DE102016109432B4 - Procedure for compensating for long-term drifts and creep phenomena on bolt sensors in earthquake-prone areas - Google Patents

Abstract

Method for compensating for long-term drifts in bolt sensors, comprising:Periodic implementation of the following steps with a predetermined measurement period in an evaluation routine,detecting a current bolt sensor signal,checking whether the detected bolt sensor signal is in a predetermined detection range,outputting an alarm signal if the bolt sensor signal is not in the detection range and aborting the evaluation routine,storing the detected bolt sensor signal in a memory if the bolt sensor signal is within the detection range and continuing with the evaluation routine,comparing the detected bolt sensor signal with at least one most recent previous bolt sensor signal,determining whether the detected bolt sensor signal differs from the at least most recent previous bolt sensor signal differs by more than a predetermined threshold, and issuing an alarm signal when the threshold is exceeded.

Description

FIELD OF THE INVENTION

The invention relates to a method for compensating for long-term drifts and creep phenomena in bolt sensors in areas at risk of earthquakes and a system with a bolt sensor and a device for carrying out the method.

TECHNICAL BACKGROUND

Bolted connections, such as screw connections, can not only be destroyed by earthquakes, they can also become loose and thus cause accidents as the long-term consequences of an earthquake. In Japan, for example, there are regulations that require critical screw connections to be checked. In many cases this is still done using a torque wrench. Alternatively, however, bolt sensors can also be used to monitor the bolt preload. Since the bolt tension is a static measured variable, signal drifts or creep effects, such as those that can occur in strain gauge (DMS)-based bolt sensors, can falsify the measurement signal.

DE 10 2010 001 144 A1 discloses a concept for the continuous monitoring of a mechanical load on a mechanical component. A bolt sensor is used for this, with which the mechanical load on the bolt can be recorded. An alarm signal is generated based on the evaluation of one or more measured values. When evaluating individual measured values, they are checked for falling below fixed limit values. If several measured values are evaluated, an integral is formed in order to detect a permanent overload and to issue an alarm signal based on this. It is also possible to read out and evaluate the recorded and logged measured values at a later point in time, for example in order to carry out long-term examinations, in which case no alarm signal is output.

DE 10 2012 020 851 A1 discloses a system for connecting a first component and a second component to form a rigid frame corner. In order to connect the components to one another, connecting plates are arranged on the components, which have a plurality of bores in which screws for fastening the connecting plates are arranged. A sensor device is provided for monitoring the pressure load between the connecting plates, so that the pressure on the contact surfaces of the connecting plates is permanently monitored. In the course of using the connection system, it is possible to check whether a previously set preload is still present.

KR 10 2014 055 013 A discloses a stud sensor. A sensor device is provided for monitoring the pressure load between two components, so that the pressure on the contact surfaces of the components is permanently monitored. An alarm signal is output when the value falls below a fixed limit value.

DESCRIPTION

It is an object of the invention to eliminate or at least reduce the disadvantages of the prior art. In particular, it is an object to provide a method and a system that enable better statements to be made regarding the change in bolt preload, in particular in the event of earthquakes, and can compensate for signal drifts.

According to one aspect of the invention, a method for compensating for long-term drifts on bolt sensors in earthquake-prone areas is provided. In general, the method (evaluation routine) is periodically started again and again after a predetermined measurement period has elapsed, unless it is completely terminated due to certain conditions explained below.

A current bolt sensor signal can first be detected as part of the implementation of the method.

A bolt sensor signal is a signal that provides information about how tight a bolt connection is. Bolt sensors are advantageously used here, which are located, for example, in the form of a washer between a head of the bolt and a counterpart. The bolt sensor is set up to detect the forces between the bolt head and the counterpart and to output a corresponding signal that is a function of the forces. A large number of different bolt sensors are known which are based on strain gauges or, more advantageously, on piezoelectric or piezoresistive effects. The term bolt in the present context includes in particular screws and generally denotes an elongate object that is suitable for fastening.

