape, material, size, etc. of the aquarium, even more accurate vibration detection can be achieved by obtaining various vibration patterns for each type of aquarium, or by installing a liquid level detection sensor and obtaining various vibration patterns for each aquarium in which fish are cultivated.

[0036] As described above, by detecting water surface vibrations in real time, it is possible to monitor the condition of the farmed fish and the operating status of the equipment. In particular, it is preferable to store the vibration state when only a certain amount of water is placed in the tank, the vibration patterns when each piece of equipment is operated individually, the vibration patterns when various pieces of equipment are operated in combination, and the vibration patterns when each piece of equipment is operated with farmed fish inside. By comparing these various stored vibration patterns with the current vibration pattern, it is possible to grasp the operating status of the equipment and the activity status of the farmed fish relatively accurately.

[0037] Typically, multiple farmed fish are raised in an aquarium, and since the vibrations caused by the activity of each healthy individual fish are thought to be nearly identical, the vibrations on the water surface caused by all the healthy farmed fish in the aquarium are a composite of these individual vibrations. Also, the overall vibration of the aquarium wave surface is a composite of the vibrations caused by the farmed fish, signals from the equipment, and signals from external factors.

[0038] Therefore, simply by analyzing the vibration state of the water surface, it is possible to comprehensively detect the condition of the farmed fish, the operating state of the equipment, and abnormal conditions caused by external factors. This makes it possible to simultaneously perform multiple monitoring tasks, such as equipment monitoring, monitoring of the farmed fish, and monitoring for the intrusion of suspicious individuals or animals, simply by monitoring the vibration state of the water surface. This eliminates the need to install multiple sensors in multiple locations to monitor the condition of the farmed fish, the operating state of the equipment, and abnormal conditions caused by external factors such as intrusion, making it possible to simplify the monitoring equipment and significantly reduce monitoring costs.

[0039] FIG. 1 shows the basic configuration of a liquid surface vibration detection sensor of the present invention. The liquid surface vibration detection sensor 10 comprises a light source 11, an optical system 12, and a light receiving element 13. The optical system 12 has an irradiation optical system (14, 15, 16 in FIG. 1) that irradiates the liquid surface (the water surface in aquaculture; hereinafter referred to as "the water surface" where appropriate) with irradiation light, and a light receiving optical system (16, 15, 17 in FIG. 1) that irradiates the light receiving element 13 with reflected light of the irradiation light. The light source 11 is preferably a laser light source, which emits near-infrared laser light and irradiates the elliptically polarized irradiation light vertically onto the liquid surface (water surface) 80 by the irradiation optical system.

[0040] When the liquid surface to be irradiated is the water surface, it is preferable to use near-infrared light, particularly a wavelength in the range of 1000 nm to 1700 nm. The reason for using near-infrared light wavelengths is that irradiating visible light may cause stress to farmed fish, and near-infrared light has a wavelength range in which water has high absorption. If the irradiated light 61 is highly absorbed by water, the ratio of the amount of light reflected to the amount of light absorbed can be increased, making it possible to further increase sensitivity during vibration. Therefore, when irradiating the water surface, it is desirable to use near-infrared light with a wavelength that is particularly highly absorbed by water. Furthermore, it is preferable to use pulsed laser light, as this makes it easier to control the amount of laser light emitted.

[0041] The configuration, operation, and effect of a liquid surface vibration detection sensor 10 according to one embodiment of the present invention will be described with reference to Figure 1. A laser beam emitted from a light source 11 enters an optical system 12, passes through a collimator lens 14, a polarizing beam splitter (PBS) 15, and a quarter-wave plate 16, and is irradiated vertically onto a liquid surface (water surface) 80 as elliptically polarized laser beam irradiation light 61.

