KR101465996B1

KR101465996B1 - Method for measurement of high speed 3d shape using selective long period

Info

Publication number: KR101465996B1
Application number: KR1020140057760A
Authority: KR
Inventors: 오상민; 구자명
Original assignee: 주식회사 미르기술
Priority date: 2014-05-14
Filing date: 2014-05-14
Publication date: 2014-11-27

Abstract

The present invention relates to a method of measuring a three-dimensional shape in high speed by using a selective long period, capable of reducing time required to measure a three-dimensional shape while accurately measuring the shape, by irradiating a grid pattern light having mutually different periods from a projector, and irradiating a grid pattern light having one period from another projector to calculate height information.

Description

[0001] METHOD FOR MEASUREMENT OF HIGH SPEED 3D SHAPE USING SELECTIVE LONG PERIOD [0002]

More particularly, the present invention relates to a method of measuring a three-dimensional shape, and more particularly, to a method of measuring a three-dimensional shape by irradiating a grid pattern light having a period of different sizes only in a selected one of the projectors, Dimensional shape measuring method capable of accurately measuring a shape while shortening a three-dimensional shape measuring time.

The three-dimensional shape measurement technique has been developed and used, for example, a laser triangulation method, a stereo measurement method, and a moiré principle measurement method. Since these measurement methods use optical, a fast and accurate three-dimensional shape can be obtained.

The three-dimensional measurement method using moiré is to measure the three-dimensional shape of the object to be inspected using the pattern image reflected after illuminating the pattern illumination as the object to be inspected, and to analyze the three-dimensional shape of the object to be inspected using the pattern image There is a phase shifting method.

The phase shift method obtains a pattern image according to a plurality of interference signals while moving the reference plane of the object to be inspected and analyzes the mathematical relationship between the shape and the height of the interference signal at each measurement point of the obtained pattern image, Dimensional shape.

The 3-D shape measurement method using the phase shift method has a problem of 2? Ambiguity in which a measurement error occurs when the height difference between adjacent two measurement points is equal to or greater than an integral multiple of the equivalent wavelength of the light source. A problem arises in that the measurement range of the sensor is limited.

To solve the problem of 2? Ambiguity in the conventional method, when the phase shift of the point to be measured differs by 2? Or more relative to the surrounding point, the height value of the measurement point is corrected to 2? .

However, in the three-dimensional shape measuring method using the phase shift method according to the related art, when two measurement objects are located apart from each other by 2? Or more, whether the measurement result is a result of 2? Ambiguity or a measurement object having a depth of 2? It is difficult to distinguish the recognition, and there still exists a problem that an inaccurate result may occur. That is, 2π ambiguity can be obtained to obtain relative three-dimensional information, but it is impossible to obtain accurate three-dimensional information.

As a technique for solving the ambiguity of 2?, Korean Patent No. 0558325 has proposed a technique of "3D inspection method and apparatus using stereo vision and moire".

Korean Patent No. 0558325 discloses that when a light projection part scans a certain pattern several times and phase shifts the measurement object with a motor, each of the two cameras measures each object to be measured at each time point, and a plurality of three- So that the three-dimensional shape information of the measurement object is finally measured. However, this disclosure technique also did not completely solve the 2π ambiguity. That is, 2π ambiguity occurs again at a position that is a multiple of the left and right phase information. In addition, the problem of finding the matching point has not been solved.

In order to improve the problem of 2? Ambiguity in the case of measuring an object to be inspected having a different measurement range in a three-dimensional shape measuring apparatus using one projection moire, a method of replacing the lattice corresponding to the measurement range of each object to be inspected However, in this case, since it takes time to replace the lattice, the inspection speed is lowered.

As a technique for improving this, a pattern illumination having a different equivalent wavelength is generated for each of a plurality of projectors, and the height information is calculated using the phase information obtained by irradiating the pattern illumination to the object to be inspected, Korean Patent No. 1190122 has proposed a three-dimensional shape measuring device and a measuring method using multiple wavelengths.

