JP2010230523A - Phase connection method and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for performing accurate phase connection, in a three-dimensional measuring system for measuring a surface shape by observing an image obtained by irradiating a measuring object with sine-wave pattern light. <P>SOLUTION: This method has a constitution including: a phase value data calculation means for calculating phase value data for measurement from an observation image group obtained by an observation means by changing in a plurality of times, an initial phase of the sine-wave pattern light A for measurement, and calculating phase value data for phase connection reference from the observation image group obtained by the observation means by changing in a plurality of times, an initial phase of sine-wave pattern light B for phase connection reference; and a sine-wave pattern period determination means for phase connection reference for determining a period of the sine-wave pattern light A for phase connection reference so that the least common multiple between pixel width equivalent to one period of the sine-wave pattern light A for measurement and pixel width equivalent to one period of the sine-wave pattern light B for phase connection reference becomes equal to or larger than the number effective pixels on a projection surface of the measuring object 1. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a phase connection method and an apparatus for three-dimensionally measuring an object by a phase shift method.

A three-dimensional measurement system based on the sine wave grating phase shift method is a method for measuring the surface shape of an object consisting of means for projecting a sine wave pattern onto the object (projector) and means for observing the pattern on the object (camera or video). This is a measurement system.
The relative position and orientation between the projection means and the observation means are known (geometrically calibrated), from which direction of the projection means the light is projected onto each point on the object surface, and the observation If the direction from which the reflected light is observed is known, the surface shape of the object can be determined based on the principle of triangulation.
In the following, a method for determining from which direction of the projection means the light is projected at each point on the object surface, that is, which pixel on the projection means plane irradiates the object surface will be described.

The projection means emits parallel stripes represented by the expression (1) in FIG.
Here, L _g (x, y) is the minimum input luminance of the projection means, L _d (x, y) is the offset between the maximum input luminance and the minimum input luminance, and I _i (x, y) is ( x, y) is the input luminance. [Phi] (x, y) is a phase corresponding to the pixel position on the projection means plane, and if it is a sine wave pattern parallel to the y-axis on the projection means plane, it is expressed by equation (2) in FIG.
However, _xf is expressed as a pixel width corresponding to one cycle of the sine wave pattern. δ _i is an initial phase, and changing this value shifts the sine wave pattern.

When the luminance value I _i (x, y) of each pixel projected at the initial phase δ _i is observed by the observation means on the surface of the object, the unknowns in the equation (1) are Φ (x, y), L _d (x, y), L _g (x, y), and simultaneous equations can be established by observing I _i (x, y) multiple times (theoretically three times or more) at different initial phases. These unknowns can be calculated. When the initial phase is changed discretely, the relationship between the following expression (3) in FIG. 3 and expression (4) in FIG. 3 is obtained from the expression (1) in FIG.
The left side of both equations (3) and (4) in FIG. 3 is a known value, and equation (5) in FIG. 3 is obtained from these two equations.
By substituting Equation (5) in FIG. 3 into Equation (3) in FIG. 3 and Equation (4) in FIG. 3, Φ (x, y) is obtained in the range of 0 to 2π. This is the phase value data for measurement.

  However, Φ (x, y) is originally a phase represented by equation (2) in FIG. On the other hand, since Φ (x, y) obtained on the observation means has a discontinuous phase convoluted from 0 to 2π, it is necessary to resolve the ambiguity of the 2π period. A method for solving this is called a phase connection method.

By the way, in Patent Documents 1 and 2, it is assumed that a discontinuous boundary (2π = 0) generated by 2π is generated on the assumption that only the phase value data for measurement is used and the phase between adjacent pixels changes smoothly. The possibility of phase connection is judged. However, since this assumption is synonymous with the assumption that the surface of the object does not include a discontinuous surface, it is impossible to obtain the three-dimensional shape of the object surface having a complicated shape.
In Patent Document 4, the possibility of phase connection is determined by masking an image with the amplitude value L _d (x, y) and dividing the region. This is based on the assumption that the amplitude value is different for different depths, but this assumption is not strictly correct in the real world and is not applicable to all objects.
Further, in Patent Document 5, a method is obtained in which the phase of a pattern projected on the reference plane is obtained in the entire effective pixel region, and then the difference from the phase of the pattern on the measurement object is converted into height information. In addition, a reference plane is required, and a three-dimensional shape of the object surface having a gradient such that the phase difference between the pattern on the reference plane and the measurement object is 2π or more cannot be obtained.

  On the other hand, the phase connection reference phase data is obtained by changing the initial phase in the same way as the measurement sine wave pattern light, using one or more types of phase connection reference sine wave pattern light having a different period from the measurement sine wave pattern light. There is a method of calculating and connecting the phase data for measurement based on this. Patent Document 3 and Non-Patent Document 1 disclose necessary conditions regarding the period of the phase connection reference sine wave pattern with respect to the luminance amplitude in the measurement sine wave pattern light.

