KR20000053779A - Three dimension measuring system using two dimensional linear grid patterns - Google Patents

Abstract

PURPOSE: A two dimensional shape measurement system using a two dimensional check pattern is provided to reduce a producing cost and to maximize the environmental adaptability of a system with a compact system structure by generating a moire pattern by software in a computer instead of using hardware with a lens and a check. CONSTITUTION: A counter(51) is reset by the beginning of the input a start address, the size of an image and the number of checks to a latch register(49) and the operation thereof. An address operator(50) calculates an address with the counter and the value of a register. By using the address, a proper check among the check measured by a multiplexer(46) and the checks previously generated from a computer is selected and the selected address is filled in a buffer(47). Operation is performed in pixels, thus the size of the buffer is to be larger than square of the number of using phase transitions. An average unit(48) averages the value of the corresponding buffer and the corresponding value is written in a computer memory(45). A moire pattern is generated at a high speed by performing the corresponding sequences repeatedly as many times as needed.

Description

THREE DIMENSION MEASURING SYSTEM USING TWO DIMENSIONAL LINEAR GRID PATTERNS}

The present invention relates to the development of a three-dimensional shape measurement system using a grid pattern and moiré. More specifically, information on a grid having height information through two-dimensional measurement or two measurements on a horizontal grid and a vertical grid. Accurate measurement is possible by generating the information of the grid with and without the height information and supplementing the measurement result by the grid with the height information, and using the LCD as the grid generator. It can be said that the technical field of a three-dimensional shape measurement system using a two-dimensional grid pattern to facilitate the creation of a dimensional grid or horizontal, vertical grid.

Originally, moiré is a pattern generated when two or more lattice patterns having a certain spatial frequency overlap. The principle of the shape measurement technique using moiré is basically the same as that of triangulation. The shape measurement technology using moiré can be divided into projection type and shadow type. The shadow type method is mainly projected type because there is a disadvantage that the shadow does not appear when the area to be measured increases. The shape of the object is measured using. A general projection moiré shape measuring apparatus is shown in FIG. 1. When the grid 2 is projected onto the object 4 by the lens 3, the grid pattern is deformed according to the height change of the object. When the grid pattern deformed by the shape of the object is projected back to the reference grid 6 with the lens 5, a moire pattern is formed on the reference grid 6, and the generated moire pattern has information corresponding to the height of the object. do. In a three-dimensional shape measuring apparatus using moiré, the moiré generated on the reference grid 6 is measured with a camera 7 and analyzed by a computer to find three-dimensional information of the measurement object 4.

In recent years, the shape measurement apparatus using moiré uses a phase shift method to improve measurement accuracy. The phase shifting method is a technique that does not analyze using only one measurement result but measures more than desired number by moving the position of one grating of two gratings smaller than the pitch interval of grating and enables more accurate measurement. Also, the moving gray extracts only moiré patterns that are not affected by the grid movement by using gratings having a smaller grid spacing than the camera's measurement resolution or moving both gratings at the same speed to extract only the moiré patterns from the measured image. Use a moving grating method.

In addition, the lens 5 and the reference lattice are projected by using the lens 5 to project the grid projected onto the object to the reference lattice 6 and to measure the moiré pattern generated on the reference lattice with the camera 7.

There is a need for the design of an extremely precise relay optic system in conjunction with the camera.

Since the grating 2 is projected onto the object 4 using the lens 3, the distance between the measuring object 4 and the lens 3 changes, so that the distance between the gratings projected on the same object also changes according to the distance. . The moiré pattern is affected by the spacing of the grids projected onto the object, and as a result, the shape of the object changes with distance. In the existing system, to solve this problem, the lattice projection unit (2), (3) and the lattice generating unit (5) and (6) are designed to be exactly the same and a laser pointer is installed on the lattice (2) and the camera (7). The method of limiting the position of the measurement object to the point where two light meets is used. However, the system of these methods has disadvantages such as impairing the adaptation force and deforming the grid pattern projected on the object 4 by aberrations by the lenses 3 and 5.

The present invention obtains the measurement without height information and the measurement results without height information through two measurements on the horizontal grid and the vertical grid, or the measurement on the two-dimensional grid. To solve the problems as described above by complementing the errors, and by using the lens (5) and the grating (6) to create the moiré pattern created in hardware in the computer software to reduce the production cost through a simple system configuration The goal is to drastically reduce and maximize the system's environmental adaptability.