FIG. 1 is a view for explaining a three-dimensional shape measuring method of Korean Patent No. 1190122, wherein two projectors around a camera have a similar period, that is, a lattice pattern light having a first period and a lattice pattern light having a second period, And obtains a pattern image having a third period according to a beat component to calculate height information.

Specifically, a first phase is calculated using a plurality of first pattern images obtained by irradiating the surface of the object to be inspected with a grating pattern light having a first period using an N-bucket algorithm, and a first phase is calculated using a grid pattern light having a second period Is applied to the surface of the object to be inspected, and a second phase is calculated using a plurality of second pattern images obtained by using the N-bucket algorithm.

When the first and second phases are calculated, the third phase is calculated according to the beating phenomenon caused by the lattice pattern light having the first period and the lattice pattern light having the second period

Then, when the third phase is calculated, the first order and the second order of the second phase are calculated using the third phase. As shown in FIG. 1, the first order is A and the second order is (X, y) = 2πh / λ1 + M · 2π, and the second order N is φ1 (x, y) = 2πh / λ1 + N · 2π And calculates first and second height information using the calculated first and second orders and the first and second phases

However, in this case, if all of the patterns are not accurately projected, accurate measurement is difficult. That is, when an obstacle having a height is located in the vicinity of the object to be inspected, shadows may be generated for a pattern projected from one of the projectors. In this case, accurate height measurement is impossible.

For example, a pattern having the first frequency component f1 projected from the first projector is accurately photographed through the camera, but a pattern having the second frequency component f2 projected from the second projector is generated by the inspected object There is a problem in that the third frequency component due to the beat components of the two wavelengths can not be accurately obtained.

Korean Patent No. 1190122 "Apparatus and method for measuring three-dimensional shape using multiple wavelengths" Korean Patent No. 0558325 entitled " 3-D Inspection Method and Apparatus Using Stereo Vision and Moire "

The present invention for solving the drawbacks of the background art differs from the prior art in that a projector selected among a plurality of projectors irradiates grating pattern light having first and second periods of different sizes to form first and second phases Information is obtained and the first height information is calculated. In another projector, only the grid pattern light of the third period is irradiated to obtain the third phase information, and then the second height information is obtained using the first phase information and the third phase information Dimensional shape measuring method using an optional large period to calculate a high-speed three-dimensional shape.

According to an aspect of the present invention, there is provided a three-dimensional shape measuring apparatus having a plurality of projectors installed in different directions and emitting grid pattern light, The first projector projects a first grating pattern light having a first period and a second grating pattern light having a second period larger than the first period on the object surface, Obtaining a first pattern image of the second grid pattern light and a plurality of second pattern images of the second grid pattern light; A second step of projecting, on a surface of an object, only a third grating pattern light having a third period smaller than the second period in a second projector located in a direction different from the first projector to obtain a plurality of third pattern images; Calculating a first phase information from the plurality of first pattern images, calculating second phase information from the plurality of second pattern images, and calculating first height information using the first phase information and the second phase information, step; A fourth step of calculating third phase information from the plurality of third pattern images and calculating second height information using the first phase information and the third phase information and a fourth step of calculating the second height information using the first height information and the second height information And a fifth step of calculating final height information of the object.

At this time, the second grating pattern light has a period of at least twice as much as that of the first grating pattern light or the third grating pattern light.

Further, the first projector can be selected by referring to surrounding obstacle information capable of generating a shadow on the object surface at the time of illuminating the object grid pattern light.

If the first projector is selected in step 1, the ratio of the second period to the third period of each pixel of the second projector is calculated as the condition for using the second pattern image in calculating the second height information, And in the fourth step, the second height information can be calculated by reflecting the reference correction data.

Here, the reference correction data setting process may include loading a plane jig having a height smaller than a height corresponding to the first period at a position where the object is to be loaded, Calculating phase information on the first pattern image and phase information on the second pattern image by projecting the grating pattern light to obtain a first pattern image and a second pattern image, calculating phase information on the first pattern image and phase information on the second pattern image, Calculating a third pattern image by projecting the third grating pattern light and calculating phase information for the third pattern image, calculating a phase difference between the second period and the third period in the second projector using the calculated phase information, And calculating the information.

