Position measuring apparatus and method

Abstract

[Project] Reduce position measurement errors caused by the accumulation of minute errors. [Solution] The position measuring device (1) comprises a sensor (11) for measuring the acceleration or angular velocity of the valve rod of the ON-OFF valve (200), a position information generating unit (12) for integrating the acceleration or angular velocity measured by the sensor (11) and converting it into position information, a sensor (13) for detecting mechanical vibrations that occur in conjunction with the opening and closing of the ON-OFF valve (200), a reference position defining unit (14) for storing position information as reference position information when vibrations are detected by the sensor (13), and a calibration processing unit (15) for performing calibration processing to reduce position measurement errors based on the position information obtained by the position information generating unit (12) and the reference position information when vibrations are detected by the sensor (13).

Description

Technology Field

[0001] The present invention relates to a position measuring device and method for converting the acceleration or angular velocity of a measurement target into position information by integrating it. Background Technology

[0002] Valves used in petrochemical plants, etc. (e.g., the control valve of FIG. 8) require particular attention to safety, and therefore, regular maintenance is performed. The control valve shown in FIG. 8 consists of a valve body (100) that opens and closes a passage through which fluid flows, a positioner (101) that converts an input electrical signal into air pressure, and an actuator (102) that operates the valve body (100) according to the air pressure supplied from the positioner (101).

[0003] In order to improve the efficiency of valve maintenance work in a plant in which a number of valves as shown in Fig. 8 are installed, techniques for detecting stick-slip in the sliding part of the valve (see Patent Document 1), techniques for determining the hunting state of the valve (see Patent Document 2), and techniques for detecting scale adhesion to the valve (see Patent Document 3) have been proposed.

[0004] Meanwhile, there is an ON-OFF valve, which is a type of valve different from a control valve capable of continuously changing the opening, and which can only take two positions of opening: fully open and fully closed. The ON-OFF valve (200) shown in FIG. 9 uses a ball valve and has a structure in which a ball (201) that is a valve chain is fitted into a seat ring (202) called a ball seat, and the valve can be opened or closed by rotating the valve stem (203) 90 degrees by an actuator (204). In addition, depending on the type, there are also valves other than 90 degrees.

[0005] As a method for detecting defects with ON-OFF valves as the diagnostic target, a technique has been proposed to detect defects by using the time required to open and close the valve as a diagnostic indicator, or by using the maximum operating speed and minimum operating speed as diagnostic indicators (see Patent Document 4). In addition, a technique has been proposed to monitor the supply air pressure for operating the ON-OFF valve (see Patent Documents 5 and 6).

[0006] In the diagnosis of ON-OFF valves, it is required to apply the method to multiple ON-OFF valves already installed in the plant. From the perspective of the ON-OFF valve diagnosis method, an opening measurement method is considered in which an acceleration sensor or an angular velocity sensor (gyro sensor), etc., is installed on the valve stem and the integral of the acceleration or angular velocity is converted into position information. That is, it is desirable to perform valve diagnosis by attaching an opening meter equipped with an acceleration sensor or an angular velocity sensor to the ON-OFF valves already installed in the plant.

[0007] When converting the integral of acceleration or angular velocity into position information, even if the acceleration or angular velocity can be measured with a precision within an acceptable range without defects, the position measurement error (opening measurement error in the above example) caused by the accumulation of minute errors (such as rounding errors or noise components in the processor) cannot be ignored. Furthermore, this error can lead to a decrease in the reliability of the entire diagnostic or control system. Since the mounting environment and mounting angle of the valve vary, it is difficult to use geomagnetism or medium acceleration for calibration. Additionally, although calibration becomes possible by attaching other devices at locations other than the valve stem where the acceleration or angular velocity sensor is attached, this is difficult to realize due to the diverse shapes of the valves. Therefore, it is required to reduce the position measurement error using a single position measurement device.

