JP2019035666A - Constantly vibration monitoring system of equipment and device - Google Patents

Abstract

To provide a vibration monitoring system that detects a vibration state of acceleration of a social infrastructure facility, industrial equipment and a production device and determines its operation/failed state and necessity of maintenance, which is a practical system that is not conventionally expensive and large-sized system but can be inexpensively constantly operated and is battery-driven.SOLUTION: There is provided an inexpensive vibration monitoring system which is equipped with an analog frequency analyzer that can automatically switch or control a center frequency of a band-pass filter without using expensive and large-sized high-speed amplifier and numerical calculation computer necessary for large power consumption, and thereby can acquire frequency-analyzed vibration data with small size at inexpensive cost by battery-driven, and can transfer or store data at the time of only abnormality in consistently operated state.SELECTED DRAWING: Figure 1

Description

The present invention monitors the vibration state of industrial machinery such as bridges, buildings, generators, and other social infrastructure, production equipment and equipment, etc. The purpose is to monitor.

In this technical field, the vibration frequency of the object varies greatly depending on the size, type, and mechanism of the object, and the frequency of vibration due to scratches on gears and ball bearings in the motor system is about several Hz to 100 Hz for bridges that are large buildings. The vibration of the tool tool bit may be about 1k-5kHz.

Conventionally, a piezoelectric pickup is used in a high frequency band, and a MEMS acceleration sensor is used in a low frequency band. This signal is converted into high-speed analog-digital data and temporarily stored in a storage device. Processing and Fourier transform were performed, but with such a method, it was not possible to always monitor a large number of inexpensive sensors attached to an object.

As another means proposed in the prior art document 2, there is also a means for obtaining a frequency characteristic or the like using a means such as modulation or FM demodulation using a digital filter after analog-to-digital conversion of the sensor signal. As shown, in order to realize a digital filter, a high-speed programmable gate array is necessary, which is expensive and consumes a large amount of power.

Further, as a means for performing Fourier transform at high speed, a method of processing with a small number of computations called fast Fourier transform has been devised, but when performing with a small MPU mounted on a sensor terminal, that is, a microcomputer, for example, a microchip. Even when using a 16-bit microcomputer manufactured by the company, a current of 15 mA is required at a voltage of 3.3 V in order to perform processing at a clock frequency of 32 MHz and perform a time of 100 ms or less, which is almost similar to real-time processing.

Assuming constant vibration monitoring here, this MPU must be kept in constant operation. If the current consumption of the entire sensor system is 20 mA, a 5000 mAh AA alkaline battery with a relatively large current capacity can be used. 250 hours and continuous operation for about 10 days will be full.

As described above, it has been found that it is difficult to perform analog-to-digital conversion, to perform high-speed digital conversion including fast Fourier transform for a long period of one month or more, and to reduce the size.

Therefore, this proposal uses analog signal processing using an operational amplifier to extract only the amplitudes of multiple specific frequencies using a simple method to extract the frequency characteristics up to about 5 kHz required for vibration monitoring, and send this extracted data. Here, we build a system that can operate for months on batteries.

As a prior art of this method, Patent Document 3 discloses an earthquake sensing device using a plurality of high-pass filters for detecting vibrations having an amplitude higher than a certain frequency. However, sufficient information cannot be obtained with a high-pass filter that defines the frequency of the low frequency range of vibration.

Patent Document 4 discloses a configuration in which a high-pass filter is mounted in a circuit for detecting that there is a certain abnormal vibration in order to determine a lower limit of a certain vibration frequency region. This configuration is not sufficient because vibrations having a plurality of frequencies are observed in the mechanical system and equipment.

Furthermore, as a possible means, there is an example of connecting a spectrum analyzer, which is a measurement device, after adjusting the gain of the sensor with a variable resistor, amplifying it with a power amplifier, but it is expensive and consumes a large amount of power. A spectrum analyzer with is not suitable for constant monitoring.

