JP3157001B2 - 3D shape measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a three-dimensional shape measuring apparatus for measuring the three-dimensional shape of the surface of a measurement object, and particularly, even if the measurement object is a living body. The present invention relates to a three-dimensional shape measuring device capable of measuring a fine three-dimensional shape of the surface.

If a fine three-dimensional shape such as wrinkles on a living body surface can be measured, for example, the effect of the wrinkle removing cream can be objectively evaluated. However, if the measurement target is a living body,
The measurement environment has various restrictions as described below, and a resolution of up to 10 μm is required for detecting fine lines having a depth of several tens to 100 μm and measuring the shape.

The present invention refers to a three-dimensional shape measuring apparatus capable of performing measurement satisfying required specifications even under such a limited measurement environment.

[Conventional technology]

The three-dimensional shape measuring method is roughly classified into a contact type in which the shape is measured in a state where a part of the measuring device is in contact with an object to be measured and a non-contact type in which non-contact measurement is performed using light or the like. .

In the contact type, for example, the stylus is moved at each measurement point on the surface of the measurement object until the tip of the stylus comes into contact with the measurement object, and the amount of movement is used as a measurement value, and the measurement object is a soft object. In the case of, it is difficult to determine the contact point correctly and has drawbacks such as requiring an enormous amount of measurement time, it can not be adopted for the measurement of the biological surface, but because the measurement principle is extremely simple and high accuracy, This is a method that can serve as a standard for evaluating the accuracy of other measurement methods.

Various non-contact methods using light have been proposed and put into practical use, and typical examples include a light cutting method, a grid pattern projection method, and a fringe scanning method.

The light cutting method is a measurement method in which a slit-shaped laser beam is projected onto a measurement object, observed from an angle different from the projection direction, and a three-dimensional shape is grasped from a deformed state of the slit. This method has the disadvantage that it takes some time to measure the entire measurement target because measurement is performed for each section while moving the slit light. The measurement accuracy is the general accuracy of image measurement (about 0.5%).

The measurement principle of the grating pattern projection method is described in the Journal of the Japan Society of Precision Engineering, 53 , (3), pp. 422-426. Is projected by a projector. The feature is that the reference central stripe is thicker than the other stripes in order to number the projected grid. This measurement method has the advantage that the shape of the object can be grasped in a short time and the device configuration is simple (only the projector and the camera). However, when there are complicated shapes or patterns on the surface, it becomes difficult to recognize the stripes. Therefore, there is a disadvantage that measurement cannot be performed. Further, since the measurement points can be obtained only on the grid, there is a problem that the density of the measurement points becomes coarse. The accuracy of the measured value is about 0.5% as in the case of the cutting method.

In the fringe scanning method, light fringes having a sinusoidal intensity distribution are
The projection is performed on the measurement object while changing the phase of the fringe in three or more ways, and the image taken for each of the three or more phases from a direction different from the projection direction is analyzed to obtain a measured value. Light fringes having a sinusoidal intensity distribution required for measurement are formed by causing laser light to interfere, and the phase of the fringes is changed by changing the optical path difference of the interference wave. In addition, since the accuracy of the optical path length in the order of the wavelength of light is required in the interferometer, the measurement is performed on the vibration isolator. This method has an advantage that the measurement value can be obtained over the entire fringe, not only on the line having the maximum intensity as in the case of the grid pattern projection method.

By the way, when the measurement target is a living body, the following restrictions on the measurement environment or conditions can be considered.

For example, it is dangerous to irradiate a laser beam that concentrates energy even if the intensity is not high, especially to irradiate the vicinity of the eyes, so that the laser beam cannot be used.

It is not possible to cut a sample into an arbitrary size and set it on a sample stage.

The measurement must be completed in a short time without being affected by the fluctuations of the living body.

As described above, in order to detect fine lines with a depth of several tens to 100 μm, a resolution with a depth of about 10 μm is required.

In order to accurately grasp the three-dimensional shape of a living body, not only the resolution in the depth but also the resolution in the spreading direction is required to some extent.

Considering these restrictions, first, the light section method is not an appropriate method for measuring the three-dimensional shape of a living body because it uses a laser beam and takes too much measurement time. Although the grid pattern projection method satisfies the condition (1), it is technically difficult to increase the resolution because the depth resolution is determined by the roughness of the pixels. The fringe scanning method satisfies the following conditions, but it takes some time to measure because the optical path length must be changed with high accuracy on the order of the wavelength of light, and the measurement of living organisms requires the use of laser light. Not applicable.