Japanese Patent No. 3178436 JP 2008-082869 A JP 2006-003212 A JP 2006-079275 A JP 2006-084286 A

"Proposal of high-speed 3D measurement method using phase shift method", IEICE technical report, PRMU pattern recognition / media understanding, vol. 99, No. 515, pp. 43-50, 1999

The above-mentioned Patent Document 3 and Non-Patent Document 1 show the necessary conditions related to the period of the phase connection reference sine wave pattern, taking into account the resolution in the luminance amplitude of the measurement sine wave pattern light.
Therefore, in the present invention, in addition to the above-mentioned necessary conditions, a cycle in which phase connection can be performed with only one type of phase connection reference sine wave pattern is calculated, and a theoretical phase connection error in a plurality of calculated values is calculated. Evaluate and search for a period that minimizes the error.
Thus, the present invention improves the efficiency by using only one type of phase connection reference sine wave pattern to be referred to at the time of phase connection, and a phase connection method and apparatus capable of performing phase connection calculation with high accuracy. The purpose is to provide.

  In order to achieve the above object, the invention according to claim 1 is characterized in that the measurement sine wave pattern light is projected onto the measurement object, and the initial phase value of the measurement sine wave pattern light is changed a plurality of times to thereby measure the measurement object. The phase value data for measurement is calculated from the observation image group observed by relatively shifting the above, and the phase connection reference sine wave pattern light having a different period from the measurement sine wave pattern light is applied to the measurement object. The phase connection reference phase value data is calculated from the observed image group by projecting and changing the initial phase of the phase connection reference sine wave pattern light a plurality of times and relatively shifting on the measurement object. And a phase connection using the phase value data for measurement and the phase value data for phase connection reference, the pixel width corresponding to one cycle of the sine wave pattern light for measurement and the phase connection The period of the phase connection reference sine wave pattern light is determined so that the least common multiple of the pixel width corresponding to one period of the illumination sine wave pattern light is equal to or greater than the number of effective pixels on the projection surface of the measurement object. It is characterized by that.

  According to a second aspect of the present invention, in the phase connection method according to the first aspect, an arbitrary phase value in the phase connection reference sine wave pattern is obtained at each location showing the same phase in the calculated phase value data for measurement. The minimum value of the absolute values of the differences between the two values determines the maximum period by changing the period of the phase connection reference sine wave pattern.

  Invention of Claim 3 is a phase connection apparatus, Comprising: The projection means which projects the measurement sine wave pattern light and the phase connection reference sine wave pattern light having a different period from the measurement sine wave pattern light onto the measurement object The observation means for observing the measurement sine wave pattern light and the measurement sine wave pattern light projected on the measurement object, and changing the initial phase value of the measurement sine wave pattern light a plurality of times Phase connection from the observation image group obtained by the observation unit by calculating phase value data for measurement from the observation image group obtained by the observation unit and changing the initial phase of the phase connection reference sine wave pattern light a plurality of times Phase value data calculating means for calculating reference phase value data; a pixel width corresponding to one cycle of the measurement sine wave pattern light; and one of the phase connection reference sine wave pattern light. A phase connection reference sine wave pattern period for determining a period of the phase connection reference sine wave pattern light so that a least common multiple with a pixel width corresponding to a period is equal to or greater than the effective pixel number of the projection surface of the measurement object And a determining means.

  According to a fourth aspect of the present invention, in the phase connection device according to the third aspect, the phase connection reference sine wave pattern cycle determining means is provided at each location indicating the same phase in the calculated phase value data for measurement. The minimum value of the absolute value of the difference between any two values of the phase value in the phase connection reference sine wave pattern is determined by changing the period of the phase connection reference sine wave pattern. It is characterized by doing.

  According to the phase connection method and the transfer connection device of the present invention, the efficiency is improved by using only one type of phase connection reference sine wave pattern to be referred to at the time of phase connection, and the phase connection calculation can be performed with high accuracy. it can.

It is a block diagram which shows an example of the three-dimensional shape measuring apparatus using the phase connection method of this invention. It is a figure which shows the process in which phase value data and integer value data are calculated from two sine wave patterns for a measurement and a phase connection reference input into a projection means by the phase connection method of this invention, and each sine wave pattern. It is a figure which shows the numerical formula used conventionally and this invention.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2.
As shown in FIG. 1, the three-dimensional shape measuring apparatus includes an observation optical system 2 and an observation recording apparatus 3, which are arranged obliquely downward from above with respect to the surface of the measurement object 1, Contrary to the recording apparatus 3, the projection unit 50 including the projection optical system 4 and the projection light source 5, the sine wave pattern observation unit 6, and the sine wave, which are disposed obliquely downward from above with respect to the surface of the measurement object 1. A pattern input unit 7, a phase value data calculation unit 8, a phase connection processing unit 9, a three-dimensional shape calculation unit 10, a phase connection reference sine wave pattern cycle determination unit 11, and a measurement sine wave pattern cycle input unit 12 are configured. Is done.

