State quantity estimation method and state quantity estimation device

Abstract

To provide a state quantity estimation method and a state quantity statement device which shorten a calculation time and can calculate an accurate estimation value, even if an initial state is inaccurately imparted.SOLUTION: A state quantity estimation method includes an acquisition step of acquiring a measurement value of a potential around a sacrificial anode while moving a mobile body to which a plurality of potential sensors are fixed in an electrolyte, an initial state imparting step of imparting a plurality of initial states, a calculation step of calculating estimation values of the state quantities for each of the plurality of initial states, and a determination step of determining the most probable estimation value among the plurality of estimation values calculated in the calculation step. The determination step classifies values close to each other among the plurality of estimation values calculated corresponding to the plurality of initial states as the same group into a plurality of groups, and determines the largest number of estimation values belonging to the plurality of groups to be a most probable estimation value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a state quantity estimation method and a state quantity estimation device. [Background technology]

[0002] Sacrificial anodes are generally used to prevent corrosion of steel structures installed underwater. The sacrificial anodes are made of alloys mainly composed of aluminum, zinc, and magnesium, which have a higher electrochemical ionization tendency than steel. The sacrificial anodes are attached to structures and corrode themselves, suppressing corrosion of the structures. The sacrificial anodes wear over time and therefore need to be replaced periodically. In order to evaluate the soundness of the sacrificial anodes and to know when they need to be replaced, there is a method of estimating the degree of wear of the sacrificial anodes by measuring their volume and weight. For example, a diver measures the circumference of the sacrificial anode underwater, calculates its volume, and determines the remaining life. However, measurements by divers are not only a safety concern, but also a laborious and time-consuming inspection, which increases costs.

[0003] The applicant has proposed a method for estimating the value of the anticorrosive current output from the sacrificial anode by analyzing the potential around the sacrificial anode in water, thereby determining the remaining life of the sacrificial anode (for example, Patent Document 1). In the method described in Patent Document 1, a plurality of measuring parts for measuring the potential are moved vertically in water to measure the potential around the sacrificial anode. Patent Document 1 also proposes performing state quantity estimation using a particle filter to estimate the value of the anticorrosive current output from the sacrificial anode, even when the position of the measuring parts in water is unclear. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-039036 Summary of the Invention [Problem to be solved by the invention]

[0005] The estimation method using a particle filter has an advantage that a correct estimated value can be calculated even if there is an error in the initial state to be applied, since the state quantities are estimated while predicting and correcting the changes in the multiple state quantities. However, on the other hand, when using a particle filter, there is a problem that the amount of calculation is huge and the calculation time is too long because predictions and corrections are performed for all of the multiple state quantities. Therefore, the present inventors have considered shortening the calculation time by adopting other estimation methods such as an extended Kalman filter. However, with these estimation methods, if there is an error in the input initial state, there are cases where a correct estimated value cannot be calculated. Therefore, if the measurer does not accurately grasp the initial position of the measurement unit, or if he / she grasps it incorrectly, there is a risk that an accurate estimated value cannot be calculated.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a state quantity estimation method and a state quantity estimation device that can shorten calculation time and calculate accurate estimated values ​​even if the initial state is assigned inaccurately. [Means for solving the problem]

[0007] One embodiment of a state quantity estimation method is a state quantity estimation method that estimates unknown state quantities that represent the electrolytic protection state of a metal structure protected by a sacrificial anode in an electrolyte using a state quantity estimation model, and includes an acquisition step of acquiring measured values ​​of the potential around the sacrificial anode while moving a moving body to which a plurality of potential sensors are fixed in the electrolyte for a predetermined period of time, an initial state assignment step of assigning a plurality of initial states, a calculation step of calculating estimated values ​​of the state quantities for each of the plurality of initial states, and a determination step of determining the most likely one of the plurality of estimated values ​​calculated in the calculation step.

[0008] According to this configuration, when measuring the potential around a sacrificial anode placed in an electrolyte, a plurality of estimated values ​​are calculated based on a plurality of initial states in the calculation step, and the most probable estimated value is determined in the determination step. Therefore, the calculation for determining the accuracy of the values ​​in the calculation step can be omitted, the amount of calculation required in the calculation step can be reduced, and the overall calculation time can be shortened.

[0009] In the above-mentioned state quantity estimation method, the calculation step includes a prediction step of predicting a next state updated over time from the previous state, with the initial state being set as an initial "previous state", using the state quantity estimation model; a conversion step of converting the state quantity predicted in the prediction step into a predicted value of potential; a comparison step of comparing the predicted value of the potential calculated in the conversion step with an observed value; and a correction step of correcting the next state to a state probabilistically closest to a true value based on a result of the comparison in the comparison step. In the calculation step, the prediction step, the conversion step, the comparison step, and the correction step are repeatedly performed within an observation time to calculate the estimated values ​​of the state quantities including the position and attitude of the moving body and the value of the anticorrosive current output from the sacrificial anode, and in the determination step, the estimated values ​​calculated corresponding to the multiple initial states and having similar values ​​are classified into a plurality of groups as the same group, and the group with the largest number of the estimated values ​​is determined to be the most likely estimated value.

[0010] According to this configuration, even if the position and attitude of the moving body are unstable, the value of the anticorrosive current of the sacrificial anode can be calculated by estimating the state quantity. Furthermore, in the determination step, the most likely estimated value is determined based on the number of estimated values ​​that are close to the estimated value, so that the calculation time is hardly spent on the determination step, and a correct estimated value can be calculated.

[0011] In the above-described state quantity estimation method, in the calculation step, the prediction step, the conversion step, the comparison step, and the correction step may be repeated n times (n=A / T) at a constant sampling interval T within an observation time A.

[0012] According to this configuration, the prediction step, the conversion step, the comparison step, and the correction step are performed at regular sampling intervals, thereby making it possible to improve the accuracy of the estimated value calculated in the calculation step.

[0013] In the above-mentioned state quantity estimation method, in the acquisition step, the moving body is moved vertically in the electrolyte, and the multiple initial states assigned in the initial state assignment step may be initial positions of the moving body in a horizontal direction.

[0014] According to this configuration, a plurality of initial positions of the moving body in the horizontal direction are given to perform the calculation step. Therefore, it is not necessary to give an accurate value for the initial position of the moving body to the calculation step. As a result, the worker who measures the initial position of the moving body does not need to know the exact position, and the burden on the worker can be reduced. Furthermore, according to this configuration, since the measurement of the initial position by the worker is not required, it is possible to suppress the influence of the measurement habits and variations of each worker on the measurement result. Furthermore, in this configuration, "moving the moving body in the vertical direction" means lowering the moving body straight down or pulling it straight up. Therefore, according to this configuration, the moving body moves only in the vertical direction. According to this configuration, in the calculation step, an estimated value can be calculated assuming that the state quantity representing the horizontal position of the moving body is constant. This allows the amount of calculation in the calculation step to be significantly reduced.

[0015] In the above-described state quantity estimating method, in the acquiring step, the vertical position of the moving object in the electrolyte may be acquired as the water depth using a water depth sensor fixed to the moving object.

[0016] According to this configuration, since the water depth sensor can measure the vertical direction z position of the moving object over time, the vertical direction z position can be excluded from the estimation of the multiple state quantities, which can significantly reduce the amount of calculation in the calculation step.

[0017] In the above-described state quantity estimating method, the calculation step may be performed assuming that the attitude of the moving body is constant when the acquisition step is performed.