Figure 1-Typical Projected Moate Interferometer

2-Grid Projection System of the Invention

Figure 3-Throwing moiré using a color filter and two cameras of the present invention

4-Interferometer grating projection system using a color filter of the present invention and two cameras

5-Schematic diagram of the grid projection and image acquisition system of the present invention

Figure 6-System for creating a clear moiré pattern at high speed of the present invention

The moiré pattern is generated only when the projection direction and the viewing direction of the grid have a certain angle and the grid has an intensity distribution on the plane composed of the grid and the camera. Accordingly, as shown in FIG. 5, the grid is generated when it exists on a plane consisting of the center X (40) axis and the Z (41) axis of the gratings 33, 38, the lenses 34, 37, and the camera 39. When the vertical grid 36 is formed on the device 35 and projected onto the object, deformation due to the shape of the object occurs. However, when the horizontal grid 35 is generated and projected, the deformation due to the shape does not occur. However, according to the focal length of the lens 34 projecting the grating 33, the horizontal lattice spacing varies according to the distance. The horizontal grid is also deformed by aberrations or the like of the two lenses 34 and 38. This measurement error in the horizontal grid and the measurement error in the vertical grid have a strong correlation and appear almost similar. Therefore, the measurement result by the vertical grid can be corrected using the information of the horizontal grid. The moiré generated by the horizontal grid has no information about the height change of the object, so if the optical system is perfect, it should not have any intensity change. By correcting the moire generated by the vertical lattice with the moiré generated by the horizontal lattice, it is possible to extract the height information contained in the vertical lattice more accurately. In the present invention, an LCD is used in the grid generating apparatus of the projection moiré interferometer such as FIG. 1 to facilitate the transition between the horizontal grid and the vertical grid. In case of using the lattice manufactured by Ronchi Ruler or Lithography, the lattice should be replaced but the horizontal and vertical lattice can be measured. Since it is produced and measured, it is possible to measure horizontal and vertical grids without replacing the grid.

Fig. 1 shows a shape measuring apparatus which works on this principle. After generating a horizontal grid or a vertical grid on the LCD (2), (6), the LCD (2) is illuminated with a halogen lamp or flash lamp (1) and the grid pattern generated by the lens (3) is projected on the object (4) . When the lattice projected on the object is reflected on the LCD 6 with the lens 5 again, a moire pattern is generated on the LCD. The moiré pattern thus generated is measured by the camera 7. If you create a grid pattern that is not used again on LCD (2) and (6) and repeat the above process, you can create a moire pattern with measurement error and a moire pattern with shape information, respectively. Accurate measurement is possible by correcting moire patterns with shape information as patterns.

At this time, the grid pattern that is denser than the spatial resolution of the camera is generated or the moire pattern is extracted using the moving grating method, and the phase shift method is used to improve the measurement accuracy.

If a quick measurement is required, a faster measurement is possible by taking a method of extracting more information in one measurement using the two-dimensional grid 44 rather than sequential measurement of the vertical grid and the horizontal grid. Create a moire pattern by creating a grid with different colors for each axis using the color LCD, and separate the incoming signal for each color of the camera to create moire patterns by vertical grids and moire patterns by horizontal grids. Measurement is possible. In order to effectively separate the two moire fringes, a camera having a small bandwidth (spectral response) or a mirror having a constant bandwidth and two cameras may be used by beam splitting 21. In the system as shown in FIG. 1, when the grid generating apparatuses 2 and 6 are replaced with a color LCD and a small bandwidth digital camera and a color separation algorithm are applied, measurement using the two-dimensional grid is possible. If more precise measurement is required, the system as shown in FIG. 3 is configured and measured. The light emitted from the light source 15 illuminates the two-dimensional grid formed on the Color LCD 16, and the grid is projected on the surface of the object 18 by the achromatic lens 17, and then the grid appeared on the object is achromatic lens 19 Moiré pattern is created by overlapping the grid created on the color LCD. The moire pattern generated in this way is measured by two cameras 22 and 23. At this time, the two cameras measure the color LCD through the mirror 21 having a constant bandwidth (bandwidth corresponding to the color gamut to be measured by the camera 23) so that the moire patterns separated by the two cameras are measured. . Combine the moiré patterns measured on the two cameras on the same principle as described above. Enable accurate measurements

The system of Figure 1 performs the formation of moirés in hardware. However, the moiré pattern can also be formed by software. In other words, the moire pattern is formed by measuring the grid pattern projected on the object with a computer-generated grid pattern. Since the moiré pattern generated in this way includes the term corresponding to the grid used, the moiré pattern is generally extracted using a low pass filter. However, when the frequencies of moire patterns and lattice patterns are similar, it is difficult to extract the moire patterns efficiently. In the present invention, the moiré pattern is extracted using the property that the moiré pattern depends only on the order difference of the lattice without using a low pass filter.

N-step (N: natural number greater than 2) When moiré is generated using the phase shift method, the lattice generated in the lattice generator 10 is moved by p / N (P: Pitch Size of the lattice) smaller than the lattice pitch. Will be measured. Since the moiré pattern depends only on the relative difference between two overlapping gratings, the computer-generated gratings are also phase-shifted by the same value as the grating used for measurement, and when they overlap, the same moiré pattern is generated regardless of the phase shift value. That is, when the grating having the same intensity distribution as the cosine function is generated in the grating generating device 10, the grating is projected on the measurement object 12 with the lens 11, and the image is acquired by the camera 13, the measured image is It would look like this:

Since the spatial frequency of the projected grid when accurately projecting the object measured by the lens 11 can be known, in an ideal case, a grid obtained by the camera and having the same spatial frequency can be generated inside the computer as follows. .