As part of the method or the evaluation routine, it can be determined whether the current bolt sensor signal is within a permissible detection range, ie whether it is, for example, within an upper and lower limit value. If the current bolt sensor signal is outside of the permissible detection range, a corresponding alarm signal is output which indicates that a current bolt sensor signal could not be detected (alarm signal: "measured value not in the detection range"). The evaluation routine can then be aborted.

If the current bolt sensor signal is within a permissible detection range, the current bolt sensor signal is saved. This is preferably done in a rolling memory. This means that the oldest previously stored bolt sensor signal will be overwritten with the current bolt sensor signal. At least the last previous bolt sensor signal is advantageously kept in memory for further calculations. The memory is therefore advantageously designed to store at least two stud sensor signals, the current one and the previous one.

Slow drift processes on the bolt are already compensated for by the continuous, periodic or regular detection of current bolt sensor signals and the cyclical replacement of the stored values.

After the current bolt sensor signal has been recorded and stored, a signal (earthquake indicator) is evaluated which indicates whether an earthquake is present or whether it was present between the last recording time and the current recording time.

If such an earthquake indicator is activated, i.e. if an earthquake is present or was present within the last measurement period, the current bolt sensor signal is compared with at least one previously (advantageously last) stored bolt sensor signal. If the current bolt sensor signal and the previously saved bolt sensor signal deviate from one another by more than a defined threshold value, an alarm signal is output that indicates that the bolt connection is defective (alarm signal: "Bolt connection defective"). The procedure ends.

If it is determined in the previous step when evaluating the earthquake indicator that the earthquake indicator is not activated, i.e. there is no earthquake, the evaluation routine can be terminated at this point. At a later point in time, for example after a measurement period has elapsed, the acquisition of a further bolt sensor signal can be continued.

According to a further aspect, an acceleration at the bolt sensor, for example in the form of an acceleration value or acceleration vector, can be detected within the method. The earthquake indicator can advantageously be activated when an acceleration value or an amplitude of the acceleration vector exceeds a defined limit value. The bolt sensor can thus decide autonomously whether there is an earthquake.

According to another aspect, the earthquake signal can also be received from an external signal transmitter. The transmission can then take place by means of data buses or by means of a network, in particular a wireless network (also the Internet or mobile communications, etc.). If a corresponding earthquake signal is received, then the earthquake indicator can be activated.

According to a further aspect, a difference can be formed between the current bolt sensor signal and the last (previously) stored bolt sensor signal. If this difference is greater than a defined threshold value, an alarm signal is issued. Correspondingly, a first alarm signal ("faulty bolt connection") can be issued when checking whether an earthquake is present has revealed that an earthquake is present. In addition or as an alternative, a second alarm signal (“loosened bolt connection”) can be issued even if checking whether an earthquake is present has shown that no earthquake is present.

According to a further aspect, the difference can advantageously be divided by the measurement period duration. The quotient of the difference and the length of the measurement period can then be evaluated or output. This normalizes the change (difference) in the bolt sensor signal over time. In this way, an additional statement can be made about the speed of the change and the associated risk. The determined values can be an indication of an early failure, so that preventive maintenance can be carried out.

The formation of the difference between at least two bolt sensor signals and, if necessary, dividing by the measurement period can of course also be carried out advantageously when an earthquake has been detected and it is to be determined whether and, if so, to what extent the detected temporally offset bolt sensor signals differ from one another.

According to a further aspect, the duration of the measurement period can be shortened in order to increase a monitoring density, for example after earthquakes have been detected.

Furthermore, the measurement period can be lengthened to achieve a reduction in power consumption.

According to a further aspect, a message can be sent using a network infrastructure and/or a message bus, which message comprises one of the alarm signals.

According to a further aspect, a system is provided which includes at least one bolt sensor and evaluation electronics. The system is then advantageously designed to carry out the method described herein according to the different aspects and exemplary embodiments.