JP 2014-98566 A "Vibration analysis apparatus, vibration analysis method, and vibration analysis program" JP-A-6-307923 "Multi-point simultaneous vibration measuring device" Japanese Unexamined Patent Publication No. 2000-346701 Japanese Patent Laid-Open No. 2-21533 "Vibration monitoring device" Japanese Utility Model Publication No. 5-90335 "Noise Monitor"

In a conventional broadband vibration monitoring system using a sensor such as a piezoelectric pickup, sensor signal data is once taken into an SD card or a computer, and processing such as Fourier transform is performed on the computer to analyze the vibration state. there were.

Alternatively, sensors, signal processing devices, and devices that display analysis results on the sensor system require high-speed digital signal processing such as high-speed analog-digital conversion, digital filter, and fast Fourier transform, so large size, high cost, and high power consumption. In general, a commercial power supply of 100 V is used.

However, when installing a large amount on large-scale objects and factory production equipment based on such research and experimental equipment data, these systems are expensive and require a large amount of power. In addition, it has been difficult to constantly monitor batteries and energy harvesting power generation devices over a long period of time.

This proposal is able to measure the vibration state of a relatively high frequency up to 5kHz, which is essential for industry by installing in large quantities on large-scale objects and factory production equipment, for many months with battery operation, and to judge abnormalities. For this purpose, the present invention proposes a system that effectively uses analog signal processing that operates with low power consumption.

Assuming that the target current consumption can be driven by a single alkaline battery with a capacity of about 5000 mAh for one month, an average current of about 6.9 mA or less is essential, and storage to an external storage device or wireless data transfer is intermittent. Assuming that the average is a little less than 1 mA assuming that it is performed only when necessary for operation, the maximum current of the sensor system is 6 mA.

The sensor system consists of an analog circuit and a digital circuit that process sensor signals, and if both operate at high speed, the current consumption is proportional to the processing frequency, so the frequency band must be lowered in the first analog circuit. The present invention proposes to perform frequency analysis in an analog circuit.

As a frequency analysis using this analog circuit, the first is to configure a plurality of band-pass filters composed of relatively narrow-band analog circuits with different center frequencies in parallel. By multiplying, a value proportional to the root mean square of the amplitude of the center frequency of the bandpass filter can be obtained, and this value is output as the amplitude of the frequency of vibration acceleration.

The second method is to construct a center frequency variable band pass filter by temporally changing the circuit parameter that determines the center frequency inside the band pass filter composed of one relatively narrow band analog circuit. The output is full-wave rectified and a low-pass filter is applied to obtain a value that is proportional to the root mean square of the amplitude of the center frequency of the frequency variable bandpass filter. Is output as

Both of these methods require signal processing at a certain high frequency in the analog circuit, but low-speed digital signal processing may be used to digitally convert the output of the analog circuit and transfer the data to a storage device or a wireless module. Therefore, the drive frequency of the MPU or the like may be small. For example, if the MPU has a drive frequency of 4 MHz, only 0.5 mA of current is consumed at 3.3 V, resulting in low power consumption as a whole.

Low power consumption of analog circuits drives low-cut-off frequency operational amplifiers composed of low-consumption CMOS circuits at low voltage, and these low-consumption operational amplifiers have low output impedance drive capability, so the next stage It is necessary to design the circuit to increase the input impedance of the circuit as much as possible and to suppress the amplification factor.

The structure of the Example (Example 1) of this invention is shown. The structure of Example 2 is shown. The example of the concrete circuit diagram of Example 2 is shown. The example of the concrete circuit diagram of Example 3 is shown. The example of the concrete circuit diagram of Example 3 is shown. The concrete structure of Example 4 is shown.

FIG. 1 is a configuration diagram of an embodiment (embodiment 1) of the present invention. An amplifier 2 connected to a vibration detection sensor 1 that captures an acceleration as a vibration intensity from an object, and a specific vibration is determined by an analog signal processing method. A circuit that calculates a value proportional to the root mean square (rms value) of amplitude using a frequency variable bandpass filter 7, a detection circuit 3, and a lowpass filter 4, which is a circuit through which only a frequency component passes (frequency component analysis) Circuit), and a controller for changing and controlling the center frequency of the frequency component analysis circuit (the microcomputer 5 with the ADC) and a means for converting the equivalent of the rms value into a digital signal. .

