JPH11211433A - Method and system for measuring surface shape of molded article - Google Patents

Abstract

(57) [Problem] To provide a measuring method and a measuring system capable of measuring the surface shape of a three-dimensional molded product easily and in a short time without contacting the molded product, with any sensitivity. A molded article (1) is mounted on a mounting table (2), and a semi-transparent white plastic ball (3) is provided between the molded article (1) and a surrounding incandescent lamp (4). Then, a light beam is made incident on the surface of the molded article 1, and the intensity of the linearly polarized light in the specularly reflected light is measured by the CCD camera 6 through the polarizing film 5 over the entire polarization angle, and a straight line having the minimum value Imin is obtained. The plane of polarization of the polarization component is defined as the plane of incidence. Further, the incident angle Ψ is calculated from the maximum value Imax and the minimum value Imin, and the direction forming the angle Ψ with the traveling direction of the reflected light in the incident surface is determined on the surface of the molded article 1 corresponding to the pixel of the CCD camera 6. It is calculated as the normal direction of the measurement site.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a system for measuring the surface shape of a molded article, and more particularly, to the method of measuring the surface shape of a three-dimensional molded article without contacting the molded article.
Moreover, regardless of the size of the molded product, with any sensitivity,
The present invention relates to a measurement method and a measurement system that can easily measure.

[0002]

2. Description of the Related Art As a method for measuring the surface shape of a molded article without contacting the molded article, an optical measuring method is widely used.

[0003] Such optical surface shape measuring methods can be broadly classified into point measuring methods and surface measuring methods.

The point measuring method is a method of measuring a three-dimensional shape by measuring the size and depth of each point of an object.
An example is a triangulation method. Among these point measurement methods, the optical probe method is used particularly for optical surface roughness measurement because the sensitivity of an optical minute displacement sensor for an optical pickup is extremely high.

[0005] The optical probe method can be further classified into a critical angle method, an astigmatism method, a knife edge method, a heterodyne method, and the like. In any of these methods, a coherent incident light beam is applied to the surface of a molded article to be measured. The reflected light is detected, and the surface shape of the molded article is calculated from the reflected light. The sensitivity of the optical probe method is extremely high (for example, a sensitivity of the order of 10 ° is obtained), and therefore, it is a method suitable for measuring the surface roughness of a minute component. However, since the measurement sensitivity cannot be adjusted arbitrarily, even when applied to the measurement of the surface shape of a large article, an optical system for connecting an extremely small light spot corresponding to the high sensitivity and this optical system are used. It requires a long measurement time to scan the spot, which is extremely uneconomical and inefficient. Therefore, these methods are not suitable for measuring the surface shape of a large article.

In the triangulation method, a coherent laser beam is projected onto an object, a bright point appearing on the surface of the object when observed from a specific observation position is observed, and the coordinates of the bright point are calculated based on the principle of triangulation. This is a calculation method and is used to measure the surface shape of large objects. However, since this method also requires scanning with a small light beam, it requires a long measurement time for the scanning and is inefficient.

On the other hand, the surface measurement method is a method of directly obtaining contour lines of an object in the form of a fringe image, and is a method of obtaining a shape by performing fringe analysis based on this contour figure. As surface measurement methods, interferometry, holographic interferometry, light sectioning, moire topography, stereo method, and the like are known. Of these, interferometry, moire topography, and stereo method are widely used. .

[0008] The interferometry is a method of measuring a mirror surface shape using the principle of interference of light waves. Light from a light source is divided and one of the divided light is applied to an object to be measured. This method is a method of creating an interference fringe by superimposing it on the reference wave, and calculating the contours from the interference fringe to obtain the surface shape. Since this method has a sensitivity of about 10 to 10 nm, it is suitable for measuring the surface shape of a minute component such as a precision processed product. However, the necessity of forming the interference fringes requires a coherent light source and an accurate optical alignment that does not allow slight vibration. Also,
Since the sensitivity depends on the pitch of the interference fringes and the measurement range is limited by the size of the optical system, it is not suitable for measuring a large article and is uneconomical.

