CN205718873U - A kind of double frequency phase shift tripleplane measuring instrument - Google Patents

Abstract

This utility model provides a kind of grating pair, is made up of the sinusoidal grating of high and low frequency fringe period, and its fringe period meetsWherein, T₁For low frequency fringes cycle, T₂For the high frequency fringes cycle,Represent and take downwardsMaximum integer, T₂It is C₁Integral multiple.This utility model also provides for a kind of double frequency phase shift tripleplane measuring instrument applying described grating pair.The grating that this utility model provides to and double frequency phase shift tripleplane measuring instrument can expand tolerance, the problem solving erroneous judgement striped numbering.

Description

A dual-frequency phase-shift three-dimensional projection measuring instrument

technical field

The utility model relates to the field of optical three-dimensional measurement, in particular to a grating pair whose period satisfies a specific combination of dual-frequency fringe periods and a dual-frequency phase-shifting three-dimensional projection measuring instrument using the grating pair.

Background technique

At present, the optical three-dimensional measuring instrument based on grating projection is mainly composed of projection system, image acquisition system and information processing system: the projection system is composed of white light source, condenser lens group, projection lens, sinusoidal grating template and phase shifter, used to generate sinusoidal grating And project it on the surface of the object; the image acquisition system is mainly composed of a high-resolution CCD camera, a camera platform and a camera lens, which acquires the grating deformed image on the surface of the object and then transmits it to the information processing system; the information processing system is mainly a computer and related processing Software for 3D reconstruction and information output of objects.

The unwrapping technology adopted by the dual-frequency phase-shift 3D projection measuring instrument mainly includes dual-frequency heterodyne method and look-up table method. The dual-frequency heterodyne method has strict requirements on the phase error. The obtained package phase accuracy has a lower error tolerance than the look-up table method in application. The table look-up method makes use of the relationship between phase difference and period to make a "phase difference" → "period number" mapping table, and directly obtains the period number of the position (pixel) by looking up the table, and adds the wrapped phase value to obtain the real phase. However, when determining the period number, a tolerance is formed by the distribution interval of each value in the mapping table. Due to the irregular distribution, the tolerance is always too small, making it very difficult to determine the period number, resulting in a judgment error. It can only be applied when the signal-to-noise ratio of the system is very high, and its practical use is greatly limited.

Utility model content

The purpose of the utility model is to solve the technical problem in the prior art that the table look-up method has a small tolerance and easily leads to errors when determining the stripe number.

The purpose of this utility model is to adopt the following technical solutions to achieve:

A grating pair consisting of sinusoidal gratings with high and low frequency fringe periods, whose fringe periods satisfy Among them, T1 is the low _- frequency fringe period, T2 is the high _- frequency fringe period, means take down The largest integer, T ₂ is an integer multiple of C ₁ , and C ₁ is the multiple of the set range to low frequency period T ₁ .

A dual-frequency phase-shift three-dimensional projection measuring instrument, including a computer, a CCD camera, a projection system, and a platform for a measured object, the projection system includes a pair of gratings, and the projection system projects the pair of gratings successively on the measured object On the object, the CCD camera collects the fringes modulated by the measured object and transmits them to the computer for phase analysis. The grating pair is composed of sinusoidal gratings with high and low frequency fringe periods, and the fringe periods satisfy Among them, T1 is the low _- frequency fringe period, T2 is the high _- frequency fringe period, means take down The largest integer, T ₂ is an integer multiple of C ₁ , and C ₁ is the multiple of the set range to low frequency period T ₁ .

Compared with the prior art, the grating pair designed by the utility model and the dual-frequency phase-shift three-dimensional projection measuring instrument using the grating pair can expand the tolerance and solve the problem of misjudgment of the stripe number.

The above description is only an overview of the technical solutions of the present utility model. In order to better understand the technical means of the present utility model, it can be implemented according to the contents of the description, and in order to make the above-mentioned and other purposes, features and advantages of the present utility model better It is obvious and easy to understand. The preferred embodiments are specifically cited below, together with the accompanying drawings, and detailed descriptions are as follows.

Description of drawings

Fig. 1 is a schematic diagram of the optical path of the dual-frequency phase-shift three-dimensional projection measuring instrument provided by the first embodiment of the present invention.

Fig. 2 is a schematic structural diagram of the dual-frequency phase-shift three-dimensional projection measuring instrument provided by the first embodiment of the present invention.

Fig. 3 is a flow chart of the measuring method of the dual-frequency phase-shifting three-dimensional projection measuring instrument.

