CN107607923B - LFMCW radar-based vibration monitoring system and signal processing method - Google Patents
LFMCW radar-based vibration monitoring system and signal processing method Download PDFInfo
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Abstract
The invention provides a vibration monitoring system based on an LFMCW radar and a signal processing method. The signal processing method comprises the following steps: step 1, intercepting an effective baseband beat signal within each sweep frequency period time, and generating a complex beat signal; step 2, estimating beat frequency; step 3, carrying out phase estimation by using an approximate maximum likelihood estimation algorithm; step 4, carrying out phase jump correction processing on the estimated initial phase time sequence; and 5, extracting vibration displacement time domain information. According to the invention, the LFMCW radar is used for non-contact vibration motion sensing, the initial phase of the beat signal in each sweep frequency period is accurately estimated, and the vibration displacement time domain information is extracted, so that the vibration monitoring requirements of target objects in extreme environments and medium and short distances can be met.
Description
Technical Field
The invention relates to the technical field of vibration monitoring, in particular to a vibration monitoring system and a signal processing method based on an LFMCW radar, wherein the LFMCW represents a linear frequency modulation continuous wave.
Background
Vibration monitoring is widely applied to various fields of production and life, and is an important means for realizing state monitoring and fault diagnosis. Generally, vibration monitoring senses vibration movement through a contact sensor, such as an accelerometer, and extracts information such as displacement and frequency of vibration through subsequent signal processing. Motion perception technology based on microwave radar belongs to a non-contact measurement technique, can be in stable work under adverse circumstances, and does not receive the influence of weather conditions such as sleet, can realize all-weather monitoring measurement, has used in human vital sign monitoring and the vibration monitoring field of big bridge at present. The Continuous Wave (CW) radar is sensitive to motion information, can sense tiny vibration displacement changes, and obtains displacement time domain information of vibration by extracting modulation phase information. However, a baseband signal of the CW radar often has a large dc offset, and it is difficult to perform accurate dc offset compensation and realize high-precision monitoring of vibration displacement under the condition of a low signal-to-noise ratio. In addition, because the CW radar lacks distance information, multi-target object monitoring is difficult to realize, and background noise interference cannot be effectively eliminated. On the other hand, Linear Frequency Modulation Continuous Wave (LFMCW) radar has a distance sensing capability and can distinguish multiple target objects.
The LFMCW radar transmits linear frequency modulation continuous waves and receives electromagnetic echoes scattered by a target, and the echoes and local oscillation signals are subjected to frequency mixing and filtering to obtain intermediate-frequency baseband beat signals. The range information of the target range radar is obtained by estimating the frequency of the beat signal, but the range resolution is limited due to the limitation of radar transmission bandwidth, and the small range change caused by vibration is difficult to extract. In order to effectively monitor vibration and accurately extract vibration displacement time domain information of a target object, the vibration displacement information needs to be accurately extracted by utilizing evolution of a phase in a beat signal based on a radar interferometry technology.
Disclosure of Invention
In view of this, the present invention provides a vibration monitoring system and a signal processing method based on an LFMCW radar, which use the LFMCW radar to sense vibration motion, obtain a corresponding phase evolution sequence by estimating an initial phase of a beat signal in each sweep frequency period, further calculate vibration displacement time domain information of a target object, and implement high-precision vibration monitoring.
In order to realize the purpose, the invention is realized according to the following technical scheme:
the invention discloses a vibration monitoring system based on an LFMCW radar, which comprises:
the radar transceiver is used for generating radar emission waves, receiving the scattered echoes, and obtaining intermediate frequency baseband beat signals through amplification, frequency mixing and filtering processing;
the tuning signal generator is used for generating a periodic linear modulation wave voltage signal so as to control the radar transceiver to generate a linear frequency modulation transmitted wave;
the data acquisition module is used for carrying out ADC data acquisition on the intermediate frequency baseband beat signals and the modulation wave signals of the I channel and the Q channel;
the signal processing module is used for carrying out signal processing on the intermediate frequency baseband beat signal, estimating the initial phase of the beat signal in each sweep frequency period time and extracting vibration displacement time domain information;
and the display and analysis module is used for displaying the vibration displacement time domain information of the detection target and analyzing and processing the vibration displacement time domain information to achieve the purposes of state monitoring and fault diagnosis.