[0008] Furthermore, this challenge is not limited to the measurement of the opening of ON-OFF valves, but can occur in many cases when employing a measurement method that converts the integral of acceleration or angular velocity into position information. Prior art literature

[0009] Japanese Patent Publication No. 3254624 Japanese Patent Publication No. 6200309 Japanese Patent Publication No. 6216633 Japanese Patent Publication No. 7265328 Japanese Patent Publication No. Hei 7-119862 Japanese Patent Publication No. Hei 11-210921 The problem to be solved

[0010] The present invention is made to solve the above problem, and aims to reduce position measurement error (drift) caused by the accumulation of minute errors in a position measurement device and method that converts the acceleration or angular velocity of a measurement target into position information by integrating it. means of solving the problem

[0011] The position measuring device of the present invention is characterized by comprising: a first sensor configured to measure the acceleration or angular velocity of a measurement target; a position information generating unit configured to convert the acceleration or angular velocity into position information by integrating it over time; a second sensor configured to detect mechanical vibrations occurring in conjunction with the movement of the measurement target; a reference position defining unit configured to store the position information of the measurement target as reference position information when vibrations are detected by the second sensor; and a calibration processing unit configured to perform a calibration process to reduce position measurement errors based on the position information obtained by the position information generating unit and the reference position information when vibrations are detected by the second sensor.

[0012] In addition, in one configuration example of the position measuring device of the present invention, the reference position information is stored in advance for each movement direction of the measurement target, and the calibration processing unit performs calibration processing using the reference position information according to the movement direction of the measurement target.

[0013] In addition, in one configuration of the position measuring device of the present invention, the first sensor measures the acceleration or angular velocity of the valve stem of the ON-OFF valve, the position information generating unit converts the acceleration or angular velocity into the opening degree of the ON-OFF valve, which is the position information, the second sensor detects mechanical vibrations that occur when the ON-OFF valve moves from full closing to full opening, or mechanical vibrations that occur when the ON-OFF valve moves from full opening to full closing, the reference position defining unit stores the reference position information during the opening operation of the ON-OFF valve and the reference position information during the closing operation in advance, and the calibration processing unit performs calibration processing using the reference position information during the opening operation of the ON-OFF valve during the opening operation, and performs calibration processing using the reference position information during the closing operation of the ON-OFF valve during the closing operation.

[0014] In addition, in one embodiment of the position measuring device of the present invention, the second sensor is characterized by detecting vibrations generated by the operation of a first limit switch that turns on when the ON-OFF valve reaches the vicinity of the open position, or vibrations generated by the operation of a second limit switch that turns on when the ON-OFF valve reaches the vicinity of the fully closed position.

[0015] In addition, the position measurement method of the present invention is characterized by comprising: a first step of measuring the acceleration or angular velocity of a measurement target; a second step of converting the acceleration or angular velocity into position information by integrating it over time; a third step of detecting mechanical vibrations that occur in conjunction with the movement of the measurement target; a fourth step of referring to a reference position specification unit that stores the position information of the measurement target when the vibration is detected as reference position information, and performing a correction process to reduce the position measurement error based on the position information obtained by the second step and the reference position information when the vibration is detected. Effects of the invention

[0016] According to the present invention, by installing a second sensor, a reference position defining unit, and a calibration processing unit, position measurement error (drift) caused by the accumulation of minute errors can be reduced by the position measuring device alone. Brief explanation of the drawing

[0017] FIG. 1 is a block diagram showing the configuration of a position measuring device according to a first embodiment of the present invention. FIG. 2 is a flowchart illustrating the operation of a position measuring device according to a first embodiment of the present invention. Figure 3 is an instrumentation diagram of an ON-OFF valve. FIG. 4 is a diagram illustrating the correction processing by the calibration processing unit according to the first embodiment of the present invention. FIG. 5 is a block diagram showing the configuration of a position measuring device according to a second embodiment of the present invention. FIG. 6 is a flowchart illustrating the operation of a position measuring device according to a second embodiment of the present invention. FIG. 7 is a block diagram showing an example of the configuration of a computer realizing a position measuring device according to the first and second embodiments of the present invention. Figure 8 is a drawing showing one example of a control valve. Figure 9 is a drawing showing one example of an ON-OFF valve. Specific details for implementing the invention

[0018] [Principles of Invention]

[0019] Generally, when the measurement error is a "deviation" known as drift, it is advisable to perform proper calibration. However, in the case of the above-mentioned ON-OFF valve, it is necessary to add a function to detect full closure / opening in order to obtain information on the reference position corresponding to full closure (0% opening) or openness (100% opening), and even if such a function is already provided, it is necessary to add a signal line to acquire the detection information. Therefore, since the position measurement error cannot be corrected merely by adding an opening gauge to the ON-OFF valve, it is difficult to make it possible to add it simply.

