CN103983211A - Three-dimensional shape measuring system of fringe projection based on sine phase modulation four-step integral - Google Patents

Abstract

The invention discloses a three-dimensional shape measuring system of fringe projection based on a sine phase modulation four-step integral, and relates to the field of three-dimensional shape measuring. The method includes the steps that an optical fiber interference fringe projection mathematical model is built; a phase error compensation system extracts phase drift amount caused by environment factors, and phase compensation voltage is generated and is injected into a dual-channel piezoelectric ceramic driver; a sine phase modulation signal is directly injected into the dual-channel piezoelectric ceramic driver to achieve sine modulation of a fringe phase, injected into the phase error compensation system to serve as a phase generation carrier and injected into a CCD time sequence controller to serve as a reference signal of the CCD time sequence controller, a time sequence generated by the CCD time sequence controller controls a planar array CCD camera to collect a fringe image on the surface of an object to be measured, the image is uploaded to an image processing and shape restoring system, and finally surface shape reconstruction of the object is achieved. The method meets the technical requirements for non-contact, full view, quickness, high precision and the like of multiple application fields.

Description

Striped projection three dimensional shape measurement system based on sinusoidal phase modulation four step integrations

Technical field

The present invention relates to measuring three-dimensional morphology field, relate in particular to a kind of projection of the striped based on sinusoidal phase modulation four step integrations three dimensional shape measurement system.

Background technology

Measuring three-dimensional morphology technology is in field widespread uses such as product quality detection, reverse engineering, authentication, pathological diagnosis, historical relic measurement, cultural video display amusements, and high-precision surface topography interferometric method mainly contains laser heterodyne interferometry method, phase shift interference method, sinusoidal phase modulation interferometric method etc.Laser heterodyne interferometry system architecture is more complicated, requires to produce high precision frequency difference; Phase shift interference method requires high to Phase shift precision, be easily subject to environmental interference; Sinusoidal phase modulation interferometric method has the advantages such as phase-modulation is simple, measuring accuracy is high, antijamming capability is strong, in surface topography, displacement, angle and vibration survey, is widely used.

Early stage striped mode of delivery mainly realizes candy strip projection and phase shifts by physical grating and mechanical translation device, but fringe density and the striped Phase shift precision of projection are relatively low; Conventional method is to utilize digital projector (DLP) to project the digital stripe pattern being generated by computer programming at present, its fringe density is also subject to the restriction of projector resolution and projection scope, thereby make measuring accuracy not high, the nonlinear relationship between projector voltage and brightness also will cause measurement result to occur error simultaneously.Existing relevant scholar utilizes two bundle coherent light waveses produce interference fringe structured light and be projected to testee surface both at home and abroad at present, within the scope of small field of view, realize the projection of high density interference fringe, but striped projection system structure relative complex based on coherent light interference, and be very easily subject to the impact of the factor such as temperature fluctuation, ambient vibration, cause stiffness of system not high, therefore in actual measuring three-dimensional morphology, be subject to certain limitation.

Summary of the invention

The invention provides a kind of projection of the striped based on sinusoidal phase modulation four step integrations three dimensional shape measurement system, the present invention starts with from measuring accuracy and real-time, propose to project and obtain stripe pattern by fiber interference fringe, analyze simultaneously and compensated the fringe phase drift that environmental factor causes, adopt sinusoidal phase modulation four step integral principles, recover pattern by digital image processing method, while realizing the high-precision real of three-dimensional appearance, measure, described below:

A kind of projection of the striped based on sinusoidal phase modulation four step integrations three dimensional shape measurement system, comprise: He-Ne laser instrument, described He-Ne laser instrument is as output light source, and output beam is after coupled lens converges, enter 2 × 2 type fiber couplers by the first fiber arm

After described fiber coupler light splitting, enter respectively in the second fiber arm, the 3rd fiber arm, described the second fiber arm is closely wrapped on modulation piezoelectric ceramics, described the 3rd fiber arm is closely wrapped on cylindrical piezoelectric pottery, the output terminal of the second fiber arm, the 3rd fiber arm is fixed by optical fiber clamping tool, forms Mach-Zehnder interferometer structure; Build fiber interference fringe projection mathematical model;