[0042] The laser beam 60 emitted from the light source 11 is collimated by a collimating lens and enters the polarizing beam splitter 15. The polarizing beam splitter (PBS) 15 allows only S-polarized or P-polarized light to pass through, but not the other polarized light. The S-polarized or P-polarized beam light that passes through the PBS 15 enters the quarter-wave plate 16. The angle of incidence on the quarter-wave plate 16 is adjusted so that it is slightly deviated from the specified angle of 45 degrees (for example, a deviation angle within a range of 2% to 10%; depending on the vibration of the monitored object, a deviation angle of approximately 2% to 5%), and the beam is emitted from the quarter-wave plate 16 as an elliptically polarized beam of irradiation light 61. This irradiation light 61 is set to be irradiated perpendicularly to the liquid surface (water surface) 80.

[0043] Illumination light 61 irradiated vertically onto a non-vibrating liquid surface (water surface) 80 is almost totally reflected by the specular reflection of the liquid surface (water surface) 80 and is again incident on the quarter-wave plate 16 from the opposite direction. When elliptically polarized reflected light 62 is irradiated onto the quarter-wave plate 16 from the opposite direction, the transmitted light becomes a linearly polarized beam of light. However, because this reflected light is incident on the quarter-wave plate 16 from the opposite direction to when it was irradiated from the light source 11 and passed through the PBS 15, its polarization is shifted by 90 degrees from the original polarization. Therefore, if the light was P-polarized on its first pass, the reflected light 62 is polarized to S-polarized light, and if it was S-polarized, it becomes P-polarized and is incident on the PBS 15 from the opposite direction.

[0044] Reflected light 62, which is linearly polarized by the quarter-wave plate 16 and enters the PBS 15 in the opposite direction, is polarized 90 degrees opposite to the light emitted, and is therefore unable to pass through the PBS 15 but is reflected and split. The split reflected light 62 enters the condenser lens 17 of the light-receiving optical system and is condensed onto the light-receiving element 13, and the light that reaches the light-receiving element 13 is converted by the light-receiving element 13 into an electrical signal that corresponds to the amount of light received. When the water surface vibrates, the angle of the reflecting surface changes, causing the amount of reflected light to change (vibrate), and the electrical signal output by the light-receiving element 13 also fluctuates. By capturing the fluctuations in the electrical signal that accompany these fluctuations in the amount of received light, it is possible to detect vibrations on the water surface.

[0045] The liquid surface vibration detection sensor 10 is controlled by an external control unit 19, as shown by the dashed line in FIG. 1 . The light source 11 is controlled to emit light at regular intervals to detect the vibration state of the liquid surface, and output signals from the light receiving element 13 are output sequentially in accordance with the timing of the light source's light emission. The output signals from the light receiving element 13 are output sequentially to the control unit 19, where they are subjected to predetermined processing and then output to an analyzer for analysis. The control unit 19 may amplify and output the output signal from the light receiving element 13 directly, but it is preferable to convert it to a digital signal and output it to the analyzer. The analyzer may also convert it to a digital signal. The continuous detection signals and signal patterns output from the control unit 19 are analyzed by the analyzer. At this time, they may be compared with various vibration patterns stored in advance for analysis. In this way, it is possible to detect abnormal conditions due to the activity of farmed fish, the operating status of the equipment, external factors, and other factors.

[0046] The relationship between the irradiated light 61, the reflected light 62, and the vibration of the liquid surface 80 will be described. When light is irradiated vertically onto the water surface, and the water surface is not vibrating, the strongest reflected light can be obtained when the irradiated light is circularly polarized, but elliptically polarized irradiated light 61 results in weaker reflected light 62 than circularly polarized irradiated light. On the other hand, when the water surface is pulsating, the irradiated light 61 is no longer perpendicular to the water surface, but if the pulsation is very slight, the deviation from the perpendicular is very small. However, when considering the wavefront of the irradiated light beam irradiated onto the water surface, since the irradiated light is elliptically polarized, if the water surface is slightly distorted, the wavefront may become similar to circularly polarized light, or the polarization state may even become elliptical.