[0020] The inventor focused on the fact that the object of position measurement involves mechanical movement. That is, in the case of the aforementioned ON-OFF valve, residual vibration when the valve shaft moves from open to fully closed and stops, or vibration generated by a pre-equipped mechanical limit switch for detecting fully closed / open positions, occurs as a highly reproducible phenomenon at a specific reference position, even if it is not exactly at the fully closed / open position.

[0021] In addition, it was hypothesized that by detecting this vibration with a vibration sensor and using it as a reference position for vibration detection that is predetermined, a calibration can be performed to reduce position measurement error (drift). That is, there is no need to add new signal lines, and the configuration can be made by simply adding a position measuring device (opening meter) equipped with an acceleration sensor or an angular velocity sensor and a vibration sensor to the ON-OFF valve.

[0022] In addition, if a measurement method is employed to convert the integral of acceleration or angular velocity into position information, and if the object of position measurement involves reproducible vibration caused by any cause, then the present invention is applicable.

[0023] [1st Example]

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a position measuring device according to a first embodiment of the present invention. The position measuring device (1) is a battery-driven wireless opening meter, and comprises a valve ID memory unit (10) that stores a unique ID (identification information) on an ON-OFF valve (200) which is the mounting site of the position measuring device (1), a sensor (11) that measures the acceleration or angular velocity of the valve stem of the ON-OFF valve (200), a position information generation unit (12) that integrates the acceleration or angular velocity measured by the sensor (11) and converts it into position information, a sensor (13) that detects mechanical vibrations occurring in conjunction with the opening and closing of the ON-OFF valve (200), a reference position definition unit (14) that stores position information as reference position information when vibrations are detected by the sensor (13), a calibration processing unit (15) that performs a correction process to reduce position measurement errors based on the position information obtained by the position information generation unit (12) and the reference position information when vibrations are detected by the sensor (13), and a unit that stores position information. It is equipped with a memory unit (16), a fault diagnosis unit (17) that calculates an indicator of change leading to a fault in the ON-OFF valve (200) based on location information and performs a fault diagnosis of the ON-OFF valve (200) based on the indicator, a wireless communication unit (18) that wirelessly transmits data to a valve maintenance support device (not shown), and a battery (19) that supplies power to each part of the location measurement device (1).

[0025] FIG. 2 is a flowchart explaining the operation of a position measuring device (1). A sensor (11) of the position measuring device (1), mounted on the ON-OFF valve (200) to be measured, measures the acceleration or angular velocity of the valve stem of the ON-OFF valve (200) (Step S100 of FIG. 2). For example, if the ON-OFF valve (200) is of the type in which the valve stem moves up and down to open or fully close, it is preferable to measure the acceleration of the valve stem. In addition, if the ON-OFF valve (200) is of the type such as a ball valve in which the valve stem rotates to open or fully close, it is preferable to measure the angular velocity of the valve stem.

[0026] The position information generating unit (12) converts the acceleration or angular velocity measured by the sensor (11) into position information by integrating it over time (Step S101 of FIG. 2). Specifically, when the acceleration of the valve stem is measured by the sensor (11), the position information generating unit (12) converts the acceleration into position information (displacement) of the valve stem by integrating it twice over time. In addition, when the angular velocity is measured by the sensor (11), the position information generating unit (12) converts the angular velocity into position information (angular displacement) by integrating it once over time.

[0027] The initial value of the opening (100% or 0%) when the ON-OFF valve (200) is stopped in the open or fully closed position is known. Additionally, the direction of operation of the ON-OFF valve (200) (from open to fully closed or from fully closed to open) can be determined from the displacement or angular displacement of the valve rod. Thus, the position information generating unit (12) can convert the position (displacement or angular displacement) of the valve rod into the opening of the ON-OFF valve (200) by using the initial value of the opening (0%) and the known relationship between the linear displacement of the valve rod and the change in the opening of the ON-OFF valve (200) or the known relationship between the angular displacement of the valve rod and the change in the opening of the ON-OFF valve (200) when the ON-OFF valve (200) is opened. Additionally, the position information generation unit (12) can convert the position (displacement or angular displacement) of the valve rod into an opening by using the initial value (100%) of the opening when the ON-OFF valve (200) closes, and the known relationship between the linear displacement of the valve rod and the change in the opening of the ON-OFF valve (200) or the known relationship between the angular displacement of the valve rod and the change in the opening of the ON-OFF valve (200).