In the above technical solution, the radar transceiver includes a voltage-controlled oscillator, a power divider, a power amplifier, a low noise amplifier, an orthogonal mixer, a low pass filter, a transmitting antenna, and a receiving antenna, wherein the voltage-controlled vibrator is connected to the power divider, the power divider is connected to the power amplifier, the power amplifier is connected to the transmitting antenna, a signal is generated by the voltage-controlled oscillator, the voltage-controlled vibrator is divided by the power divider, one path of the signal is amplified by the power amplifier, an electromagnetic wave is transmitted to a space through the transmitting antenna, and the other path of the signal is transmitted to the orthogonal mixer connected to the power divider. The receiving antenna is connected with the low-noise amplifier, an amplified signal generated by the low-noise amplifier flows to the orthogonal frequency mixer, orthogonal frequency mixing is carried out on the amplified signal and a signal flowing out of the power divider, and the mixed signal flows to the low-pass filter.
In the above technical solution, the signal processing module includes: the device comprises a signal preprocessing unit, a beat frequency estimation unit, a phase estimation unit and a vibration displacement extraction unit, wherein the signal preprocessing unit is connected with the beat frequency estimation unit, the beat frequency estimation unit is connected with the phase estimation unit, and the phase estimation unit is connected with the vibration displacement extraction unit.
In the technical scheme, the data acquisition module synchronously samples intermediate frequency baseband beat signals and modulation wave signals of an I channel and a Q channel; or the data acquisition module provides a synchronous signal by the modulating wave signal and triggers and synchronously acquires the baseband signals of the I channel and the Q channel.
The invention discloses a signal processing method based on LFMCW radar vibration monitoring, which is realized according to the LFMCW radar-based vibration monitoring system and comprises the following steps:
step 1: intercepting effective baseband beat signals in each sweep frequency period time, and combining the intercepted I channel signals I (t) and Q channel signals Q (t) to generate complex beat signals SB(t) in which SB(t) ═ i (t) + j × q (t), where j is an imaginary unit;
step 2: for frequency f of complex beat signalbCarrying out estimation;
and step 3: carrying out initial phase estimation on the intercepted complex beat signal in each sweep frequency period time;
and 4, step 4: carrying out phase jump correction processing on the estimated initial phase time sequence;
and 5: and calculating vibration displacement time domain information according to the obtained initial phase time sequence.
In the above technical solution, the effective baseband beat signal in step 1 uses a modulated wave signal as a synchronization signal.
In the above technical solution, the frequency f of the beat signal in the step 2 is adjustedbThe estimation method of (2) is fast fourier transform, as shown in the following equation:
in the formula:
in order to be an estimate of the beat frequency,
representing an operation of finding a parameter f that yields a maximum value, f having a value in the range of 0 to fs/2，fsFor sampling frequency, abs (-) represents the complex magnitude operation and F {. denotes the fast Fourier transform operation.
In the above technical solution, the method for estimating the initial phase of the complex beat signal in step 3 is an approximate maximum likelihood estimation method, which is shown as the following formula:
In the above technical solution, the method for performing the phase jump correction processing in step 4 includes: by judging whether the difference of the initial phase estimation values of the beat signals in the time of adjacent sweep periods is larger than a fixed value delta or not, if so, the phase jump is considered to occur, and 2 delta is added or subtracted to the second value to enable the difference of the two phases to be smaller than the fixed value delta.
