CN107764389A - A kind of method of low speed video camera measurement higher-frequency vibration based on fringe projection method - Google Patents
A kind of method of low speed video camera measurement higher-frequency vibration based on fringe projection method Download PDFInfo
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- CN107764389A CN107764389A CN201710807463.2A CN201710807463A CN107764389A CN 107764389 A CN107764389 A CN 107764389A CN 201710807463 A CN201710807463 A CN 201710807463A CN 107764389 A CN107764389 A CN 107764389A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
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Abstract
The present invention relates to a kind of method of the measurement higher-frequency vibration of low speed video camera based on fringe projection method, including：Black and white strip image will be generated by projector projects in body surface.Set camera sample frequency and time for exposure.Regulation camera exposure degree makes stripe pattern black and white partial width equal.Measuring system parameter.Chosen to photographing streaky part in all stripe patterns, recover height change of the vibrating object surface in each sampling instant using Fourier transform profilometry.The change curve for drawing out the sampled point height of selection is oscillation trajectory.Amplitude data can be directly obtained by the difference in height contrasted between geometric locus maximum and minimum value, vibration frequency data need the number of image to be multiplied by the time for exposure by calculating sampling whole cycle to obtain.
Description
Technical field
The present invention relates to a kind of method for realizing the vibration of low frequency camera measurement higher-frequency, belong to vibration of optical fields of measurement.
Background technology
According to nyquist sampling theorem, if intactly to recover the information in primary signal, the frequency of sampling will
More than 2 times of highest frequency in primary signal.Ensure 2.56~4 that sample frequency is signal highest frequency in general practical application
Times.The frame of general industry camera 40 sampling rate per second, the signal for the highest frequency that can be measured in theory is 20Hz, is had very big
Limitation.And the camera cost for purchasing high-speed is bigger, and with the raising of camera sample frequency, data storage into
This is also greatly improved, and more considerably increases measurement cost.
The content of the invention
The present invention provides a kind of method of the low speed video camera measurement higher-frequency vibration based on fringe projection method, can use
General industry camera measurement is higher by the stable vibration of its sampling rate several times, meets the requirement of most of industrial vibration measurements.This
The technical scheme of invention is as follows：
A kind of method of low speed video camera measurement higher-frequency vibration based on fringe projection method, comprises the following steps：
(1) stable vibration object to be measured is put on the reference plane, computer is connected into upper projecting apparatus, black and white will be generated
Stripe pattern is by projector projects in body surface.
(2) camera sample frequency and time for exposure are set, it is an actual vibration cycle additional small phase to take the sampling interval
The machine time for exposure.
(3) regulation camera exposure degree makes stripe pattern black and white partial width equal, is clapped using CCD camera with certain speed
Take the photograph the stripe pattern for projecting to vibrating object surface.
(4) measuring system parameter, obtains the distance that CCD camera arrives vibrating object surface, CCD camera and projecting apparatus level away from
From, camera focus, actual fringe period length data.
(5) chosen to photographing streaky part in all stripe patterns, it is extensive using Fourier transform profilometry
Height change of the multiplex vibration body surface in each sampling instant.
(6) sampled point is chosen in a series of restored images of acquisition, obtains the height of each sampling instant point
Information.
(7) drawing function is used in Matlab, to shoot number as transverse axis, the altitude information in step (6) is the longitudinal axis,
The change curve for drawing out the sampled point height of selection is oscillation trajectory.
(8) amplitude data can be directly obtained by the difference in height contrasted between geometric locus maximum and minimum value, shaken
Dynamic frequency data need the number of image to be multiplied by the time for exposure by calculating sampling whole cycle to obtain.
Beneficial effects of the present invention are as follows：
1st, the present invention realizes the target of low sampling rate camera measurement higher-frequency vibration.
2nd, it is portable good, for the vibration measurement of different frequency, it is only necessary to change the numerical value of time for exposure, test
Program also can be general under various operating systems.
The measurement cost that higher-frequency is vibrated when the 3rd, reducing vibration measurement, and with very high reliability.
Brief description of the drawings
Principle schematic of Fig. 1 present invention based on fringe projection method
The principle schematic in Fig. 2 camera sampling intervals of the present invention
The calculation flow chart of Fig. 3 present invention
The measurement result schematic diagram of Fig. 4 present invention
Embodiment
The present invention is further detailed elaboration with instantiation below in conjunction with the accompanying drawings.
Referring to Fig. 1, the principle schematic of the invention based on fringe projection method：Stable vibration object to be measured is placed in reference
In plane, its surface is in different positions at different moments each.By Program Generating black and white strip image, projection is connected to
Instrument is simultaneously incident upon body surface, and CCD camera is responsible for gathering object image at different moments and storage.
Striped generate equipment produced by program in dotted line frame shown in black and white strip, the upper projecting apparatus of connection, adjust and project
The focusing knob of instrument is projected on vibrating object to be measured with making the image clearly of generation.Control vibrating object generation one constant
The low-frequency vibration of frequency and amplitude.The exposure of regulation CCD camera makes the black and white part of striped wide, focuses and is allowed to focus
On vibrating object surface.By programme-control CCD sampling rate (this experiment is 10 frames/second) and all images are preserved, then are led to
Cross frequency and amplitude that Matlab softwares calculate vibration.