The system can advantageously include an acceleration sensor which is coupled to the evaluation electronics and is set up to provide an acceleration value in response to an earthquake

Furthermore, the system can include an energy store, with the evaluation electronics being able to be operated autonomously with energy stored in the energy store.

The evaluation electronics can also be set up to charge the energy store with freely available energy, for example from solar energy, wind energy or energy harvesting.

character list

• - 1 ein vereinfachtes schematisches Flussdiagramm gemäß einem Ausführungsbeispiel,
• - 2 eine vereinfachtes Diagramm zur Erläuterung der Driftkompensation, und
• - 3 eine vereinfachte Darstellung eines Systems gemäß einem Ausführungsbeispiel.

The features and aspects of the invention are explained in more detail below on the basis of exemplary embodiments and with reference to the accompanying figures, in which:

• - 1 a simplified schematic flowchart according to an embodiment,
• - 2 a simplified diagram to explain drift compensation, and
• - 3 a simplified representation of a system according to an embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The method and the evaluation routine according to an embodiment is based on the flow chart in 1 explained.

The method begins in step S1, in which the system is either initialized or, after the method has been carried out, returns to step S1. This occurs as a result of one of the termination conditions that are explained below and advantageously after a preset measurement period T0.

In step S2, the bolt sensor signal is detected.

Overall, the flowchart is as per 1 The evaluation routine shown is carried out periodically with a specified measurement period duration T0 (where T0 is generally variable) as long as it does not come to a complete abort.

If the current bolt sensor signal is detected in step S2, it is determined in step S5 whether the bolt sensor signal is within a predetermined detection range. If the bolt sensor signal is not within the detection range, an alarm is triggered in step S3. The evaluation is then terminated in step S4.

If the bolt sensor signal is in the detection range, the current bolt sensor signal is stored in step S6. This can be done, for example, in a rolling or circulating memory. That is, the memory may be configured to store a limited number (e.g., two or more) of stud sensor signals. If the maximum number is reached, the memory is overwritten again from the beginning.

This is followed by step S7, in which it is generally determined whether an earthquake is present. If such a signal, ie an earthquake indicator, is not activated, the process returns to step S1, ie the evaluation routine is aborted in step S7 and continued with step S1. Step S1 or S2 is advantageously continued only after a full predetermined measurement period duration T0 has elapsed. If the earthquake indicator is activated, ie if there is an indicator of an earthquake, it is determined in step S8 whether the bolt sensor signal has changed. If the stud sensor signal has not changed, the process returns to step S1, ie the evaluation routine is aborted at this point. It is also advantageous to wait for a measurement period to expire before the evaluation routine starts over.

If the bolt sensor signal has changed too much after an earthquake has occurred, an alarm indicating that the bolt is defective ("bolt connection defective") is triggered in step S9. The method is then ended in step S10.

The verification of the bolt sensor signal in step S8 but also in a separate optional step S11 can be designed such that a difference between the current bolt sensor signal and the last or previously stored bolt sensor signal is checked with respect to a defined threshold value. As long as the difference is less than the specified threshold value, the routine is terminated in step S8 and a return is made to step S1. If the difference is outside the limits set by the threshold value, in step S9 a Alarm triggered ("bolt connection defective"). The method is then ended in step S10. A similar procedure can also be used in step S11.

In addition to forming the difference between the previous and the current bolt sensor signal, the difference can also be divided by the respective measurement period duration T0.

As illustrated in particular by step S11, it can be continuously monitored within the method how the respectively detected bolt sensor signals develop. If it is determined that a difference between the current bolt sensor signal and one or more bolt sensor signals last saved (i.e. earlier bolt sensor signals) has changed too much, an alarm "bolt connection loosened" can be triggered. This check can preferably consist in determining differences between previously stored bolt sensor signals and current bolt sensor signals. It is also checked whether this difference or differences exceeds or exceeds a threshold value. In principle, the difference can be divided by the length of the measurement period in order to obtain a qualitative and quantitative statement about the change over time. This quotient of the difference and the length of the measurement period can also be output or evaluated. This allows acute changes in the bolt connection to be distinguished from "normal" long-term changes (drift). In particular, the bolt sensor signals can be evaluated over a longer period of time for a "normal" drift, which is compensated for at regular intervals.