Output terminal at the 4th fiber arm is placed photodetector, and the signal detecting is received by phase error compensation system, the phase drift amount that phase error compensation system extraction environment factor causes, and generate phase compensation voltage injection binary channels piezoelectric ceramic actuator; The described binary channels piezoelectric ceramic actuator of the direct injection of sinusoidal phase modulation signal is realized the Sine Modulated of fringe phase; Inject phase error compensation system, use as phase generated carrier; Inject CCD time schedule controller, as the reference signal of described CCD time schedule controller;

The sequential control area array CCD camera that described CCD time schedule controller generates gathers the lip-deep stripe pattern of object under test, is uploaded to image and processes and shape recovery system, finally realizes object surface appearance and rebuilds.

Described phase error compensation system comprises: phase generated carrier module,

Described phase generated carrier module is extracted the sinusoidal component, the cosine component that comprise phase error, uses rotational coordinates teaching machine to solve phase error; Described phase error is converted to voltage signal by phase place-voltage transformation module, drives described modulation piezoelectric ceramics to produce optical path difference Δ l _ccarry out compensation of phase error.

Described image is processed with shape recovery system and is comprised: image capture module,

Described in described image capture module control, CCD camera gathers four width images within modulation period, strengthens module, revolves filtration module and realize Digital Image Processing through greyscale transformation module, Gaussian image; Phase extraction module is used for realizing four step integrations, extracts the phase information of surface topography from stripe pattern; The noise that low-pass filtering module is caused by pattern edge reflections for filtering; Demarcating module, for the structural parameters of calibration measurements system, finally obtains object under test three-dimensional surface shape.

Described fiber interference fringe projection mathematical model is specially:

$\left\{\begin{array}{c}x=-\frac{m\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}\\ y=-\frac{n\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}\\ z=-\frac{d\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}-L\end{array}\right.$

Wherein, m, n are the pixel sequence number of level and vertical direction, and d is the distance that image planes are arrived in lens center, and L is the distance that model initial point is arrived in lens center, and R is radius, and β is projectional angle, for phase place, l ₀for fiber core distance, λ is optical wavelength; for initial phase; β ₀for the projectional angle of zero order fringe.

The beneficial effect of technical scheme provided by the invention is: the present invention adopts sinusoidal phase modulation four step integral principles, in conjunction with fiber interference fringe projective techniques to body surface projected fringe image, introduce phase error analysis and bucking-out system and eliminate the fringe phase drift that environmental factor causes, gather body surface stripe pattern, use digital image processing method to recover pattern, meet the technical requirements such as the noncontact in other many utilizations field, full visual field, rapidity, high precision.

Brief description of the drawings

Fig. 1 is the striped projection three dimensional shape measurement system schematic diagram based on sinusoidal phase modulation four step integral principles;

Fig. 2 is fiber interference fringe projection mathematical model;

Fig. 3 is phase error compensation schematic diagram;

Fig. 4 is sinusoidal phase modulation four step integral principle figure;

Fig. 5 is Digital Image Processing and shape recovery schematic diagram.

In Fig. 1,1 is laser instrument, 2 is coupled lens, and 3 is 3dB fiber coupler, and 4 is modulation piezoelectric ceramics, 5 is compensation piezoelectric ceramics, 6 is optical fiber clamping tool, and 7 is object under test, and 8 is binary channels piezoelectric ceramic actuator, 9 is area array CCD camera, 10 is photodetector, and 11 is phase error compensation system, and 12 is sinusoidal phase modulation signal, 13 is CCD time schedule controller, 14 process and shape recovery system for image, and a is the first fiber arm, and b is the second fiber arm, c is the 3rd fiber arm, and d is the 4th fiber arm.

In Fig. 2,15 is object under test surface, and 16 is zero order fringe, and 17 is the imaging surface of stripe pattern in CCD; 18 is the striped projector.

In Fig. 3,19 is phase generated carrier (PGC) module, 20 and 21 be respectively band solve phase place just, cosine component, 22 is rotational coordinates teaching machine (CORDIC), 23 is phase place-electric pressure converter.

In Fig. 4,24 become stripe signal, the 25 four spoke print images for CCD collection for object under test when surface.

