JPH0498111A - Three-dimensional shape measuring device - Google Patents

Abstract

PURPOSE:To easily measure the three-dimensional shape of an organism or the like by imaging the lattice pattern formed on the surface of a measuring object for outputting a picture-image signal, and while shifting the phase of the lattice pattern by a prescribed amount, by analizing the measured values of the three-dimensional shape. CONSTITUTION:Between a reference point for measuring a three-dimensional shape and the center of a light source 6, and on the optical axis connecting the center of the light source 6 and that of the reference point, a lattice plate 5 is provided, and a condenser lens 2 for concentrating the light transmitted through the lattice plate 5 is arranged. And the lattice pattern formed on the surface of a measuring object 20 is output as a picture-image signal via an imaging means 4, and the phase of the lattice pattern is shifted by means of a lattice- plate moving means 1 by a prescribed amount in the perpendicular direction to the optical axis. Then, the picture-image signals output by the imaging means 4 are stored in a picture- image-signal taking-in/storing means 14 with regard to a plurality of phases so as to synchronize with the lattice-plate moving means 1, and the plurality of picture-image signals are analized by an analizing means 16 to calculate the measured values of the three-dimensional shape of the measuring object 20. Thus, the three-dimensional shape of the surface of an organism can be promptly measured with an inexpensive device.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for measuring the three-dimensional shape of the surface of an object to be measured.
The present invention relates to a dimensional shape measuring device, and particularly to a three-dimensional shape measuring device that can measure the fine three-dimensional shape of the surface of a living body without any trouble even if the object to be measured is a living body.

If minute three-dimensional shapes such as wrinkles on the surface of living organisms can be measured,
For example, it becomes possible to objectively evaluate the effectiveness of anti-wrinkle creams. However, if the measurement target is a living body, there are various constraints on the measurement environment as described below, and the depth is several tens to hundreds of meters. In order to detect fine wrinkles of mn and measure their shape, a resolution of up to 10 degrees is required.

The present invention refers to a three-dimensional shape measuring device that can perform measurements that satisfy required specifications even under such a restricted measurement environment.

[Conventional technology]

Three-dimensional shape measurement methods are broadly divided into contact methods, in which the shape is measured with a part of the measuring device in contact with the object to be measured, and non-contact methods, in which measurements are made without contact using light, etc. .

For example, in the contact type, the stylus is moved at each measurement point on the surface of the object until the tip of the stylus touches the object, and the amount of movement is taken as the measurement value. In this case, there are disadvantages such as it is difficult to determine the contact point correctly and it requires a huge amount of measurement time, so it cannot be used for measuring biological surfaces, but the measurement principle is extremely simple and highly accurate. This method 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 optical cutting method is a measurement method in which a slit-shaped laser beam is projected onto a measurement target, observed from an angle different from the projection direction, and the three-dimensional shape is determined from the deformed state of the slit. This method has the disadvantage that it takes some time to measure the entire object because it measures each cross section while moving the slit light. Furthermore, the measurement accuracy is -i-like accuracy (approximately 0.5%) of image measurement.

The measurement principle of the grid pattern projection method is published in the Journal of Precision Engineering,
It is described in Sputum, (3), pp422-426, and in order to simultaneously project a plurality of Surin I of the above-mentioned photosection method, a slide with a grid pattern drawn thereon is projected by a projector. It is distinctive in that the central stripe, which serves as a reference for numbering the projected grid, is thicker than the other stripes. The method of measuring objects has the advantage of being able to grasp the shape of an object in a short time and having a simple device configuration (only a projector and camera), but it becomes difficult to recognize stripes when the shape is complex or there are patterns on the surface. There is a drawback that it cannot be measured. Furthermore, since measurement points can only be obtained on a grid, there is also the problem that the density of measurement points becomes coarse.

The accuracy of the measured value is about 0.5%, similar to the optical sectioning method.

In the fringe scanning method, light stripes with a sinusoidal intensity distribution are projected onto the measurement target with three or more different phases of the stripes, and images are taken at each of the three or more phases from a direction different from the projection direction. It is used to analyze and obtain measured values. Light fringes having a sinusoidal intensity distribution necessary for measurement are formed by interfering laser beams, and the phase of the fringes is changed by changing the optical path difference of the interference waves. Furthermore, since the interferometer requires precision in the optical path length on the order of the wavelength of the light, the measurement is performed on a vibration isolating device.