2 shows a simplified diagram to explain the drift compensation. The time profile of a bolt sensor signal BS over time is shown here, taking into account a "normal" drift, which is compensated for at regular intervals (T0, 2T0, 3T0...).

For example, the bolt sensor signals BS _i to BS _i+4 are recorded at times 0, T0, 2T0, 3T0 and 4T0. Here, T0 is the measurement period. This can be adjusted as described above. Due to drift or creep effects, the values slowly increase within the measurement period T0. First of all, it is assumed that the last value always corresponds to the zero line (amplitude BS). The respectively preceding value BS _i thus serves as a reference for the subsequent value BS _i+1 . This already compensates for creep effects and drifts. Furthermore, based on the behavior of the bolt sensor signals over a certain period of time, predictions about normal drift behavior can also be made. This behavior can then be used as a basis for the evaluation with regard to an earthquake. In particular, by dividing the difference (BS _i+1 −BS _i ) by the measurement period duration T0 (where T0 can generally be variable), it is possible to standardize over time. In this way, a conspicuous behavior can be better evaluated even with a variable measurement period.

In general, the earthquake indicator can be based on an acceleration sensor, which is arranged, for example, on or in the bolt sensor. This acceleration sensor can measure an acceleration in one, two or three directions that are preferably orthogonal to one another. An acceleration vector results accordingly. If one, several or all values of this acceleration vector exceed a defined limit value, for example in the form of an amplitude of the acceleration vector, an earthquake is recognized as extremely likely or given and the earthquake indicator is activated accordingly (step S7). It is also possible that in step S7 an earthquake indicator is provided by an external signal generator. The earthquake signal can then be transmitted to the evaluation circuit by means of a data bus or by means of a network, in particular a mobile network. Once such a signal is received, the earthquake indicator can be activated and the routine can continue with step S8.

Checking whether an earthquake has occurred can also combine both alternatives described. The earthquake indicator can then be activated when at least one of the methods or one of the devices, ie the detection and evaluation of an acceleration value or the evaluation of a signal from an external signal transmitter, detects an earthquake. It is also possible that the earthquake indicator is only activated if both methods detect an earthquake.

3 10 is a simplified representation of a system 100 according to an embodiment. The system 100 comprises at least one bolt sensor 1 and evaluation electronics 2. A bolt 3 and a device 6, which is not relevant any further, in which the bolt 3 is fastened, are also shown. The bolt sensor 1 is designed here in the form of a washer, in which there are elements which, for example, detect forces in the axial direction AX. The bolt sensor signal would then be a function of the axial forces occurring between the bolt and the device 6. Evaluation electronics 2, which are advantageously partially or completely located in the bolt sensor 1, are also shown only schematically. In other configurations, the evaluation electronics 2 could also located outside of stud sensor 1. The electronic evaluation system 2 is advantageously designed in such a way that it can carry out the method described above or the evaluation routine. The evaluation electronics 2 can contain a processor, a memory and other components. It can be hard-coded or hard-wired.

In the present exemplary embodiment, an acceleration sensor 5 is also provided, which is arranged in bolt sensor 1 by way of example. Alternatively, this acceleration sensor 5 could also be arranged on the bolt sensor. The acceleration sensor 5 supplies an acceleration vector (electrical signal) to the evaluation electronics 2. The acceleration vector can be used to detect whether an earthquake has occurred.

Furthermore, the evaluation electronics 2 can be designed to send a message, which includes one of the alarms, to a message receiver, for example by means of a network infrastructure and/or message bus. In addition, an earthquake indicator could also be transmitted from a signal transmitter 7 to the evaluation electronics 2 via a network or a bus.

