JP4084015B2 - Stress measuring device using piezoelectric element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a stress measurement device using a piezoelectric element. For example, it is applied to strain measurement of structures such as bridges.
[0002]
[Prior art]
For the measurement of stress generated in a structure such as a bridge, a method of measuring by attaching a strain gauge 1 as shown in FIG. 10 is used.
That is, the strain gauge 1 is attached to the target portion, and the Wheatstone bridge circuit is configured by combining the three fixed resistors 2, 3, 4 having the same resistance value as the strain gauge 1.
[0003]
A current is supplied from the power supply unit 5 to the Wheatstone bridge circuit, and a resistance change due to the distortion is amplified by the amplifier 6 to obtain a voltage signal proportional to the distortion (stress).
In some cases, a frequency counting unit 7 for calculating the frequency is connected.
Further, as a Wheatstone bridge circuit, there are cases where two strain gauges and two fixed resistors, all of which are strain gauges or the like.
[0004]
[Problems to be solved by the invention]
In the conventional apparatus shown in FIG. 10, since a stable current is always supplied to the strain gauge 1, when measuring for a long period of time, a commercial power source, a solar cell, or a large capacity battery is used. It is necessary to adopt a method of exchanging every few days.
[0005]
However, in mountainous areas where there is no power supply, there are problems such as a great deal of preparation for installing the power supply and the need to visit people every few days.
An object of the present invention is to use, as a sensor, a piezoelectric element that outputs a voltage proportional to a strain rate as a method for reducing current consumption, which is a problem in long-term stress measurement of the prior art.
[0006]
[Means for Solving the Problems]
Stress measuring apparatus according to claim 1 of the present invention to achieve the such objects, a piezoelectric element which outputs a voltage proportional to the strain rate, an amplifying circuit for amplifying the voltage output from the piezoelectric element, the amplifier circuit in an integrating circuit for converting the distortion signal amplified voltage integrating, in the stress measuring device that includes a frequency counter for counting the frequency of the converted the distorted signal by the integrator circuit, including the integration circuit The processing circuit has a high-pass filter characteristic such that the gain decreases at a low frequency, and the frequency measurement unit further compares the distortion signal converted by the integration circuit with a plurality of set values, The distortion signal includes a plurality of counters that display the number of levels at which the distortion signal exceeds the plurality of set values by comparison with a comparator .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A specific basic configuration of the stress measuring apparatus of the present invention is shown in FIG.
As shown in FIG. 1, this stress measuring device is composed of a piezoelectric element 8, a connection 9, and a processing circuit unit 10, and a frequency count display unit 11 is installed as necessary.
The piezoelectric element 8 is known to have a characteristic of outputting a voltage proportional to the strain rate based on its composition. FIG. 2 shows the result of an experiment conducted to confirm the characteristics.
[0010]
FIG. 2 shows the results of a test conducted on a steel plate with the piezoelectric element 8 bonded thereto so that distortion at a certain frequency occurs. The horizontal axis represents the strain rate and the vertical axis represents the output voltage. ing.
The set frequency was selected from 0.1 to 20 Hz.
As a result, as shown in FIG. 2, it was confirmed that the output voltage of the piezoelectric element 8 was output in proportion to the strain rate.
In order to measure the strain, it is necessary to integrate a voltage proportional to the strain rate output from the piezoelectric element 8.
[0011]
Therefore, in the present invention, an integrating circuit is provided inside the processing circuit unit 10 shown in FIG.
As an example of the characteristics of the integrating circuit, the characteristics shown in FIG. 3 can be considered.
FIG. 4 shows the relationship between the output voltage and distortion as a result of installing the integrating circuit shown in FIG. 3 behind the output voltage of the piezoelectric element 8.
As shown in FIG. 4, it was confirmed that the voltage proportional to the distortion was output by providing the integration circuit.
[0012]
As a feature of the integration circuit, as shown in FIG. 5, a high-pass filter is devised so that the gain decreases at a low frequency.
The reason for this is that when used for a long period of time, the DC temperature of the output voltage from the piezoelectric element 8 changes because the outside air temperature changes, thereby preventing deterioration in measurement accuracy.
For example, as shown in FIG. 6, there is a problem that the output voltage drifts in a certain direction when there is no high-pass filter, but such inconvenience can be prevented by providing a high-pass filter.
[0013]
A specific circuit diagram of the processing circuit unit 10 and the frequency count display unit 11 according to the present invention is shown in FIG.
As shown in FIG. 7, the processing circuit unit 10 includes fixed resistors 13 to 17, capacitors 18 to 19, a first stage amplifier 21, and an integrating circuit 22.
