KR100483345B1 - A scanning system based upon two-wavelength projection Moire method and its autonomous calibration using registration for multi-head system - Google Patents

Abstract

The present invention relates to a dual wavelength projection moiré-based shape measuring apparatus and a calibration method of a multihead system. The dual wavelength projection type moiré-based shape measuring device according to the present invention is installed in parallel with the optical axis of the projection system and the imaging system, and by applying the dual wavelength method, which is one of the multiple wavelength methods, the measurement is performed regardless of the large step. The shape of the object can be measured. In addition, by using a computer instead of a physically fixed grid, two adjustable virtual reference grids with different pitches can be created to measure objects of varying heights while controlling the resolution. Can be reduced. In addition, since it is a non-contact measurement method using white light, it is possible to measure an object that is harmless to the human body and that damage should be thoroughly excluded, such as a cultural property. In addition, by flexibly connecting a plurality of individual measuring instruments to apply a registration-based calibration method, it is possible to perform a simple and precise calibration of the multi-head system without limiting the size of the object to be measured.

Description

A calibration system based upon two-wavelength projection Moire method and its autonomous calibration using registration for multi-head system}

The present invention relates to an apparatus and a calibration method for measuring a three-dimensional shape of an object. Specifically, an object having a high measurement height and a large step by applying a registration-based automatic calibration method to a shape measurement device based on a dual-wavelength projection moire. And it relates to an apparatus capable of measuring the three-dimensional shape of objects of various sizes.

In general, the optical system of the projection type moire mainly consists of a projection system and an imaging system. The projection system is composed of a light source, a condenser lens, a projection lattice, and a projection lens, and the imaging system uses an image of a strain grating formed on a measurement object as a reference lattice. It consists of an imaging lens, a reference grid, a relay lens, and a CCD camera as an image input unit. In this case, the projection lattice and the reference lattice are the same linear lattice having the same pitch, and are implemented as a physical lattice. In this case, a separate lattice driving unit is required. There is a problem that the lattice driving increases measurement time.

In the shape measurement based on the projection moiré, a phase shift method of obtaining four images by moving the lattice and obtaining a moiré phase diagram was used.However, due to the arc tangent of the phase obtained by the phase shift method, When is large, the phase diagram is obtained discontinuously, and accurate shape measurement is difficult.

To overcome this problem, two measurements were made using two similar wavelength gratings, and then the double-wavelength method was used to synthesize two moiré topologies to obtain images without discontinuities. However, even in this case, the projection lattice and the reference lattice are implemented as a physical lattice, and thus a lattice driving unit is required, and the problem of increasing the measurement time by the lattice driving still remains.

Apparatuses for measuring the shape of three-dimensional objects often employ a multihead system using a plurality of measuring devices. That is, by measuring a three-dimensional object in conjunction with a plurality of measuring devices, the user can quickly obtain a three-dimensional shape that can be rotated 360 ° without a separate operation. In such a multihead system, a calibration process is required to combine the data measured by each measuring instrument. For the calibration work of such a multi-head system, a registration work is performed to unify the data measured at various positions, that is, the data having different viewpoints, into one coordinate system. The registration algorithm based on ICP (Iterative Closest Point), which calculates the transformation matrix so that the distance difference between each polygonal model in the area where each measurement data overlaps, is most used for registration. The conventional ICP-based registration algorithm performs registration on the assumption that the data measured at one location should be a subset of the data measured at another location. In reality, however, there is no data that satisfies these assumptions, and thus there is a problem in that an additional calculation process is required to overcome this disadvantage.

The present invention has been made to solve the above-mentioned conventional problems, the object of the present invention is a measurement time that occurs because the projection grid and the reference grid of the optical system in the three-dimensional shape measurement apparatus using the projection moiré is a physical grating In order to overcome this prolonged shortcoming and to eliminate unrealistic assumptions in the calibration algorithm between data measured by each measuring device, which is a problem when introducing a multihead system, a method of removing the limitation of the calibration algorithm is provided.