This method has the advantage that measurement points can be obtained over the entire stripe, rather than just on the line of maximum intensity, as in the grid pattern projection method.

By the way, when the measurement target is a living body, the following measurement environment or condition constraints may be considered.

■ Even if the intensity is not strong, it is dangerous to irradiate laser light with concentrated energy, especially near the eyes, so laser light cannot be used.

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

■ Measurement must be completed within a short period of time without being affected by fluctuations in the living body.

(2) As mentioned above, in order to detect small wrinkles with a depth of several tens to 100 μm, a depth resolution of about 10 μm is required.

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

Taking these constraints into consideration, firstly, the optical cutting method uses laser light and takes too long to measure.
It is not an appropriate method for measuring dimensional shapes. Although the lattice pattern projection method satisfies the conditions of ■■, it is technically difficult to increase the resolution because the depth resolution is determined by the roughness of the pixels, and it is also inappropriate in terms of ■. . Although the fringe scanning method satisfies the conditions described in ■■, it takes some time to measure because the optical path length must be changed accurately on the order of the wavelength of the light, and it is difficult to measure living organisms because it uses laser light. cannot be applied to

On the other hand, the present inventor's Journal of Precision Engineering, Mutual 5. (10)
The lattice pattern projection method that introduces fringe scanning described in pages 1817 to 1822.1989 will be described in detail later, but according to the lattice pattern projection method, a lattice consisting of a plurality of parallel slits is projected onto the measurement target, and an image obtained by photographing it. This method is based on the discovery that the intensity distribution in can be regarded as a sine wave, and satisfies the above-mentioned conditions, making it a promising method for measuring the three-dimensional shape of a living body.

[Problem to be solved by the invention]

However, according to the device configuration described in the above-mentioned paper, the measurement target is fixed with respect to the measurement coordinate axis and measurements are performed, making it possible to measure a portion of a relatively large target such as the human body. Therefore, the condition (■) cannot be satisfied. Furthermore, there is no means to continuously measure a plurality of images having different phases of fringes in a short period of time, and the condition (2) cannot be satisfied.

Therefore, an object of the present invention is to improve the method described in the above-mentioned paper and to propose a three-dimensional shape measuring device suitable for measuring the three-dimensional shape of a living body.

[Means for solving the problem] The three-dimensional shape measuring device of the present invention that achieves the above-mentioned object has the following features:
A grating plate placed between a light source that generates visible light and a reference point for three-dimensional shape measurement on an optical axis connecting the center of the light source and the reference point, A grating plate has a plurality of slits formed at a constant pitch that transmit at least a portion of the slit, and the visible light transmitted through the grating plate is focused to form a grating pattern on the surface of the measurement target near the reference point. A condensing lens for imaging, and a condenser lens installed at a position where the grating pattern can be imaged when the grating pattern is imaged on a plane including the reference point, and the grating pattern formed on the surface of the measurement object is imaged. a grating plate moving means for moving the grating plate by a predetermined amount in a direction perpendicular to the optical axis in order to shift the phase of the grating pattern by a predetermined amount; image signal capture storage means for capturing and storing image signals output by the imaging means for a plurality of phases in synchronization with the grid plate moving means; and analysis of the plurality of image signals stored in the image signal capture storage means. The present invention is characterized by comprising an analysis means for calculating a three-dimensional shape side settlement of the measurement object.

[For production]

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 this grid pattern can be imaged, the object to be measured can be placed near this reference point and the depth of focus of the lens can be adjusted. Since measurement can be performed immediately if placed within the range, it is easy to measure objects such as living organisms that cannot be accurately fixed to a desired position on a sample stage. Furthermore, since the grating plate only needs to be moved by a distance on the order of 0.1 mm, as will be described later, it can be moved quickly using a moving means such as a motor, and multiple objects with different phases can be moved in a relatively short period of time. Images can be obtained, and it is also possible to measure objects with fluctuations such as living bodies.

