JP4255865B2 - Non-contact three-dimensional shape measuring method and apparatus - Google Patents

Description

  The present invention relates to a non-contact three-dimensional shape measuring method and apparatus, and more particularly, to a non-contact digitizer for development to CAD by digitizing a design shape and shape accuracy evaluation (reverse engineering) of prototype / mass production parts. It is possible to measure a three-dimensional shape in a large measurement range, such as a full-size automobile, in a non-contact manner in a short time. The present invention relates to a non-contact three-dimensional shape measuring method and apparatus for obtaining a shape by analyzing the contrast of a lattice image deformed according to the shape of a measurement object by observing from another direction.

  As a technique for measuring a three-dimensional shape in a non-contact manner in a short time, a grid-like pattern is projected onto the measurement target as described in Patent Document 1, Patent Document 2, and Patent Document 3, and the height of each part of the measurement target is measured. There is a moire method using moire topography that measures a three-dimensional shape from a lattice image deformed according to the distribution. In this moire method, as shown in FIG. 1, two gratings G1 and G2 for projection and observation are arranged in front of the projection lens L1 and the imaging lens L2, and the grating G1 is projected onto the measurement object by the lens L1. A grating line deformed according to the object shape is imaged on another grating G2 through the lens L2, and fringe contour lines are generated at predetermined distances h1, h2, h3,... From the reference plane. As shown in FIG. 2, a large grating G is arranged on the reference plane, the point light source S is arranged at the position of the projection lens L1, and the observation eye e is arranged at the position of the imaging lens L2. The shadow of the light source S is dropped on the object to be measured, the shadow of the lattice G deformed according to the object shape is formed, and this is observed by the observation eye e through the lattice G. I'll observe the moire fringes caused by There are entities lattice type you. Further, Patent Document 4 describes that the phase shift method can be applied to the tangential lattice type moire method.

  On the other hand, Non-Patent Document 1 describes a non-contact shape measuring method in which a phase shift is combined with grating pattern projection as shown in FIG.

  The shape is measured by the following procedure.

  (1) For example, by using the illumination lamp 10 to illuminate the grating filter 12 disposed in front of the projection lens 14, a grating pattern is measured from a position different from the focal position of the imaging optical system (imaging lens 20). 8 is projected.

  (2) The grating shift mechanism 16 moves the grating filter 12 in the lateral direction indicated by the arrow A (phase shift), and changes the shade of the pixel of the image obtained by the imaging element 22 via the imaging lens 20 into a sine wave shape. To do.

  (3) A plurality of images are taken for each phase shift amount at equal intervals.

  (4) Calculate the phase and contrast of each pixel.

  (5) Step the position of the measurement workpiece 8 in the height direction (or focus direction, etc.) and repeat (2) to (4). The position of the measurement workpiece 8 moves at least twice.

  (6) A focus position for obtaining the maximum contrast of each pixel is obtained, and a fringe order is obtained.

  (7) The phase at the maximum contrast of each pixel is selected to obtain the phase distribution.

  (8) The phase difference from the reference phase is calculated.

  (9) The distance (height) in the depth direction is calculated using the phase difference and the fringe order.

Japanese Patent Laid-Open No. 10-246612 US Pat. No. 5,175,601 US Pat. No. 5,319,445 JP 2002-267429 A Masahito Tonooka and 6 others, “Surface shape measurement by phase and contrast detection using lattice pattern projection method”, Journal of Precision Engineering, Japan Society for Precision Engineering, January 2000, Vol. 66, No. 1, p132-136

  However, in Patent Documents 1 to 4, since the same output is repeated every time the phase changes by 2π as shown in FIG. 4, it is not possible to specify which line of the projected grating is reflected only by the phase shift. The order of the stripes cannot be determined. Therefore, the measurement range is limited to any one of A, B, C, D,..., And if the measurement range is within the order of one stripe, the lattice spacing is widened and the measurement accuracy is lowered. On the other hand, if the lattice interval is reduced to ensure high accuracy, the measurement range in the depth direction is reduced. In addition, compared with a pixel that is in focus, a pixel that is out of focus has problems such as poor measurement accuracy.