On the other hand, the journal of the Japan Society of Precision Engineering, 55 , (10), p18
17 ~ 1822, 1989 grid pattern projection method that introduces the fringe scanning, which will be described in detail later, according to the grid pattern projection method, a grid consisting of a plurality of parallel slits is projected on a measurement target, and an image obtained by capturing the image. Is based on the discovery that the intensity distribution at can be regarded as a sine wave, which satisfies the above-mentioned conditions, and is promising as a method for measuring the three-dimensional shape of a living body.

[Problems to be solved by the invention]

However, according to the apparatus configuration described in the above-mentioned paper, the measurement is performed with the measurement target fixed to the coordinate axis of the measurement, and the measurement of a part of a relatively large object such as a human body is realized. Cannot satisfy the condition of In addition, there is no means for continuously measuring a plurality of images having different fringe phases in a short time, and the above condition cannot be satisfied.

Accordingly, an object of the present invention is to propose a three-dimensional shape measuring apparatus suitable for measuring a three-dimensional shape of a living body by improving the method described in the above-mentioned paper.

[Means for solving the problem]

A three-dimensional shape measuring apparatus according to the present invention that achieves the above object connects a center of the light source and the reference point between the light source that generates visible light and the reference point of the three-dimensional shape measurement. A grating plate placed on the optical axis, a grating plate formed with a plurality of slits that transmit at least a part of the visible light at a constant pitch, and condensing visible light transmitted through the grating plate. ,
A condenser lens that forms a grid pattern on the surface of the measurement target near the reference point, and is installed at a position where the grid pattern can be imaged when the grid pattern is formed on a plane including the reference point, Imaging means for imaging a grid pattern formed on the surface of the measurement object and outputting an image signal; and moving the grid plate in a direction perpendicular to the optical axis to shift the phase of the grid pattern by a predetermined amount. A grid plate moving means for moving the image signal by a predetermined amount; an image signal taking / storing means for taking and storing image signals output from the imaging means for a plurality of phases in synchronization with the grid plate moving means; Analysis means for analyzing a plurality of image signals stored in the embedded storage means and calculating a three-dimensional shape measurement value of the measurement object.

(Operation)

For example, if a grid pattern is imaged on a plane placed at a reference point, and the position of the imaging means is adjusted so that the grid pattern can be imaged, the measurement object can be moved near the reference point with the depth of focus of the lens. Since the measurement can be performed immediately if it is located within the range, it is easy to measure an object such as a living body that cannot be accurately fixed to a desired position on a sample table.
Further, since the grating plate may be moved at a distance on the order of about 0.1 mm, for example, as described later, it is possible to move quickly by moving means such as a motor, and a plurality of images having different phases can be obtained in a relatively short time. Obtained, it is possible to measure a subject having fluctuation such as a living body.

〔Example〕

FIG. 1 is a diagram showing a schematic configuration of an embodiment of a three-dimensional shape measuring apparatus according to the present invention.

The light from the projector 6 passes through the grid plate 5 to form a plurality of equally spaced slit-like luminous fluxes, is condensed by the projector lens 2, and forms a grid pattern on the measurement target. The grid plate 5 is formed by forming a grid pattern on a glass plate by transfer plate making. The CCD camera 4 is installed at a position where the lattice pattern formed on the object to be measured can be photographed. The image signal output from the CCD camera 4 is transmitted to the computer 16
Is stored in the image input / output device 14 in accordance with a command from
Input to the computer 16. The grid moving motor 1
A driving current output from the motor driving device 15 based on a control signal from the computer 16 causes the grid plate 5 to move in a direction perpendicular to the optical axis in units of a length corresponding to / 4 of the pitch of the grid on the grid plate 5. Designed to move to The projector lens 2 can also be moved in the optical axis direction by a projector lens moving motor 3 driven by a motor driving device 15. The projector 6, the grid moving motor 1, the projector lens moving motor 3, and the CCD camera 4 are fixed at predetermined positions on a front-rear movement stage 7, and the front-rear movement stage 7 is a left-right movement stage. The stage 8 for horizontal movement is mounted on a stage 9 for vertical movement. Therefore, the position of the entire device can be adjusted by manually adjusting the knobs 10, 11, 12. In addition, a drive unit such as an electric motor may be provided so that the drive unit can be adjusted by a control signal from the computer 16.

