Position measuring apparatus and method for measuring position

Abstract

To reduce errors in positional measurement caused by accumulation of minute errors.SOLUTION: A position measuring apparatus 1 includes: a sensor 11 for measuring one of the acceleration and the angular velocity of a valve stem of an ON-OFF valve 200; a position information generation unit 12 for integrating one of the acceleration and the angular velocity measured by the sensor 11 and converting the integrated one of the acceleration and the angular velocity into position information; a sensor 13 for detecting mechanical vibration generated in association with opening and closing of the ON-OFF valve 200; a reference position definition unit 14 configured to store, in advance, as reference position information, position information corresponding to a time when vibration is detected by the sensor 13; and a calibration processing unit 15 for performing a calibration process for reducing position measurement errors on the basis of the position information obtained by the position information generation unit 12 and the reference position information when vibration is detected by the sensor 13.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a position measurement device and method for integrating the acceleration or angular velocity of an object to be measured and converting it into position information. [Background technology]

[0002] Valves used in petrochemical plants and the like (for example, the control valve in Figure 8) require particular attention to safety, and therefore undergo regular maintenance. The control valve shown in Figure 8 is composed of a valve body 100 that opens and closes the passage through which the fluid flows, a positioner 101 that converts an input electrical signal into air pressure, and an actuator 102 that operates the valve body 100 in response to the air pressure supplied from the positioner 101.

[0003] In order to improve the efficiency of valve maintenance work in plants where a large number of valves such as that shown in Figure 8 are installed, various techniques have been proposed, such as a technique for detecting the occurrence of stick-slip in the sliding parts of the valve (see Patent Document 1), a technique for determining the hunting state of the valve (see Patent Document 2), and a technique for detecting the adhesion of scale to the valve (see Patent Document 3).

[0004] On the other hand, there is another type of valve other than the control valve, which can continuously change the opening degree: the ON-OFF valve, which can only take two positions, fully open and fully closed. The ON-OFF valve 200 shown in Figure 9 uses a ball valve, and has a structure in which a ball 201, which is the valve body, is sandwiched between a seat ring 202 called a ball seat, and the valve can be opened or closed by rotating the valve stem 203 90 degrees using an actuator 204. Also, some types can be rotated by angles other than 90 degrees.

[0005] As a method for detecting malfunctions in an ON-OFF valve, a technology has been proposed that uses the time required for the valve to open and close, or the maximum and minimum operating speeds as diagnostic indices to detect malfunctions (see Patent Document 4).In addition, a technology has also been proposed that monitors the supply air pressure used to operate the ON-OFF valve (see Patent Documents 5 and 6).

[0006] Diagnosis of ON-OFF valves requires that it be applicable to the many ON-OFF valves already installed in a plant. From the perspective of a diagnostic method for ON-OFF valves, one possible method is to install an acceleration sensor or angular velocity sensor (gyro sensor) on the valve stem and measure the valve position by converting the integral of the acceleration or angular velocity into position information. In other words, it is preferable to retrofit a valve position meter equipped with an acceleration sensor or angular velocity sensor to an ON-OFF valve already installed in a plant and diagnose the valve.

[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 tolerance for accuracy, the accumulation of minute errors (such as rounding errors in the processor or noise components) can lead to position measurement errors (such as the position measurement error in the above example). These errors can potentially reduce the reliability of the entire diagnostic and control system. The wide variety of valve installation environments and installation angles makes it difficult to use geomagnetism or gravity acceleration for calibration. While calibration is possible by installing a separate device in a location other than the valve stem where the acceleration or angular velocity sensor is attached, this is difficult to achieve due to the variety of valve shapes. Therefore, there is a need to reduce position measurement errors using a single position measurement device. This issue is not limited to measuring the opening of an ON-OFF valve, but can occur in many cases when using a measurement method that converts the integral of acceleration or angular velocity into position information. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 3254624 [Patent Document 2] Patent No. 6200309 [Patent Document 3] Patent No. 6216633 [Patent Document 4] Patent No. 7265328 [Patent Document 5] Japanese Patent Application Publication No. 7-119862 [Patent Document 6] Japanese Patent Application Publication No. 11-210921 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above-mentioned problems, and aims to reduce position measurement errors (drift) caused by the accumulation and buildup of minute errors in a position measurement device and method that integrates the acceleration or angular velocity of an object to be measured and converts it into position information. [Means for solving the problem]