An object of the present invention as described above, a virtual grid forming unit for making a virtual grid having a predetermined lattice spacing, a projection unit for projecting a virtual grid made by the virtual grid forming unit on the object to be measured, the measured object is projected virtual grid An image input unit for obtaining the image data of the strain grating according to the moiré phenomenon caused by the irregularities of the surface of the object under measurement on the object, a digital conversion unit for converting the image data received by the image input unit into digital data, and the digital conversion unit The image data calculation unit receives the digital data of the strain grating transformed from and generates shape data of the object under measurement by calculating the received digital data and the data of the reference grating of the same linear grating having the same pitch as the virtual grating. It is achieved by providing a dual wavelength projection moiré-based shape measuring apparatus.

Here, the virtual grid forming unit may adjust the grid spacing of the virtual grid without a separate driving device.

In addition, the shape measuring apparatus may be configured as a multihead system arranged to form a predetermined angle around the object under consideration in consideration of the size of the object under measurement.

In addition, an object of the present invention, the virtual grid forming step of making a virtual grid having a predetermined lattice spacing, the projection step of projecting the virtual grid on the object to be measured, the object to be measured on the measured object on which the virtual grid is projected Obtaining the image data of the strain grating according to the moire phenomenon caused by the irregularities of the surface of the surface, converting the image data of the strain grating to digital data, and through calculation of the digital data of the strain grating and the data of the reference grid It can be achieved by providing a dual wavelength projection moiré-based shape measurement method consisting of generating the shape data of the object under measurement.

The shape measuring method may include setting a predetermined angle and a position around the object under consideration in consideration of the size of the object to be measured, and generating a plurality of shape data of the object under measurement through the method for each set position. It may further include.

Here, it is also possible to simultaneously measure the shape data of the object under measurement at different positions.

In addition, a registration step of unifying the position of the shape data measured by generating a plurality of shape data of the object to be measured in one coordinate system, and obtaining a relative position matrix between each measurement position from the result of the registration step The method may further include a calibration step of flexibly connecting the respective measurement data by precisely calculating the relative position between the respective measurement positions from the relative position matrix.

In this case, the calibration step may use a registration algorithm based on ICP.

In addition, when the registration algorithm based on the ICP is used, all the pairs of points that have a distance greater than or equal to a reference limit, a pair of points at least one point on a mesh boundary, and other points having different geometrical properties, such as distance or normal vector, are It is also possible to apply heuristic conditions not included in the use of a registration algorithm based on ICP.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

As shown in FIG. 1, the dual wavelength projection type moire-based shape measuring apparatus 1 according to the present invention includes a virtual lattice forming unit 16, a projection unit 12, an image input unit 15, and a digital conversion unit 13. And an image data calculation unit 17, and a parallel optical axis optical system having an angle of 0 degrees between the projection optical axis and the imaging optical axis to form an accurate contour line on the object to be measured.

The virtual lattice forming unit 16 creates a virtual lattice that can arbitrarily adjust the lattice spacing, and the projection unit 12 projects the virtual lattice made by the virtual lattice forming unit 16 onto the object to be measured. On the measurement target object 10 on which the virtual grid is projected by the projection unit 12, a deformation grid due to moiré phenomenon occurs due to the irregularities of the surface of the measurement object 10. That is, the shape of the projected grating is deformed along the contour of the surface according to the height of the surface of the object 10 to be measured. The image data having received the strain grating to the image input unit 15 should be converted into digital data to facilitate data calculation when the output of the image input unit 15 is an analog signal. This role is played by the digital conversion unit 13. The digital data of the strain grating transformed by the digital converter 13 is sent to the image data calculator 17. The image data operation unit 17 can obtain the moiré phase diagram of the object to be measured 10 by comparing with the data of the reference grid before deformation occurs in the image data of the strain grating.