[0018] According to this configuration, in the calculation step, the estimated value can be calculated assuming that the state quantity representing the attitude of the moving body is constant, thereby making it possible to significantly reduce the amount of calculation in the calculation step.

[0019] In the above-described state quantity estimating method, the estimated value of the state quantity may be a value of the anticorrosive current, and in the determining step, the estimated value falling within a range of ±0.1 A may be classified into the same group.

[0020] According to this configuration, estimated values ​​within a range of ±0.1 A are grouped together, so that the estimated values ​​can be mechanically grouped, and the determination step can be automated.

[0021] In the above-mentioned state quantity estimation method, the calculation step may be performed assuming that the attitude of the moving body is constant when the acquisition step is performed, the calculation step is performed assuming that the horizontal position of the moving body is constant when the acquisition step is performed, or the vertical position of the moving body in the electrolyte is acquired as the water depth using a water depth sensor fixed to the moving body in the acquisition step, and the vertical position of the moving body is treated as a known value in the calculation step.

[0022] According to this configuration, it is possible to reduce the amount of calculation in the calculation step while adopting a configuration suited to the measurement environment, device, etc.

[0023] In the above-described state quantity estimating method, the calculation step may use the state quantity estimation model using an extended Kalman filter.

[0024] According to this configuration, by using the extended Kalman filter as the state quantity estimation model, the amount of calculation in the calculation step can be significantly reduced compared to the case where other state quantity estimation models such as a particle filter are used.

[0025] One embodiment of a state quantity estimation device is a state quantity estimation device that performs the above-mentioned state quantity estimation method, and includes a moving body that is submerged in the electrolyte, a measurement unit that is fixed to the moving body and has a plurality of potential sensors that measure the potential in the electrolyte, and a calculation unit that performs the calculation step.

[0026] According to this configuration, it is possible to provide a state quantity estimation device capable of carrying out the above-mentioned state quantity estimation method.

[0027] In the above-described state quantity estimating device, the measuring unit may have a water depth sensor fixed to the moving body.

[0028] According to this configuration, since the water depth sensor can measure the vertical direction z position of the moving object over time, the vertical direction z position can be excluded from the estimation of the multiple state quantities, which can significantly reduce the amount of calculation in the calculation step.

[0029] The state quantity estimating device may be configured to include a main wire and an auxiliary wire for suspending the moving body, and a winding device for simultaneously reeling out and winding the main wire and the auxiliary wire.

[0030] According to this configuration, it is possible to suppress the rotation of the moving body in the electrolyte, compared to the case where the moving body is suspended by only one wire. This makes it possible to suppress the rotation of the measuring unit fixed to the moving body, and it becomes possible to exclude the rotation parameter from the state quantity to be estimated in the state quantity estimation method. As a result, it is possible to reduce the amount of calculation performed by the calculation unit. Furthermore, according to this configuration, since the moving body is suspended by the wire, it is possible to move the moving body only in the vertical direction by fixing the fulcrum of the wire. This makes it possible to calculate an estimate value in the calculation step by assuming that the state quantity representing the horizontal position of the moving body is constant, and it is possible to significantly reduce the amount of calculation in the calculation step. Effect of the Invention

[0031] According to the present invention, it is possible to provide a state quantity estimation method and a state quantity estimation device that can reduce calculation time and calculate accurate estimated values ​​even if the initial state is imprecisely assigned. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram of a sacrificial anode as an estimation target of the state quantity estimation method according to the embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a state quantity estimating device according to the embodiment. [Diagram 3] FIG. 3 is a perspective view of a frame and a measuring unit according to the embodiment. [Figure 4] FIG. 4 is a flowchart showing the flow of the state quantity estimation method according to the embodiment. [Diagram 5] FIG. 5 is a diagram showing an example of coordinates in an initial state in the embodiment. [Figure 6] FIG. 6 is a graph showing estimated values ​​in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, a state quantity estimation method and a state quantity estimation device according to an embodiment will be described with reference to the drawings. Note that the drawings used in the following description may show characteristic parts in an enlarged manner for the purpose of emphasizing the characteristic parts, and the dimensional ratios of each component may not be the same as in reality. Also, for the same purpose, non-characteristic parts may be omitted in the drawings.

[0034] The drawings also show an x-axis, a y-axis, and a z-axis as appropriate. The x-axis shows one of the horizontal directions. The y-axis shows the other of the horizontal directions. The z-axis shows the vertical direction.

[0035] <Sacrificial anode> FIG. 1 is a schematic diagram of a sacrificial anode 80 as an estimation target in the state quantity estimation method of the present embodiment. The sacrificial anode 80 is attached to a surface of a structure 90 made of a metal material such as steel in seawater (electrolyte), the surface being submerged in the seawater.

[0036] The sacrificial anode 80 has an anode portion 81, a core metal portion 82, and a pair of fixing portions 83. The anode portion 81 is made of, for example, a rod-shaped metal material extending in the vertical direction. The anode portion 81 is made of, for example, an alloy mainly composed of aluminum, zinc, and magnesium. The core metal portion 82 is disposed inside the anode portion 81. The core metal portion 82 extends in the vertical direction inside the anode portion 81. The core metal portion 82 is made of a steel material. The pair of fixing portions 83 extend from the upper end and the lower end of the core metal portion 82 to the outside of the anode portion 81, respectively. The pair of fixing portions 83 are fixed to the surface of the structure 90 by means of welding or the like. Note that the configuration of the fixing portion 83 in this embodiment is an example, and the configuration of the fixing portion 83 is not limited as long as it electrically and mechanically connects the sacrificial anode 80 and the structure 90.

[0037] In seawater (electrolyte), a potential difference occurs between the anode portion 81 and the structure 90 due to the difference in ionization tendency. As a result, the anode portion 81 is ionized and dissolved in the seawater, and an anticorrosive current I flows from the anode portion 81 to the structure 90. That is, according to this configuration, the anode portion 81 dissolves preferentially, thereby achieving electrolytic protection of the structure. In addition, an electric field is formed around the sacrificial anode 80 as the anticorrosive current I flows from the anode portion 81 to the structure 90.

[0038] <State quantity estimator> FIG. 2 is a schematic diagram of the state quantity estimating device 1 of this embodiment. 2, the horizontal direction along the quay of the structure 90 is called the “left-right direction x,” and the horizontal direction perpendicular to the quay is called the “front-back direction y.” The left-right direction x, the front-back direction y, and the vertical direction z are perpendicular to each other.

[0039] The state quantity estimation device 1 has a measurement unit 30, a frame (moving body) 10, a carriage 20, a guide rod 25, a winding device 21, a main wire 22, an auxiliary wire 23, and a terminal device 15.

[0040] The measurement unit 30 has multiple (four in this embodiment) electric potential sensors 31 and one water depth sensor 32. The water depth sensor 32 measures the distance from the water surface in seawater (i.e., the water depth). The multiple electric potential sensors 31 and the water depth sensor 32 are fixed to the frame 10. The frame 10 and the measurement unit 30 fixed to the frame 10 are suspended by the main wire 22 and the auxiliary wire 23 and submerged in seawater.

[0041] The multiple potential sensors 31 measure the potential around the sacrificial anode 80 in seawater. In the following description, when the multiple potential sensors 31 are to be distinguished from one another, they are referred to as a reference potential sensor 31o, a first potential sensor 31a, a second potential sensor 31b, and a third potential sensor 31c. The multiple potential sensors 31 are fixed to the frame 10, and thus their relative positions are fixed relative to one another. The measurement unit 30 detects potentials using the multiple potential sensors 31 and obtains measurement values.