[0010] The position measurement device of the present invention is characterized by comprising: a first sensor configured to measure the acceleration or angular velocity of a measurement object; a position information generation unit configured to integrate the acceleration or angular velocity over time and convert it into position information; a second sensor configured to detect mechanical vibrations that occur as the measurement object moves; a reference position determination unit configured to pre-store the position information of the measurement object when vibrations are detected by the second sensor as reference position information; 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 generation unit when vibrations are detected by the second sensor and the reference position information. In addition, in one configuration example of the position measurement device of the present invention, the reference position information is stored in advance for each movement direction of the measurement object, and the calibration processing unit performs calibration processing using the reference position information corresponding to the movement direction of the measurement object.

[0011] Furthermore, in one configuration example of the position measurement device of the present invention, the first sensor measures the acceleration or angular velocity of a valve stem of an ON-OFF valve, the position information generation unit converts the acceleration or the angular velocity into the position information, i.e., the opening of the ON-OFF valve, the second sensor detects mechanical vibrations generated when the ON-OFF valve moves from fully closed to fully open, or mechanical vibrations generated when the ON-OFF valve moves from fully open to fully closed, the reference position determination unit pre-stores the reference position information for the opening operation of the ON-OFF valve and the reference position information for the closing operation, and the calibration processing unit performs a calibration process using the reference position information for the opening operation of the ON-OFF valve when the ON-OFF valve is opened, and performs a calibration process using the reference position information for the closing operation of the ON-OFF valve when the ON-OFF valve is closed. In addition, in one configuration example of the position measuring device of the present invention, the second sensor is characterized in that it detects vibrations generated by the operation of a first limit switch that turns on when the ON-OFF valve reaches near the fully open position, or vibrations generated by the operation of a second limit switch that turns on when the ON-OFF valve reaches near the fully closed position.

[0012] Furthermore, the position measurement method of the present invention is characterized by including a first step of measuring the acceleration or angular velocity of a measurement object, a second step of integrating the acceleration or angular velocity over time to convert it into position information, a third step of detecting mechanical vibrations that occur as the measurement object moves, and a fourth step of referring to a reference position determination unit that pre-stores the position information of the measurement object at the time the vibration is detected as reference position information, and performing a calibration process when the vibration is detected based on the position information obtained by the second step and the reference position information to reduce position measurement errors. [Effects of the Invention]

[0013] According to the present invention, by providing the second sensor, the reference position defining unit, and the calibration processing unit, it is possible to reduce position measurement errors (drift) caused by the accumulation and buildup of minute errors in the position measurement device alone. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram showing the configuration of a position measurement device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart illustrating the operation of the position measurement device according to the first embodiment of the present invention. [Figure 3] Figure 3 is an instrumentation diagram of an ON-OFF valve. [Figure 4] FIG. 4 is a diagram illustrating the calibration process performed by the calibration processing unit according to the first embodiment of the present invention. [Figure 5] FIG. 5 is a block diagram showing the configuration of a position measurement device according to a second embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart illustrating the operation of the position measurement device according to the second embodiment of the present invention. [Figure 7] FIG. 7 is a block diagram showing an example of the configuration of a computer that realizes the position measurement devices according to the first and second embodiments of the present invention. [Figure 8]FIG. 8 is a diagram showing an example of a control valve. [Figure 9] FIG. 9 is a diagram showing an example of an ON-OFF valve. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Principle of the Invention] Generally, if the measurement error is a "deviation" known as drift, it is sufficient to perform calibration as appropriate. However, in the case of the ON-OFF valve mentioned above, in order to obtain information on the reference positions corresponding to fully closed (0% opening) and fully open (100% opening), it is necessary to add a function to detect fully closed / fully open, and even if this function is already provided, it is necessary to add a signal line to obtain the detection information. Therefore, simply retrofitting an opening meter to an ON-OFF valve will not correct the position measurement error, and it is unlikely to be easily retrofitted.

