JPH0942904A - Method of measuring inner diameter of pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can measure an inner diameter of a pipe such as a steel pipe with less errors. SOLUTION: During measurement of an inner diameter of a pipe 1 with the use of a pair of contact needles 2a, 2b, the contact needles 2a, 2b are displaced from the center positions thereof by a where (a) (a>0) is a maximum difference between the center positions of the contact needles 2a, 2b and the center point of the pipe in a direction orthogonal to an inner diameter measuring direction, and the inner diameter of the pipe is measured at that positions. Then, they are displaced from that positions by +2a, and the inner diameter of the pipe is measured at that positions. A measuring and computing device 22 computes four coordinates on the circumference of a true circle from the measured points, estimating that the inner surface of the pipe depicts the true circle so as to obtain a true inner diameter. It is thereby possible to measure an inner diameter of a pipe with a high degree of accuracy even though the center positions of the contact needles 2a, 2b are shifted from the center line of the pipe 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the inner diameter of a pipe such as a steel pipe with a small error.

[0002]

2. Description of the Related Art Conventionally, when manufacturing a pipe such as a steel pipe, it is necessary to accurately measure dimensions such as length, outer diameter and inner diameter, and the inner diameter is particularly important. To measure the inner diameter of the pipe, for example, as shown in FIG.
A contact-type inner diameter in which a pair of contact needles 2a and 2b are inserted from a, the tips of the contact needles 2a and 2b are brought into contact with the inner surface of the pipe, and the inner diameter d of the pipe 1 is measured from their opening y. The measuring device 3 is used. Note that a non-contact type such as an eddy current sensor or a laser displacement meter may be used instead of the contact needles 2a and 2b, but the measurement principle is the same.

By the way, when the inner diameter of the pipe is measured using the above-mentioned contact type (or non-contact type) inner diameter measuring device, as shown in FIG. It is necessary to perform alignment with the center point O of 1 each time measurement is performed.

[0004]

However, in the above-mentioned prior art, due to the positioning error of the pipe to be measured and the bending of the pipe itself or the deflection due to its own weight,
There is a problem that a deviation occurs between the center position C of the inner diameter measuring device 3 and the center point O of the tube 1, which causes an error. The occurrence of the error will be described in detail. As shown in FIG. 3, when the center position C of the inner diameter measuring device 3 is horizontally displaced from the center point O of the tube 1 by g, the inner diameter measuring device 3 causes The measured inner diameter d ^* is d ^* <d with respect to the true inner diameter d.
For example, an inner diameter d of a tube having an outer diameter of 60.3 mm and a tube thickness of 2 mm is 56.3 mm, but due to bending, the center point O of the tube 1 and the inner diameter measuring device 3
When there is a difference of 2 mm in the center position C of, the measured inner diameter d ^* is
It will be 56.26 mm, which means a difference of 40 μm.

As a measure against such a problem, the pipe center point is previously measured by another means, and a mechanism for aligning the center position of the inner diameter measuring device with the pipe center point is provided, or the calculated pipe center point and inner diameter are provided. Although it is conceivable to make a correction based on the difference from the center position of the measuring device, there is a problem that the device becomes large and the equipment cost is high. It is an object of the present invention to provide a method for measuring the inner diameter of a pipe, which solves the above-mentioned problems of the prior art.

[0006]

According to the present invention, when measuring the inner diameter of a pipe using a non-contact type or a contact type inner diameter measuring means, the difference between the center position of the inner diameter measuring means and the center point of the tube is In the direction orthogonal to the inner diameter measurement direction, at most a (however, a
> 0), the inner diameter measuring means is first moved by -a from the center position to measure the inner diameter of the pipe at that position, and then moved by + 2a from the measuring position to measure the inner diameter of the pipe at that position. A pipe inner diameter measuring method is characterized in that the true inner diameter is obtained by calculating the coordinates of four points on the circumference of the circumference from the measured values with the inner surface of the pipe as a perfect circle.

[0007]

[Operation] Regarding the measurement principle of the present invention, the case of measuring the inner diameter in the y-axis direction will be described below with reference to FIG.
It is assumed that the displacement between the center point O of the tube 1 and the center position C of the inner diameter measuring device 3 is at most a distance (a> 0) in the x-axis direction. At this time, the contact needle is allowed to move in the directions of + a and -a in the x-axis direction on the line of y = 0. Then, the inner diameter equivalent is measured at two points (-a, 0) and (a, 0), and at this time, points P ₁ , P ₂ ,
P _3, P ₄ of the coordinates, respectively _{(-a, b 1), (} - a,
-B _2), and _{(a, b 3), (} a, -b 4). However, b ₁ > 0, b ₂ > 0, b ₃ > 0, b ₄ > 0.

Now, the coordinates of the center point O of the tube 1 are (x ₀ , y
₀ ) and its radius is r, (x−x ₀ ) ² + (y−y ₀ ) ² = r ² ……………… (1) Points P ₁ , P ₂ , P _{3 on the} inner wall of the pipe , P ₄ are points on the circle corresponding to the inner diameter, the following equation (2) is established. ^{_{(-A-x 0) 2 +}} (b 1 -y 0) 2 = r 2 (-a-x 0) 2 + (- b 2 -y 0) 2 = r 2 (a-x 0) 2 + ( ^{_{b 3 -y 0) 2 = r}} 2 (a-x 0) 2 + (- b 4 -y 0) 2 = r 2 .................. (2) from these, the following (3) is obtained .

