Disclosure of Invention
In order to solve one or more technical problems in the prior art, the applicant finds that the triangular wave voltage signal can provide higher precision and stability than the sine wave voltage signal when four speckle interference images at four moments are acquired at equal time intervals. Based on the research result, according to one aspect of the invention, the invention provides a high-precision high-stability electronic speckle interference real-time phase measurement system, which can remarkably improve the stability of a phase image and the accuracy of phase information, and can realize the quick calculation and real-time display of the phase image, thereby realizing the real-time high-precision phase measurement, and further realizing the work of high-quality nondestructive inspection and the like.
This high accuracy high stability electron speckle interference real-time phase measurement system includes:
a michelson interferometer comprising a phase-shifting mirror and an optical camera;
the piezoelectric ceramic is used for moving the phase shift mirror back and forth;
a driver for driving the piezoelectric ceramic;
the synchronous generator of the square wave voltage signal and the triangular wave voltage signal is respectively connected with the driver and the digital camera, the square wave voltage signal is used for controlling the high-speed camera to pick images, and the triangular wave voltage signal is used for driving the piezoelectric ceramics; wherein the number isThe camera collects A, B, C, D speckle interference images at four moments at equal time intervals within the rising segment 4t time of the triangular wave voltage signal by the period t to obtain corresponding light intensity distribution IA、IB、IC、IDThe displacement of the phase shift mirror is 3 lambda/4 or 3 lambda/8 in the 4t time, and lambda is the wavelength of interference light; and
a processor for converting the IA、IB、IC、IDAnd n equal divisions are carried out, partial overlapping areas of the equally divided sub-images are reserved, n sub-phase diagrams are obtained through multi-thread parallel calculation of the n equal divided sub-images, and the n sub-phase diagrams are spliced to obtain real-time phases representing the out-of-plane displacement or the out-of-plane displacement derivative of the measured object.
According to another aspect of the invention, the high-precision high-stability electronic speckle interference real-time phase measurement system further comprises a display unit for displaying the phase value of the measured object in real time. And 4T is the acquisition period of the four speckle interference images and the calculation period T of the phase image. The 4t is 4 times of the sampling period of the digital camera.
According to yet another aspect of the invention, IA、IB、IC、IDFor phase calculation, the phase difference between two is pi/2, which is expressed as follows:
wherein, I
0Is a speckle patternThe background light intensity, mu, is the amplitude of the modulated light intensity,
are random phase values of the speckle pattern.
According to still another aspect of the invention, the four speckle images comprise two or more sets of the four speckle images captured by a high speed camera, the two or more sets of the four speckle images forming a sequence { [ I ]A0,IB0,IC0,ID0];[IA1,IB1,IC1,ID1]…[IAi,IBi,ICi,IDi]I is a natural number;
[ I ] of the first set of four speckle images
A0,I
B0,I
C0,I
D0]For calculating the initial random phase of the object to be measured
Of the ith group of four speckle images
Ai,I
Bi,I
Ci,I
Di]For calculating phase corresponding to deformation of object to be measured
i is a natural number,
the processor is used for pairing
And
mean value filtering is carried out to eliminate noise, and the mean value filtering and the noise elimination are respectively obtained
And
the phase difference of the measured object caused by deformation at each moment can be obtained
The display unit is also used for displaying the phase difference in real time.
According to another aspect of the invention, a real-time out-of-plane displacement measurement system is further provided, which comprises the high-precision high-stability electronic speckle interferometry real-time phase measurement system, wherein the processor is used for calculating out-of-plane displacement of the measured object
According to yet another aspect of the invention, the processor is configured to calculate an out-of-plane displacement derivative
Where δ is the shear number.