〔Example〕

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

The light from the projector 6 passes through the grating plate 5 and becomes a plurality of equally spaced slit-shaped light beams, which are condensed by the projector lens 2 to form a grating pattern image on the object to be measured. The lattice plate 5 is a glass plate with a lattice pattern formed by photolithography. The COD camera 4 is installed at a position where it can photograph the lattice pattern imaged on the object to be measured. Image signals output by the CCD camera 4 are stored in the image input/output device 14 according to instructions from the computer 16, and then input to the computer 16. The grating moving motor 1 moves the grating plate 5 by a drive current output by a motor drive device 15 based on a control signal from a computer 16.
It is designed to move the grating plate 5 in a direction perpendicular to the optical axis in units of length corresponding to 1/4 of the pitch of the upper grating. The projector lens 2 also has a motor drive device 1.
The projector lens can be moved in the optical axis direction by a projector lens moving motor 3 driven by a projector lens. The projector 6, the grating movement motor 11, the projector lens movement motor 3, and the CCD camera 4 are fixed at predetermined positions on a front-back movement stage 7, and the front-back movement stage 7 is a left-right movement stage. The stage 8 for horizontal movement is placed on the stage 9 for vertical movement. Therefore, the position of the entire device is the knobs 10, 11 .
It can be adjusted by manually adjusting 12. Also,
A drive means such as an electric motor may also be provided and adjustable by control signals from the computer 16.

Next, a method for adjusting the optical system will be explained. As shown in FIG. 2, a reference surface 32 on which a cross pattern 30 is drawn is placed perpendicularly to the optical axis so that the intersection of the crosses coincides with the optical axis and the horizontal line of the cross is horizontal. The intersection of the crosses on this reference plane 32 becomes the reference point for three-dimensional shape measurement. Next, computer 1
6 to move the projector lens 2 back and forth in the optical axis direction via the motor drive device 15 and the projector lens moving motor 3 to create a grating pattern on the reference surface 32 ( (not shown), and then adjust the inclination of the grid plate 5 so that the grid is parallel to the horizontal lines of the cross pattern 3o. Reference plane 3 with CCD camera 4
The cross pattern 3o on 2 is photographed, and its image 30' is continuously displayed together with the cross cursor 34 on the display of the computer 16. In this state, the focus of the lens of the CCD camera 4 is adjusted to make the image 30' clear, and the direction and position of the CCD camera 4 are adjusted to match the image 30' with the cursor 34. Furthermore, at this time,
Reference point, principal point of projector lens 2, and CCD camera 4
The triangle connecting the principal point of the lens is the projector lens 2.
Arrange them so that they form a right triangle with the principal point of as the right angle vertex.

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

For the measurement, the person to be measured is fixed by placing, for example, the head and chin on a predetermined table (not shown) as shown in FIG. Note that, for example, if the part to be measured is the outer corner of the eye, this table is arranged so that the outer corner of the subject's eye is near the reference point, and by adjusting the knobs 10 and 1112, individual differences in size can be accommodated.

Next, a grid pattern is projected onto the measurement target area, and it is
Take pictures with CD camera 4. At this time, if the depth of focus of the projector lens 2 is insufficient and the grating image becomes blurred, the position of the projector lens 2 may be finely adjusted to focus using commands from the keyboard of the computer 16.

When these preparations are completed, a measurement start command is input from the keyboard of the computer 16, and a grid movement signal is output from the computer 16, and the grid plate 5 is moved in the vertical direction via the motor drive device 15 and the grid movement morph 1. An image signal is captured every time the grating plate 5 moves by a distance of 174 times the grating pitch, and the phase of the grating changes to 174 times.
The image data of four images shifted by each other is input.

Computer 16 is the aforementioned Journal of Precision Engineering, 55° (10
), ρ1817-1822.According to the method described in 1989, a measured value of a three-dimensional shape is calculated from manually generated image data and constants. An outline of each method is explained below.

According to the fringe scanning method, when fringes with a sinusoidal intensity distribution are projected onto a measurement target and observed from a direction different from the projection direction, the phase of the fringes is modulated according to the shape of the measurement target. Ru. The modulated bone or phase amount α at each point (x, y) on the two-dimensional child surface to be observed is determined by the intensity I at each point (x, y) on the two-dimensional child surface.