As shown in FIG. 2, in implementing the dual wavelength projection type moire-based shape measuring apparatus according to the present invention, the virtual grid forming unit 16 may be implemented by a PC 4 and the projection unit 12. The beam projector 2 and the like can be used. As the image input unit 15, a CCD camera 5 or a digital camera may be used. As a digital converter 13 of image data, a frame grabber 3 or a vision processor may be used. As the image data calculator 17, a PC 4 may be used. Of course, it is possible for the image processing module 14 including the virtual grid forming unit 16 and the image data calculating unit 17 to use one PC 4. However, the embodiment shown in FIG. 2 is an example for implementing the dual wavelength projection type moire-based shape measuring apparatus 1 according to the present invention for the purpose of describing the present invention and not for limiting the configuration of the present invention.

The dual wavelength projection type moire-based shape measuring apparatus 1 according to the present invention applies the double wavelength method in order to prevent the measured data from being distorted and to make an accurate measurement. That is, one more moiré phase diagram is obtained by repeating this process one more time using another grating of similar frequency to the virtual grating used in the above-described measurement process. The two moiré topologies are synthesized to obtain the final moiré topologies. From this final moiré phase diagram, the exact three-dimensional height at each point of the object to be measured 10 can be known.

As shown in FIG. 3, the plurality of dual-wave projection type moire-based shape measuring devices 1 are arranged to form a constant angle φ around the object 10 in consideration of the size of the object 10 to be measured. To configure a multihead dual wavelength projection moire-based shape measurement system 31. In this case, it is also possible to share the image processing module 14 and the digital converter 13 between the dual wavelength projection type moire-based shape measurement apparatus 1.

Measurement of three-dimensional phenomena by the multihead dual wavelength projection moiré-based shape measurement system 31 is performed by each of the dual wavelength projection moiré-based shape measurement device 1 at different positions of the object to be measured. The shape data, that is, the final moiré phase diagram is measured and a registration operation is performed to unify the position of each measured multi-view shape data in one coordinate system.

As shown in FIG. 4, measurement is performed at the image inputs 15 ′ and 15 ″ of two adjacent double wavelength projection moire based shape measurement apparatuses 1 among the dual wavelength projection type moire based shape measurement apparatus 1. The registration operation between the acquired data finds the angles a, b, and c which are rotated in the direction of each axis of x, y, z with respect to the other one, and then, on one coordinate axis x1, y1, z1 axis. This is achieved by obtaining a transformation matrix on the other coordinate axis x2, y2, z2 axes, that is, a relative position matrix represented by the following expression (1).

The registration process calculates the relative position matrix between the adjacent dual-wavelength projection moiré-based shape measuring apparatus 1 and between the coordinate axes of the image input units 15 'and 15 "of each shape measuring apparatus from the calculated relative position matrix. By performing a calibration operation, three-dimensional shapes can be measured at once.

The calibration operation applies an ICP-based registration algorithm that calculates a transformation matrix value that minimizes the distance difference between each polygon model in an area where each measurement data overlaps.

As shown in FIG. 5, considering the case of registering mesh A and mesh B, the ICP-based registration algorithm first finds which point on mesh B is located at the shortest distance for each point on mesh A. FIG. Accordingly, the points drawn by the dashed lines in part (a) of FIG. 5 are located at the shortest distance from the point β located at the left outer side of the mesh B. FIG. Even for each of the points on the mesh B, a little work shows that the points of part (b) are all at the shortest distance to the point α. Since the points in (A) and (B) are unnecessary to register two meshes A and B, in the application of the ICP-based registration algorithm, a pair of points or distances exceeding a certain limit are placed on the mesh boundary. A heuristic condition is applied together that does not include all the pairs of points, and all pairs of points that differ from other points of adjacent geometric properties, such as distance or normal vectors.