Referring to Fig. 2, the principle schematic in camera sampling interval of the present invention：Because the sampling rate for sampling camera is likely lower than
The actual frequency of vibrating object, so we take the camera exposure time that the sampling interval is an actual vibration cycle additional very little
Tb(this experiment is 400 microseconds), (T2-T1 ') as in figure, so reduce vibration period needs (T1 '-T1)/(T2-
T1 ') two field picture, so the frequency of object actual vibration counter can be inferred by the geometric locus of acquisition.
Referring to Fig. 3, calculation flow chart of the invention, its corresponding steps described briefly below：
(1) experiment equipments such as vibrating object, CCD camera are first well placed, measure CCD camera to the distance d, CCD of projecting apparatus
Distance l of the camera to reference planes0And Cycle Length (the 1/f of striped0)。
(2) set camera sample frequency, regard vibrating object substantially frequency determine (in this experiment vibrating object frequency as
30Hz, therefore it is 10 frames/second to set sampling rate).
(3) and then regulation exposes and focal length so that the striped in image reaches clearly degree, shoots photo.
(4) width is selected from the image got as reference picture I0, remaining image is respectively as I1, I2... ..., IM
(wherein M is the total number for photographing image), to the wherein streaky part of all image selections.
(5) all images chosen to previous step carry out two-dimensional Fourier transform, filter, two-dimensional inverse Fourier transform,
Convolution is multiplied, and logarithm, takes the computings such as imaginary part to obtain phase difference
(6) step (5) kind is obtainedIt is brought into phase height conversion formulaIn, can
Obtain the restored image at vibrating object surface each moment.
(7) sampled point of a same coordinate, extraction are chosen in a series of height recovery images obtained in step (6)
Height value of the restored image at each moment in sample point
(8) the oscillation trajectory curve of the sampled point, the amplitude vibrated from geometric locus are drawn according to time order and function
Information, and sampling number N needed for the cycle.
(9) Oscillation Amplitude AMDirectly obtained by previous step, vibration frequency information is needed of image by sampling whole cycle
Number is multiplied by the time for exposure, i.e. N × TbObtain.
Referring to Fig. 4, measurement result schematic diagram of the invention, it can be seen that each cycle takes around 90 images, i.e., and 90
Secondary sampling can describe.So its vibration period is 36ms.30Hz vibration, its cycle are about 33.3ms, it is contemplated that input letter
Number issuable non-linear distortion, measurement result substantially conform to actual vibration situation.
Claims (1)
1. a kind of method of low speed video camera measurement higher-frequency vibration based on fringe projection method, comprises the following steps：
(1) stable vibration object to be measured is put on the reference plane, computer is connected into upper projecting apparatus, black and white strip will be generated
Image is by projector projects in body surface；
(2) camera sample frequency and time for exposure are set, takes the sampling interval to be exposed for additional one of actual vibration cycle small camera
Between light time；
(3) regulation camera exposure degree makes stripe pattern black and white partial width equal, is shot and thrown with certain speed using CCD camera
Stripe pattern of the shadow to vibrating object surface；
(4) measuring system parameter, the distance of acquisition CCD camera to vibrating object surface, CCD camera and projecting apparatus horizontal range,
Camera focus, actual fringe period length data；
(5) chosen to photographing streaky part in all stripe patterns, recover to shake using Fourier transform profilometry
Height change of the animal body surface in each sampling instant；
(6) sampled point is chosen in a series of restored images of acquisition, obtains the elevation information of each sampling instant point.
(7) drawing function is used in Matlab, to shoot number as transverse axis, the altitude information in step (6) is the longitudinal axis, is drawn
The change curve for going out the sampled point height of selection is oscillation trajectory.
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110686619A (en) * | 2019-09-21 | 2020-01-14 | 天津大学 | Non-contact low-frequency vibration measurement method based on tone-height mapping |
| CN111413064A (en) * | 2020-03-27 | 2020-07-14 | 智方达(天津)科技有限公司 | Response measurement method for aircraft model in wind tunnel |
| CN112556821A (en) * | 2020-12-03 | 2021-03-26 | 天津大学 | Vibration measuring device based on single color camera and single projector |
| CN112697259A (en) * | 2020-12-31 | 2021-04-23 | 福州大学 | Beam structure modal shape measuring device and method based on combined stripes |
| CN112697258A (en) * | 2020-12-17 | 2021-04-23 | 天津大学 | Visual vibration measurement method based on single-frame coding illumination |
| CN113892015A (en) * | 2019-09-03 | 2022-01-04 | 株式会社新川 | Vibration detection system |
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| CN113892015A (en) * | 2019-09-03 | 2022-01-04 | 株式会社新川 | Vibration detection system |
| CN110686619A (en) * | 2019-09-21 | 2020-01-14 | 天津大学 | Non-contact low-frequency vibration measurement method based on tone-height mapping |
| CN111413064A (en) * | 2020-03-27 | 2020-07-14 | 智方达(天津)科技有限公司 | Response measurement method for aircraft model in wind tunnel |
| CN112556821A (en) * | 2020-12-03 | 2021-03-26 | 天津大学 | Vibration measuring device based on single color camera and single projector |
| CN112697258A (en) * | 2020-12-17 | 2021-04-23 | 天津大学 | Visual vibration measurement method based on single-frame coding illumination |
| CN112697259A (en) * | 2020-12-31 | 2021-04-23 | 福州大学 | Beam structure modal shape measuring device and method based on combined stripes |
| CN112697259B (en) * | 2020-12-31 | 2022-04-08 | 福州大学 | Beam structure modal shape measuring device and method based on combined stripes |
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