In the above technical solution, the method for calculating the vibration displacement time domain information from the initial phase time sequence in step 5 includes:
the time series of vibrational displacements along the radar line of sight x (it) can be expressed as:
by using the geometric position relationship between the radar and the vibration direction of the monitored target, the vibration displacement time sequence d (it) of the monitored target can be obtained as shown in the following formula:
Compared with the prior art, the invention has the following beneficial effects:
the vibration monitoring system can sense the vibration motion of the target object in a non-contact mode and monitor the vibration motion in real time, can meet the vibration monitoring requirements of the target object in extreme environments and in medium and short distance ranges, and can work all weather under various climatic and weather conditions. By using the distance resolution capability of the LFMCW radar, target objects in different distance units in the radar sight line can be distinguished, and the interference of other objects is effectively isolated. The modular design and the efficient signal processing module realize good system integration and high-precision vibration displacement monitoring.
In addition, the signal processing method provided by the invention can be used for accurately estimating the initial phase of the beat signal in each sweep frequency period time to calculate the vibration displacement time domain information, thereby realizing high-precision vibration displacement monitoring. The maximum likelihood phase estimation algorithm based on approximation has strong anti-noise capability, high estimation precision and smaller calculation amount, and can meet the requirement of real-time monitoring.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of the LFMCW-based radar vibration monitoring of the present invention;
FIG. 2 is a block diagram of the LFMCW radar-based vibration monitoring system of the present invention;
fig. 3 is a schematic structural diagram of a radar transceiver based on an LFMCW radar vibration monitoring system according to the present invention;
FIG. 4 is a schematic diagram of a signal processing module structure unit of the LFMCW radar vibration monitoring system according to the present invention;
FIG. 5 is a flow chart of a signal processing method based on LFMCW radar vibration monitoring according to the present invention;
FIG. 6 is a schematic diagram of a time-frequency relationship between signals transmitted and received by an LFMCW radar modulated by sawtooth waves in the embodiment of the present invention;
among them, 1-LFMCW radar, 2-monitored vibration target.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The invention discloses a vibration monitoring system based on an LFMCW radar, which adopts a linear frequency modulation continuous wave radar to monitor the vibration motion of a target object, and extracts vibration displacement time domain information by estimating an initial phase time sequence of a baseband beat signal based on the principle of a radar interference technology. Referring to fig. 1, a schematic diagram of vibration monitoring based on the LFMCW radar is shown, where a radar antenna faces a monitoring target, and an included angle between a radar center line of sight and a vibration direction to be detected is θ. The vibration displacement d (t) is therefore related to the change in motion x (t) induced by the radar in the direction of the central line of sight as follows:
as shown in fig. 2, a vibration monitoring system based on LFMCW radar, the vibration monitoring system based on LFMCW radar of the present invention, includes:
the radar transceiver is used for generating radar emission waves, receiving the scattered echoes, and obtaining intermediate frequency baseband beat signals through amplification, frequency mixing and filtering processing;
the tuning signal generator is used for generating a periodic linear modulation wave voltage signal so as to control the radar transceiver to generate a linear frequency modulation transmitted wave;
the data acquisition module is used for carrying out ADC data acquisition on the intermediate frequency baseband beat signals and the modulation wave signals of the I channel and the Q channel;
the signal processing module is used for carrying out signal processing on the intermediate frequency baseband beat signal, estimating the initial phase of the beat signal in each sweep frequency period time and extracting vibration displacement time domain information;
and the display and analysis module is used for displaying the vibration displacement time domain information of the detection target and analyzing and processing the vibration displacement time domain information to achieve the purposes of state monitoring and fault diagnosis.