As shown in FIG. 6, in the dual wavelength projection type moire-based shape measuring method according to the present invention, a virtual lattice forming step (S1) of forming a virtual lattice having a predetermined lattice spacing, the virtual lattice on the object to be measured 10. Projection step (S2) of projecting, obtaining the image data of the strain grating according to the moiré phenomenon caused by the irregularities of the surface of the object to be measured 10 on the object to be projected virtual grid (S3), deformation Converting the image data of the grid into digital data (S4), and generating shape data of the object to be measured through calculation of the digital data of the strain grating and the data of the reference grating (S5).

As shown in FIG. 7, in the multi-head dual wavelength projection moiré-based shape measuring method according to the present invention, the angle and position of the individual shape measuring apparatus are set in consideration of the size of the object 10 to be measured (S11). ), By measuring the data of the object to be measured 10 by the shape measuring method according to the present invention shown in FIG. 6 for each position (S12), the shape data obtained in each measuring position is unified in one coordinate system Registration step (S13), calculating the relative position matrix between adjacent measurement positions from the registration result (S14), and calculating the relative position between each measurement position from the relative position matrix with precision by measuring each measurement data. Through the calibration step S15 of flexibly connecting, complete three-dimensional shape data of the object under measurement can be obtained (S16).

The measurement at each individual measurement position set above can also be constituted by a multihead system in which a plurality of shape measuring devices 1 are placed at each position and measured at once to greatly shorten the measurement time.

In the calibration step, a registration algorithm based on ICP is used.

When using the ICP-based registration algorithm, all pairs of points whose distance is greater than or equal to a limit, a pair of points that are at one point above the mesh boundary, and all other point pairs that have different geometric properties, such as distance or normal vectors, are based on the ICP. The heuristic conditions that are not included in the application of the registration algorithm are applied together.

As described above, according to the present invention, the resolution can be freely adjusted by using a computer-based virtual grating while applying the principle of dual wavelength projection moiré in measuring a three-dimensional shape, and in the case of using a physical grating It is possible to overcome the problem that a separate driving unit is required and the measurement time is longer by the time for driving the driving unit.

In addition, according to the present invention, by applying a multi-head system to a three-dimensional shape measurement apparatus based on a dual-wavelength projection moiré, when there is a movement like a person, when it is impossible to take pictures while rotating objects, or at various angles You can measure even when you need a lot of data quickly.

In addition, according to the present invention, the ICP-based registration algorithm is applied to the calibration process required when the multihead system is applied to the three-dimensional shape measurement apparatus based on the dual wavelength projection moiré, and the heuristic condition described above is applied to the ICP. Eliminate the constraints of the based registration algorithm.

In the above, certain preferred embodiments of the present invention have been illustrated and described. However, the present invention is not limited to the above-described embodiments, and various modifications can be made by those skilled in the art without departing from the gist of the present invention as claimed in the claims. will be.

1 is a block diagram of a dual wavelength projection moire-based shape measuring apparatus according to the present invention.

Figure 2 is a block diagram showing an embodiment of a dual wavelength projection moire-based shape measurement apparatus according to the present invention.

Figure 3 is a block diagram of a multi-head dual wavelength projection moire-based shape measurement system according to the present invention.

FIG. 4 is a diagram illustrating a registration operation by rotationally converting a coordinate system of each shape measuring apparatus in a multihead dual wavelength projection type moire-based shape measuring system according to the present invention. FIG.

5 is a view for explaining a background for deriving a heuristic condition according to the present invention applied when registering a portion where measurement data overlaps between data measured in an adjacent shape measuring apparatus.

Figure 6 is a flow chart illustrating a dual wavelength projection moiré-based shape measurement method according to the present invention.