  On the other hand, in Non-Patent Document 1, when the number of measurement steps is small, an error occurs at the time of fitting a Gaussian function performed when obtaining the maximum contrast, so that the accuracy of the points located between the steps decreases. By increasing the number of movements, this error can be reduced, but with an increase in measurement time. Further, since the measurement work is moved or the illumination optical system and the imaging optical system are moved, the apparatus becomes complicated. Furthermore, although the measurement range in the depth direction can be expanded by increasing the number of steps, there are problems such as limitations on measurement time and apparatus surface.

  The present invention has been made to solve the above-described conventional problems, and with a simple configuration that can be reduced in size, expands the measurement range in the depth direction and realizes high-accuracy measurement over the entire measurement range. This is the issue.

The present invention analyzes the contrast of the lattice image deformed according to the shape of the measurement object by observing the lattice pattern projected on the measurement object while shifting the phase from a direction different from the projection direction. In the non-contact three-dimensional shape measurement method that obtains the above-mentioned problem, the focus on the projection side and the imaging side is continuously shifted simultaneously with the phase to expand the measurement range in the depth direction. is there.

  The present invention also analyzes the contrast of the lattice image deformed according to the shape of the measurement object by observing the lattice pattern projected onto the measurement object while shifting the phase from a direction different from the projection direction. In a non-contact three-dimensional shape measuring apparatus that obtains a shape by means of, a means for projecting a lattice pattern onto the measurement object while shifting the focus and phase, and image data of the pattern projected onto the measurement object while shifting the focus The above-mentioned problem is similarly solved by providing a means for inputting the image data and a means for processing the input image data to create a three-dimensional map.

  Further, the means for creating the three-dimensional map determines the fringe order from the focus center, unwraps the phase, calculates the absolute value of the phase, and the intersection of the grating plane of the fringe order and the epipolar line of the imaging point And a means for calculating the three-dimensional position.

  Further, a means for correcting distortion (distortion) of the projection optical system and the imaging optical system is provided.

  Further, the projection optical system and the imaging optical system are mounted on one shift mechanism and driven in the Z-axis direction.

  In the present invention, the focus shift is combined to enable determination of the fringe order of the grating and to extend the measurement range in the depth direction with high accuracy.

  According to the present invention, the fringe order of the grating pattern is obtained from the focus center, the phase is unwrapped, the absolute value in the depth (Z) direction is obtained, and the focus is continuously shifted, so that high accuracy is maintained. However, the measurement range in the depth direction is dramatically expanded. In addition, since the three-dimensional coordinate value is calculated from the phase when each pixel is in focus, the coordinate value can be obtained with all the measurement points in focus, and the XY directions can also be measured with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 5 shows the overall configuration of an apparatus for carrying out the present invention.

  In this embodiment, in the same apparatus as the conventional example shown in FIG. 3, the lattice filter 12 is indicated by an arrow B together with the lattice shift mechanism 16 that moves the lattice filter 12 at a constant speed in the lateral direction indicated by the arrow A. A first focus shift mechanism 18 for moving in the front-rear direction at a constant speed, and a second focus shift mechanism 24 for moving the image sensor 22 such as a camera in the front-rear direction, also indicated by arrow B, at a constant speed. In addition, both the projection lens 15 and the imaging lens 21 are image-side telecentric optical systems so that the imaging point on the measurement workpiece 8 shown in the pixel does not change even when the focus is shifted.

  The first focus shift mechanism 18 for the lattice filter 12 and the second focus shift mechanism 24 for the image sensor 22 are controlled to move in synchronization.

  Corresponding to the phase shift amount of the grating filter 12, the imaging timing of the imaging element 22 is determined. The illumination lamp 10 is turned on in accordance with this imaging timing. As the illumination lamp 10, for example, a xenon flash or a halogen lamp is used.

  The processing according to the present invention is performed according to a procedure as shown in FIG. That is, first, in step 100, image data of the measurement workpiece 8 is continuously input while shifting the focus and phase at a constant speed. An example of the light and shade waveform of a certain pixel is shown in FIG. The data input time is 4.3 seconds assuming that 128 images are captured by a 30 fps camera (image sensor 22), for example. Here, the time t on the horizontal axis corresponds to the number of captured images.

  Next, the process proceeds to step 200, where the input data is processed in the computer to create a three-dimensional map. That is, since the focus center and the phase are in a relationship as shown in FIG. 8, in step 210, the fringe order is determined from the focus center, and the phase connection (referred to as unwrapping) is performed from 0 to 2π → 0 to nπ. Calculate the absolute value of the phase. Further, as shown in FIG. 9, the lattice plane of the fringe order and the epipolar line of the imaging surface are obtained from known parameters such as the camera location, focal length, and image center, and the absolute phase obtained in step 210. Then, the three-dimensional position of the intersection is calculated as the three-dimensional position of the imaging point of the screen coordinates (u, v). A three-dimensional map is created by calculating this over the entire image.

