JPS632322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a tube-shaped object to be measured that is effectively transparent to a certain wavelength (not necessarily visible light) and whose inner diameter is about half or less than the outer diameter. The present invention relates to a non-contact, highly accurate inner diameter measurement method that is particularly effective when the inner diameter itself is small.

For transparent tubes such as those mentioned above, the inner diameter value usually has a greater meaning in terms of performance and usage classification than the outer diameter value, but if the inner diameter value is small, the inner diameter measurement is more important than the outer diameter value. It was very difficult.

Conventionally, as a method for measuring the inner diameter of this type of object to be measured, there has been a method in which a metal core rod having a standard outer diameter is inserted into a tube of the object to be measured. This is done by dividing the variation range of the inner diameter value of the object to be measured into equal parts at a fixed pitch determined from the measurement accuracy, and preparing in advance a plurality of reference core rods with each value as the outer diameter value. When inserting core rods with various outer diameter values into the inner diameter of the object to be measured, find the maximum value D _L of the outer diameter of the core rod that could pass through and the minimum value D _H of the outer diameter of the core rod that could not be passed through, and find the inner diameter of the object to be measured. D _H over D _L
It is determined that the value is within a range less than or equal to However, with the above method, it is only possible to know that the inner diameter value exists within a certain range, and if the accuracy is to be improved, it is necessary to make the outer diameter pitch of the reference core rod finer. In addition, in the case of an object to be measured with a deformed cross section as shown in Figure 1 a and b, the value measured by this method indicates the maximum inscribed circle diameter for the inner diameter profile, and the value measured by this method indicates the maximum inscribed circle diameter for the inner diameter profile. If the inner diameter profiles also differ in the tube axis direction, only the smallest of the maximum inscribed circle diameters in each cross section is measured. Measurement also depends largely on the experience and subjectivity of the operator, and the labor required for the measurement work is also large. moreover,
When manufacturing a reference core rod, it is necessary to strictly limit the outer diameter accuracy and straightness, and care must be taken when storing it.

As described above, the conventional measurement method using a reference core rod requires time and labor, and has the disadvantage that the accuracy and reliability of the measured values are low.

On the other hand, as a non-contact inner diameter measuring method, a method of measuring the inner diameter using an outer diameter measuring machine that is currently in practical use can be considered. The measurement principle will be briefly explained below using FIG. 2.

FIG. 2 is a diagram showing a conventional configuration of an outer diameter measuring device using a laser as an example of such a device.

The object to be measured 11 is an opaque cylindrical object, and the laser oscillator 1 is
The laser beam emitted from 4 scans the object 11 as a parallel spot in a direction perpendicular to its central axis.

The scanning light is transmitted to a photoelectric element 16 by a condensing lens 15.
However, when the scanning light hits the object to be measured, the output level at the light receiving section decreases, and the output waveform is as shown in Figure 3, with the light receiving section output on the vertical axis and the scanning time on the horizontal axis. become. The measuring principle of this device is that the value TV obtained by multiplying the time T from the fall to the rise of the output level in the figure by the scanning speed V of the laser spot represents the outer diameter value. If a glass tube or the like is used as the object to be measured and the laser spot is scanned in the same way, it is expected that some change will occur in the output level of the light receiving photoelectric element immediately before and after the scanning light intersects with the inner wall. Therefore, if we extract this change point that should appear twice and discover that there is a certain correlation between the time difference between the change points and the inner diameter value,
This means that it can be used as an inner diameter measuring device. However, in this case, it is thought that the object to be measured itself exerts a lens effect on the scanning light, and the relational expression between the time difference between changing points and the inner diameter value has not been elucidated at present. Furthermore, the degree of change in the output level is also small compared to the case of outer diameter measurement, and it is expected that extracting the change point will be quite difficult.

Compared to the conventional contact measurement method using a core rod, the present invention allows easy confirmation of measurement position and direction settings, and provides non-contact, high accuracy and high reliability through simple configuration and measurement work. The present invention provides a method for measuring an inner diameter.