Specifically, as shown in fig. 3, the radar transceiver includes a Voltage Controlled Oscillator (VCO), a power divider, a Power Amplifier (PA), a Low Noise Amplifier (LNA), a quadrature mixer, a low pass filter, a transmitting antenna, and a receiving antenna, wherein the voltage controlled oscillator is connected to the power divider, the power divider is connected to the power amplifier and the quadrature mixer, respectively, the power amplifier is connected to the transmitting antenna, the receiving antenna is connected to the low noise amplifier, the low noise amplifier is connected to the quadrature mixer, and the quadrature mixer is connected to the low pass filter. The tuning signal generator generates periodic modulation wave signals, such as typical sawtooth wave voltage signals, is connected with a VCO (voltage controlled oscillator) of the radar transceiver, is controlled by the VCO to generate linear frequency modulation radio frequency waves, and is divided into two paths through the power divider. One path of the signals is amplified by the PA and then transmits frequency modulation electromagnetic waves through a transmitting antenna, the other path of the signals is used as local oscillation signals to carry out orthogonal frequency mixing with received signals, and the signals after frequency mixing are processed by a low-pass filter to generate I/Q channel intermediate frequency baseband beat signals which are I (t) and Q (t) respectively. The echo signal scattered by the target is received by the radar receiving antenna, and is subjected to quadrature frequency mixing with the local oscillator signal after passing through the LNA. In the present embodiment, the sawtooth wave is used as a tuning signal to perform the following signal processing description.
Referring to fig. 2, two-channel baseband beat signals i (t) and q (t), and a modulation wave signal generated by the tuning signal generator are synchronously acquired by the data acquisition module to maintain coherent characteristics in radar phase estimation.
The signal processing module comprises: the device comprises a signal preprocessing unit, a beat frequency estimation unit, a phase estimation unit and a vibration displacement extraction unit, wherein the signal preprocessing unit is connected with the beat frequency estimation unit, the beat frequency estimation unit is connected with the phase estimation unit, and the phase estimation unit is connected with the vibration displacement extraction unit. The signal preprocessing unit is used for synchronously intercepting the baseband beat signal of each frequency sweeping period by combining the modulation wave signal. And carrying out fast Fourier transform on the intercepted baseband beat signal, indexing the peak value of the frequency spectrum amplitude value, and estimating a beat frequency value. The phase estimation unit estimates the initial phase of the beat signal in each frequency sweep period through an approximate maximum likelihood estimation algorithm. And the vibration displacement extraction unit is used for correcting phase jump and removing average value of the estimated phase sequence and calculating vibration displacement time domain information.
The data acquisition module synchronously samples the intermediate frequency baseband beat signals and the modulation wave signals of the I channel and the Q channel; or the data acquisition module provides a synchronous signal by the modulating wave signal and triggers and synchronously acquires the baseband signals of the I channel and the Q channel.
And the display and analysis module is used for carrying out graphic display on the vibration displacement time domain information obtained by the signal processing module and analyzing the vibration condition of the detected target by utilizing the existing vibration analysis technology, such as extraction of physical quantities such as amplitude, frequency and the like, so as to realize the purposes of carrying out state monitoring and fault diagnosis on the target object.
The signal processing method based on LFMCW radar vibration monitoring is realized according to the vibration monitoring system based on LFMCW radar, as shown in figure 5, and comprises the following steps:
step 1: intercepting effective baseband beat signals in each sweep frequency period time, and combining the intercepted I channel signals I (t) and Q channel signals Q (t) to generate complex beat signals SBAnd (t) synchronously sampling the baseband beat signals and the modulation wave signals in a plurality of sweep frequency period times, intercepting effective beat signals in each sweep frequency period by using the modulation wave signals, synchronizing clocks of the intercepted beat signals in each sweep frequency period, and performing subsequent phase estimation by using a radar interference technology. As shown in fig. 6, in this embodiment, taking a sawtooth modulation signal as an example, two captured beat signals of each sweep frequency period are combined to generate a complex beat signal SB(t) represented by the following formula:
SB(t) ═ i (t) + j × q (t), where j is an imaginary unit.