  Specifically, the image data input in the above step 100 is performed according to the procedure shown in FIG. That is, first, in step 102, the focus shift mechanisms 18 and 24 of the projection optical system and the imaging optical system are moved to the initial positions.

  Next, at step 104, the illumination lamp 10 is turned on, and the pattern of the grid filter 12 is projected onto the measurement work 8.

  Next, at step 106, the focus shift mechanisms 18, 24 of the projection optical system and the imaging optical system are moved at a constant speed V as shown in the following equation.

z _f = V * t + z ₀ (1)

  Next, in step 108, the lattice shift mechanism 16 is moved at a constant speed ω as shown in the following equation.

φ = ω * t + φ ₀ (2)

  Next, the routine proceeds to step 110, where it is determined whether or not the necessary number of images K has been reached. When the number of shots i has reached K, this procedure is terminated.

  On the other hand, if the number i of images to be captured is smaller than the required number K of images to be captured, the process proceeds to step 112, where the image is captured, the image is transferred to the memory of the computer at step 114, Wait until.

  When creating the three-dimensional map in the above step 200, as shown in FIG. 11, with respect to all the pixels of the image, the pixel at the upper left corner is (u, v) = (0, 0), and v = 0, that is, 1 For the pixels in the row, from the left end u = 0 to u = w, the processing from the extraction of the grayscale waveform to the calculation of the three-dimensional position (4) is performed, and then the above processing is performed for the row of v = 1. This is repeated until v = h, and the calculation of the three-dimensional positions of all the pixels of the image is completed.

  Specifically, as shown in FIG. 12, after extracting the grayscale waveform of the image coordinates in step 250, the process proceeds to step 260, where the offset component and the fluctuation component of the grayscale waveform are removed. The removal of the offset component of the grayscale waveform and the fluctuation component in this step 260 eliminates the offset component of the grayscale waveform, and the fluctuation of the offset component due to the incident of reflected light from the vicinity of the workpiece imaging point due to defocusing or illumination change in the surrounding environment. To eliminate. However, the change in fluctuation is assumed to be more gradual than the change in density due to the phase shift.

Specifically, as shown in FIG. 13, the offset and fluctuation components can be removed by calculating the differential waveform of the grayscale waveform in step 262. That is, the gray waveform of the image coordinates (u, v) with the number of images taken is the following expression: Gi = A (i) sin {(2πi / n) + φ} + B + ε (i) (3)
(However, A (i) = Amplitude fluctuation of waveform, B = Offset, ε (i) = Fluctuation component)
In this case, the differential waveform becomes the following equation, and the offset and fluctuation components can be removed.

  Further, in order to differentiate discrete data, the phase of the differentiated waveform advances by π / n.

  Note that the grayscale waveform offset component and the fluctuation component in step 260 are removed in step 264 by changing the grayscale waveform offset value at a certain phase shift amount in the vicinity (before and after) ± π as in the modification shown in FIG. It is also possible to remove it as an average value of gray values.

That is, when the grayscale waveform of the image coordinates (u, v) is expressed by the above equation (3), the offset + fluctuation component B + ε (i) at i becomes the following equation (4a), and the offset and fluctuation are expressed as follows: The gray waveform g _i from which the component is removed is expressed by the following equation (4b).

  In this case, the phase of the grayscale waveform after removal is not shifted.

  After step 260 in FIG. 12 is completed, the process proceeds to step 270 to calculate the focus center ((1) in FIG. 8). The calculation of the focus center in step 270 is performed in order to calculate the depth in the Z-axis direction in focus in order to determine the fringe order. That is, if the phase shift pitch of the grating projection is 2π / n (where n is an integer), the density change every n data becomes the focus contrast curve, and the vertex of the contrast curve, that is, the position where the density value is maximum. Becomes the focus center. Accordingly, the contrast curve is regarded as a normal distribution curve, and the vertex can be obtained by statistical calculation.