The moire topography is a method of measuring a surface shape by arranging a light source and a linear grating, and is a simple method in that measurement can be performed with an incoherent light source.
It is suitable for measuring the surface shape of large objects and human bodies. However, since the measurement range and sensitivity are limited by the size of the linear grating, it is impossible to perform measurement at an arbitrary sensitivity. This sensitivity and range can be improved to some extent by using a projection optical system, but the moire fringes obtained by the moire topography method do not indicate the height of the surface to be measured at equal intervals, Its sensitivity is limited.

[0010]

SUMMARY OF THE INVENTION The present invention has been made based on such a background.
This is a non-contact type surface shape measurement method that belongs to the point measurement method. The surface shape of a three-dimensional molded product can be easily adjusted without any contact with the molded product and with any sensitivity regardless of the size of the molded product. It is another object of the present invention to provide a measurement method and a measurement system capable of performing measurement in a short time.

[0011]

In the meantime, it is known that in the specular reflection phenomenon on the surface of an object such as a molded product, the reflectance varies depending on the plane of polarization of an incident light beam. That is, the maximum value of the reflectance is when the incident light has a plane of polarization (that is, in the case of s-polarized light) orthogonal to the plane of incidence (the plane to which the traveling direction of the incident light and the normal of the object surface belong), and The value is given if the incident ray has a plane of polarization in the plane of incidence (ie,
p-polarized light). And this difference in reflectance is
As it is, it is reflected on the intensity of the reflected light.

For this reason, when random polarized light (light having no plane of polarization, such as natural light or room light) is used as incident light, the maximum value of the intensity of the linearly polarized light component contained in the specularly reflected light is used. By detecting the plane of polarization of the linearly polarized light component showing Imax or the plane of polarized light of the linearly polarized light component showing the minimum value Imin, the incident surface can be known.

The ratio between the maximum value Imax and the minimum value Imin depends on the angle of incidence, and they have the following relationship.

(Equation 3) (Where n is the refractive index of the molded product and ρ is the degree of polarization of the reflected light.)

For this reason, it is possible to calculate the incident angle by solving the above equation. In the specular reflection phenomenon, it is known that the incident angle and the reflection angle are equal. Therefore, in the incident plane, the direction forming the calculated incident angle with the traveling direction of the reflected light is the surface of the molded article. , Ie, the gradient of the surface of the molded article.

The present invention has been made based on such findings. That is, the invention according to claim 1 divides the surface of a molded article having a known refractive index n into a measurement area having a small area, irradiates the measurement area with an incident light beam, and is specularly reflected at the measurement area surface. The intensity of the linearly polarized light component in the reflected light is measured over the entire polarization plane, the maximum value Imax and the minimum value Imin of the intensity on the entire polarization plane are calculated, and the linearly polarized light component having the minimum value Imin is calculated. The polarization plane is taken as the entrance plane, and then the incident angle Ψ is calculated according to the following equation,

(Equation 4) Provided is a method for measuring the surface shape of a molded article, wherein a direction forming an angle と with a traveling direction of reflected light in the incident surface is measured as a normal direction of the measurement site.

The principle of the measurement according to the first aspect of the present invention is that the coherent light is used as the incident light because the content of the p-polarized light and the s-polarized light contained in the specularly reflected light depends on the incident angle. No need. For example, natural light, light from an incandescent lamp, or the like is sufficient.

The unit of measurement, that is, the area of the measurement site is arbitrary, and is limited by, for example, the area measured by each pixel of the light intensity measuring means such as an image pickup tube. For this reason, depending on the magnification of a pixel of the light intensity measuring unit and a magnifying lens applied to the light intensity measuring unit,
The area of the measurement site can be arbitrarily controlled.

In the invention according to claim 1,
Since the measurement sensitivity depends on the area of the measurement site, it is possible to control the measurement sensitivity by controlling the area of the measurement site. That is, it is possible to perform measurement with an arbitrary sensitivity by selecting the pixel of the light intensity measuring unit, the magnification of the magnifying lens, and the like.