[0047] When the relationship between the elliptically polarized illumination light 61 and the wavefront of the water surface becomes similar to that of circularly polarized light due to distortion of the water surface caused by pulsation, a situation similar to total reflection occurs. Therefore, when there is distortion of the water surface at the wavelength level due to vibration of the water surface, the light incident on the water is reflected, and the amount of light detected by the light receiving element 13 increases. Conversely, if the degree of elliptically polarized light increases due to vibration of the water surface, the amount of light detected by the light receiving element 13 decreases in accordance with the pulsation of the water surface. When the water surface pulsates, it vibrates to its upper limit, so by using elliptically polarized illumination light 61, it becomes possible to detect peaks both when the water surface rises and when it falls.

[0048] Next, another feature of the optical circuit of the liquid level vibration detection sensor of the present invention will be described with reference to Fig. 2. Fig. 2 is a schematic diagram illustrating the focusing position of the reflected light beam after passing through the quarter-wave plate 16 and the PBS 15. Normally, the optical circuit of a device for measuring light is designed so that the center of the optical axis coincides with the center of the light receiving surface 13a of the light receiving element, as shown by the dashed line in Fig. 2. In contrast, in the present invention, it is desirable to adjust the center of the optical axis so that it is slightly offset from the center of the light-receiving surface 13a of the light-receiving element 13, as shown by the solid line. The reflected light 62 branched by the PBS 15 is focused by the focusing lens 17, but as shown in Figure 2, not all of the reflected focused beam 63b, which is focused at a different position, is irradiated onto the light-receiving surface 13a.

[0049] FIG. 3 shows the relationship between the light-condensing position on the light-receiving surface 13a and the profile of the received reflected light beam. The profile 64 of the focused beam of reflected light has intensity characteristics similar to a normal distribution, with the intensity increasing toward the center. In other words, the brightness increases and decreases the further away from the center. If the water surface is turbulent in this state, the reflected water surface will tilt, which is the same as shifting the optical axis. If the optical axis shifts toward the center of the light-receiving surface 13a, the amount of light detected by the light-receiving surface 13a will increase, and conversely, if it shifts outward, the amount of received light will decrease.

[0050] The fluctuation of the water surface is detected by such a change in the amount of received light. The change in the light-collecting position on the light-receiving surface 13a due to the fluctuation of the optical axis is also affected by the NA or depth of the condenser lens 17. The shallower the depth, the more the amount of light changes even with a slight deviation. As a result, the amount of light detected by the light-receiving element 13 changes due to the vibration of the water surface.

[0051] According to the present invention, minute changes in the water surface can be detected with high sensitivity by capturing changes in the wavefront of light using elliptically polarized light and detecting changes in the optical axis. When a large shock-like vibration occurs (for example, when something is thrown into the tank), the amplitude of the vibration is too large for the light receiving element 13 to detect, resulting in an output with almost zero light intensity. In such cases, by setting a threshold, the signal can be used as a manageable signal indicating an abnormal condition.

[0052] Fig. 4 is a vibration waveform diagram showing an example of a vibration signal recorded as the output of the liquid surface vibration detection sensor 10, collected by causing the light source 11 to emit light for a fixed period of time in a continuous cycle. Such a vibration waveform and the spectrum shown in Fig. 5 can be acquired by a liquid surface vibration monitoring device (system) described later that uses the vibration detection sensor according to the present invention.

[0053] In the figure, 65 is a vibration waveform when an impact due to an external factor is detected, and 66 is a vibration waveform caused by vibrations in the water. The vibration waveform includes standing waves caused by the equipment and vibrations caused by the swimming of farmed fish. The period of these vibrations is thought to be almost constant. Therefore, when analyzing the frequency of this vibration waveform, for example, by using a fast Fourier transform (FFT) to analyze the frequency components and intensity, the spectrum is almost constant. Therefore, by monitoring the spectrum, it is possible to detect the presence or absence of an abnormality from the vibration waveform.