  A specific processing procedure is shown in FIG. Here, the frequency average value is obtained for each of the square waveforms of the gradation change curve (j extracted waveforms) every n data, and the weighting coefficient by the coefficient (area ratio) corresponding to the peak height of the extracted waveform is obtained. Add and average.

  After step 270 in FIG. 12 is completed, the process proceeds to step 290, where the phase at the focus center ((2) in FIG. 8) (−π to π) is calculated. The phase calculation in this step 290 is performed to calculate the phase of the fringes of the grating pattern projection. Here, since the reflected light near the imaging point is mixed in the waveform deviated from the focus, the phase can be obtained by increasing the weight of data close to the focus center.

  That is, if the phase shift pitch of the lattice pattern projection is 2π / n (where n is an integer), the differential waveform value every n data becomes a normal distribution curve, and the phase 2πi / n (where i = 0, 1,..., N) 1 represents a focusing contrast curve in -1). The contrast curve for each phase is proportional to the height of the vertex at the focus center. Furthermore, the area surrounded by the center line of the contrast curve and the gray value (≈the sum of differential waveform values every n data) is proportional to the height of the vertex of the contrast curve. Therefore, as shown in a specific processing procedure in FIG. 16, the phase is obtained by integrating with the mother wave mj obtained in step 292 and performing Fourier integration in step 300. That is, since there are eight phase contrast curves for each π / 4 from π / 8 to (15π) / 8, the area surrounded by each curve and the central line of the gray value is obtained, and as shown in FIG. Find the sine wave formed by the area of the phase interval (Fourier integration). Then, the phase difference between the mother wave and the sine wave is obtained as φ. This is performed for all pixels (u, v).

After step 290 in FIG. 12 is completed, the process proceeds to step 310 where the phase is unwrapped and the absolute phase ((3) in FIG. 8) is calculated as the phase of the fringe order closest to the focus center. The unwrapping of the phase in step 310 is performed in order to obtain the fringe closest to the focus center and calculate the absolute phase. A specific processing procedure is shown in FIG. That is, in (2) of FIG. 8, which fringe order of the lattice is counted from the left end. Therefore, φfocus in step 322 becomes an approximate value of unwrapping (a value close to the phase of unwrapping). In the expression in step 324, exp (iφ) is an accurate phase between −π and + π, and the second term on the right side obtains an angle (fractional angle of φ−φfocus),
Since φfocus = (2π × order) + φfocus fractional angle,
φunwrap = (2π × order) + φ
Therefore, an accurate phase is obtained.

  After step 310 in FIG. 12 is completed, the process proceeds to step 330, where the actual three-dimensional position of the point Pi ((4) in FIG. 8) is calculated, and the process returns to step 240. The calculation of the three-dimensional position in step 330 is performed to calculate the three-dimensional position of the point being imaged. A specific processing procedure is shown in FIG.

  When calculating the three-dimensional position in step 220 in FIG. 6, if necessary, the distortion (distortion) of the measurement head is corrected in step 400 to achieve high accuracy.

  Specifically, since the projection optical system and the imaging optical system have a distortion as shown in FIG. 20, the correction is performed by a camera model formula taking this distortion into consideration.

An example of a camera model formula for obtaining the original pinhole coordinates (x _pin , y _pin ) from the distortion coordinates (u _dist , v _dist ) obtained by photographing a known lattice pattern in advance is shown below.

x _dist = (u _dist −u ₀ ) / f _u , y _dist = (v _dist −v ₀ ) / f _v (5)
x _pin = x _dist + (g ₁ + g ₃ ) x _dist ² + g ₄ x _dist y _dist
+ G ₁ y _dist ² + (k ₁ r ² + k ₂ r ⁴ ) x _dist (6)
y _pin = x _dist + g ₂ x _dist ² + g ₃ x _dist y _dist
+ (G ₂ + g ₄ ) y _dist ² + (k ₁ r ² + k ₂ r ⁴ ) y _dist (7)
However, r ² = x _dist ² + y _dist ²

On the other hand, calculation for _obtaining distortion coordinates (u _dist , v _dist ) from pinhole coordinates (x _pin , y _pin ) in order to correct distortion due to the projection lens can be obtained by convergence calculation by Newton's method. Specifically, this is performed as follows.

(1) Initial value setting (x _dist , y _dist ) = (x _pin , y _pin ) (8)

(2) Error calculation The distortion coordinates (x _dist , y _dist ) are converted into temporary pinhole coordinates (x _temp , y _temp ), and errors (x _err , y _err ) with the desired pinhole coordinates are calculated.