[0009]

[Equation 1]

Therefore, the true inner diameter d can be obtained by the following equation (4). d = 2r = 2√ {(- a-x 0) 2 + (b 1 -y 0) 2} .................. (4) In the case of measuring the inner diameter of the x-axis direction, as described above It goes without saying that the above method can be used.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective view showing the configuration of an embodiment of an inner diameter measuring device 10 according to the present invention. In this figure, 11 is a base, 12 is a first moving mount mounted on the base 11 by a first cylinder 13 so as to be slidable in the X direction shown by the arrow, and 14 is a first moving mount 12. Second cylinder 15 on top
Is a second movable mount which is slidably mounted in the Z direction indicated by the arrow.

Reference numerals 16a and 16b denote holders for holding the contact needles 2a and 2b, respectively. The holders 16a and 16b are screwed to a screw shaft 17 provided with screws opposite to each other in the height direction. 18 is the screw shaft 17
Is a drive motor for rotating and rotating the contact needles 2a and 2b in the Y direction shown by the arrow. Reference numeral 19 is a guide rod for guiding the contact needles 2a and 2b. Reference numeral 20 denotes a gap sensor which is attached to the holders 16a and 16b and measures the distance between the contact needles 2a and 2b, and inputs a signal to the measurement calculation device 22 via the line 21. A skid 23 conveys the pipe 1.

The operation of the inner diameter measuring device 10 thus constructed will be described. The pipe 1 for measuring the inner diameter is conveyed by the skid 23, and positioned so that the center of the pipe 1 is located substantially at the center of the contact needles 2a, 2b of the inner diameter measuring device 10. First, the first cylinder 13 is operated to operate the first moving rack.
12 is moved in the X direction indicated by the arrow by -a, and then is moved in the Z direction indicated by the second cylinder 15 to move the contact needles 2a, 2b.
Is inserted into the inner surface of the tube 1.

Then, the drive motor 18 is rotated to move the interval between the contact needles 2a and 2b in the direction of enlarging in the Y direction shown by the arrow. Then, at the point of contact with the inner surface of the tube, the tube sensor is stopped, the gap in the y-axis direction is detected by the gap sensor 20, and it is input to the measurement calculation device 22. As a result, in the measurement calculation device 22, the coordinates of the contact points P ₁ and P ₂ of the contact needles 2a and 2b at that time are obtained.

After rotating the drive motor 18 in the opposite direction to move the contact needles 2 a, 2 b in a direction to reduce the distance between them, the second cylinder 15 is operated in the opposite direction to move the contact needles 2 a, 2 b into the tube 1. Pull out from the inside. Further, after operating the first cylinder 13 to move the first moving base 12 to the opposite side in the X direction indicated by the arrow by 2a, the second cylinder 15 is operated to move the contact needles 2a and 2b into the pipe 1. Inserted on the inner surface and rotating the drive motor 18 to bring the contact needles 2a and 2b into contact.
The interval of is moved in the direction of expanding in the Y direction shown by the arrow. Then, the gap sensor 20 detects the interval in the y-axis direction and inputs it to the measurement calculation device 22, so that the measurement calculation device 22 makes contact points P ₃ , P ₄ of the contact needles 2a, 2b at that time.
Is calculated.

In the measurement calculation device 22, the above (1)
The true inner diameter d of the pipe 1 is calculated by calculating the equation (4). Using the method of the present invention, the inner diameter of 100 steel pipes having a nominal inner diameter of 56.3 mm was measured. The average of the difference from the true value at that time and its standard deviation are shown in Table 1 together with the results of the conventional method.

[0017]

[Table 1]

The true value is measured using an inner diameter measuring micrometer. As can be seen from this table, in the case of the method of the present invention, the standard deviation increased, but the difference from the true value greatly decreased, which clearly contributes to the reduction of the measurement error.

[0019]

As described above, according to the present invention,
When the difference between the center position of the inner diameter measuring means and the center point of the pipe is a at the maximum in the direction orthogonal to the inner diameter measuring direction (where a> 0), the inner diameter measuring means is first moved from the center position by -a.
The pipe inner diameter at that position is measured, and then the pipe inner diameter at that position is measured by moving + 2a from the measurement position. From these measured values, the inner surface of the pipe is regarded as a perfect circle, and four points on the circumference are measured. Since the true inner diameter is calculated by calculating the coordinates of, the pipe inner diameter can be measured with high accuracy even if there is a deviation between the center position of the inner diameter measuring means and the center point of the pipe.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an embodiment of an inner diameter measuring device according to the present invention.

FIG. 2 is a (a) side sectional view showing a conventional example, and (b) a front view taken along the line AA.

FIG. 3 is an explanatory diagram of a measurement error in a conventional example.

FIG. 4 is an explanatory diagram of a measurement principle of the present invention.

[Explanation of symbols]

 1 pipe 1a pipe ends 2a, 2b contact needle (inner diameter measuring means) 10 inner diameter measuring device 11 base 12 first moving mount 13 first cylinder 14 second moving mount 15 second cylinder 16a, 16b holder 17 screw Axis 18 Drive motor 19 Guide rod 20 Gap sensor 21 Line 22 Measurement / calculation device 23 Skid

Claims (1)

[Claims] 1. When measuring the inner diameter of a pipe using a non-contact type or contact type inner diameter measuring means, the difference between the center position of the inner diameter measuring means and the center point of the pipe is in a direction orthogonal to the inner diameter measuring direction. At most a (however, a> 0)
Then, the inner diameter measuring means is first moved by -a from its center position to measure the pipe inner diameter at that position,
Then, the pipe inner diameter at that position is measured by moving + 2a from the measurement position, and the true inner diameter is calculated by calculating the coordinates of four points on the circumference with the inner surface of the pipe as a perfect circle from these measured values. Characteristic method of measuring inner diameter of pipe.