In Fig. 5,26 is Digital Image Processing module, 27 is shape recovery module, and 28 is image capture module, and 29 is greyscale transformation module, 30 is Gaussian image enhancing module, 31 for revolving filtration module, and 32 is phase extraction module, and 33 is low-pass filtering module, 34 is demarcating module, and 35 is object under test surface topography.

Embodiment

For making the object, technical solutions and advantages of the present invention clearer, below embodiment of the present invention is described further in detail.

Referring to Fig. 1, fiber interference fringe projection system, comprising: He-Ne laser instrument 1, and He-Ne laser instrument 1 is as output light source, and output beam, after coupled lens 2 converges, enters 2 × 2 type fiber couplers 3 by the first fiber arm a.After fiber coupler 3 light splitting, enter respectively in the second fiber arm b, the 3rd fiber arm c, the second fiber arm b is closely wrapped on modulation piezoelectric ceramics 4, the 3rd fiber arm c is closely wrapped on cylindrical piezoelectric pottery 5, the output terminal of the second fiber arm b, the 3rd fiber arm c is fixing by optical fiber clamping tool 6, forms Mach-Zehnder interferometer structure.The output end face of the second fiber arm b, the 3rd fiber arm c is equivalent to pointolite, and fibre core spacing is enough little, meets Mechanical Study On Young Interference condition.In the time meeting the paraxial condition in far field, fibre core spacing much smaller than optical fiber projection end to optical screen apart from time, can on object under test 7 surfaces, project highdensity cosine distribution striped.

Binary channels piezoelectric ceramic actuator 8 drives modulation piezoelectric ceramics 4 and cylindrical piezoelectric pottery 5 simultaneously.

The stripe pattern phase drift causing in order to eliminate environmental factor, output terminal at the 4th fiber arm d is placed photodetector 10, the signal detecting is received by phase error compensation system 11, the phase drift amount that phase error compensation system 11 extraction environment factors cause, and generate phase compensation voltage injection binary channels piezoelectric ceramic actuator 8.The direct injection binary channels of sinusoidal phase modulation signal 12 piezoelectric ceramic actuator 8 is realized the Sine Modulated of fringe phase; Inject phase error compensation system 11, use as phase generated carrier; Inject CCD time schedule controller 13, as the reference signal of CCD time schedule controller 13.The sequential control area array CCD camera 9 that CCD time schedule controller 13 generates gathers the lip-deep stripe pattern of object under test 7, is uploaded to image and processes and shape recovery system 14, finally realizes object surface appearance and rebuilds.

Referring to Fig. 2, selecting optical screen Plane-point O is model initial point, and xOz is optical screen plane.The optical centre of CCD camera lens is positioned at an A, and camera light direction of principal axis is y axle.X, z axle are parallel to respectively level, the vertical direction of camera pixel.Optical Fibers Projector is placed in a C, is positioned at radius and is R, precision rotation edge of table edge along the rotation of z axle, can relatively easily make by adjusting universal stage be parallel to x axle.Testee is placed on optical screen, supposes that P (x, y, z) is a bit on tested object plane, is projected as P on plane xOy _xy; Picture point P _ifor the imaging point of object point P in CCD image planes.At Δ P _xyin BC, calculating projectional angle β obtains

$\tan \mathrm{\β}=\frac{\stackrel{\‾}{P_{\mathrm{xy}}B}}{\stackrel{\‾}{\mathrm{BC}}}=\frac{L+z}{\sqrt{R^2-L^2}-x}---\left(1\right)$

Wherein L is the distance that model initial point is arrived in lens center.From camera Perspective transformation model, object point P and picture point P _imeet following mapping relations

$\frac{x}{-m}=\frac{y}{-n}=\frac{L+z}{d}---\left(2\right)$

Wherein, m, n are the pixel sequence number of level and vertical direction, and d is the distance that image planes are arrived in lens center.Simultaneous formula (1)-(2) solve coordinate (x, y, z) and obtain

$\left\{\begin{array}{c}x=-\frac{m\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}\\ y=-\frac{n\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}\\ z=-\frac{d\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}-L\end{array}\right.---\left(3\right)$

In calibrated measuring system, coordinate (x, y) represents the two-dimensional position of measured point, the phase place of this point represent along the elevation information of y axle, measured phase place can obtain surface topography.Phase place there is following relation with projectional angle β