(X _err , y _err ) = (x _temp , y _temp ) − (x _pin , y _pin ) (9)

(3) Correction amount calculation (∂x _pin / ∂x _dist ) = 1 + 2 (g ₁ + g ₃ ) x _dist + g ₄ y _dist
+ K ₁ (3x _dist ² + y _dist ² ) + k ₂ (5x _dist ⁴ + 6x _dist ² y _dist ² + y _dist ⁴ )
…(Ten)
(∂x _pin / ∂y _dist ) = g ₄ x _dist + 2g ₁ y _dist + 2k ₁ x _dist y _dist
+ 4k ₂ (x _dist ³ y _dist + x _dist y _dist ³ ) (11)
(∂y _pin / ∂x _dist ) = 2g ₂ x _dist + g ₃ y _dist + 2k ₁ x _dist y _dist
+ 4k ₂ (x _dist ³ y _dist + x _dist y _dist ³ ) (12)
(∂y _pin / ∂y _dist ) = 1 + g ₃ y _dist +2 (g ₂ + g ₄ ) y _dist
+ K ₁ (x _dist ² + 3y _dist ² ) + k ₂ (x _dist ⁴ + 6x _dist ² y _dist ² + 5y _dist ⁴ )
…(13)

  However, in order to reduce the influence amount by the second term and to reduce the calculation amount, the second term may be omitted and the calculation may be performed as follows.

(4) Correction of distortion coordinates (x _dist , y _dist ) = (x _dist , y _dist ) − (x _diff , y _diff ) (16)

(5) Convergence determination For example, if (x _diff <ε) and (y _diff <ε), the convergence calculation is terminated. Otherwise, return to (2) to correct the coordinates.

Here, f _u and f _v are focal lengths (X-axis and Y-axis), u ₀ and v ₀ are linear parameters representing the image center, k ₁ and k ₂ are radial distortion coefficients, g ₀ , g ₁ , g ₂ and g ₃ are distortion parameters representing distortion coefficients in the orthogonal direction.

According to the inventor's experiment, when ε = 1 × e ^{−8 in} the camera model, convergence is achieved on average 1.5 times and maximum 6 times.

  The distortion correction is described in detail in the following document.

Juyang Weng, “Camera Calibration with Distribution Models and Accuracy Evaluation” IEEE Trans. Patt. Anal. Machining Intel. vol. 14, no. 4, pp 965-980
Zhengyou Zhang, “AFlexible New Technique for Camera Calibration” Dec. 2.1998, MSR-TR-98-71

  The reason why the convergence calculation is performed by the Newton-Raphson method in steps 342 to 354 in FIG. 19 is to eliminate the influence of distortion because the distortion is nonlinear.

  Thus, by correcting the distortion of the lens optical system and the shift mechanism system, the measurement accuracy in the XY directions can be increased. Depending on the application, correction of distortion can be omitted.

  The system configuration of a specific embodiment is shown in FIG.

  In this embodiment, a measurement unit 40 having a projection unit for projecting a lattice pattern and an imaging unit for imaging from different viewpoints, and a computer (PC) 50 for calculating a three-dimensional map from the captured image data are connected. And the cable 60 to be configured.

  Specifically, the measuring head 40 moves the grating filter 12 at a constant speed as shown in FIG. 22 (cross-sectional view seen from above) and FIG. 23 (cross-sectional view taken along line XXIII-XXIII in FIG. 22). A grating shift mechanism 16, an illumination lamp 10 for projecting the grating pattern, an imaging device (camera) 22 for imaging the projected grating pattern, and a first for moving the focus of the projection optical system at a constant speed. The focus shift mechanism 18, the second focus shift mechanism 24 that moves the focus of the imaging optical system at a constant speed, and even if the focus is shifted, the imaging point on the workpiece shown in the pixel does not change. The shift amount of the projection lens 15B having the image side telecentric optical system, the imaging lens 21, and the grating filter 12 is detected, and the imaging timing signal is transmitted to the camera 22. A control circuit (not shown) for moving the camera control board 42 for generating a signal, the driving device for the lattice shift mechanism 16 and the driving devices for the focus shift mechanisms 18 and 24 in synchronization, and the illumination lamp 10 for imaging. And a projector control board 44 to be lit. In the figure, 46 is a manual diaphragm, for example, and 48 is a cooling fan.