In the present invention, a transparent tube, which is an object to be measured, is placed in a parallel beam of light that includes a wavelength that can pass through the transparent tube, and this transmitted light is guided to an imaging system to form an image. Transparent, characterized in that the distance between two bright lines shining in a dark area is measured on the image, and the desired inner diameter is indirectly measured from the refractive index at the wavelength of a separately prepared object to be measured and the measured value. This is a method for measuring the inner diameter of a pipe. The word transparent here refers to the relationship that exists between the object to be measured, the light source, and the imaging system; the object to be measured transmits the light emitted from the light source, and the imaging system detects changes in the amount of light. For example, if the object to be measured can be output as a change in signal output such as an electric signal, it is assumed that the object to be measured is transparent to the light source.

Next, the configuration and measurement principle of the present invention will be explained in detail using FIGS. 4, 5, 6, 7, and 8.

FIG. 4 is a perspective view of one embodiment of the present invention. The object to be measured is a glass tube 21, and the object to be measured holder 2
It is fixed vertically by 2. Parallel light source 23
The method uses a tungsten lamp and a lens system, and illuminates the object from the position and direction on the central axis of the object to be measured. The imaging system includes an imaging vidicon camera 24 and an imaging lens system 25, which are arranged so as to image the measurement location from the side opposite to the light source. The imaging system is placed on an imaging system holder 26 that has a guide to enable focus alignment. 27 is a monitor for viewing the video signal of the imaging vidicon camera.

Figure 5 is a cross-sectional view of the glass tube at the measurement position.
The paths of parallel rays are shown. These parallel ray groups include those that pass through the outer surface of the object to be measured (group A), as shown in 31 and 32, and those that enter the object to be measured, as shown in 33 and 34, but do not intersect with the inner wall. Those going out again (group B), 35 and 3
As shown in 6, after entering the object to be measured, it is totally reflected on the inner wall and goes out (group C), and 37, 38,
39, which passes through the inner diameter of the object to be measured (D
It is classified into four groups. When the imaging system is focused at the position indicated by 40 in the figure, an image as shown in FIG. 6 is displayed on the monitor 27. here 5
Reference numerals 1 and 52 refer to the outer diameter line of the object to be measured, and the bright areas outside thereof are due to the light rays of group A described above. Reference numeral 53 indicates a bright area generated by the light ray group of the D group. The width is narrower than the bright part 53,
Bright lines 54 and 55 with high contrast with the surroundings
is projected as an image of the C group of rays. The reason why this bright line appears is as follows. Among the incident rays, those classified as group C are the fifth
It is limited to those that intersect with the inner wall in the very vicinity of points 41 and 42 on the inner wall in the figure. Therefore, after total reflection, the light rays of group C proceed as if point light sources were placed at the positions of points 41 and 42. Considering the outer circumference of the object to be measured as a refractive surface, the outer radius of the object to be measured is R, the refractive index is N, and the seventh
Formula for spherical refraction using symbols as shown in the figure: n/S-n'/S'=n-n'/γ, α=nS'/n
'S n: refractive index on the incident side, S: object point distance n': refractive index on the exit side, S': image point distance γ: radius of refracting surface, α: magnification S = -R, γ = R, n = N , n'=1, S'=-R, α=-N. That is, as shown in FIG. 8, the virtual images 41 and 42 in FIG. 5 are created at a distance N times from the center axis of the object to be measured. Based on this principle, when the focal position of the imaging system is adjusted to the position shown in FIG. 4, the inner diameter image is enlarged N times and formed. During actual measurement, focus alignment is complete when these two bright lines are the thinnest and clearest on the monitor screen.

If the magnification of the imaging lens system is m and the magnification between the monitor image sensors is M, then the relationship between the inner diameter of the object to be measured d and the distance between the bright lines D on the monitor is as follows: D=N・m・M・d Therefore, by measuring the distance between the bright lines at the measurement position on the monitor, the inner diameter of the object to be measured can be calculated.