[0054] FIG. 5 is a graph showing the results of fast Fourier transform processing of the vibration waveform of FIG. Signal 67 corresponds to the DC component of the input signal and is the level (detected amount of light, intensity, when the detection signal is stationary) of the center of oscillation in Figure 4 (the signal oscillates up and down around this level), and if this signal 67 changes significantly, it can be used to indicate that there is an impulsive fluctuation in the water surface. Components (spectrum) higher than this DC component make it possible to comprehensively see vibrations caused by the equipment, vibrations caused by the swimming of farmed fish, and changes in the state of impulsive displacement. Signal 68 is a signal that indicates slow oscillations of the liquid surface, and signal 69 is a signal that indicates that the liquid surface is oscillating minutely at high speed.

[0055] Next, an example of the configuration and operation of a water surface vibration detection unit will be described with reference to Fig. 6. Fig. 6 is a functional block diagram showing one embodiment of a liquid surface vibration detection unit that detects changes in the vibration state of the liquid surface using a liquid surface vibration detection sensor of the present invention. Note that Fig. 6 shows an example in which the sensor control unit 24 is realized by an MPU or the like, but it can also be realized by combining circuits for each function without using an MPU (not shown).

[0056] The diagram showing an ellipse on the left side of Figure 6 illustrates an example of elliptically polarized irradiation light 61. The left side of the liquid surface vibration detection unit 20 has the same configuration as the liquid surface vibration detection sensor 10, and block 21 on the right side is a light source drive unit that drives the light source 11, which is composed of an LED driver or the like. Block 22 is an emission control unit that controls the emission timing of the light source 11, block 23 is a voltage conversion amplifier circuit, and block 24 is a sensor control unit. These units 21 to 24 correspond to the control unit 19 in Figure 1. The emission control unit 22 drives the drive unit 21 at a predetermined timing. This causes the light source 11 to emit laser light at a predetermined timing. This emission is preferably pulsed, but CW emission may also be used.

[0057] When pulsed light is emitted, the light emission period should be at least twice the maximum detectable vibration. This is due to the so-called Nyquist criterion. Figure 7 shows the light emission pulse 22a, pulse width 22b, light emission period 22c, and AD input signal 23a. While a shorter pulse width 22b is desirable, it is difficult to amplify and ADC convert a light emission pulse 22a with an extremely short pulse width 22b. Therefore, it is preferable to select a width of, for example, 1 μm to 10 μm seconds. This pulse width has almost no visible effect, and it is desirable to select a pulse width that is safe to look directly at given the optical output intensity. As mentioned above, the light emission period 22c is selected to be shorter than the period that satisfies the Nyquist criterion for the maximum frequency of the signal to be detected. AD conversion is performed at this period, but shortening the light emission period allows for pseudo-CW light emission.

[0058] When the light source 11 is driven to emit light, the irradiation optical system (14, 15, 16) irradiates the water surface 80 with elliptically polarized irradiation light 61 at a slightly shifted angle, as explained in Fig. 1. This reflected light is collected via the light-receiving optical system (16, 15, 17) at a position slightly shifted from the center of the light-receiving surface 13a of the light-receiving element 13, and the light-receiving element 13 outputs an electrical signal according to the amount of light received.

[0059] The output signal from the light receiving element 13 is amplified by an amplification factor that matches the state of the detected signal and is input to the sensor control unit 24 in synchronization with the light emission timing. Even if the light emission is in a CW state, a signal may be sent to the sensor control unit 24 at a minimum discrete period that complies with the Nyquist criterion. In the sensor control unit 24, the peak value of the amplified signal is input to an AD conversion circuit (assuming that it is built into the control circuit), converted to a digital signal, and output as a detection signal. The signal before AD conversion is an analog signal that is output as a signal that roughly indicates the pulsation of the water surface, so it can be used simply for waveform observation, and it is also possible to analyze water surface vibrations by monitoring this signal.