[0016] The inventors focused on the fact that the object of position measurement involves mechanical operation. In other words, in the case of the above-mentioned ON-OFF valve, the residual vibration when the valve stem moves from fully open to fully closed and stops, or the vibration generated by the pre-installed mechanical limit switch for fully open / closed detection, occurs as a highly reproducible phenomenon at a specific reference position, even if it is not at the exact fully closed / fully open position.

[0017] We then came up with the idea that if this vibration is detected by a vibration sensor and used as a predetermined reference position for vibration detection, calibration can be performed to reduce position measurement errors (drift).In other words, there is no need to add new signal lines, and the system can be configured simply by retrofitting a position measurement device (opening gauge) equipped with an acceleration sensor or angular velocity sensor and a vibration sensor to the ON-OFF valve.

[0018] The present invention is applicable to any measurement method that converts the integral of acceleration or angular velocity into position information and where the object of position measurement is accompanied by reproducible vibration due to some cause.

[0019] [First Example] 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 measurement device according to a first embodiment of the present invention. The position measurement device 1 is a battery-powered wireless valve position indicator, and includes a valve ID storage unit 10 that stores an ID (identification information) unique to an ON-OFF valve 200 to which the position measurement device 1 is attached, a sensor 11 that measures the acceleration or angular velocity of a 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 that occur when the ON-OFF valve 200 is opened or closed, and a reference position determination unit 14 that pre-stores, as reference position information, the position information when the vibration is detected by the sensor 13. 4, a calibration processing unit 15 that performs calibration processing to reduce position measurement errors based on the position information obtained by the position information generation unit 12 when vibration is detected by the sensor 13 and the reference position information, a memory unit 16 that stores the position information, a malfunction diagnosis unit 17 that calculates an index of changes that will lead to a malfunction of the ON-OFF valve 200 based on the position information and performs malfunction diagnosis of the ON-OFF valve 200 based on the index, 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 unit of the position measurement device 1.

[0020] 2 is a flowchart illustrating the operation of the position measurement device 1. The sensor 11 of the position measurement device 1, which is attached to 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 in FIG. 2). For example, if the ON-OFF valve 200 is of the type in which the valve stem moves up and down to become fully open or fully closed, it is preferable to measure the acceleration of the valve stem. Also, if the ON-OFF valve 200 is of the type in which the valve stem moves up and down to become fully open or fully closed, such as a ball valve, it is preferable to measure the angular velocity of the valve stem.

[0021] The position information generator 12 converts the acceleration or angular velocity measured by the sensor 11 into position information by integrating it with respect to time (step S101 in FIG. 2). Specifically, when the acceleration of the valve rod is measured by the sensor 11, the position information generator 12 converts it into position information (displacement) of the valve rod by integrating the acceleration twice with respect to time. When the angular velocity is measured by the sensor 11, the position information generator 12 converts it into position information (angular displacement) by integrating the angular velocity once with respect to time.

[0022] The initial value (100% or 0%) of the opening degree when the ON-OFF valve 200 is stopped at the fully open or fully closed position is known. In addition, the operating direction of the ON-OFF valve 200 (from fully open to fully closed or from fully closed to fully open) can be determined from the displacement or angular displacement of the valve stem. Therefore, during the opening operation of the ON-OFF valve 200, the position information generating unit 12 can convert the position (displacement or angular displacement) of the valve stem into the opening degree of the ON-OFF valve 200 using the initial value (0%) of the opening degree and a known relationship between the linear displacement of the valve stem and the change in the opening degree of the ON-OFF valve 200 or a known relationship between the angular displacement of the valve stem and the change in the opening degree of the ON-OFF valve 200. In addition, when the ON-OFF valve 200 is closing, the position information generating unit 12 can convert the position (displacement or angular displacement) of the valve stem into an opening using the initial value (100%) of the opening and a known relationship between the linear displacement of the valve stem and the change in the opening of the ON-OFF valve 200, or a known relationship between the angular displacement of the valve stem and the change in the opening of the ON-OFF valve 200.

[0023] The sensor 11 and the position information generating unit 12 periodically perform the processes of steps S100 and S101. By repeating the processes of steps S100 and S101, time series data of the opening of the ON-OFF valve 200 is stored in the memory unit 16. The time series data of the opening calculated by the position information generating unit 12 is defined as D(t).