  Here, the projection optical system (15) and the imaging optical system (21) are image-side telecentric so that the imaging point on the measurement workpiece 8 shown in the pixel does not change even when the focus is shifted. It is.

  The computer 50 controls the frame grabber 52 that captures an image input from the image sensor 22 of the measurement head 40, the motion control board 54 that controls the shift mechanisms 16, 18, and 24 of the measurement head 40, and the measurement head 40. A function for inputting continuous images while simultaneously shifting the focus and phase and transferring them to the main memory of the computer 50, a function for live display of an image corresponding to the measurement range of the measurement head 40, and a measurement depth range. The function to calculate the focus center from the grayscale waveform whose amplitude changes due to the focus shift to create a 3D map and the phase of the grayscale waveform near the focus center to create a 3D map Function, unwrapping phase using focus center data, optical system The function to correct the coordinates on the image taking into account only the intersection of the epipolar line starting from the pixel of the image sensor 22 and the lattice plane of the lattice pattern projection, and calculating the three-dimensional position projected on the pixel Function to replay the input continuous image, the function to display the created 3D map, and the point cloud data of the 3D map to IGES etc. Software (not shown) having a function of saving in the CAD format.

  FIG. 24 shows a state in which the measurement workpiece (in this case, an automobile) 8 is being measured according to this embodiment.

  Hereinafter, a measurement example in which the number of captured images is 128 and the interval between the projection side and the imaging side is set to 500 mm will be described. Here, when the interval is widened, the stripe order is narrowed, and the resolution is increased. Now, the measurement workpiece 8 is a full-size automobile having a shape as shown in FIG. 25, the measurement range is 4000 mm in the X direction, 3000 mm in the Y direction, 2000 mm in the Z direction, the distance to the center of the workpiece is 4800 mm, and the image size is 320 × 240. If it is a pixel, in the case of a pinhole optical system with an infinite depth of focus, as shown in FIG. 26, a lattice pattern is clearly projected from the near side to the back and imaged. On the other hand, since the actual optical system has a limited depth of focus, the projection range of the lattice pattern is limited by the focal position as shown in FIG.

  Next, the process of creating a three-dimensional map is shown in FIGS. Now, when the three-dimensional map obtained from only the focus center image is as shown in FIG. 28A in full scale depth representation and in FIG. 28B in 200 mm pitch depth representation, the phase image is as shown in FIG. The unwrapped phase image is as shown in FIG. 30, and the finally obtained three-dimensional map image is as shown in FIG. 31 (a) with a full-scale depth representation and as shown in FIG. 31 (b) with a depth representation of 200 mm pitch. Become. Although it is difficult to understand in the figure, it is clear that a smooth shape is obtained in FIG. 31B compared to FIG.

  FIG. 30 shows an error in the measurement result of data added with noise components assuming an actual machine. Since tires do not return light, they are buried in noise and have low accuracy, but high-precision measurement results are obtained for other portions.

  In the embodiment, the automobile is the measurement object, but the type of the measurement object is not limited to this. The light source is not limited to a xenon flash or a halogen lamp.

  Next, an example of an image measuring machine will be described. In this embodiment, (1) the imaging optical system (measurement optical system) of the image measuring machine is used as it is and a projection optical system is added, or (2) the imaging optical system of the image measuring machine is not used. 33, a measuring head 40 incorporating an imaging optical system and a projection optical system is attached to the Z axis of the image measuring machine in parallel with the imaging optical system of the image measuring machine, and a lattice shift and a focus shift are imaged. There is a method in which the measuring machine performs Z-axis driving.

  In the embodiment of FIG. 33, the lattice shift mechanism and the focus shift mechanism can be substituted by the guide mechanism 60 in the Z-axis direction. The focus shift is performed by the measurement head 40 moving up and down in the Z-axis direction as in the current image measuring machine. Since the grating pattern is projected obliquely, the grating pattern projected onto the measurement workpiece 8 moves and is phase-shifted when the measuring head 40 moves up and down. The focus shift speed and the phase shift speed are set by adjusting the angle of the projection optical system or adjusting the lattice spacing.

  In the figure, 6 is a stage on which a measurement workpiece 8 is placed, 11 is a light emitting element, 15 and 21 are both telecentric projection and imaging lenses, 45 is an illumination control circuit, and 62 is a Z-axis guide mechanism feed motor. 64 are motion control units for controlling the feed motor 62.

