JPH0473523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to three-dimensional measurement using stripes, particularly as typified by moiré topography.

(Prior art and its problems) Moiré topography projects a striped pattern onto a physical surface, superimposes the striped pattern deformed by the shape of the object and the standard striped pattern, and analyzes the moiré fringes that occur as the difference frequency. This is a method of measuring the shape of an object. For more information, see the magazine ``Applied Optics''.
Optics, Volume 9, 1970, pages 1467-1472, in the article "Moire'Topography". This method includes a grating irradiation type in which a point light source 21 illuminates a grating 22 placed just in front of an object 23 as shown in FIG. There is a grating projection type that forms 24 images on the object plane. When comparing both methods, the latter is more flexible and has a wider range of applications in terms of operability. Regarding grid projection type moiré topography, for example, see the paper "Projection method using moving grid method in automatic three-dimensional topography" published in the magazine "Applied Optics", Vol. 22, 1983, pages 850-855.
Moire′ moving with moving grantings for
antomated 3-D topography). Generally, moiré measurement produces high-order moiré fringes, so when automatically analyzing fringes,
It was difficult to separate the desired moire fringes.
In order to remove these high-order moiré fringes, a moving grid method was developed that averages out the high-order moiré fringes by moving the grating during observation. For more details, please refer to the magazine ``Applied Optics''.
Optics, Volume 9, 1970, pages 1467-1472, in the article "Moire'Topography".

(Problems to be Solved by the Invention) The conventional moving grating method requires mechanical movement to move the grating, making automatic measurement difficult. The disadvantage was that the contrast was low.

(Objective of the Invention) The object of the present invention is to provide a three-dimensional measurement method that eliminates high-order moiré fringes without moving the grating, facilitates automatic measurement, and obtains desired moiré fringes with high contrast. It's about doing.

(Means for Solving the Problem) This invention scans an object to be measured with sinusoidal intensity-modulated light having a constant modulation frequency to generate a striped pattern on the object surface, which is deformed depending on the shape of the object. This three-dimensional measurement method is characterized in that the striped pattern is superimposed on a reference striped pattern in the form of a sine wave having the same frequency as the intensity modulated light.

(Operation/Principle) In a holographic laser beam scanning device such as a holographic laser scanner, several holograms are arranged and fixed on the circumference of a disk, and the laser beam is scanned by rotating them at high speed. . If the front optical system of a holographic laser scanner is adjusted so that the scanning beam converges in the scanning direction on the object plane and diverges in the sub-scanning direction, the beam width in the sub-scanning direction
The length determined as the scan length is scanned over the entire surface. At this time, a striped pattern can be created in the scanning direction by modulating the laser. Consider a conventionally used rectangular grid with amplitude transmittance of 0 or 1. Define the following periodic function f(x).

f(x)=1 (4n-1) Π/2<x<(4n+1)
Π/2 0 x=±(2n-1)Π/2 (n: integer) -1 (4n+1)Π/2<x<(4n+3)Π/2...(1) Expand formula (1) into a Fourier series Then, f(x)=4/Π _∞ 〓 ⁿ⁼¹ (-1) ^n-1 cos {(2n-1)x}/2n-1...(2). According to equation (2), the amplitude transmission function of a simple rectangular grid with a black-to-white ratio of 1:1 is V(x,y)=1/2[1+4/Π _∞ 〓 〓 ⁿ⁼¹ (-1) ⁿ cos {( 2n−1) 2Π(μx+vy)/2n−1
]…(3). In equation (3), μ and v represent spatial frequencies in the x direction and y direction, respectively. When formula (3) is Fourier transformed, A(x,y)=1/2∫∫ ^∞ _-∞ [1+4/n _∞ 〓 〓 ⁿ⁼¹ (-1) ^n-1 cos {(2n-1) 2Π(μx+vy )/2n−
1]×exp{2Πi/λf(xξ+yη)}dxdy = [1/2δ(x,y)+1/Π{δ(x−λfμ,
y−λfv)+δ(x+λfμ,y+λfv)}] −1/3Π{δ(x−3λfμ,y−3λfv)+δ(x+
3λfμ,y+3λfv)} +1/5Π{δ(x-5λfμ,y-5λfv)+δ(x+
5λfμ,y+5λfv)}...](λf) ² ...(4) However, λ represents the wavelength, and f represents the focal length of the Fourier transform lens. The second term in equation (4) represents ±1-order moire fringes, and the third and subsequent terms represent unnecessary higher-order moire fringes.