Further, as described above, any light such as natural light can be applied as the incident light, and an imaging tube or the like can be used as the light intensity measuring means, so that it is not necessary to scan the surface of the molded product. For this reason, it is possible to measure the surface shape of a molded article having an arbitrary size from a large object to a small part with a required sensitivity. The measurement time is the time required to measure the intensity of the linearly polarized light component over its entire polarization plane, and specifically, the time required to make one rotation of the polarizing film, and Does not depend on the size of

As the three-dimensional molded product according to the first aspect, for example, any one of plastic molded products, glass molded products, and molded products of wood and metal can be applied. Further, when observed with the naked eye, the surface shape may have a curved surface, or may appear flat. Preferably,
It contains sufficient specularly reflected light. in this case,
This is because measurement can be performed with high accuracy.

For these reasons, it is desirable that the invention according to claim 1 be applied to a transparent molded article. In the case of a transparent molded article, the change in the refractive index inside the molded article is small, and diffuse reflection light based on light scattering inside the molded article is hardly generated. For this reason, the reflected light from the molded article contains sufficient specular reflected light, while almost no diffuse reflected light serving as noise is included. The transparent molded article may be a colorless transparent molded article or a colored transparent molded article.

The invention according to claim 2 has been made for such a reason. That is, the invention according to claim 2 is based on the invention according to claim 1, and is characterized in that the molded article is transparent.

Examples of such molded articles include plastic molded articles and glass molded articles that do not contain a coloring agent such as a dye or a pigment. Further, a plastic molded article or a glass molded article containing a colorant to such an extent that the transparency is not impaired and the measurement accuracy is not impaired may be used. Preferred colorants are dyes that do not impair the refractive index uniformity.

In the invention according to claims 1 and 2,
In order to measure the intensity of the linearly polarized light component, a polarizing film and an image pickup tube may be arranged in the traveling path of the reflected light. Then, while rotating the polarizing film around the central axis with the traveling direction of the reflected light as the central axis, the intensity of light transmitted through the polarizing film and incident on each pixel of the image pickup tube is measured. The intensity of the linearly polarized light component in the reflected light can be measured over the entire polarization plane.

In the invention according to claims 1 and 2,
The steps of calculating the maximum values Imax and Imin from the measured intensity, calculating the incident surface, calculating the incident angle, and calculating the normal direction of the measurement site,
It is easy to do by computer.

Next, the invention according to claim 3 relates to a measuring system applied to the measuring method according to claim 1.

In other words, the invention according to claim 3 divides the mounting table on which a molded article having a known refractive index n is mounted and the surface of the molded article mounted on the mounting table into a measurement area having a small area. A light source for irradiating the measurement site obtained with the incident light beam, and a light intensity measuring means for measuring the intensity of the linearly polarized light component in the reflected light specularly reflected on the surface of the molded product over the entire polarization plane. , The maximum value Imax of the intensity in all polarization planes
And the minimum value Imin, and the plane of polarization of the linearly polarized light component having the minimum value Imin as the plane of incidence. Then, the incident angle Ψ is calculated according to the following equation.

(Equation 5) In the incident surface, there is provided calculation means for calculating a direction forming an angle Ψ with the traveling direction of the reflected light as a normal direction of the measurement site.

[0028] In the invention according to claim 3, when the incident light beam is irradiated toward the molded product from substantially all spatial angles,
It is not necessary to move the light intensity measuring means in the traveling path of the reflected light every time each measurement site is measured, and it is possible to measure the intensity of any measurement site of the molded article while keeping the position fixed. . This is because, in any part of the molded article, a light ray that causes the light intensity measuring device to emit reflected light surely exists in the incident light rays that are emitted from the substantially whole space angle toward this part. In addition, in order to irradiate an incident light beam from a substantially entire spatial angle toward the molded product, the molded product may be substantially surrounded by a light diffusing material. This is because light from a light source provided outside the light diffusing material is diffused and transmitted by the light diffusing material, and the diffusely transmitted light is incident as an incident light beam from almost all spatial angles. In addition, it is desirable that the incident light beam is applied to the molded product from all spatial angles, but the traveling path of the reflected light to the light intensity measuring means,
Because of the mounting table or other equipment, it is sufficient to provide these equipment in a position where they do not interfere.