[0028] The sensor (11) and the position information generation unit (12) periodically perform the processing of steps S100 and S101. By repeating the processing of steps S100 and S101, time series data of the opening degree of the ON-OFF valve (200) is stored in the memory unit (16). The time series data of the opening degree calculated by the position information generation unit (12) is designated as D(t).

[0029] Next, the sensor (13) detects mechanical vibrations occurring in conjunction with the opening and closing of the ON-OFF valve (200) (Step S102 of FIG. 2). Most of the ON-OFF valve (200) is instrumented as shown in FIG. 3, and actuator air is supplied to the actuator (204) of the ON-OFF valve (200) through the solenoid valve (205). The open state of the ON-OFF valve (200) is detected by the limit switch (206), and the closed state is detected by the limit switch (207). When the limit switch (206) is turned ON during the opening operation of the ON-OFF valve (200), mechanical vibrations are generated by the operation of the limit switch (206). Likewise, when the limit switch (207) is turned on during the closing operation of the ON-OFF valve (200), mechanical vibration is generated by the operation of the limit switch (207). The sensor (13) detects this vibration.

[0030] The sensor (13) may detect residual vibration when the valve rod of the ON-OFF valve (200) moves from open to fully closed, or from fully closed to open, and stops.

[0031] Next, the reference position specification unit (14) stores in advance the position information of the valve stem (opening degree of the ON-OFF valve (200)) when vibration is detected by the sensor (13) as reference position information (reference opening degree). An operator who installs the position measuring device (1) on the ON-OFF valve (200) can investigate the reference position information (reference opening degree) through a calibration test at the time of installation and store it in the reference position specification unit (14). The reference position information includes reference position information during the opening operation of the ON-OFF valve (200) and reference position information during the closing operation.

[0032] At the time when the limit switch (206) is turned on, there is a possibility that the ON-OFF valve (200) is not exactly in the open position (opening degree 100%), but it is good to remember the position near the open position (opening degree near 100%) when vibration caused by the limit switch (206) being turned on as reference position information for the opening operation. Likewise, at the time when the limit switch (207) is turned on, there is a possibility that the ON-OFF valve (200) is not exactly in the fully closed position (opening degree 0%), but it is good to remember the position near the fully closed position (opening degree near 0%) when vibration caused by the limit switch (207) being turned on as reference position information for the closing operation.

[0033] When vibration is detected by the sensor (13), the calibration processing unit (15) corrects the time series data D(t) of the opening degree stored in the memory unit (16) based on the reference position information (reference opening degree) stored in the reference position definition unit (14) (Step S103 of FIG. 2).

[0034] The operating direction of the ON-OFF valve (200) (from open to fully closed or from fully closed to open) can be determined from the displacement or angular displacement of the valve stem. Accordingly, when vibration is detected by the sensor (13), it can be determined which of the reference position information during the opening operation of the ON-OFF valve (200) and the reference position information during the closing operation should be used for correction.

[0035] When the ON-OFF valve (200) is opened, the calibration processing unit (15) corrects the value of the opening degree when vibration is detected by the sensor (13) among the time series data D(t) of the opening degree calculated by the position information generation unit (12) to the value of the reference position information (reference opening degree near 100%) during the opening operation. Likewise, when the ON-OFF valve (200) is closed, the calibration processing unit (15) corrects the value of the opening degree when vibration is detected by the sensor (13) among the time series data D(t) of the opening degree calculated by the position information generation unit (12) to the value of the reference position information (reference opening degree near 0%) during the closing operation. By performing calibration processing in this way, the position measurement error can be corrected. In addition, although the calibration process is described in FIG. 2 as a necessary condition for the following flow, it is not limited to this, and calibration based on reference position information (reference opening) may be appropriately performed, for example, only when the accumulated error by integration exceeds the allowable value.

[0036] In this example, only drift due to integration is assumed, and correction is performed using only the value of the opening degree of either the open or fully closed state when vibration is detected by the sensor (13). However, if an error in acceleration or angular velocity itself is assumed, correction may be performed using the opening degree where vibration is detected by the sensor (13) in both the open and fully closed states. As shown in FIG. 4, when the correct opening degree to be detected on the horizontal axis and the opening degree output including the error on the vertical axis are taken based on the time series data D(t) of the opening degree, if the reference position information (reference opening degree) is Dref and the value of the opening degree when vibration is detected by the sensor (13) during the open state is D(ton), then the error of the opening degree when vibration is detected by the sensor (13) is ΔD(ton) = Dref - D(ton). Likewise, ΔD(toff) is obtained as an error during the fully closed state. Accordingly, the error ΔD(t) at each opening can be calculated from ΔD(ton) and ΔD(toff). By adding the error ΔD(t) at that opening to each of the detected opening data D(t), the opening data D'(t) after calibration processing can be obtained. In this way, the calibration processing unit (15) can correct the opening when vibration is detected by the sensor (13), even if the error of the acceleration or angular velocity itself is included.