On the other hand, the amplitude transmission function of a sinusoidal simple grating is V' (x, y) = 1/2 [1 + cos {2Π (μx + vy)}]
…(5). When formula (5) is Fourier transformed, A′(x,y)=1/2∫∫ ^∞ _-∞ [1+cos{2Π(μx
+vy)]×exp{2Πi/λf(xξ+yη)}dxdy ={1/2δ(x,y)+1/4δ(x−λfμ,y
−λfv)+1/4δ(x+λfμ,y+λfv)}(λf)
² ...(6) It can be seen that formula (6) does not produce higher-order moiré fringes compared to formula (4). The above discussion also holds true for general grids. Therefore, by modulating the laser into a sinusoidal waveform and projecting it onto the object, measurement that does not generate high-order moiré fringes can be realized.

(Embodiment) FIG. 1 shows an embodiment in which the method of the present invention is applied to a moiré topography composed of a semiconductor laser 1 and a holographic laser scanner 4. The light emitted from the semiconductor laser 1 is collimated by the collimating lens 2 and then converted into an elliptical beam by the cylindrical lens 3. Scan 6. At this time, as shown in the timing chart shown in FIG. 2, the rotation period signal a of the scanner is input by the encoder 12 to the arithmetic and control unit 11, such as a microcomputer having a GP-IB interface. The arithmetic and control unit 11 receives the encoder output synchronization signal a,
For example, a control signal b is sent to a waveform forming device 10 such as a function generator having a GP-IB interface so as to output a sine wave c of a predetermined frequency. The determined frequency is (n+w)/60Hz, where Wrpm is the rotational speed of the scanner, n is the number of lenses arranged in the scanner, and t is the number of stripes to be scanned on the object plane. The output signal c of the waveform forming device 10 is made into a current d sufficient to drive the semiconductor laser 1 by the amplifier 9, and then modulates the laser into a sinusoidal waveform. An example of the output of the waveform forming device is shown in FIG. The sinusoidal stripes deformed on the object plane are imaged with a TV camera that can accumulate light. A striped pattern corresponding to the signal generated by the waveform forming device 10 is created in advance in a multi-gradation image processing device 8 that has a plurality of frame memories and a GP-IB interface and has functions for integrating and adding/subtracting between images. Moiré fringes are generated by inputting the information from the arithmetic and control device 11 and superimposing it on an image captured by the TV camera 7. FIG. 4 shows an example of a striped pattern that is input in advance to the image processing device 8. The four arithmetic operations for images are to digitally represent the gradation of an image and perform gradation calculations for each dot. Since there are intermediate tones in the stripes, there are also intermediate tones in the moiré fringes, and an image processing device that can perform multi-gradation calculations is required. With this image processing device,
Moiré fringes are generated by performing the calculations explained in the section of operation and principle.

(Effects of the Invention) As detailed above, according to the three-dimensional measurement method of the present invention, high-contrast images can be obtained as high-order moiré fringes without moving the grating, unlike the conventional grating movement method. is obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIG.
Figure 3 shows a timing chart of system signals, Figure 3 shows the waveform of the current injected into the semiconductor laser in the example, and Figure 4 shows the density distribution of the reference stripes to be stored in the image processing device in the example. FIG. 5 is a diagram showing a conventional example of grating irradiation type moire topography, and FIG. 6 is a diagram showing a conventional example of grating projection type moire topography. In the figure, 1... semiconductor laser, 2... collimating lens, 3... cylindrical lens, 4... holographic laser scanner, 5... hologram lens, 6... object, 7... TV camera, 8... image processing device, 9... Amplifier, 10... Waveform forming device, 11... Arithmetic control device, 12... Encoder, 21... Light source, 2
2... Lattice, 23... Object, 24... Lattice.

Claims (1)

[Claims] 1. Scan the object to be measured with sinusoidal intensity modulated light with a constant modulation frequency to generate a striped pattern on the object surface, and then create a striped pattern deformed depending on the shape of the object and the intensity modulated light with the same frequency as the intensity modulated light. A three-dimensional measurement method characterized by overlapping a sinusoidal reference striped pattern.