The ratio information of the second cycle and the third cycle can be calculated by the following equation.

here,

The position of the pixel,

(The second period of the second grating pattern light projected from the first projector) / (the third period of the third grating pattern light projected from the second projector)

The phase difference of the second period of the first projector

The phase difference of the third period of the second projector

The ratio of the second period to the third period

A coefficient N for correcting the 2? Ambiguity can be calculated and used to correct the 2? Ambiguity, and a coefficient N for correcting the 2? Ambiguity can be calculated by the following equation.

Further, the 2? Ambiguity can be corrected by the following equation.

In one projector, a pattern image is obtained by irradiating grating pattern light having different periods, and another projector irradiates grating pattern light having one period to obtain a pattern image, thereby shortening the pattern image acquisition time So that the measurement time of the three-dimensional shape can be shortened.

In addition, the present invention has an advantage of increasing the measurement accuracy by obtaining a pattern image by irradiating grating pattern light in a direction in which no shadow occurs due to an obstacle even if an obstacle having a height is present around the object.

1 is a reference diagram for explaining a three-dimensional shape measuring method of Korean Patent No. 1190122
BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]
FIG. 3 is a flowchart sequentially illustrating a method of measuring a high-speed three-dimensional shape using an optional large period according to the present invention.
4 is a view for explaining a method of measuring a high-speed three-dimensional shape using a selective large period according to the present invention.

The description of the present invention is merely an example for structural or functional explanation, and the scope of the present invention should not be construed as being limited by the embodiments described in the text. That is, the embodiments are to be construed as being variously embodied and having various forms, so that the scope of the present invention should be understood to include equivalents capable of realizing technical ideas. Also, the purpose or effect of the present invention should not be construed as limiting the scope of the present invention, since it does not mean that a specific embodiment should include all or only such effect.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used predefined terms should be interpreted to be consistent with the meanings in the context of the related art and can not be interpreted as having ideal or overly formal meaning unless explicitly defined in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

FIG. 2 is a block diagram of an apparatus for applying a high-speed three-dimensional shape measuring method using a selective large period according to the present invention. The apparatus includes a stage 10, an image pickup unit 20, a plurality of projectors 31 and 32, 40 and a controller 50.

At this time, the stage 10 is for positioning the object in the inspection region, and the image pickup section 20 is for photographing the image of the object surface.

The imaging unit 20 is disposed above the stage 10 to capture a surface image of the object 60 and may include a camera, an imaging lens, a filter, and the like. At this time, the camera captures a plane image of the object 60 by receiving light reflected from the surface of the object 60, and a CCD camera, a CMOS camera, or the like can be used. The image-forming lens is disposed at the lower portion of the camera, so that light reflected by the object 60 is imaged by the camera. The filter is disposed at a lower portion of the image-forming lens, and filters the light reflected by the object 60 to provide the image-forming lens. The filter may include a frequency filter, a color filter, and a light intensity adjusting filter.

The plurality of projectors 31 and 32 are installed on the upper portion of the object at different angles of a side portion inclined at a predetermined angle from the image pickup unit 20 and selectively irradiate the grid pattern light to the printing grid or the liquid crystal panel or the digital micromirror A display (DMD: Digital Micromirror Display) or the like, and a light source for emitting light.

In addition, the plurality of projectors 31 and 32 may include a first projector 31 (e.g., a projector) for projecting the first lattice pattern light having the first period in the first direction and the second lattice pattern light having the period longer than the first period, And a second projector 32 provided in a direction different from that of the first projector 31 and emitting only a third grating pattern light having a third period. Here, the first period or the third period may be the same or different, and the second period may be at least twice as long as the first period or the third period Or more.

Further, the first projector for irradiating the different wavelengths is determined in the inspection process according to a preset reference, not predetermined. That is, when there is an obstacle 70 having a height around an object placed on the stage, shadows may be generated by the pattern light irradiated by the projector in the specific direction. Therefore, the first projector which irradiates both the first lattice pattern light and the second pattern light is selected as a projector positioned in a direction in which there is no possibility of shadow caused by the surrounding obstacles. At this time, the selection of the first projector may be such that the user directly inputs the selection signal or is automatically selected based on the information of the peripheral obstacles according to the arrangement structure of the objects.