Wherein, λ is optical wavelength; for initial phase; β ₀for the projectional angle of zero order fringe, in the time of Optical Fibers Projector Alignment model initial point O, the projection of zero order fringe on plane xOz overlaps with z axle; Two optical fiber connectors that use fibre clip can be equivalent to pointolite are evenly fixed, and fiber core distance is l ₀, meet Mechanical Study On Young Interference condition.Because l ₀distance much smaller than optical fiber projection end to optical screen, tan (β-β while meeting the paraxial condition in far field ₀) be approximately equal to as β-β ₀, formula (4) abbreviation is:

From formula (3), (5), obtain the phase place of body surface every bit obtain projectional angle by formula (5), recover surface topography by formula (3), so solve the phase place of surface topography become the key of shape recovery.

But the second fiber arm b, the 3rd fiber arm c are exposed in air, are subject to the such environmental effects such as temperature, vibration, cause two fiber arm phase differential to change, there is drift in interference fringe phase place.

For realizing the sinusoidal phase modulation to interferometric fringe signal, cylindrical piezoelectric pottery 5 is applied to following driving signal:

M(t)＝a·cos(ωt+θ) (6)

Wherein, a is modulation signal amplitude, and ω is modulation angular frequency, the initial phase that θ is modulation signal.Be subject to such environmental effects, temperature drift causes that wavelength variations is Δ λ _t, microvibration causes optical path difference changes delta l _v, body surface interference fringe phase place can produce drift.Generate compensating signal by Phase Compensation System, by the flexible extra optical path difference Δ l that increases of modulation piezoelectric ceramics 4 _ccarry out compensation of phase drift.Time become interferometric fringe signal be expressed as

s(x,y,t)＝A+Bcos[zcos(ωt+θ)+φ(x,y)+δ(t)] (7)

Wherein, A is DC component; B is AC compounent amplitude; Z is depth of modulation; δ (t) is Δ λ _t, Δ l _v, Δ l _cthe phase place that acting in conjunction generates, in the time that δ (t) is zero, the impact of environmental factor is completely eliminated.δ (t) is expressed as

$\mathrm{\δ}\left(t\right)=\frac{2\mathrm{\π}}{\mathrm{\λ}}(\mathrm{\Δ}{l}_V+\mathrm{\Δ}{l}_C-\frac{1}{\mathrm{\λ}}\mathrm{\Δ}{\mathrm{\λ}}_T)---\left(8\right)$

Object under test striated surface signal is time varying signal, within 1/4th cycles to time become stripe signal continuous integration, can be within modulation period continuous acquisition four spoke print images, use sinusoidal phase modulation four step integral principles to recover patterns.As shown in Figure 3, adopt four step integral principles ^[9], in modulation period T=2 π/ω, gather with CCD camera 9 intensity that four width images obtain in 1/4th cycles and be

$\begin{array}{cc}{E}_p=\frac{4}{T}{\∫}_{\frac{(p-1)T}{4}}^{\frac{p^T}{4}}s(x,y,t)\mathrm{dt}& (p=1-4)---\left(9\right)\end{array}$

Under optimum sinusoidal phase modulation (z=2.45, θ=0.98rad) condition, the phase place of surface topography be reduced to:

Visible, δ (t) will directly affect the phase measurement accuracy of surface topography, must generate Δ l _cδ (t) is compensated to zero.

As shown in Figure 4, in order to suppress such environmental effects, utilize the Fresnel reflection of outgoing end face, form Michelson at the exit end of the 4th fiber arm d and interfere.Photodetector 10 gathers this interference signal, in phase error compensation system 11, adopt phase generated carrier (PGC) module 19 to extract the sinusoidal component 20, the cosine component 21 that comprise phase error, use rotational coordinates teaching machine (CORDIC) 22 rapid solving phase errors, improved the real-time of measuring simultaneously.Phase error is converted to voltage signal by phase place-voltage transformation module 23, drives piezoelectric ceramics 4 to produce Δ l _ccarry out compensation of phase error.