  The method (2) is not limited to an image measuring machine, but can be used by attaching to a coordinate measuring machine (a coordinate measuring machine of a type that can be driven at a constant speed by a motor with a Z-axis). In either case, since the lattice pattern is projected obliquely, only the movement in the Z-axis direction is required.

  In the above description, the lattice shift mechanism and the focus shift mechanism are both moved at a constant speed. However, if the shift position can be grasped, it may not be moved at a constant speed.

Optical path diagram showing the measurement principle of the conventional grating projection type moire method Optical path diagram showing the measurement principle of the conventional solid lattice moire method A perspective view showing the principle of a conventional non-contact shape measurement method using grating pattern projection and phase shift Same optical path diagram The perspective view which shows the measurement principle of this invention Flow chart showing the measurement procedure according to the invention The time chart which shows the example of the shading waveform of a certain pixel in this invention Optical path diagram showing the relationship between focus and phase The perspective view which similarly shows the intersection of a lattice plane and an epipolar line A flow chart showing the procedure for inputting image data The figure which similarly shows the scanning method of a pixel A flow chart showing the same procedure for creating a 3D map Similarly, a flowchart showing an example of the procedure for removing the offset component and the fluctuation component Similarly, a flowchart showing another example of the procedure for removing the offset component and the fluctuation component A flow chart showing the procedure for calculating the focus center Flow chart showing the same phase calculation procedure Figure showing details in the same way Flow chart showing the same phase unwrap procedure Flow chart showing the same 3D position calculation procedure A perspective view showing the principle of distortion correction The figure which shows the system configuration | structure of a specific Example. Sectional drawing which shows the structure of the measurement head used in the Example Cross section along line XXIII-XXIII in FIG. The perspective view which shows the mode of the measurement in an Example Diagram showing measurement workpiece Figure showing a grid projection image when using a pinhole optical system with an infinite depth of focus The figure which shows the lattice projection image of an actual optical system Diagram showing the focus center image in the process of creating a 3D map Figure showing the same phase image Figure showing the unwrapped phase image The figure which shows the example of the same 3D map image The figure which shows the example of the error distribution image similarly The figure which shows the structure of the Example mounted in the image measuring machine

Explanation of symbols

DESCRIPTION OF SYMBOLS 6 ... Stage 8 ... Measurement workpiece 10 ... Illumination lamp 11 ... Light emitting element 12 ... Lattice filter 15, 15A, 15B ... Projection lens 16 ... Lattice shift mechanism 18, 24 ... Focus shift mechanism 21 ... Imaging lens 22 ... Imaging element 40 ... Measurement Head 50 ... Computer (PC)
60 ... Z-axis guide mechanism 62 ... Feed motor

Claims (21)