+ Il+ T2+ Calculated from 13. However, 10 to I3 are the intensities at each point (x, y) when the phase of the projected fringe is shifted by 90°.

Note that in this example, α is calculated from the intensities measured for four different phases, but it is also possible to measure more phases and then calculate α, which will improve the accuracy. improves.

In the general fringe scanning method, as mentioned above, fringes with this sinusoidal intensity distribution are obtained by interfering with laser light, and changes in the phase of the fringes change the optical path length of the interference wave to the wavelength of the light. It is obtained by changing on the order of .

On the other hand, according to the above-mentioned paper by the present inventor, the data obtained by projecting a grating pattern, capturing the image with a CCD camera, and A/D converting it is almost a sine wave distribution, and the difference from the sine wave is due to the fundamental frequency. It was experimentally confirmed that the period was twice as long, and it was further shown that this difference did not affect the measurement results.

It is also believed that if a grating plate with an appropriate pattern shape and shading is used, it is possible to obtain fringes with a perfect sinusoidal intensity distribution.

Using the value of α calculated as described above, each point (x
, y), the three-dimensional coordinate value x of the point on the measurement target surface corresponding to
, y, z are X=-sx (2) Y=
b+s (-c-ycosφ) (3) Z=a
+s (-d+ysinφ) (4) s=(-
b cos θ) / u (5) θ−t
an-' (pα/a) (6) u-
(-c-ycosφ) cosθ + (-d + ysinφ) sinθ (7)φ
-jan"'
(8) c=am
(9) d = b m
It can be calculated using (10). However, as mentioned 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 CCD camera 4 lens, and m is the length of the image and the distance on the reference plane. to the real length, p is the pitch of the grating projected onto the reference plane.

For example, when using a grating plate 5 with a pitch of about 1/3 mm, the grating plate 5 is moved in increments of 1/12 mm, and the grating plate 5 can be moved accurately and quickly with the grating moving motor l, allowing the grating plate 5 to be moved accurately and quickly. We were able to reduce the restraint time to less than 1 second.

Figures 3 to 6 are copies of the results obtained by directly outputting the results of measurements for each part of the living body in blocks in the form of three-dimensional plots.

Figure 3 shows the palm of the hand, Figure 4 shows the surface of the nail side of the first joint of the thumb, Figure 5 shows the outer corner of the eye of a subject with shallow wrinkles on the outer corner of the eye,
FIG. 6 shows the measurement results for the outer corner of the eyes of a subject with deep wrinkles.

〔Effect of the invention〕

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

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram for explaining the method of adjusting the optical system in the device shown in FIG. 1, and FIGS. 3 of each part of the living body
A diagram showing the results of measuring a dimensional shape. In the figure, ■... Motor for moving grid, 2... Projector lens, 3... Motor for moving projector, 4... CCD camera, 5... Grid plate, 6...
·projector. (1R)

Claims (1)

[Claims] 1. A light source (6) that generates visible light, and a center of the light source (6) and the reference point between the light source (6) and a reference point for three-dimensional shape measurement. a lattice plate (5) placed on the connecting optical axis, the lattice plate (5) having a plurality of slits formed at a constant pitch through which at least a portion of the visible light is transmitted; a condensing lens (2) that focuses the visible light that has passed through the reference point and forms a grating pattern on the surface of the measurement object (20) near the reference point; an imaging means (4) installed at a position where the grating pattern can be imaged when imaged, and configured to image the grating pattern formed on the surface of the measurement object (20) and output an image signal; a grating plate moving means (1) for moving the grating plate (5) by a predetermined amount in a direction perpendicular to the optical axis to shift the phase of the grating plate (5) by a predetermined amount; and an image output by the imaging means (4). Image signal acquisition storage means (14) for capturing and storing signals for each of a plurality of phases in synchronization with the grating plate moving means (1); and a plurality of image signals stored in the image signal acquisition and storage means (14). A three-dimensional shape measuring device characterized by comprising: an analysis means (16) for calculating a three-dimensional shape measurement value of the measurement object (20) by analyzing the three-dimensional shape measurement value of the measurement object (20).