[0042] It is preferable that the measured value output from the measuring unit 30 is the potential difference between the sensors. Since the natural potential of the steel material constituting the structure 90 immersed in an electrolyte such as seawater varies depending on the situation, by using the potential difference as the measured value, the effect of the natural potential of the steel material, which is an unknown value, can be cancelled.

[0043] FIG. 3 is a perspective view of the frame 10 and the measuring unit 30. As shown in FIG. The measuring unit 30 is fixed to the frame 10. The frame 10 is suspended by a main wire 22 and an auxiliary wire 23. The frame 10 is preferably made of resin or the like so that the potential sensor 31 is not affected by an electric field. The frame 10 may be made of other materials such as metal insulated with paint or the like, FRP, wood, etc. In other words, the frame 10 may be made of any material as long as it does not generate an electric field.

[0044] The frame 10 has a bottom frame portion 11, four pillar portions 12, two diagonal beam portions 13, a support portion 14, and an auxiliary beam portion 16.

[0045] The bottom frame 11 has a rectangular frame shape when viewed in the vertical direction z, and constitutes the bottom of the frame 10. The four pillars 12 extend upward from the corners of the bottom frame 11. A first potential sensor 31a, a second potential sensor 31b, and a third potential sensor 31c are fixed to three of the four pillars 12, respectively.

[0046] The two diagonal beam portions 13 connect the upper ends of two diagonally arranged pillar portions 12 out of the four pillar portions 12. The two diagonal beam portions 13 are connected to each other by intersecting with each other at an intersection portion 13a.

[0047] The support portion 14 is rod-shaped and extends upward from the intersection portion 13a. A reference potential sensor 31o and a water depth sensor 32 are fixed to the support portion 14. In addition, an end of the main wire 22 is fixed to the support portion 14. The auxiliary beam portion 16 connects the upper ends of two adjacent pillar portions 12 out of the four pillar portions 12. An end of the auxiliary wire 23 is fixed to the center of the auxiliary beam portion 16.

[0048] In this embodiment, a case will be described in which the reference potential sensor 31o is fixed to the support portion 14, and the other potential sensors (first potential sensor 31a, second potential sensor 31b, and third potential sensor 31c) are fixed to the column portion 12. However, the multiple potential sensors 31 may be fixed in any mounting positions as long as they are fixed so as to maintain the relative positional relationship.

[0049] As shown in Fig. 2, the cart 20 is disposed on the structure 90 and above the water surface. The cart 20 is disposed along the quay of the structure 90 and is movable along the quay by wheels. A winding device 21 and a terminal device 15 are mounted on the cart 20. A guide rod 25 is fixed to the cart 20. The terminal device 15 does not necessarily have to be mounted on the cart 20.

[0050] The guide rod 25 extends forward (+Y) from the carriage 20. The guide rod 25 is provided with a first pulley portion 25a and a second pulley portion 25b arranged in the front-rear direction. The main wire 22 is hung on the first pulley portion 25a. Furthermore, the auxiliary wire 23 is hung on the second pulley portion 25b.

[0051] The main wire 22 and the auxiliary wire 23 have one end fixed to the frame 10 and the other end connected to the winding device 21. The main wire 22 and the auxiliary wire 23 are made of a material such as a metal coated with an insulating material such as paint, natural fiber, or synthetic fiber. In other words, the main wire 22 and the auxiliary wire 23 may be made of any material that does not generate an electric field.

[0052] The winding device 21 simultaneously reels out and reels in the main wire 22 and the auxiliary wire 23. This allows the frame 10 to be submerged in seawater and pulled up from the water. If the state quantity estimation device 1 does not have the winding device 21, an operator may reel in and reels in the main wire 22 and the auxiliary wire 23.

[0053] According to the state quantity estimation device 1 of this embodiment, the frame 10 is suspended by a main wire 22 and an auxiliary wire 23 at positions separated from each other, and the frame 10 is moved vertically in seawater by simultaneously unwinding and winding the main wire 22 and the auxiliary wire 23. Therefore, the frame 10 can be prevented from rotating in seawater, compared to the case where the frame 10 is suspended by only one wire. This makes it possible to prevent the rotation of the measuring unit 30 fixed to the frame 10, and makes it possible to exclude the rotation parameter from the subject of estimation in the state quantity estimation method described later. As a result, it becomes possible to shorten the calculation time of the state quantity estimation method.

[0054] In this embodiment, the frame 10 moves in the vertical direction z by reeling in and reeling in the main wires 22 and the auxiliary wires 23, but the frame 10 may move in any direction, such as the left-right direction x. The frame 10 can be moved in the left-right direction x by moving the cart 20 along the quay in the left-right direction x while suspended in the water by the main wires 22 and the auxiliary wires 23.

[0055] The terminal device 15 is composed of, for example, a personal computer, a tablet terminal, a smartphone, etc. The terminal device 15 is connected to the measurement unit 30. The connection between the terminal device 15 and the measurement unit 30 may be wired or wireless. When the terminal device 15 and the measurement unit 30 are wired, the signal cable extending from the measurement unit 30 extends along the guide rod 25 together with the main wire 22 and is connected to the terminal device 15. In this case, it is preferable that the signal cable is wound or unwound by the winding device 21 together with the main wire 22. Note that the terminal device 15 and the measurement unit 30 do not necessarily need to be connected, and the data at the time of measurement of the frame 10 may be read into the terminal device 15 via a storage medium in which the data is stored, or may be acquired by the terminal device 15 via data communication via a network from the frame 10.

[0056] The terminal device 15 has, for example, an acquisition unit 15a, a calculation unit 15b, and a display unit 15c. The acquisition unit 15a acquires the measurement values ​​acquired by the measurement unit 30. The calculation unit 15b calculates an estimate of the position of the measurement unit 30 and the value of the anticorrosive current I of the sacrificial anode 80 based on the measurement values ​​acquired from the measurement unit 30. The calculation unit 15b calculates, for example, the position and posture of the frame 10 to which the measurement unit 30 is fixed, and an estimate of the value of the anticorrosive current I output from the sacrificial anode 80 by state quantity estimation using an extended Kalman filter.

[0057] The calculation unit 15b is realized by a processor such as a central processing unit (CPU) or a graphics processing unit (GPU) executing a program (software). Some or all of these functional units may be realized by hardware such as a large scale integration (LSI), an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA), or may be realized by a combination of software and hardware. The program may be stored in a storage device such as a hard disk drive (HDD) or a flash memory in advance, or may be stored in a removable storage medium such as a DVD or a CD-ROM, and installed in the storage device by mounting the storage medium in a drive device.

[0058] The display unit 15c displays the calculation result of the calculation unit 15b. The display unit 15c outputs the calculation result of the calculation unit 15b. The display unit 15c is, for example, a display device such as an LCD (Liquid Crystal Display), an organic EL (Electro Luminescence) display, or an LED (Light Emitting Diode) display.

[0059] The state quantity estimation device 1 measures the potential around the sacrificial anode 80 and the water depth where the frame 10 is located by a measuring unit 30 fixed to the frame 10 while moving the frame 10, and estimates unknown state quantities that represent the cathodic protection state of the metal structure 90 protected from corrosion by the sacrificial anode 80 based on the measurement results, using a state quantity estimation model. The state quantity estimation device 1 tracks the position of the frame 10 that moves over time, and calculates estimates of the position of the frame 10 at each time and the value of the anticorrosion current I output from the sacrificial anode.