The inventions according to claims 4 and 5 have been made for the reasons described above. That is, the invention according to claim 4 is based on the premise of the invention according to claim 3, and is characterized in that the incident light beam is irradiated toward the molded article from substantially all spatial angles. The invention according to claim 5 is based on the premise of the invention according to claim 4, and substantially surrounds the periphery of the molded article, and is provided between the molded article and the light source to diffuse light rays from the light source and thus diffuse. And a light diffusing material for irradiating the formed light beam to the molded product as the incident light beam.

As such a light diffusing material, a spherical translucent article having light scattering performance can be used. For example,
Abrasive glass, a white translucent plastic molded product into which a high refractive index powder is kneaded, a white translucent plastic molded product or a glass molded product coated or printed with a paint or printing ink containing the high refractive index powder.

Next, in the invention according to claims 3 to 5,
When an imaging tube having a large number of pixels is used as the light intensity measuring means, it is possible to simultaneously measure a number of measurement sites corresponding to the number of pixels. In particular, when the incident light beam is incident on the molded article from substantially the entire spatial angle, the specularly reflected light from the plurality of measurement sites reaches the respective pixels of the position-fixed light intensity measurement means. It is possible to perform measurement at the same time without leaking the measurement site.

The invention according to claim 6 has been made based on such technical reasons, that is, the invention according to claim 6 is based on the inventions according to claims 3 to 5, and is based on the light intensity measurement. The means is a pickup tube and a polarizing film provided between the pickup tube and the molded product.

The invention according to claim 6 is desirably applied to the case where the incident light beam is incident on the molded article from substantially all spatial angles.

In the invention according to claim 6, when the polarizing film is provided so as to be able to rotate around the central axis with the traveling direction of the reflected light as the central axis, the polarizing film is synchronized with the rotation. By measuring the light intensity, the intensity of the linearly polarized light can be efficiently measured over the entire polarization plane.

The invention according to claim 7 has been made based on such technical reasons. That is, the invention according to claim 7 is based on the invention according to claim 6, and the polarizing film has a reflective film. It is characterized by being provided so as to be able to rotate around the central axis with the traveling direction of light as the central axis.

[0036]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view for explaining a measurement system according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a colorless and transparent hemispherical plastic molded product having a known refractive index n and a surface gloss, and the refractive index n is about 1.5.

Next, in FIG. 1, the plastic molded article 1 is placed on a mounting table 2 via a jig 21 for adjusting the height and angle of the plastic molded article 1, and the entire space thereof is substantially removed. Surrounding the corner and between three incandescent lamps as light sources (only two incandescent lamps 4 and 4 are shown. The third incandescent lamp is provided on the near side of the drawing) and is a half-white lamp. A transparent plastic sphere 3 is provided. This plastic sphere 3 is applied as a light diffusing material,
The light from the incandescent lamps 4 and 4 is diffused by transmitting the light, and as shown by arrows in FIG.
A light beam is made incident from.

The plastic ball 3 is provided with holes at its bottom and top. The bottom hole (not shown) allows the mounting table 2 to pass through, and the top hole 31
Is for guiding the specularly reflected light to the light intensity measuring means.

Next, the reflected light measuring means is disposed on the traveling path of the regular reflected light, and is provided above the hole 31 in FIG. The reflected light measuring means comprises a CCD camera 6 having a large number of pixels and a polarizing film 5 provided below the CCD camera 6. The specularly reflected light passes through the polarizing film 5 and passes through the CCD. It is arranged so as to enter the camera 6. The polarizing film 5 is provided with a frame 51 for horizontally holding the polarizing film 5 and a handle 52 for rotating the polarizing film 5 around its central axis. The handle 52 is connected to a control device (not shown),
It is held so that it can rotate intermittently every degree.

The CCD camera 6 is disposed so as to be able to advance and retreat with respect to the molded article 1. The magnification can be controlled by the advance and retreat and zoom-in or zoom-out of the lens. The CCD camera 6 is connected to a computer device (not shown). The CCD camera 6 measures the intensity of specularly reflected light incident on each pixel of the CCD camera 6, and immediately stores the measured intensity. You.