Next, a method of adjusting the optical system will be described. As shown in FIG. 2, the reference plane 32 on which the cross pattern 30 is drawn is placed perpendicular to the optical axis so that the intersection of the cross matches the optical axis and the horizontal line of the cross is horizontal. The intersection of the crosses of the reference plane 32 is a reference point for three-dimensional shape measurement. Next, the keyboard (not shown) on the computer 16 is operated to move the projector lens 2 back and forth in the optical axis direction via the motor driving device 15 and the projector lens moving motor 3 so as to move the grid pattern on the reference plane 32. (Not shown) and the inclination of the grid plate 5 is adjusted so that the grid is parallel to the horizontal line of the cross pattern 30. Cross pattern 3 on reference plane 32 with CCD camera 4
0 is photographed, and the image 30 'is continuously displayed on the display of the computer 16 together with the cross cursor 34. In this state, the image 30 'is clarified by adjusting the focus of the lens of the CCD camera 4, and the direction and the position of the CCD camera 4 are adjusted so that the image 30' matches the cursor 34.
At this time, the reference point and the principal point of the projector lens 2 are
The triangle connecting the principal point of the lens of the CCD camera 4 is arranged to be a right triangle with the principal point of the projector lens 2 as a vertex of a right angle.

Thus, the adjustment of the optical system is completed. At this time, the distance a between the reference point and the principal point of the projector lens 2, the distance b between the principal point of the projector lens 2 and the principal point of the lens of the CCD camera 4, The ratio m between the length of the cross pattern 30 'and the actual length of the cross pattern 30 and the pitch p of the grid projected on 32 are measured and input to the computer 16.

In the measurement, for example, the head of the person to be measured is placed on a predetermined table (not shown) and fixed as shown in FIG. In addition, this table is arranged such that, for example, if the measurement target portion is the outer corner of the eye, the outer corner of the eye of the measurement target is near the reference point, that is, by adjusting 10, 11, 12 to correspond to individual differences in dimensions. .

Next, project the grid pattern on the measurement target site, and
Take a picture with the CCD camera 4. At this time, if the depth of focus of the projector lens 2 is not sufficient and the image of the grid is blurred, the position of the projector lens 2 may be finely adjusted by a command from the keyboard of the computer 16 to achieve focus. Once these preparations are complete, the computer
When a measurement start command is input from the 16 keyboards,
A lattice movement signal is output from the computer 16, and the lattice plate 5 moves in the vertical direction via the motor driving device 15 and the lattice movement motor 1. Each time the grating plate 5 moves by a distance of 1/4 of the grating pitch, an image signal is captured, and the phase of the grating is reduced by 1/4.
Four pieces of image data that are deviated from each other are input.

Computer 16 is described in the aforementioned Journal of Precision Engineering, 55 , (10), p.
According to the method described in 1817 to 1822, 1989, a measured value of a three-dimensional shape is calculated from input image data and constants. The outline of this method is described below.

According to the fringe scanning method, when a fringe having a sinusoidal intensity distribution is projected onto a measurement target and observed from a direction different from the projection direction, the phase of the fringe is modulated according to the shape of the measurement target and observed. You. The modulation amount at each point (x, y) on the two-dimensional plane to be observed, that is, the phase amount α is , The intensity I ₀ , I ₁ , I at each point (x, y) on the two-dimensional plane
₂ , calculated from I ₃ . Here, I _{0 to} I ₃ are the intensity at each point (x, y) when the phase of the stripe to be projected is shifted by 90 °. In this example, α is calculated from the intensities measured for the four types of phases. However, it is also possible to measure α for more phases and calculate α based on the measured values. improves.

In the general fringe scanning method, as described above, a laser beam is caused to interfere to obtain a fringe having this sinusoidal intensity distribution, and the phase change of the fringe is obtained by changing the optical path length of the interference wave to the wavelength of the light. It is obtained by changing the order.