FIG. 4 is a schematic diagram of respectively numbering the two repeated fringes caused by phase truncation.

Fig. 5 is a schematic diagram of a look-up table established by using MATLAB software.

Fig. 6 is a schematic diagram of the triangulation ranging method.

detailed description

In order to facilitate the understanding of the utility model, the utility model will be described more fully below with reference to the relevant drawings. Preferred embodiments of the utility model are provided in the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present utility model more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of this invention. The terminology used herein in the description of the utility model is only for the purpose of describing specific implementations, and is not intended to limit the utility model. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Please also refer to FIG. 1 . FIG. 1 is a schematic diagram of the optical path of the dual-frequency phase-shifting three-dimensional projection measuring instrument 20 provided by the first embodiment of the present invention. FIG. 2 is a schematic structural diagram of a dual-frequency phase-shift three-dimensional projection measuring instrument 20 provided by the first embodiment of the present invention.

The grating pair 10 is composed of a sinusoidal grating 101 with a high fringe period and a sinusoidal grating 102 with a low frequency fringe period, and the fringe period satisfies Among them, T1 is the low _- frequency fringe period, T2 is the high _- frequency fringe period, means take down The largest integer of , T ₂ is an integer multiple of C ₁ , yes The remainder, C ₁ is the multiple of the set range to the low frequency period T ₁ .

When the grating pair 10 is used for projection, the high-frequency fringes have high unpacking accuracy, but the frequency should not be too high, otherwise it is easy to be interfered by noise and cause errors. In this embodiment, T ₂ =22 may be selected as the optimal precision fringe. In order to suppress the influence of noise, the value of A generally does not exceed 5, so A is set to 4, where C ₁ is the multiple of the range S to the low frequency period T ₁ , (S=LCM(T ₁ , T ₂ ) is T ₁ , T The least common multiple of ₂ ), C ₁ try to take the middle number among the divisors of T ₂ , which is used to make the tolerance and range get larger values at the same time. According to the above data and formula, it can be concluded that the low-frequency period T ₁ =99. In this way, a sinusoidal grating pair with high and low frequency fringe periods of 99 and 22 can be fabricated.

The grating pair 10 satisfies a specific periodic relationship, and the fringes generated by projection thereof can expand the tolerance of the system when three-dimensional measurement is performed.

The dual-frequency phase-shift three-dimensional projection measuring instrument 20 includes: a computer 30 (with built-in related software), a CCD camera 40 , a projection system 50 , and a platform 60 for a measured object.

Among them, the computer 30 is used for phase analysis and three-dimensional reconstruction of the measured object, and controls the movement of the phase shifter. The CCD camera 40 is used to collect information. The measured object platform 60 serves as a platform for projecting fringes.

The projection system 50 at least includes: a white light source 51 , a grating pair 10 , a phase shifter 52 , and a condenser lens group 53 .

Wherein, the white light source 51 is used to generate white light. The grating pair 10 is used to generate stripes, the phase shifter 52 is used to make the grating pair 10 generate a four-step phase shift, and the condenser lens group 53 is used to diffuse the light emitted by the white light source 51 .

The dual-frequency phase-shifting three-dimensional projection measuring instrument 20 provided in this embodiment projects the grating pairs satisfying the specific fringe periodic relationship, which can expand the tolerance, conveniently number the fringes, and can perform normal measurement under the condition of low hardware signal-to-noise ratio.

Please refer to FIG. 3 . FIG. 3 is a flowchart of a measuring method of the dual-frequency phase-shifting three-dimensional projection measuring instrument 20 .

In step 1, two sets of four-step phase-shifted projection fringes are generated by the phase shifter 52 and the grating pair 10, and projected on the surface of the measured object.

Specifically, the phase shifter 52 can automatically control the output voltage range by the computer 30 through the D/A interface board. The circuit is designed as a closed-loop control circuit, and a stepping motor is used to generate displacement, which has high voltage stability and small phase shift. error. Before the experiment, the coherent phase detection calibration method is used to calibrate the phase shifter 52. In the experiment, when the voltage output of the phase shift driver is 110v, the phase shifter 52 produces a phase shift of 90°.

Step 2, use the CCD camera 40 to take pictures of phase shift fringes with better effects.

Step 3, use MATLAB software to analyze the phase shift information of the stripes, and obtain the wrapped phases φ ₁ , φ ₂ through four-step phase shift solution.

Step 4, use The two wrapped phases can be normalized to get where φ(x,y) is the wrapped phase value.

Step 5, respectively numbering the two repeated fringes caused by phase truncation (as shown in FIG. 4 ).