In general, since the sweep period time T is short, the vibration displacement can be approximated to a constant value within a single sweep period time, and the signal model of the complex beat signal for the ith sweep period can be expressed as:
wherein the content of the first and second substances,
in the formula: σ is the amplitude, fbIn order to be able to beat the frequency,
is the initial phase, f, of the beat signal within the time of the ith sweep cycle0The frequency of the transmitted wave at the modulation starting moment, c the propagation speed of the electromagnetic wave, K the slope of the modulation bandwidth, x (iT) the vibration displacement value in the ith sweep period time, R0Is the distance, lambda, between the vibration equilibrium position of the target object and the radar antenna0For modulating the wavelength of the emitted wave at the start of the time, lambdacTo modulate the wavelength of the emitted wave at intermediate times.
Step 2: for frequency f of beat signalbAnd estimating by using an estimation formula of the difference beat frequency in any sweep period time by using fast Fourier transform, wherein the estimation formula is as follows:
And step 3: and respectively estimating the initial phase of the intercepted complex beat signal in each sweep frequency period. Obtained by using fast Fourier transform
Having a certain difference from the ideal true value, the approximate maximum likelihood estimation algorithm is used to estimate the initial phase of the beat signal
As shown in the following formula:
And 4, step 4: and carrying out phase jump correction processing on the estimated initial phase time sequence. The method for performing the phase jump correction processing in the step 4 comprises the following steps: by judging whether the difference of the initial phase estimation values of the beat signals in the time of adjacent sweep periods is larger than a fixed value delta or not, if so, the phase jump is considered to occur, and 2 delta is added or subtracted to the second value to enable the difference of the two phases to be smaller than the fixed value delta.
In the embodiment, if the complex phase angle calculation in step 3 limits the range of the estimated value of the initial phase angle to [ -pi, pi ], a phase jump will occur when the vibration displacement is large. By determining whether the difference between the initial phase estimates of the difference signals within the time of adjacent sweep periods is greater than a fixed value, such as pi, if so, it is determined that a phase jump has occurred, and adding or subtracting 2 pi from the second value to make the difference between the two phases less than the fixed value.
And 5: and 4, calculating vibration displacement time domain information according to the initial phase time sequence obtained in the step 4. The time series of vibrational displacements along the radar line of sight x (it) can be expressed as:
By using the geometric position relationship between the radar and the vibration direction of the monitored target, the vibration displacement time sequence d (it) of the monitored target can be obtained as shown in the following formula:
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (10)
1. A LFMCW radar-based vibration monitoring system, comprising:
the radar transceiver is used for generating radar emission waves, receiving the scattered echoes, and obtaining intermediate frequency baseband beat signals through amplification, frequency mixing and filtering processing;
the tuning signal generator is used for generating a periodic linear modulation wave voltage signal so as to control the radar transceiver to generate a linear frequency modulation transmitted wave;
the data acquisition module is used for carrying out ADC data acquisition on the intermediate frequency baseband beat signals and the modulation wave signals of the I channel and the Q channel;
the signal processing module is used for carrying out signal processing on the intermediate frequency baseband beat signal, estimating the initial phase of the beat signal in each sweep frequency period time and extracting vibration displacement time domain information;
and the display and analysis module is used for displaying the vibration displacement time domain information of the detection target and analyzing and processing the vibration displacement time domain information to achieve the purposes of state monitoring and fault diagnosis.
2. The LFMCW radar-based vibration monitoring system of claim 1, wherein the radar transceiver comprises a voltage controlled oscillator, a power divider, a power amplifier, a low noise amplifier, a quadrature mixer, a low pass filter, a transmitting antenna and a receiving antenna, wherein the voltage controlled vibrator is connected to the power divider, the power divider is connected to the power amplifier, the power amplifier is connected to the transmitting antenna, a signal is generated by the voltage controlled oscillator and is divided by the power divider, one signal is amplified by the power amplifier, an electromagnetic wave is emitted to space by the transmitting antenna, and the other signal is transmitted to the quadrature mixer connected to the power divider; the receiving antenna is connected with the low-noise amplifier, an amplified signal generated by the low-noise amplifier flows to the orthogonal frequency mixer, orthogonal frequency mixing is carried out on the amplified signal and a signal flowing out of the power divider, and the mixed signal flows to the low-pass filter.