On the other hand, the image acquisition unit 40 is electrically connected to the camera of the image pickup unit 20 to acquire and store pattern images from the camera. The controller 50 controls the driving of the projectors 31 and 32, And calculates the height of the object using the pattern images obtained from the image system of the image processing unit 40.

FIG. 3 is a flowchart sequentially illustrating a method for measuring a high-speed three-dimensional shape using an optional large period according to the present invention. FIG. 4 is a flowchart illustrating a method for measuring a high- A fast 3D shape measurement method using a selective large period according to an embodiment of the present invention will be described with reference to FIGS. 2 to 4. FIG.

First, the controller 50 selects the first projector 31 that irradiates two equivalent wavelengths in accordance with a preset reference among a plurality of projectors. The controller 50 selects a first projector 31 that irradiates two objects in the direction As a first projector (S100).

When the first projector is selected, the ratio of the third period of each pixel of the second projector to the second period of the first projector is calculated as a condition for using the second pattern image at the time of calculating the second height information, And sets it as correction data (S102). That is, in the second projector, only the lattice pattern light having the third period is projected, and the second pattern image for the second lattice pattern light projected from the first projector at the time of calculating the second height information is used. In this case, since the ratio of the second cycle to the third cycle is different for each pixel position from the viewpoint of the second projector, the ratio between the second cycle and the third cycle is calculated for each pixel in the case of the projectors located in the different direction from the first projector The reference correction data is set as the reference correction data, and the correction process is performed by applying the correction data at the time of calculating the actual height information.

At this time, the reference correction data setting process is performed by the following process.

First, a plane jig having a height smaller than the height corresponding to the first period is positioned at a position where the object is to be loaded.

Then, the first projector projects the first grid pattern light and the second grid pattern light onto the surface of the plane jig to acquire the first pattern image and the second pattern image, and obtains the phase information of the first pattern image and the second pattern image As shown in FIG.

Then, the third projector projects the third grating pattern light onto the surface of the plane jig to obtain the third pattern image, and calculates the phase information of the third pattern image.

The ratio information of the second period and the third period in the second projector is calculated using the calculated phase information.

At this time, the ratio information of the second cycle and the third cycle is calculated by the following equation (1).

[Equation 1]

here,

The position of the pixel,

The phase difference of the second period of the first projector

The phase difference of the third period of the second projector

In addition, the ratio of the second cycle to the third cycle

And then calculates a coefficient N for correcting the 2 < [pi] > ambiguity.

At this time, the coefficient N for correcting the 2? Ambiguity is calculated by the following equation (2).

&Quot; (2) "

Then, the 2? Ambiguity is corrected using the calculated coefficient N, and the 2? Ambiguity is corrected by the following equation (3).

&Quot; (3) "

On the other hand, when the reference correction data is set, a pattern image corresponding to the grid pattern light is obtained by selectively projecting the grating pattern light in the first projector and the second projector (S104).

Specifically, the first projector projects a plurality of first pattern images by projecting the first lattice pattern light having a first period on a surface of an object while shifting its phase, A plurality of second pattern images are obtained by projecting the second grid pattern light having the second period on the surface of the object while shifting the phase of the second grid pattern light, .

Then, in the second projector located in a direction different from the first projector, only the third grating pattern light having the third period is projected on the object surface while phase shifting to acquire a plurality of third pattern images.

Subsequently, phase information is calculated using the respective pattern images (S106).

Specifically, a first phase is calculated using an N-Bucket algorithm for a plurality of first pattern images, a second phase is calculated using an N-Bucket algorithm for a plurality of second pattern images, A third phase is calculated using an N-Bucket algorithm for the third pattern image.

Then, height information is calculated using the first to third phase information (S108)

Specifically, the first order information A for the first phase is calculated using? 1 (x, y) = 2? H /? 1 + A? 2? As shown in FIG. 3 the second order information B for the second phase is calculated using? 1 (x, y) = 2? h /? 1 + B? 2? as shown in FIG. 3 (X, y) = 2? H /? 1 + C? 2?? Of the third order information C for the three phases.