[0060] The calculation unit 15b estimates the state quantity based on the measured value measured by the measurement unit 30. The measured value is the electric potential around the sacrificial anode 80 measured by the frame 10 including the measurement unit 30 while it moves unstably due to the influence of waves and the like. Therefore, the measured value is measured by the measurement unit 30 including a plurality of sensors provided at a position indefinitely spaced from the sacrificial anode 80 so as to maintain a relative positional relationship with the frame 10 which is in an unclear posture.

[0061] In such an observation environment, the calculation unit 15b estimates the value of the anticorrosive current I output from the sacrificial anode 80 based on a state quantity estimation method. The state quantity estimation method is a technique for estimating an unknown state by using a state quantity estimation model.

[0062] The state quantity estimation model calculates the state quantities that change from moment to moment. The state quantity estimation model is described by a state equation (system equation) and an observation equation, and involves the following two steps (1) and (2).

[0063] (1) Prediction: State X at time t based on the state equation t and predict the potential U based on the observation equation. t However, the state equation may be either linear or nonlinear. (2) Filtering: State X is calculated based on the measurements taken during the observation period from time 1 to time t. t This is the process of estimating the unknown state X from the predicted and observed potential values. t is estimated probabilistically.

[0064] A state equation is an equation that estimates a new state quantity by updating the state quantity at a certain point in time. For example, the state equation is t Add stochastic noise to the state X at time t+1. t+1 This is an equation to estimate

[0065] An observation equation is an equation that converts a state quantity into an observation value, which is the same physical quantity as the measurement value. For example, the observation equation is tBased on this, we add stochastic noise to predict the potential U t Generate.

[0066] <State quantity estimation method> Next, a state quantity estimating method according to this embodiment will be described. FIG. 4 is a flowchart showing the flow of the state quantity estimating method of this embodiment.

[0067] The state quantity estimation method includes an acquisition step S10, an initial state assignment step S20, a calculation step S30, and a determination step S40. In this embodiment, the steps are performed in the order of the acquisition step S10, the initial state assignment step S20, the calculation step S30, and the determination step S40. However, the acquisition step S10 and the initial state assignment step S20 may be performed in the opposite order.

[0068] (Acquisition step S10) The acquisition step S10 is a step of acquiring a measurement value of the electric potential in the seawater (in the electrolyte) around the sacrificial anode 80 while moving the frame 10 to which the measurement unit 30 is fixed. The measurement value acquired in the acquisition step S10 is, for example, a measurement value of the electric potential difference measured by the electric potential sensor 31 and a measurement value of the water depth measured by the water depth sensor 32.

[0069] When performing the acquisition step S10, the state quantity estimation device 1 causes the measurement unit 30 to measure the electric potential and the water depth while the winding device 21 is letting out the main wire 22 and the auxiliary wire 23.

[0070] The measured values ​​of the potential difference and the water depth measured by the measuring unit 30 are acquired by the acquiring unit 15a of the terminal device 15. Furthermore, in the terminal device 15, the measured values ​​are sent from the acquiring unit 15a to the calculating unit 15b.

[0071] (Initial state assignment step S20) The initial state providing step S20 is a step of providing a plurality of initial states to the calculation unit 15b. The initial state providing step S20 may be a step in which an operator inputs a plurality of initial states to the calculation unit 15b, or a step in which the calculation unit 15b obtains a plurality of initial states stored in the terminal device 15 in advance.

[0072] In this embodiment, a plurality of coordinates in the left-right direction x and the front-back direction y of the frame 10 when it is submerged in the water surface are given as the plurality of initial states. That is, the plurality of initial states given in the initial state giving step of this embodiment are horizontal coordinates of the frame 10 when it is submerged in seawater.

[0073] (Calculation step S30) The calculation step S30 is a step of calculating an estimated value of a state quantity for each of a plurality of initial states. The calculation step S30 is performed by the calculation unit 15b. That is, the calculation unit 15b has a program for performing the calculation step S30. The calculation unit 15b constructs a state space model for the position and posture of the frame 10 and the value of the anticorrosive current I output from the sacrificial anode 80.

[0074] In the calculation step S30 of this embodiment, a state quantity estimation model using an extended Kalman filter is used. The calculation step S30 using the extended Kalman filter will be described below. The calculation unit 15b calculates the position and attitude of the frame 10 and the anticorrosive current output from the sacrificial anode 80 by repeating the procedure of prediction, observation, and correction based on the extended Kalman filter.

[0075] In the calculation step S30, the calculation unit 15b generates a state vector X of the following formula (1) to express the state quantity. In formula (1), the subscript t represents time, and the superscript T represents the transpose of a matrix. However, t depends on the observation time A and a constant sampling interval T, and its range is 1 to A / T, where A / T is a natural number.

[0076]

number

[0077] In formula (1), the center of gravity of the sacrificial anode 80 is set as the origin of a three-dimensional coordinate system, and a state quantity including a plurality of parameters to be estimated by the measuring unit 30 is expressed as a state vector X. The origin may be set in advance at any point within the analysis area (or on the structure 90). In this embodiment, the origin is set at the end of the water's edge of the quay wall of the structure 90, directly above the sacrificial anode 80.

[0078] The state vector X includes seven parameters, for example, the three-dimensional coordinate parameters x, y, and z of the reference point of the measuring unit 30, the Euler angle parameters α, β, and γ representing the attitude of the measuring unit 30, and the anticorrosive current I. The attitude of the measuring unit 30 may be expressed not only by Euler angles but also by other methods such as a rotation vector, a rotation matrix, or a quaternion.

[0079] The reference point is the coordinate of the reference potential sensor 31o relative to the origin. The position and rotation of the measurement unit 30 are calculated using the coordinate of the reference potential sensor 31o as the reference point. Since the measurement unit 30 rotates due to the influence of various marine environments during measurement, the attitude is expressed in the state vector X using Euler angle parameters α, β, and γ.

[0080] The anticorrosive current I is a current output from the sacrificial anode 80, and in the formula (1), the value of the anticorrosive current I is expressed as "I." The value of the anticorrosive current I is set as a steady value during the measurement.

[0081] Here, a case where seven parameters are treated as state quantities as the state vector X will be mainly described. However, in this embodiment, among these seven parameters, the parameters of Euler angles α, β, and γ can be treated as constants. In this embodiment, as shown in FIG. 2, the frame 10 is suspended by two wires, a main wire 22 and an auxiliary wire 23, and is moved in the vertical direction z by simultaneously unwinding or winding these two wires. Since the frame 10 is supported at two points by the two wires, the parameters α, β, and γ of the Euler angles that represent the change in the attitude of the measuring unit 30 accompanying the change in the attitude of the frame 10 can be treated as not changing over time. This allows the amount of calculation in the calculation step S30 to be significantly reduced.

[0082] Furthermore, in this embodiment, among the seven parameters of the state vector X, the parameters for the horizontal coordinates x and y can be treated as constants. In this embodiment, the frame 10 is suspended and supported by the main wire 22 wound around the first pulley section 25a and the auxiliary wire 23 wound around the second pulley section 25b. Therefore, the frame 10 is located directly below the first pulley section 25a and the second pulley section 25b. According to this embodiment, the guide rod 25 is fixed, and the positions of the first pulley section 25a and the second pulley section 25b are fixed, so that the frame 10 can be prevented from moving in the horizontal direction. That is, according to this embodiment, the frame 10 can be moved straight along the vertical direction z by the unwinding and winding operations of the main wire 22 and the auxiliary wire 23. As a result, the coordinates x and y representing the horizontal position of the frame 10 can be treated as not changing over time, and the amount of calculation in the calculation step S30 can be significantly reduced.