On the other hand, according to the above-mentioned paper by the present inventor, data obtained by projecting a lattice pattern, photographing with a CCD camera, and performing A / D conversion is almost close to a sinusoidal distribution, and the difference from the sinusoidal wave is the fundamental frequency. It was experimentally confirmed to have twice the period, further indicating that this difference did not affect the measurement results.

Further, it is considered that a fringe having a perfect sine wave intensity distribution can be obtained by using a grid plate having an appropriate pattern shape and shading.

Using the value of α calculated as described above, the three-dimensional coordinate value of the point on the surface to be measured corresponding to each point (x, y)
X, Y and Z are as follows: X = −sx (2) Y = b + s (−cy cosφ) (3) Z = a + s (−d + y sinφ) (4) s = (− b cosθ) / u (5) θ = Tan ^-1 (pα / a) (6) u = (− cy cosφ) cosθ + (− d + y sinφ) sinθ (7) c = am (9) d = bm (10) However, as described above, a is the distance from the reference point to the principal point of the projector lens 2, b is the distance from the principal point of the projector lens 2 to the principal point of the lens of the CCD camera 4, and m is the length of the image and the reference plane. Is the pitch of the grating projected on the reference plane.

When the pitch of the grid plate 5 is, for example, about 1/3 mm, the movement is 1/12 mm, and the grid moving motor 1 can move the grid plate 5 accurately and quickly.
The restraint time of the object to be measured could be made within 1 second.

FIG. 3 to FIG. 6 are copies of the results obtained by directly outputting the results measured for each part of the living body in the form of a three-dimensional plot with a plotter.

FIG. 3 shows the palm, FIG. 4 shows the nail surface of the first joint of the thumb, FIG. 5 shows the corner of the eye of a subject with shallow wrinkles at the corner of the eye, and FIG. 6 shows the corner of the eye of the subject with a deep wrinkle. It is a measurement result about a part.

〔The invention's effect〕

As described above, according to the present invention, the three-dimensional shape of the surface of the living body, which has conventionally been impossible to measure for various reasons,
It became possible to measure quickly with an inexpensive device.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, FIG. 2 is a view for explaining a method of adjusting an optical system in the apparatus of FIG. 1, and FIGS. 3 to 6 are based on the apparatus of FIG. 3 of each part of the living body
The figure showing the result of having measured a dimensional shape. In the drawing, 1 ... a grid moving motor, 2 ... a projector lens, 3 ... a projector moving motor, 4 ... a CCD camera, 5 ... a grid plate, 6 ... a projector.

Continuing on the front page (56) References Ryohei Komatsuhara, et al., “Grating pattern projection method using fringe scanning”, Japan Society of Precision Engineering, Japan Society for Precision Engineering, October 5, 1989, Vol. 55, No. 10 (Vol. 658), pp. 1817-1822. Toru Yoshizawa, et al. “Automatic measurement of three-dimensional shape by grid pattern projection”, Journal of Precision Engineering, Japan Society of Precision Engineering, March 5, 1987, Vol. 53, No. 3 (Vol. 627) Pp. 422-426.

Claims (1)

(57) [Claims] An optical axis connecting a center of the light source (6) and the reference point between the light source (6) for generating visible light and a reference point for three-dimensional shape measurement. A grid plate (5) placed thereon, wherein a plurality of slits for transmitting at least a part of the visible light are formed at a constant pitch, and the grid plate (5) is transmitted through the grid plate (5). A condenser lens (2) for condensing visible light to form a grid pattern on the surface of the measurement object (20) near the reference point; and a grid pattern formed on a plane including the reference point. An imaging means (4) which is installed at a position where the grid pattern can be imaged and which picks up the grid pattern formed on the surface of the measuring object (20) and outputs an image signal; The lattice plate (5) is phase-shifted by a predetermined amount, and the fluctuation of the surface of the outer corner of the eye forming the measurement object (20) is measured. A grating plate moving means (1) for moving a predetermined amount in a direction perpendicular to the optical axis at a speed that does not substantially affect the fixed result; and an image signal output by the imaging means (4). An image signal acquisition and storage means (14) for acquiring and storing a plurality of phases in synchronization with the lattice plate moving means (1), and analyzing a plurality of image signals stored in the image signal acquisition and storage means (14). Analysis means (16) for calculating a three-dimensional shape measurement value of the measurement object (20).
A three-dimensional shape measurement device capable of measuring the shape of the outer corner of the eye.