  In the three-dimensional shape measuring apparatus configured as described above, the projection light source 5 is operated by the sine wave pattern signal input from the sine wave pattern input unit 7, and the sine wave pattern light passes through the projection optical system 4 to be measured 1 Project onto the surface of the. Then, the image of the sine wave pattern light projected on the surface of the measurement object 1 is recorded by the observation recording device 3 through the observation optical system 2 of the observation means 20 and output to the sine wave pattern observation unit 6. The sine wave pattern observation unit 6 observes the sine wave pattern projected on the surface of the measurement object 1, and sends the observation image to the phase value data calculation unit 8 by the sine wave pattern observation unit 6. At this time, the phase value data calculation unit 8 acquires the initial phase value of the projected sine wave pattern from the sine wave pattern input unit 7. Phase value data for measurement is acquired by the phase value data calculation unit 8 from the observation image group obtained by changing the initial phase value a plurality of times. Further, the phase connection processing unit 9 performs phase connection processing based on the phase value data calculated by the phase value data calculation unit 8 and phase value data calculated based on phase connection reference sine wave pattern light described later. The processing result is output to the three-dimensional shape calculation unit 10, and the three-dimensional shape calculation unit 10 calculates the three-dimensional shape of the surface of the measurement object 1.

FIG. 2 is a diagram schematically showing the irradiated sine wave pattern light and the phase value obtained by observing it. At the time of acquisition of measurement phase value data, phase value data is acquired by projecting measurement sine wave pattern light having a period input by the measurement sine wave pattern period input unit 12.
The period value input by the measurement sine wave pattern period input unit 12 is input to the phase connection reference sine wave pattern period determination unit 11, which enables phase connection that is robust against phase value calculation errors. The period of the reference sine wave pattern is calculated and determined.

FIG. 2 shows a mechanism for specifying a pixel position on the plane of the projection means by two sets of sine wave patterns, that is, a sine wave pattern light A for three-dimensional measurement and a sine wave pattern light B for phase connection. It is assumed that the projection unit plane has 24 pixels in the vertical direction, and the sine wave pattern light A for three-dimensional measurement and the sine wave pattern light B for phase connection reference each have 8 pixels and 6 pixels as one cycle. The observation device 20 observes each sine wave pattern light on the surface of the target object 1 and calculates each phase value data. Each obtained phase value data is converted into integer value data M (x, y) obtained by dividing the phase value data by a period corresponding to one pixel.
In FIG. 2, the periods corresponding to each pixel in the measurement sine wave pattern light A and the phase connection reference sine wave pattern light B are π / 4 (= 2π / 8) and π / 3 (= 2π). / 6). Thereby, the pixel positions of the 24 pixels having pixel numbers 0 to 23 on the projection means plane can be uniquely specified by a set of these two integer values. For example, when a set of integer values (7, 1) is obtained at a certain point on the surface of the object 1, it can be seen that light is projected from the eighth pixel having the pixel number 7.

In general, assuming that the pixel widths corresponding to one period of the sine wave pattern light A for measurement and the sine wave pattern light B for phase connection reference are x _f1 and x _f2 respectively, One of the sinusoidal pattern light a, the set of phase values assigned by B _is assigned again an integer multiple of the position of the pixel width of the least common multiple _lcm of _{x f1} and _{x f2 (x f1, x f2} ). If the effective pixels on the plane in the projection means are 1 cm (x _f1 , x _f2 ) or less, the phase connection reference sine wave pattern light can uniquely represent the effective pixels on the plane in the projection means with only this one type. If the number of effective pixels is greater than 1 cm (x _f1 , x _f2 ), a plurality of new sine wave pattern lights having a different period from the above two sine wave pattern lights until all the effective pixels can be uniquely expressed. It is necessary to prepare. As the number of sinusoidal pattern lights to be projected increases, the number of observation images to be processed also increases, which is not desirable. For this reason, the period of the phase connection reference sine wave pattern light is such that lcm (x _f1 , x _f2 ) is greater than or equal to the effective pixel on the plane of the projection unit with respect to the period of the input measurement sine wave pattern light. Then, phase connection can be achieved by using only one type of phase connection reference sine wave pattern light.