Then, the first height information is calculated using the first order and the second order, and the second height information is calculated using the first order and the third order.

That is, the first height information is calculated using the first phase information obtained according to the first grating pattern light projected from the first projector and the second phase information obtained according to the second grating pattern light projected from the first projector, The second phase information obtained according to the second grating pattern light projected from the first projector and the third phase information obtained according to the third grating pattern light projected from the second projector are used to calculate the second height information, It is possible to reduce the number of imaging times and to reduce the three-dimensional shape measurement time. In other words, conventionally, a plurality of projectors irradiate both the grating light having the first period and the grating light having the second period to obtain the pattern image. In the present invention, however, in the second projector, And the phase information for the grating pattern light having the second period is obtained by reducing the number of times of imaging by using the phase information corresponding to the grating pattern light projected by the first projector It will be possible.

Further, since the phase information obtained by the grating pattern light projected by the first projector is used at the time of calculating the second height information as described above, the ratio of the second period to the third period for each pixel It is different. Therefore, at the time of calculating the second height information, the second height information is calculated by reflecting the reference correction data set in advance.

Then, when the first height information and the second height information are calculated, final height information of the object is calculated using the first height information and the second height information (S110).

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications and variations without departing from the spirit and scope of the invention. Accordingly, the appended claims are intended to cover such modifications or changes as fall within the scope of the invention.

10: stage 20:
30: plurality of projectors 40: image acquiring unit
50: controller 60: object
70: Obstacle

Claims

In a three-dimensional shape measuring apparatus having a plurality of projectors installed in different directions and irradiating grating pattern light,
Projecting a first lattice pattern light having a first period and a second lattice pattern light having a second period larger than the first period on a first projector selected in accordance with a preset reference among the plurality of projectors, A first step of obtaining a plurality of first pattern images for the first grating pattern light and a plurality of second pattern images for the second grating pattern light;
A second step of projecting only a third grating pattern light having a third period smaller than the second period on a surface of an object at a second projector located in a direction different from the first projector to obtain a plurality of third pattern images;
Calculating first phase information from the plurality of first pattern images, calculating second phase information from the plurality of second pattern images, calculating first height information using the first phase information and second phase information, A third step;
A fourth step of calculating third phase information from the plurality of third pattern images and calculating second height information using the first phase information and the third phase information;
And a fifth step of calculating final height information of the object using the first height information and the second height information.

The method according to claim 1,
Wherein the second lattice pattern light has at least twice the period of the first lattice pattern light or the third lattice pattern light.

The method according to claim 1,
Wherein the first projector is selected by referring to surrounding obstacle information capable of generating a shadow on an object surface at the time of illuminating the object grid pattern light.

The method according to claim 1,
If the first projector is selected in step 1, the ratio of the second period to the third period of each pixel of the second projector is calculated as the condition for using the second pattern image in calculating the second height information, And further comprising:
Wherein the second height information is calculated by reflecting the reference correction data in the fourth step.

5. The method of claim 4,
The reference correction data setting process
Loading a plane jig having a height smaller than a height corresponding to the first period at a position where the object is to be loaded;
The first projector projects first and second lattice pattern lights and second lattice pattern light onto the surface of the plane jig to obtain a first pattern image and a second pattern image, Calculating phase information on the phase information;
Projecting the third grid pattern light onto the surface of the plane jig in the second projector to obtain a third pattern image and calculating phase information for the third pattern image;
And calculating ratio information of a second period and a third period in the second projector using the calculated phase information.

6. The method of claim 5,
Wherein the ratio information between the second period and the third period is calculated by the following equation.

here,

The position of the pixel,

The phase difference of the second period of the first projector

The phase difference of the third period of the second projector

The method according to claim 6,
The ratio of the second period to the third period

And calculating a coefficient N for correcting the 2? Ambiguity using the calculated coefficient and correcting the 2? Ambiguity using the calculated coefficient.

8. The method of claim 7,
Wherein the coefficient N for correcting the 2? Ambiguity is calculated by the following equation.

9. The method of claim 8,
Wherein the 2? Ambiguity is corrected by the following equation.