Compared with the prior art, the invention has one or more of the following technical effects:
firstly, the system can carry out high-precision high-stability electronic speckle interference real-time phase measurement on an engineering site;
compared with the step control piezoelectric ceramics (phase shifter) in the prior art, the system adopts the triangular wave control piezoelectric ceramics, and can accurately control the phase difference of the four speckle interference images to be equal, so that an accurate phase calculation result is obtained, and the system has high phase calculation precision and phase calculation stability;
thirdly, the frequency of the camera trigger signal is 4 times or more than several times of that of the PZT phase shift driving signal, and the PZT phase shift driving signal is a triangular wave linear signal (replacing a stepping control signal in the prior art), so that an ideal piezoelectric performance curve is easy to obtain, and the precise measurement of a real-time phase can be ensured;
fourthly, a fast algorithm of multi-thread parallel computation is adopted, and the display frame rate of the phase diagram is only related to the sampling frame rate of the optical digital camera and the computation speed of the computer. And the high frame rate digital camera and the high-performance computer are selected, so that the rapid real-time phase calculation and the phase image display can be realized.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. The examples are provided by way of explanation and are not meant as limitations. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present invention encompass such modifications and variations.
In the following description of the drawings, like reference numerals designate identical or similar structures. Generally, only the differences between the individual embodiments will be described. Descriptions of parts or aspects in one embodiment can also be applied to corresponding parts or aspects in another embodiment, unless explicitly stated otherwise.
Example 1
Referring to fig. 1-3, fig. 1 is a schematic structural diagram of a high-precision high-stability electronic speckle interferometry real-time phase measurement system according to a preferred embodiment of the present invention, fig. 2 is a schematic structural diagram of a control signal (second signal) for driving a piezoelectric ceramic according to a preferred embodiment of the present invention and acquiring a plurality of groups of four speckle images, and fig. 3 is a schematic structural diagram of a multi-thread parallel computing real-time phase shift (corresponding to the plurality of groups of four speckle images in fig. 2) according to a preferred embodiment of the present invention. This high accuracy high stability electron speckle interference real-time phase measurement system includes:
a michelson interferometer comprising a phase-shifting mirror and a high-speed camera;
the piezoelectric ceramic is used for moving the phase shift mirror back and forth;
a driver for driving the piezoelectric ceramic;
the synchronous generator of the square wave voltage signal and the triangular wave voltage signal is respectively connected with the driver and the digital camera, the square wave voltage signal (a first signal) is used for controlling the high-speed camera to pick up images, and the triangular wave voltage signal (a second signal) is used for driving the piezoelectric ceramic; the digital camera collects A, B, C, D speckle interference images at four moments at equal time intervals within 4t of the triangular wave voltage signal rising section at period t to obtain corresponding light intensity distribution IA、IB、IC、IDThe displacement of the phase shift mirror is 3 lambda/4 or 3 lambda/8 in the 4t time, and lambda is the wavelength of interference light; and
a processor for converting the IA、IB、IC、IDAnd n equal divisions are carried out, partial overlapping areas of the equally divided sub-images are reserved, n sub-phase diagrams are obtained through multi-thread parallel calculation of the n equal divided sub-images, and the n sub-phase diagrams are spliced to obtain real-time phases representing the out-of-plane displacement or the out-of-plane displacement derivative of the measured object.
It should be noted that the michelson interferometer is a prior art, and generally includes a laser, a beam splitter, a shearing mirror, and a phase shift mirror. Laser emitted by a laser device is incident on the surface of a test piece and then reflected to a spectroscope, one path of light is transmitted to a phase shift mirror after being split by the spectroscope, then is incident to a high-speed camera after being reflected by the phase shift mirror and the spectroscope in sequence, the other path of light is reflected to a shearing mirror, and then is incident to the high-speed camera after being reflected by the shearing mirror and transmitted by the spectroscope.
It can be understood that the triangular wave voltage signal synchronized with the first signal controls the piezoelectric ceramic to drive the phase shift mirror to move, so that high-frequency stable linear dynamic response can be realized, an ideal piezoelectric performance curve is easy to obtain, and the problem that high-frequency stable dynamic response cannot be realized due to step control in the prior art is solved.