This computer has the following functions. That is, first, the CCD camera 6
This function measures the maximum value Imax, minimum value Imin, and polarization plane of the linear polarization component having the minimum value Imin of the intensity of the linear polarization component for each pixel. As can be seen from FIG. 2A, the maximum value Imax is larger than the minimum value Imin and can be measured with high accuracy.
The plane of polarization of the linearly polarized light component having the minimum value Imin is determined by measuring a plane of polarization of the linearly polarized light component having x and a direction including the direction orthogonal to the plane of polarization and the traveling direction of the specularly reflected light. Is also good. Next, the function is to use the plane of polarization of the linearly polarized light component having this minimum value Imin as the plane of incidence.

The computer device also has the following functions. That is, according to the following equation, also for each pixel,
Calculate the angle of incidence Ψ,

(Equation 6) This is a function of calculating a direction forming an angle と with the traveling direction of the reflected light in the incident surface as a normal direction of a measurement site on the surface of the molded article 1 corresponding to the pixel.

The computer also has the following functions. That is, with the function of calculating the gradient from the normal direction of each measurement site calculated as described above, calculating the height of these measurement sites based on the gradient, and calculating the uneven shape of the molded product surface. is there.

Each of these functions can be realized by a computer program.

In this embodiment, the method of measuring the surface shape of the molded article 1 is as follows. That is, first, the incandescent lamps 4 and 4 are turned on, and the light is diffused by the plastic sphere 3. The diffused light enters all parts of the surface of the molded product 1 from all directions (substantially all spatial angles),
At each portion, reflected light including specularly reflected light and diffusely reflected light is generated in all directions (substantially all spatial angles). The main component in the reflected light is specularly reflected light, and the diffusely reflected light is negligibly small.

Of the specularly reflected light emitted from the respective parts of the molded article 1 at all spatial angles, only the specularly reflected light emitted in the direction of the CCD camera 6 selectively passes through the polarizing film 5 to the CCD. The intensity of the linearly polarized light that enters the camera 6 and is included in the specularly reflected light is measured.

The reflected light incident on the CCD camera 6 is:
It covers the reflected light from all parts of the surface of the molded article 1. The reflected light incident on each pixel of the CCD camera 6 is reflected light from a measurement area of a minute area on the surface of the molded article 1 determined corresponding to each pixel.

Then, the polarizing film 5 is rotated by 5 degrees around the central axis with the traveling direction of the reflected light as the central axis, and is included in the specularly reflected light incident on each pixel of the CCD camera 6 again. Measure the intensity of linearly polarized light. And
Until the rotation angle covers all polarization angles, ie, 18
It repeats until it rotates 0 degrees, and measures the intensity at all polarization angles. FIG. 2 shows an example of the intensity thus measured. FIG. 2 is a graph showing the intensity measured at one of the pixels of the CCD camera 6, wherein the horizontal axis indicates the polarization angle, the vertical axis indicates the intensity, and the small circle indicates the measurement. Strength. The line is obtained by approximating these measurement data with a cosine curve.

FIG. 2 shows that the measurement data can be sufficiently approximated by a cosine curve, and that the measurement accuracy is excellent. It can also be seen that the measured data has a maximum value and a minimum value.

Next, a computer device (not shown)
The uneven shape of the surface of the molded article 1 is calculated. That is, CCD
For each pixel of the camera 6, the value of the maximum value Imax, the value of the minimum value Imin, and the direction to which the linear polarization component belongs are measured, and then the polarization plane of the linear polarization component having the minimum value Imin is incident. Face.

Then, the incident angle Ψ is calculated for each pixel in accordance with the following equation.

(Equation 7) A direction that forms an angle Ψ with the traveling direction of the reflected light in the incident plane is calculated as a normal direction of a measurement site on the surface of the molded article 1 corresponding to the pixel.

Then, the gradient is calculated from the normal direction of each of the measurement sites thus measured, and the heights of these measurement sites are calculated based on the gradients, thereby calculating the irregularities on the surface of the molded article. FIG. 3 shows the result of printing out the irregularities on the surface of the molded product calculated in this way. FIG. 3 is a perspective view showing a state in which a lattice pattern is projected onto the surface of the molded product from above, and the unevenness of the surface of the molded product is expressed by the lattice pattern deformed by the surface of the molded product.