[0024] Next, the sensor 13 detects mechanical vibrations that occur when the ON-OFF valve 200 is opened or closed (step S102 in FIG. 2). Most ON-OFF valves 200 are instrumented as shown in FIG. 3, and actuator air is supplied to the actuator 204 of the ON-OFF valve 200 via a solenoid valve 205. The open state of the ON-OFF valve 200 is detected by a limit switch 206, and the closed state is detected by a limit switch 207. When the limit switch 206 is turned on during an opening operation of the ON-OFF valve 200, mechanical vibrations are generated due to the operation of the limit switch 206. Similarly, when the limit switch 207 is turned on during a closing operation of the ON-OFF valve 200, mechanical vibrations are generated due to the operation of the limit switch 207. The sensor 13 detects this vibration.

[0025] The sensor 13 may detect residual vibrations when the valve stem of the ON-OFF valve 200 moves from fully open to fully closed or from fully closed to fully open and then stops.

[0026] Next, the reference position determining unit 14 pre-stores the position information of the valve stem (opening of the ON-OFF valve 200) when vibration is detected by the sensor 13 as reference position information (reference opening). An operator who attaches the position measurement device 1 to the ON-OFF valve 200 can check the reference position information (reference opening) by a calibration test when attaching the device, and store the information in the reference position determining unit 14. The reference position information includes reference position information when the ON-OFF valve 200 is opened and reference position information when it is closed.

[0027] Although the ON-OFF valve 200 may not be fully open (100% opening) when limit switch 206 is turned on, the position near the fully open position (near 100% opening) when vibration caused by limit switch 206 being turned on is detected can be stored as reference position information for the opening operation. Similarly, the ON-OFF valve 200 may not be fully closed (0% opening) when limit switch 207 is turned on, but the position near the fully closed position (near 0% opening) when vibration caused by limit switch 207 being turned on is detected can be stored as reference position information for the closing operation.

[0028] When vibration is detected by the sensor 13, the calibration processing unit 15 calibrates the time series data D(t) of the opening stored in the memory unit 16 based on the reference position information (reference opening) stored in the reference position determination unit 14 (step S103 in FIG. 2). The operating direction of the ON-OFF valve 200 (from fully open to fully closed or from fully closed to fully open) can be determined from the displacement or angular displacement of the valve stem. Therefore, when vibration is detected by the sensor 13, it can also 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 calibration.

[0029] During an opening operation of the ON-OFF valve 200, the calibration processor 15 calibrates the opening value, which is calculated by the position information generator 12 and indicates when vibration is detected by the sensor 13, to the reference position information (reference opening near 100%) during the opening operation. Similarly, during a closing operation of the ON-OFF valve 200, the calibration processor 15 calibrates the opening value, which is calculated by the position information generator 12 and indicates when vibration is detected by the sensor 13, to the reference position information (reference opening near 0%) during the closing operation. By performing the calibration process in this manner, position measurement errors can be corrected. Note that, although FIG. 2 illustrates the calibration process as a necessary condition for the next flow, this is not limiting. Calibration based on the reference position information (reference opening) may be performed appropriately only when, for example, an accumulated error due to integration exceeds a tolerance.

[0030] In this example, only drift due to integration is considered, and calibration is performed using only the opening value at either the fully open or fully closed position when vibration is detected by sensor 13. However, if errors in acceleration or angular velocity themselves are also considered, calibration may be performed using the opening at which vibration is detected by sensor 13 at both the fully open and fully closed positions. As shown in Figure 4, based on the time-series data D(t), the correct opening to be detected is plotted on the horizontal axis, and the opening output with error is plotted on the vertical axis. If the reference position information (reference opening) is Dref and the opening value at which vibration is detected by sensor 13 at the fully open position is D(ton), the opening error at the time when vibration is detected by sensor 13 is ΔD(ton) = Dref - D(ton). Similarly, an error ΔD(toff) is obtained at the fully closed position. Therefore, the error ΔD(t) at each opening can be calculated from ΔD(ton) and ΔD(toff). Calibrated opening data D'(t) can be obtained by adding the error ΔD(t) at each opening to the detected opening data D(t). In this way, the calibration processing unit 15 can calibrate the opening degree when vibration is detected by the sensor 13, even if an error in the acceleration or angular velocity itself is included.