3. The LFMCW radar-based vibration monitoring system according to claim 1, wherein the signal processing module comprises: the device comprises a signal preprocessing unit, a beat frequency estimation unit, a phase estimation unit and a vibration displacement extraction unit, wherein the signal preprocessing unit is connected with the beat frequency estimation unit, the beat frequency estimation unit is connected with the phase estimation unit, and the phase estimation unit is connected with the vibration displacement extraction unit.
4. The LFMCW radar-based vibration monitoring system of claim 1, wherein the data acquisition module synchronously samples the intermediate frequency baseband beat signals and the linear modulation wave voltage signals of the I channel and the Q channel; or the data acquisition module provides a synchronous signal by the linear modulation wave voltage signal to trigger synchronous acquisition of I channel and Q channel baseband signals.
5. A signal processing method based on LFMCW radar vibration monitoring, which is implemented by the vibration monitoring system based on LFMCW radar according to any one of claims 1 to 4, and comprises the following steps:
step 1: intercepting effective baseband beat signals in each sweep frequency period time, and combining the intercepted I channel signals I (t) and Q channel signals Q (t) to generate complex beat signals SB(t) in which SB(t) ═ i (t) + j × q (t), where j is an imaginary unit;
step 2: for frequency f of complex beat signalbCarrying out estimation;
and step 3: carrying out initial phase estimation on the intercepted complex beat signal in each sweep frequency period time;
and 4, step 4: carrying out phase jump correction processing on the estimated initial phase time sequence;
and 5: and calculating vibration displacement time domain information according to the obtained initial phase time sequence.
6. The method for processing the signal based on the LFMCW radar vibration monitoring as claimed in claim 5, wherein the effective baseband beat signal in step 1 is a modulated wave signal as a synchronous signal.
7. The LFMCW radar vibration monitoring-based signal processing method according to claim 5, wherein the frequency f of the beat signal in the step 2 isbThe estimation method of (2) is fast fourier transform, as shown in the following equation:
in the formula:
in order to be an estimate of the beat frequency,
representing an operation of finding a parameter f that yields a maximum value, f having a value in the range of 0 to fs/2，fsFor the sampling frequency, abs (-) represents a complex magnitude operation,
representing a fast fourier transform operation.
8. The LFMCW radar vibration monitoring-based signal processing method according to claim 5, wherein the estimation method of the initial phase of the complex beat signal in the step 3 is an approximate maximum likelihood estimation method, which is shown as the following formula:
9. The method for processing signals based on LFMCW radar vibration monitoring as claimed in claim 5, wherein the step 4 of performing phase jump correction processing comprises: by judging whether the difference of the initial phase estimation values of the beat signals in the time of adjacent sweep periods is larger than a fixed value delta or not, if so, the phase jump is considered to occur, and 2 delta is added or subtracted to the second value to enable the difference of the two phases to be smaller than the fixed value delta.
10. The method for processing signals based on LFMCW radar vibration monitoring as claimed in claim 5, wherein the method for estimating vibration displacement time domain information from the initial phase time series in step 5 is as follows:
the time series of vibrational displacements along the radar line of sight x (it) can be expressed as:
by using the geometric position relationship between the radar and the vibration direction of the monitored target, the vibration displacement time sequence d (it) of the monitored target can be obtained as shown in the following formula:
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| CN114646279B (en) * | 2021-12-22 | 2023-03-14 | 上海交通大学 | Microwave multi-scale vibration and deformation measurement method and system |
| CN115127640B (en) * | 2022-06-08 | 2023-06-20 | 中国地质环境监测院(自然资源部地质灾害技术指导中心) | Debris flow water level extraction method and system |
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