The evaluation electronics 2 or the bolt sensor 1 can advantageously include an energy store 4, with the evaluation electronics 2 being able to be operated autonomously with the energy stored in the energy store 4.

The evaluation electronics 2 can also be suitable for charging the energy store 4 with freely available energy, for example from solar energy, wind energy or through energy harvesting.

The method or the system can also be supplemented with an absolute alarm threshold value, which ensures that a slow shaking loose of a screw or bolt connection can be detected or an alarm can be triggered before the measurement signal exceeds the limits of the measurement range of the downstream electronics reached or left.

Furthermore, the difference between the stored and the current signal can be evaluated, in particular for drift prognosis, which is then divided by the measurement period. These values give an indication of an early failure, so that preventive maintenance can be carried out. A variable period in the evaluation algorithm can, for example, reduce the energy consumption of the system. On the other hand, the information content can be increased if, for example, the measuring frequency is increased in the case of light earthquakes.

Reference List

1

bolt sensor

2

evaluation electronics

3

bolt

4

energy storage

5

accelerometer

6

contraption

7

signaller

100

system

AX

axial direction

T0

measurement period duration

BSi

bolt sensor signal

S1...S11

steps of the procedure

Claims (14)

Method for compensating for long-term drifts on bolt sensors comprising: Periodic execution of the following steps with a specified measurement period duration in an evaluation routine, detecting a current bolt sensor signal, Check whether the detected bolt sensor signal is within a specified detection range, Outputting an alarm signal if the bolt sensor signal is not in the detection range and aborting the evaluation routine, storing the detected bolt sensor signal in a memory if the bolt sensor signal is in the detection range and continuing with the evaluation routine, Comparing the detected bolt sensor signal with at least one last previous bolt sensor signal, Determining whether the detected bolt sensor signal differs from the at least most recent previous bolt sensor signal by more than a predetermined threshold value, and issuing an alarm signal if the threshold value is exceeded. procedure after claim 1 , wherein checking whether an earthquake has occurred comprises: detecting an acceleration value from an acceleration sensor, activating an earthquake indicator if the acceleration value exceeds a defined limit value. procedure after claim 1 , wherein checking whether an earthquake has occurred comprises: receiving an earthquake signal by means of a data bus or by means of a network. procedure after claim 1 until 3 , wherein the step of determining whether the detected bolt sensor signal differs from the at least last preceding bolt sensor signal by more than a predetermined threshold value, further comprises: forming a difference between the current bolt sensor signal and the at least last preceding bolt sensor signal and determining whether the difference is greater as the threshold. procedure after claim 4 , comprising: dividing the difference by the measurement period duration. A method according to any of the foregoing claims 2 until 5 , comprising: outputting a first alarm signal (“faulty bolt connection”) when checking whether an earthquake is present has revealed that an earthquake is present. A method according to any of the foregoing claims 2 until 6 , comprising: outputting a second alarm signal (“loosened bolt connection”) if checking whether an earthquake is present has shown that no earthquake is present and the threshold value is exceeded. Method according to one of the preceding claims, comprising: shortening the measurement period duration in order to increase a monitoring density. Method according to one of the preceding claims, comprising: increasing the measurement period duration in order to reduce energy consumption. Method according to one of the preceding claims, comprising: sending a message comprising one of the alarm signals by means of a network infrastructure and/or a message bus. System (100) comprising a bolt sensor (1) and evaluation electronics (2), wherein the system is set up, the method according to one of Claims 1 until 10 to perform. system (100) after claim 11 , comprising: an acceleration sensor (5), which is coupled to the evaluation electronics (2) and is set up to provide an acceleration value in response to an earthquake. system (100) after claim 11 or 12 , comprising: an energy storage device (4), wherein the evaluation electronics (2) can be operated autonomously with energy stored in the energy storage device (4). system (100) after Claim 13 , The evaluation electronics being set up to load the energy store (4) with freely available energy, for example from solar energy, wind energy or energy harvesting.

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