The embodiment 1 shown in FIG. 1 is a frequency that is a circuit that passes a specific vibration frequency component by an analog signal processing method, an amplifier 2 connected to a vibration detection sensor 1 that captures a vibration signal (usually acceleration) from an object. A circuit that calculates a value proportional to the root mean square (rms value) of the amplitude or a value corresponding to the amplitude of the equivalent acceleration by a combination of the variable band-pass filter 7, the detection circuit 3, and the low-pass filter 4; An ADC built-in microcomputer 5 for changing and controlling the center frequency of the frequency variable bandpass filter 7 and a data transfer circuit 6 are provided.

In the first embodiment, the analog-to-digital conversion is performed using the built-in type of the microcomputer 5 with built-in ADC, but this may be separated, and the data transfer device 6 may be a storage device such as an SD card, a wireless network system, a LAN, or the like. It may be a network device connected to the server.

In the second embodiment shown in FIG. 2, the frequency variable bandpass filter of the first embodiment, that is, the circuit that transmits only a specific frequency component is a plurality of bandpass filters 8, and the frequency switching is performed by an analog multiplexer. The analog switching circuit 9 including analog switches is used, and the subsequent configuration is the same as that of the first embodiment.

Here, the band-pass filter 8 may have various configurations. As shown in FIG. 3 as a specific circuit example that can be downsized with low power consumption, one operational amplifier, three resistors, An operational amplifier multiple feedback type bandpass filter composed of two capacitors is desirable, and the analog switching circuit 9 is desirably an analog multiplexer with a small number of control signals.

In the circuit shown in FIG. 3, the OP1, the buffer amplifier OP2, and the bandpass filter 8 that can change the gain are operational amplifier multiple feedback type bandpass filters. The operational amplifier OP3 includes resistors R5, R6, R7, and a capacitor C2, Using C3, the center frequency is expressed by Formula 1, and the Q value indicating the width of the band is expressed by Formula 2.

Here, the Q value is a value obtained by dividing the center frequency by the bandwidth of the frequency attenuated to 0.707 times the amplitude of the center frequency, which is a -3 dB value, and the higher the Q value, the better the frequency resolution.

This bandpass filter is very stable, and at the same time, according to Equation 1, the center frequency is mainly determined by C2, C3 and R7, and the Q value is mainly determined by the ratio of R7 and R6. Is done.

The center frequency and Q value of the band-pass filter 8 must be determined according to the application of vibration measurement and the frequency band to be observed by the attached device. However, if the center frequency is high or the Q value is large, the band / gain product is large. Care must be taken because an operational amplifier is required and power consumption increases.

In the design example of the center frequency and the Q value of the band pass filter 8, when simply monitoring a wide band of about 2 digits from about 50 Hz to 5 kHz, the Q value is 1, 125 Hz, 250 Hz, 500 Hz, This is covered by using six bandpass filters 8 of 1 kHz, 2 kHz, and 4 kHz.

As the circuit constants of each bandpass filter 8, the circuit constants of 1 kHz are C1 = 1 nF, C2 = 10 nF, R5 = 120 kΩ, R6 = 15 kΩ, R7 = 180 kΩ, the design center frequency is 1015 Hz, the Q value is 1. When the CMOS operational amplifier NJU7095 with a current consumption of 80 μA and a gain of 1 band is 1 MHz is used, the measured values are 1 kHz peak frequency, -3 dB frequencies are 650 Hz and 1700 Hz, and the Q value is 1.05, which is a good design value. It was in agreement.

Here, as a very important item in design, a plurality of band-pass filters 8 are connected to the buffer amplifiers OP1 and OP2 in FIG. 3, and the number of connectable numbers is the gain bandwidth and current (load) of the operational amplifier. ) Determined by driving ability.

Low power consumption CMOS operational amplifiers can output power to the lower and upper limits of the power supply voltage called rail-to-rail, but this is a function of frequency band and load resistance. The input resistance (R5 + R6) of the pass filter 8 must be 100 kΩ or more, and the number of buffer amplifiers connected in parallel must be 3 or less.