[0083] In this embodiment, since the measurement unit 30 has the depth sensor 32, the vertical coordinate z out of the seven parameters can be given as a measured value to the state vector X. Therefore, the coordinate z can be excluded from the calculation of the predicted value and the estimated value, and the amount of calculation in the calculation step S30 can be significantly reduced.

[0084] In this way, according to this embodiment, the amount of calculation required to calculate the Euler angles α, β, γ, and the coordinates x, y, and z among the parameters of the state vector X can be significantly reduced. In this embodiment, the case where all of the configurations for omitting the calculation of these parameters are adopted has been described. However, among the configurations for omitting the calculation of these parameters, any one or more of the configurations may be selected and adopted. In this case, the configurations for omitting the parameters may be adopted in any combination. That is, the configuration may be adopted in which one or more of the following is selected and performed: the attitude of the frame 10 when performing the acquisition step S10 is assumed to be constant, the horizontal position of the frame 10 when performing the acquisition step S10 is assumed to be constant, or the vertical position of the frame 10 in seawater is acquired as the water depth using the water depth sensor 32 fixed to the frame 10 in the acquisition step S10, and the vertical position of the frame 10 is treated as a known value in the calculation step S30. This makes it possible to reduce the amount of calculation in the calculation step S30 while adopting a configuration suited to the measurement environment, device, etc.

[0085] The calculation step S30 includes a prediction step S31, a conversion step S32, a comparison step S33, and a correction step S34.

[0086] (Prediction step S31) The prediction step S31 is a step for predicting a next state updated over time from a previous state. In the prediction step S31, the initial state of frame 10 given by the initial state giving step S20 is taken as the "previous state", and a predicted value of the next state transitioned over time from the previous state is calculated.

[0087] In the prediction step S31, the calculation unit 15b performs a process of predicting a state that has transitioned over time based on the following equations (2) and (3).

[0088]

number

[0089]

number

[0090] Equation (2) is a state equation that calculates estimates of the posture, position, and anticorrosive current I of frame 10 a predetermined time (time t+1) after the previous state (time t). The previous state indicates the initial state when t=0, and indicates a modified state (time t) described below during the iterative process.

[0091] Equation (3) expresses the state X when transitioning from the previous state (time t) to the state after a certain time (time t+1). t+1 This is the formula for calculating the variance (the squared value of the standard deviation) of P t is the variance of the forecast error at time t, P t+1 is the variance of the prediction error at time t+1.

[0092] where F is a linear or nonlinear function and w t represents the system noise, where the system noise w t follows a normal distribution. For F, for example, a random walk model is used as described later. The calculation unit 15b calculates a predicted value that predicts a transition state from the previous state (time t) after a predetermined time (time t+1) based on the formula (2).

[0093] (Conversion step S32) The conversion step S32 is a step for converting the state quantities predicted in the prediction step S31 into predicted values ​​of electric potential. In the conversion step S32, the calculation unit 15b calculates the positions of the electric potential sensors 31 (hereinafter, electric potential measurement positions) based on the predicted values ​​of the state including the predicted position and posture of the frame 10. Then, the calculation unit 15b performs an electrostatic field analysis using the boundary element method based on the calculated positions of the electric potential sensors 31 and the current values, which are one of the state quantities, to calculate predicted values ​​of electric potential.

[0094] The reference point of the frame 10 is set at the position of the reference potential sensor 31o. The relative positions of the first potential sensor 31a, the second potential sensor 31b, and the third potential sensor 31c with respect to the reference potential sensor 31o are always constant. The calculation unit 15b calculates the positions (three-dimensional coordinates) of the first potential sensor 31a, the second potential sensor 31b, and the third potential sensor 31c based on the calculated values ​​of the position and orientation of the frame 10. At this time, the position of the reference potential sensor 31o is set as the potential measurement position ot, and the potential is set as the potential φot. In addition, the position of the first potential sensor 31a is set as the potential measurement position at, and the potential is set as the potential φat. The position of the second potential sensor 31b is set as the potential measurement position bt, and the potential is set as the potential φbt. The position of the third potential sensor 31c is set as the potential measurement position ct, and the potential is set as the potential φct.

[0095] A specific method for calculating the potential measurement positions at, bt, and ct corresponding to the positions of the first potential sensor 31a, the second potential sensor 31b, and the third potential sensor 31c when the three-dimensional coordinates of the reference potential sensor 31o, which serves as the reference point, and the attitude of the measurement unit 30 are given is as follows.

[0096] First, the relative position vectors between the potential measurement position ot serving as the reference point and the potential measurement positions at, bt, and ct are expressed as constant vectors a, b, and c. The relationship between the potential measurement position ot serving as the reference point and each of the potential measurement positions at, bt, and ct follows equation (4).

[0097]

number

[0098] However, E zαt ,E yβt ,E zγt is a rotation matrix and is expressed by the following equation (5).

[0099]

number

[0100] Note that 0 is a zero vector. The calculation unit 15b calculates the potential measurement position p (p = ot, at, bt, ct) using the position and orientation values ​​of the measurement unit 30 based on the above formulas (4) and (5). Since it is the potential value that is observed at the potential measurement position p (p = ot, at, bt, ct), the calculation unit 15b calculates the relationship between the potential and the potential measurement position p.

[0101] Next, the calculation unit 15b calculates the potential φp (φp = φot, φat, φbt, φct) at the potential measurement position when the calculated potential measurement position p (p = ot, at, bt, ct) and the predicted current value are given by electrostatic field analysis. The observation equation using the nonlinear function H can be modeled as the following equation (6). U t is the observation vector summarizing the predicted values ​​of the potential, H is the function of the electrostatic field analysis described later, v t represents the observation noise.

[0102]

number

[0103] The electrostatic field analysis will be described below. Consider a region Ω surrounded by an electrolyte (seawater), and assume that no loss or gain of ions occurs within the region. The potential φ within the region Ω satisfies the Laplace equation of the following formula (7). In this embodiment, the potential φ is considered to be the potential of seawater with respect to the metal. Therefore, the sign of the potential of the metal with respect to the solution normally used in electrochemistry is reversed.

[0104]

number

[0105] From equation (7), we derive the boundary integral equation (8) according to the usual formulation of the boundary element method, where Γ is the boundary and i is the current density.

[0106]

number

[0107] Under conditions of constant potential and constant current density, equation (8) can be transformed into equation (9).

[0108]

number

[0109] s represents the surface area of ​​the sacrificial anode 80, and κ represents the electrical conductivity. * (q, p) is the fundamental solution of the three-dimensional Laplace equation and is expressed by the following equation (10).

[0110]

number

[0111] In the above equation, r represents the magnitude of the vector r from point q on the boundary to point p inside the domain. By discretizing equation (10), the potential estimate at the potential measurement position p can be numerically solved.

[0112] (Comparison step S33) The comparison step S33 is a step of comparing the predicted value U t and the observed value u t and are compared using equation (11).

[0113]

number

[0114] In the comparison step S33, the calculation unit 15b calculates the Kalman gain K for minimizing the error of the estimated value with respect to the true value, using the following equation (12).

[0115]

number

[0116] (Modification step S34) The correction step is a step of correcting the state quantity based on the result of the comparison in the comparison step S33. In the correction step S34, the calculation unit 15b calculates an estimated value by performing correction using the Kalman gain K calculated in the comparison step S33. That is, the calculation unit 15b performs a filtering process to obtain a probabilistic anticorrosive current so that the predicted value of the potential at the position of the frame 10 approaches the observed value. That is, in the correction step S34, the calculation unit 15b corrects the next state to a state that is probabilistically closest to the true value based on the measured value.