[0031] In the above explanation, the calibration processing unit 15 performs the calibration process when the sensor 13 detects vibration, but as explained above, there is a possibility that the ON-OFF valve 200 is not fully open or fully closed when the sensor 13 detects vibration. Therefore, the processes of steps S100 and S101 are continued even after the sensor 13 detects vibration and performs the calibration process. However, after the calibration process is performed, the position information generation unit 12 needs to convert the displacement or angular displacement into the opening 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.

[0032] If the state of 100% opening continues for a certain period of time or more, the position information generating unit 12 determines that the ON-OFF valve 200 has stopped at the fully open position and resets the initial value of the opening to 100%. Similarly, if the state of 0% opening continues for a certain period of time or more, the position information generating unit 12 determines that the ON-OFF valve 200 has stopped at the fully closed position and resets the initial value of the opening to 0%.

[0033] Next, at a predetermined timing, the failure diagnosis unit 17 of the position measurement device 1 calculates an index of a change that will lead to a failure of the ON-OFF valve 200 based on the time-series data D'(t) of the opening degree after the calibration process (step S104 in FIG. 2), and performs failure diagnosis of the ON-OFF valve 200 based on the index (step S105 in FIG. 2). The failure diagnosis unit 17 may perform the process, for example, when the ON-OFF valve 200 stops, but the process may also be performed at another timing.

[0034] For example, the malfunction diagnosis unit 17 uses the time required to open and close the ON-OFF valve 200 as an index of a change that may lead to a malfunction (step S104). When the time required to open and close is equal to or greater than a predetermined diagnostic threshold, the malfunction diagnosis unit 17 determines that a malfunction may have occurred in the ON-OFF valve 200, and when the time required to open and close is less than the diagnostic threshold, the malfunction diagnosis unit 17 determines that the ON-OFF valve 200 is normal (step S105).

[0035] The wireless communication unit 18 of the position measurement device 1 wirelessly transmits data including the valve ID stored in the valve ID storage unit 10, the time-series data of the opening after calibration, an index of the change leading to the malfunction, and the result of the malfunction diagnosis by the malfunction diagnosis unit 17 to a valve maintenance support device (not shown) (step S106 in FIG. 2). The valve maintenance support device presents the received index and the result of the malfunction diagnosis to the operator.

[0036] The operation of the failure diagnosis unit 17 in this embodiment is just one example, and other diagnoses may be performed. Furthermore, the failure diagnosis unit 17 is not an essential component of the present invention. If the failure diagnosis unit 17 is not provided, the wireless communication unit 18 only needs to transmit the valve ID and time-series data of the opening degree after calibration.

[0037] [Second Example] In the first embodiment, a battery-powered wireless aperture indicator has been described as an example of the position measurement device, but the present invention can be applied to any position measurement device that converts the acceleration or angular velocity of an object to be measured into position information of the object. A generalized example of the position measurement device of the first embodiment is shown in Fig. 5. In the configuration of Fig. 5, the object 300 to be measured is an object that moves linearly or rotates.

[0038] 6 is a flowchart illustrating the operation of the position measurement device 1a of this embodiment. The sensor 11 of the position measurement device 1a attached to the measurement target 300 measures the acceleration or angular velocity of the measurement target 300 (step S200 in FIG. 6). If the measurement target 300 moves linearly, it is preferable to measure the acceleration of the measurement target 300. Also, if the measurement target 300 rotates, it is preferable to measure the angular velocity of the measurement target 300.

[0039] The position information generating unit 12 converts the acceleration or angular velocity measured by the sensor 11 into position information by integrating it with respect to time (step S201 in FIG. 6). Specifically, when the acceleration of the measurement object 300 is measured by the sensor 11, the position information generating unit 12 converts it into a displacement of the measurement object 300 by integrating the acceleration twice with respect to time. When the angular velocity is measured by the sensor 11, the position information generating unit 12 converts it into an angular displacement by integrating the angular velocity once with respect to time.