If only the image corresponding to the same moiré pattern among the images generated by multiplying the two lattice generated by Equation 1 and Equation 2, only the moire pattern can be extracted using the periodicity of the lattice.

The moiré pattern thus generated can be analyzed by a phase shift method. For faster measurement, moiré pattern generation can be accelerated using a device having the structure as shown in FIG. Input information such as grid start address, image size, and number of grids into the latch register (49) and start the operation. The counter 51 is reset, and the address operator 50 of the counter and register Compute the address by value. This address is used to fill the buffer 47 by selecting the appropriate one from among the grid measured by multiplier 46 and a computer generated grid. Since the operation is performed in pixels, the size of the buffer may be larger than the square of the number of phase shifts used. When the buffer is filled, the averager 48 averages the values of the corresponding buffers and writes the values corresponding to the computer memory 45. This can be done as many times as you want to create a moire pattern at high speed. In addition, since the operation is performed pixel by pixel, it is possible to perform parallel processing using two or more devices.

This method can be used only when the phase shift method is used. However, since the low frequency filter is not used, a clear moiré pattern can be extracted. 2 shows a system for measuring the surface shape of an object in this way. The grid 14 is illuminated by the light emitted from the light source 9, and the grid generated by using the lens 11 is projected onto the measurement object 12, and then an image of the grid projected by the camera 13 is obtained to obtain a computer 14. The shape of the object is measured using the method described above by superimposing the lattice generated in Fig. Compared with the system of FIG. 1, it can be seen that the components constituting the optical system are cut in half. It is expected that this simple system configuration will reduce the price of the system to less than half and maximize the environmental stress of the system. Conceptually, the grating projected on an object is created in the optical element of the camera. Therefore, in order to minimize the change in the lattice spacing according to the distance in the conventional method, the focal length of the lens of the camera and the lens 11 projecting the lattice should be equal to the distance to the measurement object. This is a constraint on the system design. However, this limitation can be overcome by using two measurements of horizontal and vertical lattice or measurement error elimination techniques using two-dimensional lattice as described above. 4 shows a system using a mirror having a constant wavelength band. Lens (27) Color The grid pattern generated in the LCD (26) is projected onto the measurement object (28), and the grid pattern is measured by two cameras through a mirror having a constant wavelength band, and the grid pattern divided horizontally and vertically is measured. After that, the software generates moiré to measure the three-dimensional shape of the object.

In the case of generating the moiré pattern in software, unlike the case of generating the moiré pattern in hardware, the separation of the two lattice patterns can be efficiently performed by using the spatial frequency of the two lattice patterns. Of the two gratings used, the grating without height information has a constant period with little change, so the spatial frequency distribution will be localized in a specific area of the corresponding axis. Accordingly, the two lattice patterns can be efficiently separated by using a Nach filter and a band pass filter. Therefore, by generating and analyzing moiré using two software moiré generation methods that separate grid patterns through filtering, it is possible to measure horizontal and vertical grids simultaneously without using color LCD and color separation technology.

The three-dimensional shape measurement system using the two-dimensional grid pattern according to the present invention is a simple system that compensates for the disadvantage that the environmental stress of the system is not as good as in the existing system, and the grid pattern projected on the object is deformed by the aberration by the lens. The system configuration greatly reduces the production cost and maximizes the environmental stress of the system, as well as a more accurate three-dimensional shape measurement system.

Claims (4)

The lattice generated on the LCD 2 is projected onto the measurement object 4 with the lens 3 and the lattice projected on the measurement object is projected on the LCD 6 to generate a moire pattern. 3D shape measurement system that compensates for errors such as aberrations and changes in grid spacing according to distance by performing measurements without replacing the grid A two-dimensional grid (a grid for generating horizontal and vertical grids) that is color-coded on the color LCD 2 is generated, projected onto the measurement object 4, and then generated on another color LCD 6. Regenerate the moiré pattern by re-projecting onto and separate the two grid components using the RGB signal of the camera (7) or use the Color Filter (21) and two cameras (22) and (23) -Dimensional shape measurement system that separates and performs simultaneous measurements by horizontal and vertical grids The grid generated on the LCD 10 is projected onto the measurement object 12 with the lens 11, and the grid projected on the measurement object is measured by the camera 13, and then computed with a computer generated grid to generate a moire pattern. The horizontal and vertical grids can be measured separately, or the horizontal and vertical grids can be projected simultaneously to separate the two grids with a notch filter and a band-pass filter. 3D shape measurement system that generates moiré patterns by operating with grids Using a color LCD (10) and an achromatic lens (11) and using a color-coded two-dimensional grid to project the grid on the measurement object, using the RGB component of the camera 13, color filters, A three-dimensional shape measurement system that separates the grid pattern existing for each color using (29) and two cameras (30) and (31) and calculates the moiré pattern by calculating it with a computer-generated grid.