[0117] Furthermore, the calculation unit 15b calculates the observed value u t and the state X predicted from the Kalman gain K t However, u t and U t includes the potential values ​​at the potential measurement positions ot, at, bt, and ct.

[0118]

number

[0119] Finally, the variance of the prediction error at the current time is corrected using the Kalman gain K, as shown in equation (14).

[0120]

number

[0121] The calculation unit 15b judges whether a certain end condition, such as the end of the measurement period, is satisfied, and if it is judged that the end condition is not satisfied, returns the process to the prediction step S31, and outputs an estimated value at that time if the end condition is satisfied. The calculation unit 15b of this embodiment repeats the process A / T times within the time measured in the frame 10, and ends the repetitive process when this is completed. The calculation unit 15b estimates the position and attitude of the frame 10 at each time and the value of the anticorrosive current I output from the sacrificial anode, and can update the estimated value of the anticorrosive current each time the repetition is performed.

[0122] As described above, in the calculation step S30, the calculation unit 15b repeats the prediction step S31, the conversion step S32, the comparison step S33, and the correction step S34 n times (n=A / T) at a constant sampling interval T within the observation time A. In addition, the calculation unit 15b calculates estimated values ​​of state quantities including the position and attitude of the frame 10 and the value of the anticorrosive current I output from the sacrificial anode 80.

[0123] In the calculation step S30, the calculation unit 15b calculates one estimated value of the value of the anticorrosive current I output from the sacrificial anode 80 for one initial state given in the initial state setting step S20. In this embodiment, a plurality of coordinates are given as the initial state in the initial state setting step S20. The calculation unit 15b calculates estimated values ​​of the value of the anticorrosive current I corresponding to each of the plurality of initial states.

[0124] (Decision step S40) The determination step S40 is a step of determining the most likely one of the multiple estimated values ​​calculated in the calculation step S30. The determination step S40 is performed by the calculation unit 15b. Alternatively, the determination step S40 may be a step in which an operator checks the multiple estimated values ​​output from the calculation unit 15b and directly determines the most likely estimated value.

[0125] In the above-mentioned calculation step S30, even if there is an error in the initial state, the error is corrected in the correction step S34 and a correct estimate is calculated by using a state quantity estimation model of an extended Kalman filter. However, when there is a large error in the initial state, an erroneous estimate is calculated due to the error. In the calculation step S30 of this embodiment, a plurality of initial states are given, so that a plurality of estimates are calculated in the calculation step S30. In addition, the plurality of estimates are classified into several groups that converge to different values. That is, the estimate calculated when the correct initial state is given and the estimate calculated when the initial state close to the correct initial state is given both converge to the correct estimate. In addition, the estimate calculated when the initial state that is far from the correct initial state is given converges to an erroneous estimate.

[0126] Initial states that converge to the same estimated value as the estimated value when a correct initial state is given (correct estimated value) are arranged around the correct initial state. Therefore, the number of correct estimated values ​​among the multiple estimated values ​​will be greater than the number of other incorrect estimated values. In other words, the most numerous estimated value among the multiple estimated values ​​can be determined to be the correct estimated value.

[0127] In the judgment step S40 of this embodiment, the calculation unit 15b first classifies the multiple estimates calculated corresponding to multiple initial states into multiple groups that are close to each other. In this embodiment, in the judgment step S40, the calculation unit 15b classifies the estimates that are within a range of ±0.1A into the same group. The calculation unit 15b then judges the group with the largest number of estimates to be the most likely estimate.

[0128] In the state quantity estimation method, any state quantity (parameter) of the state vector X shown in formula (1) can be calculated as an estimated value. However, in this embodiment, there is no point in obtaining an estimated value other than the value of the anticorrosive current I. For this reason, the estimated value judged in the judgment step S40 may also be the value of the anticorrosive current I.

[0129] According to this embodiment, the state quantity estimation method can estimate the value of the anticorrosive current I output from the sacrificial anode 80 under inspection as the most likely estimated value. Furthermore, the calculation unit 15b may automatically calculate the remaining life of the sacrificial anode 80 from the value of the anticorrosive current I and the installation time of the sacrificial anode 80 input in advance, etc.

[0130] (summary) The configuration, operation and effects of the state quantity estimating method and state quantity estimating device of this embodiment will be described below. The state quantity estimation method of this embodiment is a state quantity estimation method that estimates unknown state quantities that represent the cathodic protection state of a metal structure protected by a sacrificial anode in an electrolyte by using a state quantity estimation model. The state quantity estimation method has an acquisition step S10, an initial state assignment step S20, a calculation step S30, and a judgment step S40. The acquisition step S10 is a step of acquiring a measured value of the electric potential around the sacrificial anode 80 while moving the frame 10 to which the multiple electric potential sensors 31 are fixed in seawater (in the electrolyte) for a predetermined time. The initial state assignment step S20 is a step of assigning multiple initial states. The calculation step S30 is a step of calculating an estimated value of the state quantity for each of the multiple initial states. The judgment step S40 is a step of determining the most likely one of the multiple estimated values ​​calculated in the calculation step S30.

[0131] According to this configuration, when measuring the potential around the sacrificial anode 80 placed in seawater, a number of estimated values ​​are calculated based on a number of initial states in calculation step S30, and the most likely estimated value is determined in judgment step S40. Therefore, the calculation for determining the accuracy of the value in calculation step S30 can be omitted, the amount of calculation required for calculation step S30 can be reduced, and the overall calculation time can be shortened.

[0132] In the state quantity estimation method of this embodiment, the calculation step S30 includes a prediction step S31, a conversion step S32, a comparison step S33, and a correction step S34. The prediction step S31 is a step of predicting a next state updated over time from the previous state by using a state quantity estimation model, with the initial state being the first "previous state". The conversion step S32 is a step of converting the state quantity predicted in the prediction step S31 into a predicted value of potential. The comparison step S33 is a step of comparing the predicted value of the potential calculated in the conversion step S32 with the observed value. The correction step S34 is a step of correcting the next state to a state probabilistically closest to the true value based on the result of the comparison in the comparison step S33. In the calculation step S30, the prediction step S31, the conversion step S32, the comparison step S33, and the correction step S34 are repeatedly performed within the observation time to calculate an estimate value of the state quantity including the position and attitude of the frame 10 and the value of the anticorrosive current I output from the sacrificial anode 80. In a judgment step S40, the multiple estimated values ​​calculated corresponding to multiple initial states are classified into multiple groups in which values ​​that are close to each other are considered to be in the same group, and the group with the largest number of estimated values ​​is judged to be the most likely estimated value.

[0133] According to this configuration, even if the position and posture of the frame 10 are unstable due to the influence of waves or the like, it is possible to calculate the value of the anticorrosive current I of the sacrificial anode 80 by performing state quantity estimation. Furthermore, in the determination step S40, the most likely estimated value is determined based on the number of close estimated values, so that a correct estimated value can be calculated without spending much calculation time on the determination step S40.

[0134] In the state quantity estimation method of this embodiment, in the calculation step S30, the prediction step S31, the conversion step S32, the comparison step S33, and the correction step S34 are repeated n times (n=A / T) at a constant sampling interval T within the observation time A.

[0135] According to this configuration, by performing the prediction step S31, the conversion step S32, the comparison step S33, and the correction step S34 at regular sampling intervals, it is possible to improve the accuracy of the estimated value calculated in the calculation step S30.