Preferably, the high-speed camera of the present invention is, for example, a 100Hz digital camera, but the present invention is not limited thereto, and the frame rate for calculating and displaying the phase map is determined by the sampling frame rate of the camera and the calculation speed of the computer. The processor of the present invention may be various components having a data processing function, such as a CPU, a computer, and the like.
According to another preferred embodiment of the present invention, the high-precision high-stability electronic speckle interferometry real-time phase measurement system further includes a display unit for displaying the phase value of the measured object in real time. Preferably, the 4T is the acquisition period of the four speckle interferograms and the calculation period T of the phase map. The 4t is 4 times of the sampling period of the digital camera.
According to still another preferred embodiment of the present invention, IA、IB、IC、IDFor phase calculation, the phase difference between two is pi/2, which is expressed as follows:
wherein, I
0Background light intensity of the speckle pattern, mu is amplitude of the modulated light intensity,
are random phase values of the speckle pattern.
According to another preferred embodiment of the present invention, the four speckle images include two or more groups of the four speckle images collected by a high-speed camera, and the two or more groups of the four speckle images form a sequence { [ I ]A0,IB0,IC0,ID0];[IA1,IB1,IC1,ID1]…[IAi,IBi,ICi,IDi]I is a natural number;
[ I ] of the first set of four speckle images
A0,I
B0,I
C0,I
D0]For calculating the initial random phase of the object to be measured
Of the ith group of four speckle images
Ai,I
Bi,I
Ci,I
Di]For calculating phase corresponding to deformation of object to be measured
i is a natural number,
the processor is used for pairing
And
mean value filtering is carried out to eliminate noise, and the mean value filtering and the noise elimination are respectively obtained
And
the phase difference of the measured object caused by deformation at each moment can be obtained
The display unit is also used for displaying the phase difference in real time.
According to another preferred embodiment of the present invention, there is further provided a real-time out-of-plane displacement measurement system, including the foregoing electronic speckle interferometry real-time phase measurement system with high precision and high stability, wherein the processor is configured to calculate out-of-plane displacement of the measured object
In accordance with yet another preferred embodiment of the present invention the processor is operative to calculate an out-of-plane displacement derivative
Where δ is the shear number.
According to another preferred embodiment of the present invention, there is provided a high-precision high-stability electronic speckle interferometry real-time phase measurement method, including the steps of:
1) two groups of continuous voltage signals are synchronously sent out by a controller (a signal generator) to respectively control the high-speed camera and the piezoelectric ceramics.
2) In the step 1), one path of signal of the signal generator is a square wave voltage signal and is used for triggering the high-speed camera to pick up the picture, the period of the square wave signal is t, namely the period of the sequence picking up the picture of the high-speed camera is t.
3) The other path of signal of the signal generator in step 1) is a triangular wave voltage signal with a period of 4t (the invention is not limited thereto, as long as the drawing requirement of step 4) can be realized), and the voltage signal is amplified by a piezoelectric ceramic voltage amplifying circuit and then used for driving a piezoelectric ceramic (PZT) phase shift mirror in the michelson interference optical path to move, so that one beam of light in the interference optical path generates a given optical path difference.
4) The invention adopts a four-step time phase shift method to carry out phase processing, and four speckle images [ I ] used for four-step phase shift calculation are collected at equal intervals t within 4t of the triangular wave voltage signal in the step 3)A,IB,IC,ID]。
5) And (3) modulating the peak value of the triangular wave voltage signal to ensure that the displacement of the piezoelectric ceramic phase shift mirror is 3 lambda/8 within 4t of the triangular wave voltage signal in the step 4), so that the optical path difference of one light in the Michelson interference optical path is 3 lambda/4. Researches show that the voltage of the rising section of the triangular wave changes linearly with time, and four speckle images [ I ] collected in the step 4)A,IB,IC,ID]The phase difference between every two is exactly pi/2 and is expressed as follows;
wherein, I
0Background light intensity of the speckle pattern, mu is amplitude of the modulated light intensity,
are random phase values of the speckle pattern.