By observing the lattice pattern projected on the measurement object while shifting the phase from a direction different from the projection direction, the shape is obtained by analyzing the contrast of the deformed lattice image corresponding to the shape of the measurement object. In the non-contact three-dimensional shape measuring method,
A non-contact three-dimensional shape measurement method, wherein the depth and the measurement range in the depth direction are expanded by continuously shifting the focus on the projection side and the imaging side simultaneously with the phase . Inputting the measurement target image data continuously while shifting the focus and phase at a constant speed;
The non-contact three-dimensional shape measuring method according to claim 1, further comprising: processing the input data in a computer to create a three-dimensional map. Creating the three-dimensional map comprises:
Determining the fringe order from the focus center, unwrapping the phase, and calculating the absolute value of the phase;
Calculating the three-dimensional position of the intersection of the fringe order lattice plane and the imaging point epipolar line;
The non-contact three-dimensional shape measuring method according to claim 2, comprising: Creating the three-dimensional map further comprises:
Extracting a gray scale waveform of image coordinates;
Removing the offset component and the fluctuation component of the gray waveform;
Calculating a focus center;
Calculating the phase of the focus center;
The non-contact three-dimensional shape measuring method according to claim 3, comprising:   5. The non-contact three-dimensional shape measuring method according to claim 4, wherein the step of removing the offset component and the fluctuation component of the gray waveform calculates a differential waveform of the gray waveform.   5. The non-contact three-dimensional image according to claim 4, wherein the step of removing the offset component and the fluctuation component of the grayscale waveform averages the grayscale values in the vicinity of a phase shift amount ± π of the grayscale waveform. Shape measurement method.   The step of calculating the focus center calculates a frequency average value for each square waveform of the gradation change curve every n data, and adds a weighting coefficient by a coefficient corresponding to the height of the peak of the extracted waveform and averages it. The non-contact three-dimensional shape measuring method according to claim 4, wherein the non-contact three-dimensional shape measuring method is obtained.   5. The non-contact three-dimensional shape measuring method according to claim 4, wherein the step of calculating the phase of the focus center is to obtain the phase by integrating with a mother wave and performing Fourier integration. By observing the lattice pattern projected on the measurement object while shifting the phase from a direction different from the projection direction, the shape is obtained by analyzing the contrast of the deformed lattice image corresponding to the shape of the measurement object. In the non-contact three-dimensional shape measuring apparatus,
Means for projecting a grating pattern onto a measurement object while shifting the focus and phase;
Means for inputting image data of a pattern projected on the measurement object while shifting the focus;
Means for processing the input image data to create a three-dimensional map;
A non-contact three-dimensional shape measuring apparatus comprising: Means for creating the three-dimensional map;
Means for determining the fringe order from the focus center, unwrapping the phase, and calculating the absolute value of the phase;
Means for calculating the three-dimensional position of the intersection of the lattice plane of the fringe order and the epipolar line of the imaging point;
The non-contact three-dimensional shape measuring apparatus according to claim 9, comprising:   The non-contact three-dimensional shape measuring apparatus according to claim 9, further comprising means for correcting distortion of the projection optical system and the imaging optical system.   The non-contact three-dimensional shape measuring apparatus according to claim 9, wherein the projection optical system and the imaging optical system are mounted on one shift mechanism and driven in the Z-axis direction. The pattern projecting means;
A grating shift mechanism for moving the grating filter in the lateral direction;
A first focus shift mechanism for moving the lattice filter in the front-rear direction for each lattice shift mechanism;
The non-contact three-dimensional shape measuring apparatus according to claim 9, comprising: The image data input means is
The non-contact three-dimensional shape measuring apparatus according to claim 9, further comprising a second focus shift mechanism that moves the image sensor in the front-rear direction.   The non-contact three-dimensional shape measuring apparatus according to claim 9, wherein the projection lens of the pattern projection unit and the imaging lens of the image data input unit are both image side telecentric optical systems.   10. The first focus shift mechanism for moving a lattice filter by the pattern projection unit and the second focus shift mechanism for moving an image sensor by the image data input unit are driven in synchronization. The non-contact three-dimensional shape measuring apparatus described in 1.   The non-contact three-dimensional shape measuring apparatus according to claim 9, further comprising an illumination unit that is turned on in accordance with a phase shift amount of the projection pattern.   The non-contact three-dimensional shape measuring apparatus according to claim 9, wherein the pattern projecting unit and the image data input unit are integrated with a measuring head. The three-dimensional map creating means is composed of a computer,
While the computer simultaneously shifts the focus and phase for controlling the measurement head, the frame grabber for capturing the image input from the image sensor of the measurement head, the motion control board for controlling the shift mechanism of the measurement head, Creates a 3D map and software that has the function of inputting continuous images and transferring them to the main memory of the computer, the function of displaying live images corresponding to the measurement range of the measurement head, and the function of setting the measurement depth range. Function to calculate the focus center from the grayscale waveform whose amplitude fluctuates due to focus shift, the function to calculate the phase of the grayscale waveform near the focus center, the function to unwrap the phase using the focus center data, the optical system A function to correct the coordinates on the image taking distortion into account A function that calculates the intersection of the epipolar line and the lattice plane of the lattice pattern projection, calculates the three-dimensional position projected on the pixel, and the input continuous image so that it can be confirmed that the image data has been input normally 11. The software according to claim 9, further comprising software having a function of playing back, a function of displaying a created three-dimensional map, and a function of saving point cloud data of the three-dimensional map in a CAD format. Non-contact three-dimensional shape measuring device.   The non-contact three-dimensional shape measuring apparatus according to claim 9, wherein the image data input means uses an imaging optical system of an image measuring machine.   19. The measuring head is attached to the Z axis of the image measuring machine in parallel with the imaging optical system of the image measuring machine, and lattice shift and focus shift are performed by Z axis driving of the image measuring machine. The non-contact three-dimensional shape measuring apparatus described in 1.

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