In addition, the frequency count display unit 11 includes, for example, a comparator 20 and a 7-digit counter.
The comparator 20 sets the set value of the 7th level to Rf1 to Rf7, and displays the number of levels exceeding this with a counter.
Therefore, the higher the numerical value displayed on each counter, the more frequently the distortion can be confirmed, which serves as an index for judging the reliability of the structure.
[0014]
As an actual measurement example, FIG. 8 shows the result of actually measuring the stress of the bridge using this stress measuring apparatus, and FIG. 9 shows the strain detected using the strain gauge.
FIG. 8 shows the output voltage when the distortion of the bridge and the voltage signal of the piezoelectric element 8 are passed through the processing circuit.
As shown in FIGS. 8 and 9, it was confirmed that the stress measuring device according to the present invention detected the strain with higher accuracy than when the strain gauge was used.
[0015]
As described above, according to the stress measuring apparatus according to the present embodiment, since the piezoelectric element 8 that generates a voltage when strain is applied is used, it is not necessary to supply current to the sensor, and the amplifier circuit is also simple. This is possible with a simple circuit configuration.
Therefore, in this embodiment, compared with the prior art, a commercial power source is not required even for current consumption reduction, device miniaturization, and long-term observation.
Further, by providing a high-pass filter in the processing circuit unit, it is possible to prevent drift caused by temperature changes.
[0016]
【The invention's effect】
As described above in detail, the stress measuring device according to claim 1 of the present invention includes a piezoelectric element which outputs a voltage proportional to the strain rate, an amplifying circuit for amplifying the voltage output from the piezoelectric element, in the stress measuring device including an integrating circuit for converting the distortion signal by integrating the amplified voltage by the amplifier circuit, and a frequency counting unit for counting the frequency of the converted the distorted signal by the integration circuit, the integration A processing circuit including a circuit has a high-pass filter characteristic such that a gain decreases at a low frequency, and the frequency measurement unit further compares the distortion signal converted by the integration circuit with a plurality of set values. If, because composed of a plurality of counters for displaying the number of levels the distortion signal exceeds a plurality of set values in comparison with the comparator supplies a current必No, also, the amplifier circuit also enables a simple circuit configuration, therefore, compared with the prior art, reduce current consumption, the commercial power source is not required in size and long-term observation of the device. In addition, since the processing circuit including the integration circuit for converting into a distortion signal has a high-pass filter characteristic that reduces the gain at a low frequency, drift caused by a temperature change can be prevented. In addition, since a frequency counting unit that counts the frequency of the distortion signal converted by the integration circuit is added, it can be confirmed that the distortion has frequently occurred, and serves as an index for judging the reliability of the structure.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a stress measuring device which is a specific device configuration of the present invention.
FIG. 2 is a graph showing the relationship between strain rate and piezoelectric film output voltage.
FIG. 3 is a graph showing characteristics of an integration circuit.
FIG. 4 is a graph showing a relationship between an integration circuit output voltage and distortion.
FIG. 5 is a graph showing transfer characteristics.
FIG. 6 is a graph showing an integration circuit output voltage waveform;
FIG. 7 is a specific circuit diagram showing a stress measuring device circuit.
FIG. 8 is a graph showing actual measurement values obtained by a stress measurement apparatus.
FIG. 9 is a graph showing measured values using a strain gauge.
FIG. 10 is a block diagram showing a stress measuring device according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Strain gauge 2-4 Fixed resistance 5 Power supply part 6 Amplifying part 7 Frequency counting part 8 Piezoelectric element 9 Connection 10 Processing circuit part 11 Frequency counting part 12 Piezoelectric element 13-17 Fixed resistance 18-19 Capacitor 20 Comparator

Claims (1)

A piezoelectric element which outputs a voltage proportional to the strain rate, an amplifying circuit for amplifying the voltage output from the piezoelectric element, an integrating circuit for converting the distortion signal by integrating the amplified voltage by the amplifier circuit, wherein In a stress measuring device including a frequency counting unit that counts the frequency of the distortion signal converted by the integration circuit, the processing circuit including the integration circuit has a high-pass filter characteristic that reduces the gain at a low frequency, Further, the frequency measurement unit includes a comparator that compares the distortion signal converted by the integration circuit with a plurality of setting values, and the number of levels at which the distortion signal exceeds the plurality of setting values by comparison with the comparator. A stress measuring device comprising: a plurality of counters for displaying .

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