Furthermore, even if the circuit constants are determined according to Equation 1 and Equation 2, parts that are inexpensive and easily available have discrete values, so it is not easy to align the frequency, Q value, and gain accurately. Then, the frequency characteristic of the circuit is measured with a function generator or the like using the microcomputer 5 with ADC, and calibration is performed to correct the preset value.

In the third embodiment shown in FIG. 4, the circuit for extracting the frequency component is a state variable filter 10, which is composed of an operational amplifier OP5 and positive and negative feedback circuits of integrating circuits OP6 and OP7, and R16 and R17. The center frequency can be changed by two variable resistors.

Here, when R16 and R17 are equal and C11 and C12 are equal, the center frequency is expressed by Equation 3 and the Q value is expressed by Equation 4, and the center frequency is dominated by the time constant of the integrating circuit of C11 and R16. Since the Q value is mainly determined by the ratio of R3 and R14, that is, the gain, the center frequency and Q can be determined independently to some extent.

In the case of concrete mounting, R16 and R17 are, for example, two 100 kΩ electronic variable resistance elements that can be linearly changed, and the resistance value is controlled by the microcomputer 5 with ADC. As described above, since the center frequency is inversely proportional to R16, the center frequency is proportional to the reciprocal (1 / n) of the digital control index n of the electronic variable resistor. turn into.

In another example of the third embodiment shown in FIG. 5, the circuit for extracting the frequency component is a state variable filter 10, and is constituted by an operational amplifier OP9 and positive and negative feedback circuits of integrating circuits OP11 and OP13, respectively. The center frequency is obtained by changing the gains of the non-inverting amplifiers OP10 and OP12 by the digital signals at the control terminals S1 and S2 of the EVR1 and EVR2 which are electronic variable resistors.

Here, the center frequency of the state variable filter 10 is specified by constant k and EVR1 (same as EVR2) if R28 and R33 are matched, SW7 is connected to C21, SW8 is connected to C24, and C21 and C24 are combined. Using the gain GOP of OP10 (same as OP12), the center frequency has a characteristic proportional to the gain GOP of OP5 as expressed in Equation 5, so the accuracy is kept constant in the frequency variable range, MPU correction is also unnecessary, so it can be put to practical use even with a low power consumption MPU.

Here, since the control of the electronic variable resistor can be obtained inexpensively from 4 bits (16 gradations) to 10 bits (1024 gradations), the frequency accuracy is improved, and the Q value can be increased to this gradation number. If the Q value is increased, it may become unstable and self-oscillation may occur, and the gain of the required operational amplifier is proportional to the Q value, so the frequency characteristics deteriorate and the signal amplitude and Q value decrease at high frequencies. Therefore, the Q value is preferably 10 or less.

Furthermore, it is necessary to set the cutoff frequency of the detection circuit 3 and the low-pass filter 4 to the lower limit of the measurement frequency band, but stable measurement can be performed by switching the electronic variable resistors EVR1 and EVR2 earlier than the time constant of this frequency. Since there is no control, the selection of 4 bits (16 gradations) to 10 bits (1024 gradations) must be taken into account when selecting the electronic variable resistance, so the minimum modulation number is set to 16 gradations.

Further, since the stable variable frequency range of the state variable filter 10 is about one digit, it is desirable to switch the capacities of the integrators OP11 and OP13 by the switching devices SW7 and SW8. Since it is desirable that the capacitance between the terminal and the ground is small, it is desirable to use an analog multiplexer or an analog switch.

In the fourth embodiment shown in FIG. 6, an amplifier 2 connected to a vibration detection sensor 1 that captures vibration intensity (usually acceleration) from an object, a frequency that is a circuit that transmits a vibration frequency component by an analog signal processing method. A circuit that calculates a value proportional to the root mean square (rms value) of the amplitude or a value corresponding to the amplitude of the equivalent acceleration by a combination of the variable bandpass filter 7, the detection circuit 3, and the low-pass filter 4. The microcomputer 5 includes an ADC built-in microcomputer 5 that changes and controls the center frequency of the frequency variable bandpass filter 7, a wireless module 13, and an external storage device 14.