On the stable basis of fringe phase, could gather image and carry out shape recovery, principle is as shown in Figure 5.Image capture module 28 is controlled CCD camera 9 and within modulation period, is gathered four width images, strengthens module 30, revolves filtration module 31 and process and realize Digital Image Processing through greyscale transformation module 29, Gaussian image.Phase extraction module fast 32, for realizing four step integral algorithms, is extracted the phase information of surface topography from stripe pattern.Low-pass filtering module 33 is mainly used in the noise that filtering causes due to factors such as pattern edge reflections.Demarcating module 34, for the structural parameters of calibration measurements system, finally obtains object under test three-dimensional surface shape 35.The present invention measures can realize the high-precision real of small size object under test three-dimensional surface shape time.

The embodiment of the present invention to the model of each device except do specified otherwise, the model of other devices does not limit, and all can as long as can complete the device of above-mentioned functions.

It will be appreciated by those skilled in the art that accompanying drawing is the schematic diagram of a preferred embodiment, the invention described above embodiment sequence number, just to describing, does not represent the quality of embodiment.

The foregoing is only preferred embodiment of the present invention, in order to limit the present invention, within the spirit and principles in the present invention not all, any amendment of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (4)

1. the projection of the striped based on a sinusoidal phase modulation four step integrations three dimensional shape measurement system, comprising: He-Ne laser instrument, and described He-Ne laser instrument is as output light source, output beam is after coupled lens converges, enter 2 × 2 type fiber couplers by the first fiber arm, it is characterized in that

After described fiber coupler light splitting, enter respectively in the second fiber arm, the 3rd fiber arm, described the second fiber arm is closely wrapped on modulation piezoelectric ceramics, described the 3rd fiber arm is closely wrapped on cylindrical piezoelectric pottery, the output terminal of described the second fiber arm, the 3rd fiber arm is fixed by optical fiber clamping tool, forms Mach-Zehnder interferometer structure; Build fiber interference fringe projection mathematical model;

Output terminal at the 4th fiber arm is placed photodetector, and the signal detecting is received by phase error compensation system, the phase drift amount that phase error compensation system extraction environment factor causes, and generate phase compensation voltage injection binary channels piezoelectric ceramic actuator; The described binary channels piezoelectric ceramic actuator of the direct injection of sinusoidal phase modulation signal is realized the Sine Modulated of fringe phase, inject phase error compensation system, use as phase generated carrier, inject CCD time schedule controller, as the reference signal of described CCD time schedule controller;

The sequential control area array CCD camera that described CCD time schedule controller generates gathers the lip-deep stripe pattern of object under test, is uploaded to image and processes and shape recovery system, finally realizes object surface appearance and rebuilds.

2. striped projection three dimensional shape measurement system according to claim 1, is characterized in that, described phase error compensation system comprises: phase generated carrier module,

Described phase generated carrier module is extracted the sinusoidal component, the cosine component that comprise phase error, uses rotational coordinates teaching machine to solve phase error; Described phase error is converted to voltage signal by phase place-voltage transformation module, drives described modulation piezoelectric ceramics to produce optical path difference Δ l _ccarry out compensation of phase error.

3. striped projection three dimensional shape measurement system according to claim 1, is characterized in that, described image is processed with shape recovery system and comprised: image capture module,

Described in described image capture module control, CCD camera gathers four width images within modulation period, strengthens module, revolves filtration module and realize Digital Image Processing through greyscale transformation module, Gaussian image; Phase extraction module is used for realizing four step integrations, extracts the phase information of surface topography from stripe pattern; The noise that low-pass filtering module is caused by pattern edge reflections for filtering; Demarcating module, for the structural parameters of calibration measurements system, finally obtains object under test three-dimensional surface shape.

4. striped projection three dimensional shape measurement system according to claim 1, is characterized in that, described fiber interference fringe projection mathematical model is specially:

$\left\{\begin{array}{c}x=-\frac{m\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}\\ y=-\frac{n\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}\\ z=-\frac{d\sqrt{R^2-L^2}}{d\cot \mathrm{\β}-m}-L\end{array}\right.$

Wherein, m, n are the pixel sequence number of level and vertical direction, and d is the distance that image planes are arrived in lens center, and L is the distance that model initial point is arrived in lens center, and R is radius, and β is projectional angle, for phase place,

L ₀for fiber core distance, λ is optical wavelength; for initial phase; β ₀for the projectional angle of zero order fringe.