Step 6, using MATLAB to establish a fringe period number combination table satisfying the relationship that "the inherent phase difference between two groups of wrapped phases corresponds to the inherent fringe period number combination" (as shown in FIG. 5 ).

In the previous step, using

The two wrapped phases can be normalized to get The camera coordinate system defined for the sinusoidal period is:

where h ₁ (x,y) represents the pixel position measured with low-frequency fringes, h ₂ (x,y) represents the pixel position measured with high-frequency fringes; T ₁ represents the period of low-frequency fringes, and T ₂ represents the high-frequency fringes period; n(x, y) represents the cycle number of low frequency fringes, and m(x, y) represents the cycle number of high frequency fringes; represents the normalized phase value of the low-frequency fringes, Indicates the normalized phase value of the high-frequency fringe.

According to the definition of camera coordinates, the camera coordinate value is a function related to fringe number, wrapping phase value and fringe period.

For the same pixel position in the unpacked scene, the camera coordinates are only related to the pixel position (x, y) of the point, and have nothing to do with the period number and phase value of the projected stripes, so

h ₁ (x,y)=h ₂ (x,y) (3)

Combine (2--1)(2--2)(3) to get

transfer available

Define the normalized phase difference function:

Define the difference function for high and low stripe numbers:

δ(n,m)=nT ₁ -mT ₂ (7)

Visible is the inherent phase difference between the two wrapped phases Corresponds to the inherent fringe period number combination δ(n,m).

Step 7, calculate the phase difference function:

Step 8, look up the table to obtain the corresponding fringe number (n, m), and then use the number to restore the absolute phase.

Note that the maximum range h _max (x)=S satisfies S=c _i T _i , which means that S is an integer multiple of T _i , i=1, 2 within this range, exhaustively enumerate all the combined values of ni, m _j , Establish a lookup table corresponding to the combination of ni, m _j and a _ij , and obtain it through formula (6) when unpacking Then get the values of _ni and m _j by looking up the table, calculate the camera coordinates, and complete the unpacking.

After the unpacking is completed, the actual height of the object can be restored by the common triangulation distance measurement method, please refer to Figure 6, which is a schematic diagram of the triangulation distance measurement method.

${\mathrm{<span\; class="notranslate">\; PP</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}$

Where λ is the grating intercept, that is, the length corresponding to one period of phase change.

The above formula is the height-phase correspondence formula of classical grating projection. Under the premise of satisfying the corresponding relationship among the camera, projector and reference plane, the phase value θ _B is obtained by calculating the grating image projected onto the reference plane X. During measurement, since the measured object 200 is placed on the reference plane X, the light beam will deform the grating image due to the modulation of the object surface, and the phase θ _A can be obtained through the deformed grating image, and finally the deformed grating is subtracted from the original grating to obtain The height of the object point can be obtained by bringing the phase difference θ _A -θ _B of the object surface into the above formula, and the conversion from the phase to the height of the object can be completed.

To sum up, the dual-frequency phase-shifting three-dimensional projection measuring instrument 20 provided in this embodiment projects the grating pairs satisfying the specific fringe periodic relationship, which can expand the tolerance and facilitate the numbering of fringes, and can also be used under the condition of low hardware signal-to-noise ratio. Normal measurement.

The above-mentioned embodiments only express several implementations of the utility model, and the description thereof is relatively specific and detailed, but it should not be construed as limiting the patent scope of the utility model. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the utility model, and these all belong to the protection scope of the utility model. Therefore, the scope of protection of the utility model patent should be based on the appended claims.

Claims (2)

1. a grating pair, it is characterised in that: described grating forms by the sinusoidal grating of high and low frequency fringe period, Its fringe period meetsWherein, T₁For low frequency fringes cycle, T₂For the high frequency fringes cycle,Represent and take downwardsMaximum integer, T₂It is C₁Integral multiple, C₁For setting range to the low-frequency cycle T₁Multiple.

2. a double frequency phase shift tripleplane measuring instrument, including computer, CCD camera, optical projection system, and quilt Surveying object platform, described optical projection system includes a grating pair, described optical projection system by described grating to respectively Successively it is projected on testee, described CCD camera collection striped after described testee is modulated, and It is transferred to described computer and carries out phase analysis, it is characterised in that: described grating is to by high and low frequency striped week The sinusoidal grating composition of phase, its fringe period meetsWherein, T₁For the low frequency fringes cycle, T₂For the high frequency fringes cycle,Represent and take downwardsMaximum integer, T₂It is C₁Integral multiple, C¹ For setting range to low-frequency cycle T₁Multiple.