The ADC built-in microcomputer 5 has a plurality of high-speed data storage units 11 for storing time dependency of a value proportional to the root mean square (rms value) of a specific frequency, and temporarily stores this value.

The high-speed data storage unit 11 is a set of values corresponding to the frequency, but may correspond to a single time, or may be a plurality of values in a certain time range, that is, matrix data of frequency and time.

The high-speed data storage unit 11 has a flag area indicating whether the data set is normal or abnormal data. If the data is abnormal data, the data storage unit 12 stores the abnormal data later. Configured to be recognized.

Whether or not the data stored in the high-speed data storage unit 11 is abnormal is determined based on a value that is proportional to the root mean square (rms value) of the specific frequency at one or a plurality of specific frequencies in advance. Judgment is made based on whether or not it exceeds.

If there is a data storage unit 12 in which abnormal data is stored after measurement for a certain period of time, the data area or the data in the high-speed data storage unit before and after the data storage unit 12 in which abnormal data is stored are wireless modules. 13 and the external storage device 14.

Since the wireless module 13 and the external storage device 14 generally consume a large current, the power is turned off when normal vibration monitoring is performed, and the power is turned on only when an abnormal signal is determined, and data is transmitted. Thus, it is possible to reduce the average power of the entire sensor system.

DESCRIPTION OF SYMBOLS 1 Vibration detection sensor 2 Amplifier 3 Detection circuit 4 Low pass filter 5 Microcomputer with built-in ADC 6 Data transfer module 7 Frequency variable band pass filter 8 Band pass filter 9 Analog switching circuit 10 State variable filter 11 High-speed data storage unit 12 Abnormal data is stored Data storage unit 13 Wireless module 14 External storage device

Claims (7)

    A circuit that transmits only a specific frequency component of the input signal from the vibration detection sensor using an analog signal processing method, a circuit that detects the signal, and a root mean square value of vibration acceleration at a specific frequency using a low-pass filter A circuit that outputs a proportional value, a controller that changes and controls the center frequency of the circuit that transmits only this specific frequency component, and a digital signal that is proportional to the root mean square value of the vibration acceleration of the specific frequency Vibration monitoring system with means to convert to    2. The vibration monitoring system according to claim 1, wherein the circuit that transmits only a specific frequency component is a band-pass filter using a plurality of operational amplifiers, and an analog multiplexer or an analog switch is used for switching the center frequency.     The bandpass filter has a Q value range of 1 to 10 and is connected to a maximum of three bandpass filters from the buffer amplifier. Each bandpass filter has an input resistance of 100 kΩ or more. The vibration monitoring system according to claim 1, wherein the range covered is 50 Hz or more and 8 kHz or less, and the average current of the entire sensor system does not exceed 7 mA.    A circuit that transmits only a specific frequency component is a state variable filter, which has two electronic variable resistors that determine the time constant of the negative feedback integrator circuit and the time constant of the positive feedback integrator circuit, and has a frequency of 16 stages or more. The vibration monitoring system according to claim 1, wherein the vibration monitoring system can be changed by the electronic variable resistor.    A circuit that transmits only a specific frequency component is a state variable filter, a pair of variable gain amplifiers having two electronic variable resistors that determine the time constant of the negative feedback integrator circuit and the time constant of the positive feedback integrator circuit. The vibration monitoring system according to claim 1, wherein a frequency of 16 tones or more can be changed by the electronic variable resistor. By changing the capacity of a pair of integrators using a pair of analog multiplexers or analog switches, the frequency band can be expanded and the variable frequency band range can be 50 Hz or more and 8 kHz or less. Item 1, 4, 5 vibration monitoring system. A value that is proportional to the root mean square value of vibration acceleration corresponding to a specific frequency is stored in a high-speed data storage device inside the microcomputer for each frequency in a time series, and the value is a preset threshold value for each frequency. If it exceeds, the data is judged to be abnormal data, a flag is set for the data set, and when the preset time measurement is finished, the abnormal data set with the flag or high-speed data before and after including the abnormal data Data stored in the storage device can be sent with a wireless module that turns on only when an abnormality is found, or written to an external storage device that turns on only when an abnormality is found The vibration monitoring system according to claim 1.