[0060] Fig. 8 shows a functional block diagram of the basic configuration of a liquid surface vibration monitoring device (system) 30 using the liquid surface vibration detection unit 20 according to the present invention. The detection signal 25 output from the liquid surface vibration detection unit 20, which continues at a constant cycle and for a constant period, is sent to a signal analysis unit 31 for analysis. A monitoring control unit 32 issues an abnormality warning signal and performs other necessary control according to the analysis results. As mentioned above, an example of signal analysis by the signal analysis unit 31 is a method using fast Fourier transform processing.

[0061] Furthermore, by storing in advance various vibration signal patterns, including normal and abnormal states, and / or their spectra after various processing, it becomes possible to make more accurate judgments about the situation by comparing the pattern and / or spectrum of the detected vibration signal with the pattern and / or spectrum of the vibration signal stored in advance.

[0062] The configuration may be such that, simply, the vibration pattern and / or vibration intensity are compared with a predetermined pattern and / or threshold, and if it is determined that the vibration exceeds a predetermined range, the monitoring control unit 32 executes a corresponding response according to the result of the comparison. The monitoring control unit 32 executes the necessary response according to the signal analysis results. Possible response responses include, for example, sending an email notifying of an abnormality or displaying an alarm.

[0063] In land-based fish farming, it is necessary to monitor the health of the fish, detect vibrations that cause stress, detect equipment abnormalities early, and monitor and detect abnormal behavior by suspicious individuals. Next, to demonstrate that the present invention is useful in land-based fish farming, we will explain an example of how water surface vibration detection data detected by the liquid surface vibration detection unit of the present invention can be used in management or supervision of fish farming.

[0064] Figure 9 shows an example of a vibration waveform detected by a liquid surface vibration detection unit when a fish is swimming. Figure 10 shows the results of FFT analysis on different time axes, where 512 points in the vibration waveform in Figure 9 have been subjected to fast Fourier transform (FFT). 70a and 70b in Figure 10 are both spectra showing the activity of fish, but in different situations.

[0065] Looking at the FFT processing results in Figure 10, we can see that although the amplitude (intensity) varies, the vibrations generated by the swimming fish are nearly the same. (In the FET diagram, the horizontal axis is frequency and the vertical axis is intensity.) In other words, the water surface vibrates at the same period. This means that if we hold the spectrum pattern at a certain point in time as a reference, and if that pattern changes, we can determine that there is some abnormality in the fish's behavior. There are several possible methods for discovering differences in patterns, but currently it is also useful to use AI technology, etc., to use spectrum patterns as learning data.

[0066] Figure 11 shows a vibration waveform diagram when an impact is applied to the water surface. The spectrum in this case is shown in Figure 12. The vibration waveform in Figure 11 also shows that a large vibration amplitude is caused by the impact. In this way, even with a direct vibration waveform, it is possible to determine that there has been some kind of impulsive vibration based on its magnitude and duration. Furthermore, by observing the waveform in Figure 12, it is clear that it is clearly different from the spectrum pattern when the fish is swimming. The amplitude is also quite large.

[0067] As mentioned before, if it is learned as an impulsive vibration, it can be determined that there has been an impulsive displacement. In such a case, it is possible that someone has tampered with the aquaculture equipment. If such a pattern is detected, it is expected that damage can be minimized by sending an email or other warning information from the water surface vibration detection device (or system).

[0068] Figure 13 shows the spectrum when impulsive vibrations and fish activity overlap. The amplitude (intensity) at the time of serving is thought to indicate the health of the fish (whether they are well or not), so by constantly monitoring the amplitude (intensity) of this spectrum, it is possible to monitor the health of the fish.