[0136] In the state quantity estimation method of this embodiment, in an acquisition step S10, a frame 10 is moved in seawater in a vertical direction z. A plurality of initial states given in an initial state giving step S20 are initial positions of the frame 10 in the horizontal direction.

[0137] According to this configuration, multiple initial positions in the horizontal direction of frame 10 are given and calculation step S30 is performed. Therefore, there is no problem even if an incorrect value is given for the initial position of frame 10 in calculation step S30. As a result, the operator who measures the initial position of frame 10 does not need to know the exact position, and the burden on the operator can be reduced. Therefore, it is possible to suppress the measurement results from being affected by the measurement habits and variations of each operator.

[0138] In addition, in this configuration, "moving the frame 10 in the vertical direction z" means lowering the frame 10 straight down or lifting it straight up. Therefore, with this configuration, the frame 10 moves only in the vertical direction z. With this configuration, in the calculation step S30, it is possible to calculate an estimated value by assuming that the state quantities representing the positions of the frame 10 in the horizontal directions x and y are constant. This makes it possible to significantly reduce the amount of calculation in the calculation step S30.

[0139] In the state quantity estimation method of this embodiment, in an acquisition step S10, the water depth sensor 32 fixed to the frame 10 is used to acquire the vertical position of the frame 10 in seawater as the water depth.

[0140] According to this configuration, the position of the frame 10 in the vertical direction z can be measured over time by the water depth sensor 32, and the position in the vertical direction z can be excluded from the estimation of the multiple state quantities. This allows the amount of calculation in the calculation step S30 to be significantly reduced.

[0141] In the state quantity estimation method of this embodiment, the calculation step S30 is performed assuming that the orientation of the frame 10 is constant when the acquisition step S10 is performed.

[0142] According to this configuration, in the calculation step S30, an estimated value can be calculated assuming that the state quantity representing the posture of the frame 10 is constant. This allows the amount of calculation in the calculation step S30 to be significantly reduced. In order to consider the posture of the frame 10 to be constant, the frame 10 of this embodiment is suspended by two wires, the main wire 22 and the auxiliary wire 23.

[0143] In the state quantity estimation method of this embodiment, the necessary state quantity among the estimated state quantities is the value of the anticorrosive current I. In the determination step S40, the estimated values ​​falling within the range of ±0.1 A are classified into the same group.

[0144] As will be shown in the embodiment described later, the estimated values ​​of different groups are sufficiently larger than 0.1 A. According to this configuration, estimated values ​​within a range of ±0.1 A are grouped together, so that the estimated values ​​can be mechanically grouped, and the determination step S40 can be automated.

[0145] In the state quantity estimation method of this embodiment, the calculation step S30 may be performed assuming that the attitude of the frame 10 is constant when performing the acquisition step S10, the calculation step S30 may be performed assuming that the horizontal position of the frame 10 is constant when performing the acquisition step S10, or the vertical position of the frame 10 in the seawater is acquired as the water depth using a water depth sensor 32 fixed to the frame 10 in the acquisition step S10, and the vertical position of the frame 10 is treated as a known value in the calculation step S30.

[0146] According to this configuration, it is possible to reduce the amount of calculation in the calculation step S30 while adopting a configuration suited to the measurement environment, device, etc.

[0147] In the state quantity estimation method of this embodiment, a state quantity estimation model by an extended Kalman filter is used in the calculation step S30.

[0148] According to this configuration, by using the extended Kalman filter as the state quantity estimation model, the amount of calculation in the calculation step S30 can be significantly reduced compared to the case where other state quantity estimation models such as a particle filter are used.

[0149] The state quantity estimation device 1 of this embodiment performs the above-mentioned state quantity estimation method. The state quantity estimation device 1 has a frame 10, a measurement unit 30, and a calculation unit 15b. The frame 10 is submerged in seawater. The measurement unit 30 is fixed to the frame 10. The measurement unit 30 has a plurality of potential sensors 31 that measure the potential in the seawater. The calculation unit 15b performs a calculation step S30.

[0150] According to this configuration, it is possible to provide a state quantity estimation device 1 capable of performing the above-mentioned state quantity estimation method.

[0151] In the above-described state quantity estimating device 1, the measuring unit 30 has a water depth sensor 32 fixed to the frame .

[0152] According to this configuration, since the position of the frame 10 in the vertical direction z can be measured over time by the water depth sensor 32, the position in the vertical direction z can be excluded from the estimation of the multiple state quantities. This allows the amount of calculation in the calculation step S30 to be significantly reduced.

[0153] The above-described state quantity estimation device 1 has a main wire 22, an auxiliary wire 23, and a winding device 21. The main wire 22 and the auxiliary wire 23 suspend the frame 10. The winding device 21 simultaneously pays out and winds up the main wire 22 and the auxiliary wire 23.

[0154] According to this configuration, the frame 10 can be prevented from rotating in seawater, compared to the case where the frame 10 is suspended by only one wire. This makes it possible to suppress the rotation of the measuring unit 30 fixed to the frame 10, and it becomes possible to exclude the rotation parameter from the state quantity to be estimated in the state quantity estimation method. As a result, the amount of calculation performed by the calculation unit 15b can be reduced. Furthermore, according to this configuration, since the frame 10 is suspended by a wire, the frame 10 can be moved only in the vertical direction z by fixing the fulcrum of the wire (the first pulley unit 25a and the second pulley unit 25b in the embodiment). As a result, in the calculation step S30, the estimated value can be calculated assuming that the state quantity representing the position of the frame 10 in the horizontal directions x and y is constant, and the amount of calculation in the calculation step S30 can be significantly reduced. EXAMPLES

[0155] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples. In the examples, the state quantity estimation device 1 described in the above embodiment was used to perform the acquisition step S10, the initial state assignment step S20, the calculation step S30, and the determination step S40.

[0156] FIG. 5 is a diagram showing an example of coordinates of the initial state given in the initial state giving step S20 of this embodiment. In this embodiment, the sacrificial anode 80 is set as the origin, and the range of -0.3m to +0.3m in the left-right direction x and +0.8m to +1.2m in the front-back direction is set as the target range A1. The worker performing the acquisition step S10 works to submerge the frame 10 below the water surface in this target range A1. In this example, the range of -0.5m to +0.5m in the left-right direction x and the range of +0.6m to +1.4m in the front-back direction outside the target range A1 is set as the error range A2. The error range A2 is a range in which the position of the frame 10 may be displaced due to the shaking of the frame 10 even if the worker tries to submerge the frame 10 within the target range A1. Note that the target range A1 and the error range A2 are the ranges of the reference position of the frame 10 (i.e., the position of the reference potential sensor 31o). Therefore, if the position of the reference potential sensor 31o is within the error range A2, it is permitted that another part of the frame 10 is placed outside the error range A2.

[0157] In the acquisition step S10 of this embodiment, the frame 10 was submerged at the center position of the target range A1, that is, at a position 1.0 m from the sacrificial anode 80 in the front-rear direction, and the measurement values ​​were acquired.

[0158] In the initial state setting step S20, the target range A1 and the error range A2 are divided into 0.05 m in the left-right direction x and the front-back direction y, and the coordinates of the vertices of each area are set to the calculation unit 15b as the initial state. In this embodiment, the target range A1 and the error range A2 are divided into 20 areas in the left-right direction x and 14 areas in the front-back direction. Therefore, in the initial state setting step S20 of this embodiment, 15 x 21 = 315 initial states are set to the calculation unit 15b.