Further, the phases corresponding to one pixel of the sine wave pattern light for measurement and phase connection reference are respectively θ _Lf1 and θ _Lf2 (π / 4 and π / 3 in FIG. 2), and the respective phase value data are θ _Lf1, theta integer divided by _Lf2 data _M f1 (x, _y), M f2 (x, y) _of, M f1 (x, y) integer data _M f2 at the location equals (x, y) (M _f2 (x, y) at a location where M _f1 (x, y) = 3 in FIG. 2 is {3, 5, 1}).
_Assuming that the minimum value of the difference between any two integers in this number is M _f2min , when the phase value calculation error is ε, satisfying the expression (6) in FIG. Become. This condition is a necessary condition that all the values of M _f1 (x, y) satisfy the same expression (6).

The period of the phase connection reference sine wave pattern most robust to the phase value calculation error is M _f1 (x, y) in a period in which lcm (x _f1 , x _f2 ) is larger than the number of effective pixels on the projection plane. It is _sufficient to select a period in which the minimum value of M _f2min calculated for all the values of) is maximized. The calculation for _obtaining a value indicating that the minimum value of M _f2min is the maximum can be performed by performing the calculation for all candidate cycles.

On the other hand, the phase connection data is converted into phase value data from the sine wave pattern light for measurement and phase connection reference projected onto the surface of the object by the above-described method. Done. If the relative position and orientation of the projection means 50 and the observation means 20 are known (if B in FIG. 1 is known), the pixel position at which light is projected onto the surface of the object (p in FIG. 1) find (see direction vector d _p in FIG. 1), and since either has been observed at any pixel location on the viewing means plane seen (seen direction vector d _c in FIG. 1), the principle of the triangulation method Based on this, the three-dimensional position of the surface of the object 1 (p in FIG. 1) can be calculated by the three-dimensional shape calculation unit 10.

  DESCRIPTION OF SYMBOLS 1 ... Measurement object, 2 ... Observation optical system, 3 ... Observation recording device, 4 ... Projection optical system, 5 ... Projection light source, 6 ... Sine wave pattern observation part, 7 ... Sine wave pattern input , 8... Phase value data calculation unit, 9... Phase connection processing unit, 10... Three-dimensional shape calculation unit, 11... Phase connection reference sine wave pattern period determination unit, 12. Period input unit, 20 ... observation means, 50 ... projection means.

Claims (4)

Project sine wave pattern light for measurement onto the object to be measured,
Calculating the phase value data for measurement from the observation image group observed by changing the initial phase value of the sine wave pattern light for measurement a plurality of times and relatively shifting on the measurement object;
Projecting the phase connection reference sine wave pattern light having a different period from the measurement sine wave pattern light onto the measurement object,
Calculating phase connection reference phase value data from an observation image group observed by changing the initial phase of the phase connection reference sine wave pattern light a plurality of times and relatively shifting on the measurement object;
A phase connection method using the phase value data for measurement and the phase value data for phase connection reference,
The least common multiple of the pixel width corresponding to one period of the sine wave pattern light for measurement and the pixel width corresponding to one period of the sine wave pattern light for phase connection reference is the number of effective pixels on the projection surface of the measurement object. Determine the period of the phase connection reference sine wave pattern light so as to be above,
A phase connection method characterized by that.   At each location showing the same phase in the calculated phase value data for measurement, the minimum value of the absolute values of the difference between any two values of the phase values in the phase connection reference sine wave pattern is 2. The phase connection method according to claim 1, wherein the maximum period is determined by changing the period of the phase connection reference sine wave pattern. Projection means for projecting measurement sine wave pattern light and phase connection reference sine wave pattern light having a period different from that of the measurement sine wave pattern light onto a measurement object;
Observation means for observing the measurement sine wave pattern light and the measurement sine wave pattern light projected on the measurement object;
Calculate phase value data for measurement from an observation image group obtained by the observation means by changing the initial phase value of the sine wave pattern light for measurement a plurality of times, and the initial phase of the sine wave pattern light for phase connection reference Phase value data calculation means for calculating phase connection reference phase value data from the observation image group obtained by the observation means by changing the multiple times,
The least common multiple of the pixel width corresponding to one period of the sine wave pattern light for measurement and the pixel width corresponding to one period of the sine wave pattern light for phase connection reference is the number of effective pixels on the projection surface of the measurement object. The phase connection reference sine wave pattern period determining means for determining the period of the phase connection reference sine wave pattern light as described above,
A phase connection device comprising:   The phase connection reference sine wave pattern cycle determining means is configured to calculate two arbitrary values of the phase values in the phase connection reference sine wave pattern at each position indicating the same phase in the calculated phase value data for measurement. 4. The phase connection device according to claim 3, wherein the minimum value of the absolute values of the differences determines the maximum period by changing the period of the phase connection reference sine wave pattern.

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