6) Speckle images [ I ] collected in the step 4)A,IB,IC,ID]Dividing by n equally along the width direction (n depends on the number of cores of the selected computer processor), and dividing into:[IA,IB,IC,ID]1、[IA,IB,IC,ID]2……[IA,IB,IC,ID]nThe image to be equally divided needs to keep a part of the overlapped area.
7) Respectively carrying out four-step phase shift calculation on the four sub-images in the n subareas obtained in the step 6) by using a formula (2), wherein the calculation of the n image subareas is completed on n cores of a computer processor in parallel, and the obtained phase is
Wherein,
8) phase map of n sections calculated in step 7)
Splicing and reducing the n subarea phase diagrams into a complete phase diagram according to the reverse process of the step 6)
9) Continuously acquiring and storing the speckle images in the deformation process of the measured object in real time according to the step 4) { [ I ]A0,IB0,IC0,ID0];[IA1,IB1,IC1,ID1]…[IAi,IBi,ICi,IDi](i=0,1,2…)}。
10) According to the processing from step 6) to step 8), the phase corresponding to the deformation of the object can be calculated in each phase shift period (16t)
(i=0,1,2,3……)。
11) According to the initial phase calculated in step 10)
The phase change caused by the deformation of the object relative to the initial moment can be calculated
Then eliminating noise by mean value filtering, and obtaining the phase difference of the object caused by deformation at any moment (the period is 16t)
(i=1,2,3……)。
12) Continuously repeating the steps 4) to 11), synchronously performing phase calculation of each partition in the step 7) by adopting computer multithread parallel calculation, so that the fast real-time phase shift calculation and the phase display can be realized, and the period of the phase shift calculation and the display is 16 t.
It can be understood that the method utilizes the signal generator to synchronously control the sequence acquisition of the high-speed camera and the driving voltage of the high-frequency response piezoelectric ceramic phase shift generator, and then carries out phase processing by a four-step phase shift method based on a multithread parallel computing fast algorithm, and can realize electronic speckle interference dynamic phase measurement and real-time nondestructive flaw detection in an engineering field. Taking a high-speed digital camera with a sampling frame rate of 100Hz as an example, the period of phase measurement of the method is approximately the same as the period of a PZT driving signal, when the high-speed digital camera with the sampling frame rate of 100Hz is selected, the calculation and display time of four phase shifts in each phase shift period is controlled within 10ms by multi-thread parallel calculation, namely the phase measurement and display frame rate of 20Hz can be realized, and the high-precision high-stability electronic speckle interference real-time phase measurement and phase display are completed.
According to another preferred embodiment of the present invention, there is provided a high-precision high-stability electronic speckle interference real-time phase measurement method, taking a rubber-metal bonding structure with internal prefabricated defects under thermal radiation loading measured in an engineering field as an example, including the following steps:
1) two groups of continuous voltage signals are synchronously sent out through a signal generator, a sequence chart of a high-speed camera and the driving voltage of a high-frequency response time phase shift system are respectively controlled, a piezoelectric ceramic phase shifter changes the optical path of one beam of light in a Michelson interferometer by driving a phase shift mirror to move back and forth, and a given phase difference is introduced;
2) one path of signal of the signal generator is a square wave voltage signal and is used for triggering the high-speed camera to acquire images, and the rising edge of the square wave signal is used for triggering the camera to acquire images. If a high-speed camera with a sampling frame rate of 100Hz is selected, the period t of the square wave signal is 10ms, as shown in FIG. 2;
3) the other path of signal of the signal generator is a triangular wave voltage signal (see fig. 2) with a period of 4t (namely 40ms), and the voltage signal is provided for piezoelectric ceramics (PZT) in a michelson interference optical path to drive the phase shift mirror to move after being amplified by a PZT driver;
4) performing phase processing by adopting a four-step time phase shift method, and collecting A, B, C and D four speckle interference images [ I ] at equal time intervals in the time of 4t (40ms) of the triangular wave voltage signal period in the step 3)A,IB,IC,ID]See fig. 2.