[0159] Fig. 6 is a graph showing a plurality of estimated values ​​calculated in the calculation step S30 when the 315 initial states shown in Fig. 5 are given. In Fig. 6, the x-axis and y-axis represent the coordinates on the horizontal plane of the frame 10 with respect to the sacrificial anode 80 given as the initial state. Also, in Fig. 6, the axis expressed in the height direction represents the anticorrosion current I as a calculated estimated value.

[0160] 6, the multiple estimated values ​​calculated in the calculation step S30 converge to values ​​in three regions according to the distance from the sacrificial anode 80. In this embodiment, the region where the estimated values ​​converge to 1.4 A±0.1 A is defined as the first region B1, the region where the estimated values ​​converge to 1.9 A±0.1 A is defined as the second region B2, and the region where the estimated values ​​converge to 2.8 A±0.1 A is defined as the third region B3. That is, in the determination step S40, the estimated values ​​that fall within the range of ±0.1 A are classified into three groups, the first region B1, the second region B2, and the third region B3.

[0161] 6, among the first region B1, the second region B2, and the third region B3, the second region B2 is the widest region. That is, the number of estimated values ​​included in the second region B2 is greater than the number of estimated values ​​included in each of the other regions (the first region B1 and the third region B3). Therefore, in this embodiment, the estimated value (1.9A) in the second region B2 is determined to be the most likely estimated value.

[0162] Table 1 is a table comparing the calculation time between this embodiment and a comparative example performed using another state quantity estimation model. In the comparative example, a particle filter was used as the state quantity estimation model. In addition, in the comparative example, the same measured values ​​as in this embodiment were given and calculations were performed. The same estimated value (1.9 A) was calculated in the embodiment and the comparative example. In addition, when the value of the anticorrosion current I of the target sacrificial anode 80 was actually measured by the voltage drop method using a shunt resistor, it was confirmed that the value was almost equal to the estimated values ​​in the embodiment and the comparative example.

[0163] [Table 1]

[0164] In particle filters, particles with numerical values ​​distributed over multiple state quantities are assumed, and the state quantities are estimated by deleting and duplicating particles from the estimated probability distribution of each particle. For this reason, when using particle filters, the amount of calculations increases exponentially with the number of state quantities. However, on the other hand, particle filters compare the likelihood of estimated values ​​from the probability distribution of each particle and provide multiple error ranges for correction, so that even if the initial state is incorrect, a single converged estimated value can be obtained.

[0165] In contrast, in the calculation step S30 using the extended Kalman filter as in the embodiment, although the calculation time can be shortened, there is a risk that a correct estimated value cannot be calculated if the initial state to be assigned is significantly different from the correct initial state. In this embodiment, the above-mentioned multiple initial states (the coordinates of the initial position of frame 10 of 315) are assigned to the calculation unit 15b in the initial state assignment step S20, and an estimated value is calculated for each initial state in the calculation step S30. In addition, the most likely one is selected from the multiple estimated values ​​in the judgment step S40. It has been confirmed that this significantly reduces the amount of calculation, shortens the calculation time, and allows the calculation of a correct estimated value.

[0166] In the calculation step S30 of this embodiment, it took about 30 seconds to calculate an estimated value for one initial state. In the initial state assignment step S20 of this embodiment, 315 initial states were given to the calculation unit 15b, and it took a total of 158 minutes to calculate an estimated value for each initial state.

[0167] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be appropriately modified without departing from the spirit of the present invention. For example, in the above embodiment, an extended Kalman filter is used as a state quantity estimation model, but other state quantity estimation methods such as a Kalman filter or an unscented Kalman filter may be used. [Explanation of symbols]

[0168] 1...state quantity estimation device, 10...frame (moving body), 15b...calculation unit, 21...winding device, 22...main wire, 23...auxiliary wire, 30...measurement unit, 31...potential sensor, 32...water depth sensor, 80...sacrificial anode, 90...structure, I...anticorrosion current, S10...acquisition step, S20...initial state assignment step, S30...calculation step, S31...prediction step, S32...conversion step, S33...comparison step, S34...correction step, S40...determination step, Xt...state, z...vertical direction

Claims

1. A state quantity estimation method for estimating an unknown state quantity that represents a cathodic protection state of a metal structure that is protected from corrosion by a sacrificial anode in an electrolyte, using a state quantity estimation model, comprising: an acquiring step of acquiring a measured value of the potential around the sacrificial anode while moving a moving body having a plurality of potential sensors fixed thereto in the electrolyte for a predetermined time; an initial state assignment step of assigning a plurality of initial states; a calculation step of calculating an estimate value of the state quantity for each of the plurality of initial states; A determination step of determining the most likely one of the plurality of estimated values ​​calculated in the calculation step. State estimation method.

2. The calculation step includes: a prediction step of predicting a next state, which is updated in time from the previous state, by using the state quantity estimation model, with the initial state being the first "previous state"; a conversion step of converting the state quantity predicted in the prediction step into a predicted value of potential; a comparison step of comparing the predicted value of the potential calculated in the conversion step with an observed value; and a correction step of correcting the next state to a state probabilistically closest to a true value based on a result of the comparison in the comparison step, In the calculation step, the prediction step, the conversion step, the comparison step, and the correction step are repeatedly performed within an observation time to calculate the estimated value of the state quantity including the position and attitude of the moving body and the value of the anticorrosive current output from the sacrificial anode; In the determining step, the estimated values ​​calculated corresponding to the initial states are classified into a plurality of groups in which values ​​that are close to each other are regarded as the same group, and the group containing the largest number of the estimated values ​​is determined to be the most likely estimated value. The state quantity estimation method according to claim 1 .

3. In the calculation step, the prediction step, the conversion step, the comparison step, and the correction step are repeated n times (n=A / T) at a constant sampling interval T within an observation time A. The state quantity estimating method according to claim 2 .

4. In the obtaining step, the moving body is moved in a vertical direction in the electrolyte; The plurality of initial states assigned in the initial state assigning step are initial positions of the moving body in a horizontal direction. The state quantity estimation method according to claim 1 .

5. In the acquiring step, a vertical position of the moving body in the electrolyte is acquired as a water depth using a water depth sensor fixed to the moving body. The state quantity estimating method according to claim 4.

6. the calculation step is performed assuming that the attitude of the moving body is constant when the acquisition step is performed. The state quantity estimating method according to claim 5 .

7. the estimated value of the state quantity is a value of the anticorrosion current, In the determination step, the estimated values ​​falling within a range of ±0.1 A are classified as the same group. The state quantity estimating method according to claim 2 .

8. the calculation step is performed assuming that the attitude of the moving body is constant when the acquisition step is performed. the calculation step is performed assuming that the horizontal position of the moving object is constant when the acquisition step is performed. Alternatively, in the acquiring step, a water depth is acquired by using a water depth sensor fixed to the moving body, and in the calculating step, the vertical position of the moving body in the electrolyte is treated as a known value. Select one or more of the following: The state quantity estimation method according to claim 1 .

9. In the calculation step, the state quantity estimation model using an extended Kalman filter is used. The state quantity estimation method according to claim 1 .

10. A state quantity estimation device that performs the state quantity estimation method according to any one of claims 1 to 9, The moving body is submerged in the electrolyte; a measurement unit having a plurality of potential sensors fixed to the moving body for measuring the potential in the electrolyte; A calculation unit that performs the calculation step. State quantity estimator.

11. The measurement unit has a water depth sensor fixed to the moving body. The state quantity estimating device according to claim 10.

12. A main wire and an auxiliary wire for suspending the moving body; a winding device that simultaneously unwinds and winds the main wire and the auxiliary wire, The state quantity estimating device according to claim 11.

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