[0040] Here, it is assumed that the initial position of the measurement target 300 when it is stationary is known. In the case of a measurement target 300 that moves linearly, the position information generating unit 12 can convert the displacement of the measurement target 300 into a position on the line using the initial position of the measurement target 300. In addition, in the case of a measurement target 300 that rotates, the position information generating unit 12 can convert the angular displacement of the measurement target 300 into a rotational position using the initial position of the measurement target 300.

[0041] The sensor 11 and the position information generating unit 12 periodically perform the processes of steps S200 and S201. By repeating the processes of steps S200 and S201, time-series data of the position of the measurement object 300 is stored in the storage unit 16. The time-series data of the position calculated by the position information generating unit 12 is defined as X(t).

[0042] Next, the sensor 13 detects mechanical vibrations that occur as the measurement object 300 moves (step S202 in FIG. 6). The sensor 13 may detect, for example, residual vibrations that occur when the measurement object 300 moves and then stops.

[0043] Next, the reference position defining unit 14 pre-stores, as reference position information, the position information of the measurement target 300 when vibration is detected by the sensor 13. An operator who attaches the position measurement device 1a to the measurement target 300 can check the reference position information through a calibration test when attaching the device, and store the reference position information in the reference position defining unit 14. The reference position information includes reference position information when the measurement target 300 moves in a first direction (for example, rightward or clockwise), and reference position information when the measurement target 300 moves in a second direction (for example, leftward or counterclockwise).

[0044] When vibration is detected by the sensor 13, the calibration processing unit 15 calibrates the position time-series data X(t) stored in the memory unit 16 based on the reference position information stored in the reference position defining unit 14 (step S203 in FIG. 6). The motion direction (first direction or second direction) of the measurement object 300 can be determined from the displacement or angular displacement of the measurement object 300. Therefore, when vibration is detected by the sensor 13, it can also be determined which of the reference position information in the first direction or the reference position information in the second direction should be used for calibration.

[0045] When the measurement target 300 moves in a first direction, the calibration processing unit 15 calibrates the position when vibration is detected by the sensor 13, among the position time-series data X(t) calculated by the position information generating unit 12, to the value of reference position information for the first direction. Similarly, when the measurement target 300 moves in a second direction, the calibration processing unit 15 calibrates the position when vibration is detected by the sensor 13, among the position time-series data X(t) calculated by the position information generating unit 12, to the value of reference position information for the second direction. Note that, although FIG. 6 describes the calibration process as a necessary condition for the next flow, this is not limiting, and calibration based on reference position information (reference opening) may be performed appropriately only when, for example, a cumulative error due to integration exceeds a tolerance.

[0046] In this example, only drift due to integration is considered, and calibration is performed using only one reference position when vibration is detected by sensor 13. However, if errors in acceleration or angular velocity themselves are also considered, calibration may be performed using multiple positions where vibration is detected by sensor 13. If reference position information is Xref and the position when vibration is detected by sensor 13 is X(ton), the position error when vibration is detected by sensor 13 is ΔX(ton) = Xref - X(ton). Similarly, an error ΔD(toff) is obtained at another 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 each position to each piece of position data X(t), the post-calibration position data X'(t) can be obtained. In this way, the calibration processing unit 15 can calibrate the position when vibration is detected by sensor 13, even if errors in acceleration or angular velocity themselves are included.

[0047] In the above explanation, the calibration processing unit 15 performs the calibration process when the sensor 13 detects vibration, but there is a possibility that the measurement object 300 has not reached the limit position when the sensor 13 detects vibration. Therefore, the processes of steps S200 and S201 are continued even after the sensor 13 detects vibration and performs the calibration process. However, after the calibration process is performed, the position information generating unit 12 needs to convert the displacement or angular displacement into the position of the measurement object 300 using the value of the reference position information as the initial position.

[0048] If the state in which the measurement target 300 has reached the limit position in the first direction continues for a certain period of time or more, the position information generating unit 12 determines that the measurement target 300 has stopped and resets the initial position to the limit position in the first direction. Similarly, if the state in which the measurement target 300 has reached the limit position in the second direction continues for a certain period of time or more, the position information generating unit 12 determines that the measurement target 300 has stopped and resets the initial position to the limit position in the second direction.