5) By modulating the peak value of the triangular wave voltage, in the time of the triangular wave voltage signal 4t (40ms) in step 4), the piezoelectric ceramic pushes the phase shift mirror to displace 3 λ/8 (a green laser is selected, λ is 512nm), that is, the optical path difference of one light in the michelson interference optical path is 3 λ/4, as shown in fig. 2. Research shows that the change of the voltage of the triangular wave along with time is approximate to linearity, and the phase difference between every two four speckle images collected in the step 4) is exactly pi/2, which is expressed as follows;
wherein, I
0Background light intensity of the speckle pattern, mu is amplitude of the modulated light intensity,
are random phase values of the speckle pattern.
6) In order to realize real-time phase processing and real-time phase display and improve the phase calculation speed, the computer with the i7 or 8-core processor is selected for use in the embodiment. Each group of speckle images [ I ] collected in the step 5)A,IB,IC,ID]The width direction is divided into 8 equal parts, which are sequentially divided into: [ I ] ofA,IB,IC,ID]1、[IA,IB,IC,ID]2……[IA,IB,IC,ID]8The halved image should preserve the overlapping area of 10 pixels.
7) Respectively carrying out four-step phase shift calculation on the four sub-graphs in the 8 subareas obtained in the step 6) by using the following formula to obtain respective phases
As shown in fig. 2.
8) The phase map of 8 subareas calculated in the step 7) is processed
Splicing and reducing into a complete phase diagram according to the reverse process of the step 6)
9) Continuously acquiring and storing the speckle images in the deformation process of the measured object in real time according to the step 5) { [ I ]A0,IB0,IC0,ID0];[IA1,IB1,IC1,ID1]…[IAi,IBi,ICi,IDi](i=0,1,2…)}。
10) Calculating the phase corresponding to the deformation of the object according to the processing from the step 6) to the step 8)
(i=0,1,2,3……),
11) According to the initial phase calculated in step 10)
The phase change caused by the deformation of the object relative to the initial moment can be calculated
Then eliminating noise through mean value filtering, and obtaining the phase difference of the object caused by deformation at any moment
(i=1,2,3……)。
12) Continuously repeating the steps 5) to 11), synchronously calculating the phase of each subarea in the step 7) by adopting computer multithread parallel calculation, so that the rapid real-time phase shift calculation and phase display can be realized, wherein the phase shift calculation and display period is 10ms, namely the real-time phase shift calculation and display frame rate can reach 20-25 frames/second and is far higher than the phase shift frame rate (less than 10 frames/second) of the existing electronic speckle interference system, and therefore, the real-time precision measurement and real-time nondestructive detection of the dynamic phase of the engineering site can be realized.
Compared with the prior art, the invention has one or more of the following technical effects:
firstly, the system can carry out high-precision high-stability electronic speckle interference real-time phase measurement on an engineering site;
compared with the step control piezoelectric ceramics (phase shifter) in the prior art, the system adopts the triangular wave control piezoelectric ceramics, and can accurately control the phase difference of the four speckle interference images to be equal, so that an accurate phase calculation result is obtained, and the system has high phase calculation precision and phase calculation stability;
thirdly, the frequency of the camera trigger signal is 4 times or more than several times of that of the PZT phase shift driving signal, and the PZT phase shift driving signal is a triangular wave linear signal (replacing a stepping control signal in the prior art), so that an ideal piezoelectric performance curve is easy to obtain, and the precise measurement of a real-time phase can be ensured;
fourthly, a fast algorithm of multi-thread parallel computation is adopted, and the display frame rate of the phase diagram is only related to the sampling frame rate of the optical digital camera and the computation speed of the computer. And the high frame rate digital camera and the high-performance computer are selected, so that the rapid real-time phase calculation and the phase image display can be realized.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the present invention, and the features of the embodiments that do not violate each other may be combined with each other. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.