[0069] Figure 14 is a graph showing the spectrum of standing waves occurring on the water surface. Standing waves are thought to be mainly caused by vibrations generated by aquaculture equipment, and are thought to change when some kind of abnormality occurs in the equipment. Figure 15 is a graph showing the spectrum of vibration signals generated through the floor. However, this spectrum may change depending on the source of the vibration and the transmission path, but it can be seen that the pattern of this spectrum is clearly different from that described above. Depending on the circumstances, such as the type of fish and the magnitude of the vibration, this vibration may be a source of stress for the fish.

[0070] The liquid surface vibration detection unit of the present invention is a sensor unit that can comprehensively detect all vibrations. As an analytical method, spectrum analysis of the vibration waveform has been used to show that there are changes in the vibration pattern of the vibration detection waveform. In actual fish farming, the appearance of these spectra makes it possible to determine the cause of vibration, abnormal conditions, and the activity state of the fish. In addition to analyzing the pattern itself, there is also the method of learning the pattern and making a judgment based on the difference, as mentioned above.

[0071] Another method is to cluster the frequency range of the spectrum, integrate that range, and compare the integrated value with a preset threshold. The vibration spectrum and wavelength magnitude detected by this liquid surface vibration detection unit are considered to be approximately constant in a steady state. If this integrated value differs, it is considered to be different from normal (ordinary) conditions, and this can be used for subsequent measures (operation of automatic control devices: ON / OFF, alarms, sending emails, etc.).

[0072] 16 is a flowchart of a control system in which the results of the above-mentioned spectrum analysis are clustered and analyzed using interval integration by the liquid surface oscillation monitoring device (system) 30. Such control is possible, for example, by configuring the signal analysis unit 31 and monitoring control unit 32 with a CPU, a memory unit, control software, analysis software, etc.

[0073] . 16, vibration signal data sampled by the liquid surface vibration detection unit according to the present invention is input (step S1), and its vibration moving average value (Sav) is calculated (step S2). After that, the calculated moving average value is compared with a previously calculated average value (SaVC) (step S3). If the value of Sav is smaller than SaVC, it is determined that an impact vibration has occurred, and branching is performed to perform corresponding processing (step S4).

[0074] If there is no impulsive vibration (step S3: No), then spectrum analysis is performed (step S5). The spectrum of the vibration signal waveform is calculated (step S5), and the spectrum is clustered into sections (a), (b), and (c), and the amplitude (intensity) of the spectrum in each section is integrated. The integral value in section (a) is designated SSa, the integral value in section (b) is designated SSb, and similarly, the integral value is designated SSc (steps S6-S8).

[0075] The SSa value is a value used to monitor the condition of the fish, and is compared with the SSaO value that has been determined in advance (step S9). If the SSa value is smaller than the SSaO value, it is assumed that the fish is not active and is abnormal, and branching is performed to handle the abnormal condition (step S10). The SSb value is considered to indicate standing waves generated by equipment, etc., and a comparison is performed to determine whether it is within the range of a lower limit value SS1 and an upper limit value SSh that have been determined in advance (step S11). If it is not within the range between the lower and upper limits, it is assumed that an abnormality may have occurred in the equipment, and branching processing is performed (step S12).

[0076] The integrated value SSc in the (c) section is considered to represent other vibrations, for example, vibrations from the floor (vibrations caused by people walking, vibrations from cars, etc.), and is compared with a value determined in advance as SScC (step S13). If the SSc value is greater, it is determined to be abnormal and an abnormal branch is made (step S14). Different response processes can be taken for the abnormal branch process depending on the branch process. For example, various countermeasures can be taken, such as turning on an indicator light to notify of an abnormality or automatically sending an emergency e-mail to the administrator.