[0049] The wireless communication unit 18 of the position measurement device 1a wirelessly transmits the time-series data of the position of the measurement target 300 to the outside (Step S204 in FIG. 6). In this way, the present invention can be applied to a position measurement device 1a that converts the integral of acceleration or angular velocity into position information.

[0050] In the first and second embodiments, there is a possibility that the sensor 13 may mistakenly detect a vibration different from the vibration that is desired to be detected, so the calibration processing unit 15 may determine, for example, by vibration pattern recognition, whether or not the desired vibration corresponding to the reference position has been detected, and perform calibration processing when it is determined that the desired vibration has been detected.

[0051] The valve ID storage unit 10, position information generation unit 12, reference position definition unit 14, calibration processing unit 15, storage unit 16, fault diagnosis unit 17, and wireless communication unit 18 of the position measurement devices 1 and 1a described in the first and second embodiments can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example configuration of this computer is shown in Figure 7.

[0052] The computer includes a CPU 400, a storage device 401, and an interface device (abbreviated as I / F) 402. The I / F 402 is connected to hardware such as the sensors 11 and 13 and the wireless communication unit 18. In such a computer, a program for realizing the present invention is stored in the storage device 401. The CPU 400 executes the processes described in the first and second embodiments in accordance with the program stored in the storage device 401. [Industrial Applicability]

[0053] The present invention can be applied to a technique for integrating acceleration or angular velocity to convert it into position information. [Explanation of symbols]

[0054] 1, 1a...position measurement device, 10...valve ID storage unit, 11, 13...sensor, 12...position information generation unit, 14...reference position determination unit, 15...calibration processing unit, 16...storage unit, 17...fault diagnosis unit, 18...wireless communication unit, 19...battery, 200...ON-OFF valve, 300...measurement object

Claims

1. a first sensor configured to measure acceleration or angular velocity of a measurement object; a position information generating unit configured to convert the acceleration or the angular velocity into position information by integrating the acceleration or the angular velocity with respect to time; a second sensor configured to detect mechanical vibrations that occur as the measurement object moves; a reference position determining unit configured to store in advance, as reference position information, position information of the measurement object when vibration is detected by the second sensor; a calibration processing unit configured to perform a calibration process so as to reduce position measurement errors based on the position information obtained by the position information generation unit when vibration is detected by the second sensor and the reference position information.

2. 2. The position measurement device according to claim 1, the reference position information is stored in advance for each movement direction of the measurement object, The position measurement device, wherein the calibration processing unit executes a calibration process using the reference position information according to the moving direction of the measurement object.

3. 3. The position measurement device according to claim 1, the first sensor measures the acceleration or angular velocity of a valve stem of an ON-OFF valve; the position information generating unit converts the acceleration or the angular velocity into the position information, which is the opening degree of the ON-OFF valve; the second sensor detects mechanical vibrations that occur when the ON-OFF valve moves from a fully closed position to a fully open position, or mechanical vibrations that occur when the ON-OFF valve moves from a fully open position to a fully closed position; the reference position defining unit pre-stores the reference position information at the time of opening operation of the ON-OFF valve and the reference position information at the time of closing operation of the ON-OFF valve, a calibration processing unit that performs a calibration process using the reference position information at the time of opening the ON-OFF valve when the ON-OFF valve is opened, and performs a calibration process using the reference position information at the time of closing the ON-OFF valve when the ON-OFF valve is closed.

4. 4. The position measurement device according to claim 3, The second sensor detects vibrations generated by the operation of a first limit switch that turns on when the ON-OFF valve reaches near the fully open position, or vibrations generated by the operation of a second limit switch that turns on when the ON-OFF valve reaches near the fully closed position. A position measuring device characterized by this.

5. a first step of measuring acceleration or angular velocity of a measurement object; a second step of integrating the acceleration or the angular velocity with respect to time to convert it into position information; a third step of detecting mechanical vibrations that occur as the measurement object moves; a fourth step of referring to a reference position definition unit that pre-stores position information of the measurement object at the time the vibration is detected as reference position information, and performing a calibration process so as to reduce position measurement errors based on the position information obtained by the second step when the vibration is detected and the reference position information.

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