[0037] In the above description, the calibration processing unit (15) performs calibration processing at the point when vibration is detected by the sensor (13), but as described above, there is a possibility that the ON-OFF valve (200) is not fully open or fully closed at the point when vibration is detected by the sensor (13). Therefore, the processing of steps S100 and S101 continues even after the point when vibration is detected by the sensor (13) and calibration processing is performed. However, after the point when calibration processing is performed, the position information generation unit (12) needs to convert the displacement or angular displacement into an opening by using the value of the reference position information (a reference opening near 100% or a reference opening near 0%) as the initial value of the opening.

[0038] If the position information generating unit (12) continues to be in a state of 100% opening for a certain period of time or longer, it determines that the ON-OFF valve (200) has stopped in the open position and resets the initial value of the opening to 100%. Likewise, if the position information generating unit (12) continues to be in a state of 0% opening for a certain period of time or longer, it determines that the ON-OFF valve (200) has stopped in the fully closed position and resets the initial value of the opening to 0%.

[0039] Next, at a predetermined timing, the fault diagnosis unit (17) of the position measuring device (1) calculates an indicator of change leading to a fault in the ON-OFF valve (200) based on the time series data D'(t) of the opening after the correction process (Step S104 of FIG. 2), and performs a fault diagnosis of the ON-OFF valve (200) based on the indicator (Step S105 of FIG. 2). As for the timing at which the fault diagnosis unit (17) performs the processing, for example, the timing when the ON-OFF valve (200) is stopped, the processing may also be performed at a separate timing.

[0040] For example, the defect diagnosis unit (17) uses the time required to open and close the ON-OFF valve (200) as an indicator of a change leading to a defect (step S104). When the time required to open and close exceeds a predetermined diagnosis threshold, the defect diagnosis unit (17) determines that there is a possibility that a defect has occurred in the ON-OFF valve (200), and when the time required to open and close is less than the diagnosis threshold, it determines that it is normal (step S105).

[0041] The wireless communication unit (18) of the position measuring device (1) wirelessly transmits data including the valve ID stored in the valve ID memory unit (10), time series data of the opening degree after calibration processing, an indicator of the change leading to the defect, and the result of the defect diagnosis by the defect diagnosis unit (17) to a valve maintenance support device not shown (Step S106 of FIG. 2). The valve maintenance support device presents the received indicator and the result of the defect diagnosis to the operator.

[0042] The operation of the defect diagnosis unit (17) in this embodiment is one example, and a separate diagnosis may be performed. In addition, the defect diagnosis unit (17) is not an essential component of the present invention. If the defect diagnosis unit (17) is not installed, the wireless communication unit (18) may transmit the valve ID and time series data of the opening degree after calibration processing.

[0043] [2nd Example]

[0044] In the first embodiment, a battery-powered wireless opening meter was described as an example of a position measuring device, but the present invention can be applied to any position measuring device that converts the acceleration or angular velocity of a measurement target into position information of the measurement target. An example of a generalized position measuring device of the first embodiment is shown in FIG. 5. In the configuration of FIG. 5, the measurement target (300) is an object moving linearly or an object undergoing rotational motion.

[0045] FIG. 6 is a flowchart explaining the operation of the position measuring device (1a) of the present embodiment. The sensor (11) of the position measuring device (1a) mounted on the measurement target (300) measures the acceleration or angular velocity of the measurement target (300) (Step S200 of FIG. 6). If the measurement target (300) is moving linearly, it is preferable to measure the acceleration of the measurement target (300). In addition, if the measurement target (300) is moving in rotation, it is preferable to measure the angular velocity of the measurement target (300).

[0046] The position information generation unit (12) converts the acceleration or angular velocity measured by the sensor (11) into position information by integrating it over time (Step S201 of FIG. 6). Specifically, when the acceleration of the measurement target (300) is measured by the sensor (11), the position information generation unit (12) converts the acceleration into the displacement of the measurement target (300) by integrating it twice over time. In addition, when the angular velocity is measured by the sensor (11), the position information generation unit (12) converts the angular velocity into angular displacement by integrating it once over time.