Figure 7 is a flow chart illustrating a multihead dual wavelength projection moire based shape measurement method according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1: Dual wavelength projection moiré based shape measuring device

2: beam projector 3: frame grabber

4: PC 5: CCD camera

10: measuring object 12: projection unit

13 digital conversion unit 14 image processing module

15, 15 ', 15 ": Image input unit 16: Virtual grid forming unit

17: image data calculation unit

31: Multihead dual wavelength projection moire based shape measurement system

Claims (9)

A virtual grid forming unit which creates a virtual grid having a predetermined lattice spacing; A projection unit for projecting a virtual grid made by the virtual grid forming unit to an object to be measured; An image input unit configured to obtain image data of a deformation grid according to a moiré phenomenon caused by irregularities of the surface of the object to be measured on the object to be projected on the virtual grid; A digital conversion unit converting the image data received by the image input unit into digital data; And Accepts the digital data of the strain grating transformed by the digital converter, and generates a moiré phase diagram of the object to be measured by calculating the received digital data and data of the reference grating of the same linear grating having the same pitch as the virtual grating. It consists of a video data calculation unit, The projection light axis of the projection unit and the imaging light axis of the image input unit are parallel to each other. The virtual grid forming unit makes a virtual grid having two different grid spacing, The image data calculation unit generates moiré phase diagrams for each of the two different virtual grids, and synthesizes the generated moiré phase diagrams to generate shape data of the object to be measured. Moiré-based shape measuring device. The apparatus of claim 1, wherein the virtual grid forming unit adjusts the grid spacing of the virtual grid without a separate driving device. The shape measuring apparatus of claim 1 or 2, wherein the shape measuring device is arranged to form a predetermined angle around the object under consideration in consideration of the size of the object to be measured to form a multihead dual-wave projection type moire-based shape measuring system. Dual-wave projection type moire-based shape measuring device, characterized in that. A first virtual grid forming step (a) of making a first virtual grid having a predetermined lattice spacing; A projection step (b) of projecting the first virtual grid onto an object to be measured; Obtaining image data of a strain grating due to moiré phenomenon caused by irregularities of the surface of the object to be measured on the object to be projected onto the first virtual lattice projected as an optical axis parallel to the projection optical axis of step (b) ( c); (D) converting the image data of the strain grating into digital data; (E) generating a first moiré phase diagram of the object to be measured by calculating digital data of the strain grating and data of a reference lattice that is the same linear lattice having the same pitch as the first virtual lattice; A second virtual grid forming step (f) of making a second virtual grid having a lattice spacing different from that of the virtual grid created in step (a); A projection step (g) of projecting the second virtual grid onto an object to be measured; Obtaining image data of a strain grating due to moiré phenomena caused by irregularities of the surface of the object under measurement on the object to be projected onto the second virtual lattice as an optical axis parallel to the projection optical axis of step (g) ( h); Converting the image data of the strain grating into digital data (i); (J) generating a second moiré phase diagram of the object to be measured by calculating the digital data of the strain grating and the data of the reference grating of the same linear grating having the same pitch as the second virtual grating; And And (k) synthesizing the first moiré phase diagram and the second moiré phase diagram to generate shape data of the object to be measured. The method of claim 4, further comprising: setting a predetermined angle and a position around the object under consideration in consideration of the size of the object to be measured, and generating a plurality of shape data of the object under measurement through the above method for each of different positions ( Dual wavelength projection moiré-based shape measurement method characterized in that it further comprises l). 6. The method of claim 5, wherein the step (l) simultaneously measures the shape data of the object under measurement at different positions. 7. The method of claim 5 or 6, further comprising: a registration step of unifying the positions of the shape data measured by the step (l) into one coordinate system; Obtaining (n) a relative position matrix between the respective measurement positions from the registration result of step (m); And The dual-wave projection type moire-based shape further comprises a calibration step (o) for flexibly connecting each measurement data by precisely calculating the relative position between each measurement position from the relative position matrix according to the step (n). How to measure. 8. The method of claim 7, wherein the calibration step (o) uses a registration algorithm based on ICP. 10. The method according to claim 8, wherein when using the registration algorithm based on the ICP, all points different from other points adjacent in geometric properties such as a pair of points whose distance is greater than or equal to a reference limit, a pair of points at least one point on a mesh boundary, and a distance or normal vector, etc. Point pair is a dual wavelength projection moire-based shape measurement method characterized by applying a heuristic condition not included in the use of the registration algorithm based on the ICP.