Next, a case where the inner diameter and outer diameter of the object to be measured are not concentric will be described. First, as shown in FIG. 9, in the case of eccentricity in the direction perpendicular to the optical axis, the bright lines are only shifted in the same direction and the magnification does not change.

When eccentric in the optical axis direction as shown in FIGS. 10a and 10b, the magnification is no longer n. If the magnification when the ray is eccentric in the traveling direction is α ₊ 〓, and the magnification when it is eccentric in the opposite direction is α _- 〓, then α ₊ 〓 = nγ / γ + (n - 1) δ, α _- 〓 = nγ /γ-(n-1)δ γ: outer diameter radius of the object to be measured n: refractive index of the object to be measured δ: amount of eccentricity. Therefore, this magnification correction is performed by averaging two pieces of data obtained by measuring from 180° opposite directions.

Letting e be the difference between the magnification when averaging and the magnification n used for calculation, e is given by the following formula.

e=α ₊ 〓+α _- 〓/2-n=n{(n-1)δ) ² /γ ²
-{(n-1)δ} ² For example, γ=5 (mm), n=1.5, δ=0.1 (mm)
When , e=2.76×10 ^-3 , which is sufficiently small compared to the measurement accuracy. Generally speaking, even for objects to be measured whose inner and outer diameters are eccentric, sufficient accuracy can be guaranteed by the above-mentioned correction.

In the present invention, as shown in FIG. 6, it is necessary that the bright area image appear in the dark area, and therefore, it is a prerequisite that the ratio of the outer diameter to the inner diameter of the cylindrical tube is at least twice the refractive index.

As described above, according to the measurement method according to the present invention, it is possible to set and confirm the measurement position and direction, which was impossible with conventional measurement methods. The inner diameter can be measured when the In addition, a significant reduction in labor can be expected in measurement work.

In the embodiments of the present invention, only the case where the object to be measured is a glass tube has been described, but the same measurement method can also be applied to other translucent materials such as plastics as the material of the object to be measured.

Furthermore, although the above explanation has been given using a cylindrical pipe as an example, equivalent measurements can be made for other cross-sectional shapes such as square, hexagonal, and octagonal shapes with some consideration. be.

[Brief explanation of the drawing]

Figures 1 a and b are explanatory diagrams of the maximum inscribed circle in the cross section of the object to be measured, Figure 2 is a configuration diagram of a conventional laser outer diameter measuring machine, and Figure 3 is a diagram of the measurement of a cylindrical workpiece using the above measuring machine. Fig. 4 is a perspective view of an embodiment of the present invention, Fig. 5 is an explanatory diagram of the trajectory of a group of rays, Fig. 6 is a monitor screen diagram in one embodiment, Fig. 7 is an explanation of the spherical refraction formula. 8, 9, and 10a and 10b are illustrations of the measurement principle of the present invention. The symbols in the figure indicate the following. 1... Outer diameter of the object to be measured, 2... Maximum inscribed circle, 11
...Object to be measured, 12... Tuning fork deflector, 13... Lens, 14... Laser oscillator, 15... Condensing lens, 16... Photoelectric element, 21... Glass tube, 22
...Measurement object holding section, 23...Parallel light source, 24...
...imaging vidicon camera, 25...imaging lens system, 26...imaging system holding unit, 27...monitor,
31, 32, 33, 34, 35, 36, 37, 3
8, 39... Ray trajectory, 40... Focus position, 4
1, 42... Total reflection center point, 51, 52... Outer diameter image of the object to be measured, 53... Bright area, 54, 55... Bright line, 60... Refraction surface, 61... Object point, 62... Image point, 70...Virtual image of point 41, 71...Virtual image of point 42.

Claims (1)

[Claims] 1 A transparent tube, which is the object to be measured, is placed in a parallel beam of light that includes a wavelength that can pass through it, and this transmitted light is guided to an imaging system to form an image. A transparent tube inner diameter measurement characterized by measuring the interval between two shining bright lines on an image and indirectly measuring a desired inner diameter from the refractive index at the wavelength of a separately prepared object to be measured and the measured value. Method.