[0047] Here, the initial position when the measurement target (300) is stationary is assumed to be a reference position. In the case of a measurement target (300) moving linearly, the position information generating unit (12) can convert the displacement of the measurement target (300) into a linear position by using the initial position of the measurement target (300). Additionally, in the case of a measurement target (300) moving in rotation, the position information generating unit (12) can convert the angular displacement of the measurement target (300) into a rotational position by using the initial position of the measurement target (300).

[0048] The sensor (11) and the position information generation unit (12) periodically perform the processing of steps S200 and S201. By repeating the processing of steps S200 and S201, time series data of the position of the measurement target (300) is stored in the memory unit (16). The time series data of the position calculated by the position information generation unit (12) is denoted as X(t).

[0049] Next, the sensor (13) detects mechanical vibrations that occur in conjunction with the movement of the measurement target (300) (Step S202 of FIG. 6). The sensor (13) may detect residual vibrations, for example, when the measurement target (300) moves and stops.

[0050] Next, the reference position specification unit (14) stores the position information of the measurement target (300) when vibration is detected by the sensor (13) as reference position information. An operator who mounts the position measuring device (1a) on the measurement target (300) can investigate the reference position information through a calibration test at the time of mounting and store it in the reference position specification unit (14). The reference position information includes reference position information when the measurement target (300) moves in a first direction (e.g., right direction or right turn) and reference position information when the measurement target (300) moves in a second direction (e.g., left direction or left turn).

[0051] When vibration is detected by the sensor (13), the calibration processing unit (15) corrects the time series data X(t) of the position stored in the memory unit (16) based on the reference position information stored in the reference position definition unit (14) (Step S203 of FIG. 6).

[0052] The direction of operation (first direction or second direction) of the measurement target (300) can be determined from the displacement or angular displacement of the measurement target (300). Accordingly, when vibration is detected by the sensor (13), it can be determined which of the reference position information of the first direction and the reference position information of the second direction should be used for calibration.

[0053] When the measurement target (300) moves in the first direction, the calibration processing unit (15) corrects the position where vibration is detected by the sensor (13) among the position time series data X(t) calculated by the position information generation unit (12) to the value of the reference position information of the first direction. Likewise, when the measurement target (300) moves in the second direction, the calibration processing unit (15) corrects the position where vibration is detected by the sensor (13) among the position time series data X(t) calculated by the position information generation unit (12) to the value of the reference position information of the second direction. In addition, although the calibration processing is described in FIG. 6 as a necessary condition for the following flow, it is not limited to this, and calibration based on reference position information (reference opening) may be appropriately performed, for example, only when the accumulated error by integration exceeds the allowable value.

[0054] In this example, only drift due to integration is assumed, and correction is performed using only one reference position where vibration is detected by the sensor (13); however, if an error in acceleration or angular velocity itself is assumed, correction may be performed using multiple positions where vibration is detected by the sensor (13). If reference position information is Xref and the position where vibration is detected by the sensor (13) is X(ton), the error in the position where vibration is detected by the sensor (13) is ΔX(ton) = Xref - X(ton). Likewise, ΔD(toff) is obtained as an error at a separate reference position. Therefore, the error ΔX(t) at each position can be calculated from ΔX(ton) and ΔX(toff). By adding the error ΔX(t) at that position to each of the position data X(t), the position data X'(t) after correction processing can be obtained. In this way, the calibration processing unit (15) can correct the position where vibration is detected by the sensor (13), even if the error in acceleration or angular velocity itself is included.

[0055] In the above description, the calibration processing unit (15) performs calibration processing at the point when vibration is detected by the sensor (13), but there is a possibility that the measurement target (300) has not reached a limit position at the point when vibration is detected by the sensor (13). Therefore, even after the point in time when vibration is detected by the sensor (13) and calibration processing is performed, the processing of steps S200 and S201 continues. However, after the point in time when calibration processing is performed, the position information generation unit (12) needs to convert the displacement or angular displacement to the position of the measurement target (300) by setting the value of the reference position information as the initial position.

[0056] The position information generation unit (12) determines that the measurement target (300) has stopped if the state in which the measurement target (300) has reached the limit position of the first direction continues for a certain period of time or longer, and resets the initial position to the limit position of the first direction. Likewise, the position information generation unit (12) determines that the measurement target (300) has stopped if the state in which the measurement target (300) has reached the limit position of the second direction continues for a certain period of time or longer, and resets the initial position to the limit position of the second direction.