[0054]

According to the first and third aspects of the present invention, any light such as natural light can be applied as an incident light, and an image pickup tube or the like can be used as light intensity measuring means. Until then, the surface shape of a molded article of any size can be measured, and at this time, it is possible to measure with any sensitivity.

The measurement time is the time required to measure the intensity of the linearly polarized light component over the entire polarization plane, and specifically, the time required to make one rotation of the polarizing film. And does not depend on the size of the molded article. For this reason,
It is also possible to measure the surface shape of a large article in a very short time.

For this reason, it is possible to measure the surface shape of a three-dimensional molded product economically and efficiently without contacting the molded product, and with any sensitivity regardless of the size of the molded product. It has the effect of being able to.

According to the second aspect of the present invention, the molded article is transparent, and the reflected light from the molded article includes a sufficient specularly reflected light, while the diffusely reflected light serving as noise hardly exists. Since it is not included, there is an effect that the measurement accuracy can be further improved.

According to the fourth and fifth aspects of the present invention,
Since the incident light beam is emitted toward the molded article from substantially all spatial angles, it is possible to measure the intensity of an arbitrary part of the molded article while the light intensity measuring means is fixed in position, so that the molded article This eliminates the necessity of alignment, and the measurement operation efficiency can be significantly improved.

According to the sixth aspect of the present invention, it is possible to simultaneously measure a large number of measurement sites of a molded article without omission, and it is possible to measure the entire surface of the molded article in one step. This has the effect that the work efficiency can be further improved.

According to the seventh aspect of the present invention, the polarizing film provided between the molded article and the image pickup tube can rotate around the central axis with the traveling direction of the reflected light as the central axis. , It is possible to efficiently measure the intensity of the linearly polarized light over the entire polarization plane.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view of a measurement system according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of measured intensity according to the embodiment of the present invention.

FIG. 3 is a perspective view showing the measured irregularities on the surface of the molded product according to the embodiment of the present invention.

[Explanation of symbols]

1 3D molded product 2 Mounting table 3 White translucent plastic sphere 4 Incandescent lamp 5 Polarizing film 6 CCD camera

Claims (7)

[Claims] 1. A surface of a molded article having a known refractive index n is divided into a measurement area having a small area, an incident light beam is irradiated on the measurement area, and a straight line in the reflected light specularly reflected at the measurement area surface. The intensity of the polarized light component is measured over the entire polarization plane, the maximum value Imax and the minimum value Imin of the intensity in the entire polarization plane are calculated, and the polarization plane of the linearly polarized light component having the minimum value Imin is converted to the incident plane. Then, the incident angle Ψ is calculated according to the following equation. A method for measuring the surface shape of a molded product, wherein a direction forming an angle と with a traveling direction of reflected light in the incident surface is measured as a normal direction of the measurement site. 2. The method according to claim 1, wherein the molded article is transparent. 3. A mounting table on which a molded article having a known refractive index n is mounted, and a measuring area obtained by dividing a surface of the molded article mounted on the mounting table into a measuring area having a small area. A light source for irradiating an incident light beam, light intensity measuring means for measuring the intensity of the linearly polarized light component in the reflected light specularly reflected on the surface of the measurement site over the entire polarization plane, and The maximum value Imax and the minimum value Imin are calculated, and the plane of polarization of the linearly polarized light component having the minimum value Imin is defined as the plane of incidence. Then, the angle of incidence Ψ is calculated according to the following equation. A measuring unit for calculating a direction forming an angle と with the traveling direction of the reflected light in the incident surface as a normal direction of the measurement site. 4. The surface profile measuring system according to claim 3, wherein the incident light beam is irradiated toward the molded product from substantially all spatial angles. 5. A light source, which substantially surrounds the periphery of a molded article and is provided between the molded article and a light source to diffuse a light beam from the light source.
5. A light diffusing material for irradiating the light beam thus diffused to the molded product as the incident light beam.
Surface profile measuring system according to 1. 6. A surface according to claim 3, wherein said light intensity measuring means is an imaging tube and a polarizing film provided between said imaging tube and a molded product. Shape measurement system. 7. The surface profile measuring system according to claim 6, wherein the polarizing film is provided so as to be able to rotate around the central axis with the traveling direction of the reflected light as the central axis.