[0077] In addition, the liquid surface vibration detection sensor, liquid surface vibration detection unit, liquid surface vibration monitoring device and the configurations of each part thereof described in the above-mentioned embodiments or claims can also be appropriately combined to form a liquid surface vibration detection sensor, liquid surface vibration detection unit, liquid surface monitoring device and liquid surface monitoring method. [Explanation of symbols]

[0078] 10. Vibration detection sensor 11 Light source 12 Optical system 13 Photodetector (PD) 13a Photosensitive surface 14 Collimating lens 15 Polarizing beam splitter (PBS) 16 1 / 4 wave plate 17 Condenser lens 19 Control Unit 20 Liquid surface vibration detection unit 21 Light source driver 22 Light emission control unit 23 Voltage conversion amplifier circuit 24 Sensor control unit 25 Detection signal 31 Signal analysis section 32 Monitoring and control section 61 Irradiation Light 62 Reflected light 63b Concentrated beam of reflected light 64 Profile of a focused beam of reflected light 65 Vibration waveform of shock due to external factors 66 Vibration waveform caused by vibrations in water 67 DC component of input signal 68 A signal representing a gentle oscillation of the liquid surface 69 Signal indicating high-speed minute vibrations of the liquid surface 80 liquid level

Claims

1. a light source that emits laser light with a wavelength in the near-infrared region; an optical system that irradiates a liquid surface with elliptically polarized light obtained by emitting the laser light from the light source vertically, and receives and splits the reflected light of the irradiation light from the liquid surface; a light receiving element that receives the reflected light from the optical system and outputs an electrical signal according to the amount of received light; A liquid surface vibration detection sensor comprising:

2. The optical system converts the laser light into parallel light using a collimating lens, then transmits only either S-polarized or P-polarized light using a polarizing beam splitter, and irradiates the transmitted light from the polarizing beam splitter at an angle shifted by 2 to 10% from the specified angle onto a quarter-wave plate, thereby irradiating the light as elliptically polarized light vertically onto the liquid surface.

3. The liquid surface vibration detection sensor described in claim 2, characterized in that the optical system receives the reflected light from the liquid surface using the quarter-wave plate, then splits it using the polarizing beam splitter, and condenses the split reflected light using a condensing lens so that the focal point is at a position shifted from the center position of the light receiving element.

4. The liquid level vibration detection sensor according to claim 1; a driving unit that drives the light source of the liquid surface vibration detection sensor; a light emission control unit that controls the drive timing of the drive unit; a unit control unit that controls each of the above components and processes and outputs an output signal from the liquid surface vibration detection sensor; A liquid surface vibration detection unit comprising:

5. The liquid surface vibration detection unit according to claim 4, characterized in that the light emission control unit pulse-drives the light source with a pulse width of 1 to 10 μsec, and the period of the drive pulse is at least twice the maximum vibration period to be detected.

6. The liquid surface vibration detection unit according to claim 4; a signal analysis unit that analyzes the continuous detection signals output from the liquid surface vibration detection unit; A liquid surface vibration monitoring device comprising the liquid surface vibration detection unit and a monitoring control unit that controls the signal analysis unit and executes predetermined response processing in accordance with the analysis results of the signal analysis unit.

7. The liquid surface vibration monitoring device described in claim 6, characterized in that the signal analysis unit acquires the detection signal output from the liquid surface vibration sensor at a constant cycle and for a constant period, compares the acquired detection signal with a predetermined threshold value or a pre-stored vibration waveform signal, and / or analyzes the vibration waveform signal consisting of the acquired continuous detection signal to detect the state of the object to be monitored.

8. 8. The liquid surface vibration monitoring device according to claim 7, wherein the signal analysis unit calculates a spectrum of the stored vibration waveform signal by fast Fourier transform processing, and analyzes the vibration of the liquid surface.

9. irradiating the liquid surface with a parallel, elliptically polarized laser beam having a wavelength in the near-infrared region perpendicularly to the liquid surface at a constant period; a step of collecting reflected light from the liquid surface and converting it into an electrical signal by a light receiving element; a step of storing a vibration waveform of an electrical signal representing a liquid surface vibration output from the light receiving element for a predetermined period of time; an analysis step of analyzing an event that caused the vibration of the liquid surface from the stored vibration waveform; outputting the analysis results; A liquid surface vibration monitoring method comprising:

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