[0057] The wireless communication unit (18) of the position measuring device (1a) wirelessly transmits time series data of the position of the measurement target (300) to the outside (step S204 of FIG. 6).

[0058] In this way, the present invention can be applied to a position measuring device (1a) that converts the integral of acceleration or angular velocity into position information.

[0059] In addition, since there is a possibility that the sensor (13) may misdetect a vibration different from the vibration that is intended to be detected in the first and second embodiments, the calibration processing unit (15) may determine whether a desired vibration corresponding to a reference position has been detected, for example by recognizing the pattern of the vibration, and perform a calibration process when it is determined that a desired vibration has been detected.

[0060] The valve ID memory unit (10), position information generation unit (12), reference position definition unit (14), calibration processing unit (15), memory unit (16), fault diagnosis unit (17), and wireless communication unit (18) of the position measurement device (1, 1a) described in the first and second embodiments can be realized by a computer equipped with a CPU (Central Processing Unit), a memory device, and an interface, and by a program that controls these hardware resources. An example of the configuration of this computer is shown in FIG. 7.

[0061] The computer is equipped with a CPU (400), a memory device (401), and an interface device (abbreviated as I / F) (402). Hardware such as sensors (11, 13) and a wireless communication unit (18) is connected to the I / F (402). In such a computer, a program for realizing the present invention is stored in the memory device (401). The CPU (400) executes the processing described in the first and second embodiments according to the program stored in the memory device (401). Industrial applicability

[0062] The present invention can be applied to a technology that converts acceleration or angular velocity into position information by integrating it. Explanation of the symbols

[0063] 1, 1a: Position measuring device 10: Valve ID memory unit 11, 13: Sensors 12: Position information generation unit 14: Reference position definition unit 15: Calibration processing unit 16: Memory Unit 17: Fault Diagnosis Unit 18: Wireless communication unit 19: Battery 200: ON-OFF valve 300: Measurement target

Claims

Claim 1 A position measuring device characterized by comprising: a first sensor configured to measure the acceleration or angular velocity of a measurement target; a position information generating unit configured to convert the acceleration or angular velocity into position information by integrating it over time; a second sensor configured to detect mechanical vibrations occurring in conjunction with the movement of the measurement target; a reference position defining unit configured to store the position information of the measurement target as reference position information when vibrations are detected by the second sensor; and a calibration processing unit configured to perform calibration processing to reduce position measurement errors based on the position information obtained by the position information generating unit and the reference position information when vibrations are detected by the second sensor. Claim 2 A position measuring device according to claim 1, wherein the reference position information is stored in advance for each movement direction of the measurement target, and the calibration processing unit performs calibration processing using the reference position information according to the movement direction of the measurement target. Claim 3 A position measuring device according to claim 1 or 2, wherein the first sensor measures the acceleration or angular velocity of the valve stem of the ON-OFF valve, the position information generating unit converts the acceleration or angular velocity into the opening degree of the ON-OFF valve, which is the position information, the second sensor detects mechanical vibrations that occur when the ON-OFF valve moves from the fully closed direction to the fully open direction, or mechanical vibrations that occur when the ON-OFF valve moves from the fully open direction to the fully closed direction, the reference position defining unit stores the reference position information during the opening operation of the ON-OFF valve and the reference position information during the closing operation in advance, and the calibration processing unit performs calibration processing using the reference position information during the opening operation of the ON-OFF valve and performs calibration processing using the reference position information during the closing operation of the ON-OFF valve. Claim 4 A position measuring device according to claim 3, wherein the second sensor detects vibration generated by the operation of a first limit switch that turns on when the ON-OFF valve reaches the vicinity of the open position, or vibration generated by the operation of a second limit switch that turns on when the ON-OFF valve reaches the vicinity of the fully closed position. Claim 5 A position measurement method characterized by comprising: a first step of measuring the acceleration or angular velocity of a measurement target; a second step of converting the acceleration or angular velocity into position information by integrating it over time; a third step of detecting mechanical vibration occurring in conjunction with the movement of the measurement target; and a fourth step of performing a correction process to reduce a position measurement error based on the position information obtained by the second step and the reference position information by referring to a reference position definition unit that stores the position information of the measurement target when the vibration is detected as reference position information.

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