JP2001194134A - Method and device for measuring thickness of resin material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure with high accuracy the thickness of a resin material having a solid phase and a liquid phase. SOLUTION: A method for measuring, using an ultrasonic wave, the thickness d of the resin material 10 having the solid phase and the liqiud phase includes: measuring propagation time Δt during which the ultrasonic wave reciprocates in the cross direction of the resin material; calculating a temperature distribution T(x) in the cross direction of the resin material from an operational parameter; calculating a sound velocity distribution C(x) in the cross direction of the resin material from the temperature distribution in the cross direction and the temperature characteristic C(T) of sound velocity within the resin material; calculating the average sound velocity Cm of the sound velocity distribution in the cross direction; and calculating the thickness d of the resin material from the average sound velocity Cm and the propagation time Δt measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the thickness of a resin material using ultrasonic waves in a process of manufacturing the resin material.

[0002]

2. Description of the Related Art In a process for producing a polyethylene pipe or a coated steel pipe, a resin material is pulled out from an extrusion die and cooled to produce a corresponding polyethylene pipe or a coated steel pipe. In this manufacturing process, it is an important management item to control the thickness (wall thickness of the pipe) of the resin material as the manufactured product to a target value. The thickness control of the resin material (tube) continuously manufactured online is based on the extrusion temperature and temperature based on the thickness measured downstream of the extruder (extrusion die).
It is performed by setting the interval of the extrusion die and the extrusion speed to appropriate values.

Generally, an ultrasonic thickness measuring method is used as a measuring device for measuring the thickness (wall thickness) of a pipe from the outer peripheral surface.
In this ultrasonic thickness measurement method, an ultrasonic probe is placed outside a resin material to be measured, and an ultrasonic wave is applied to the resin material, and a surface echo and a bottom echo of the resin material, or a multiple reflection echo thereof. Is measured. Assuming that the sound speed of the ultrasonic wave propagating in the resin material is C, the thickness d of the resin material
Is obtained by equation (1).

D = C · Δt / 2 (1) Here, since the sound speed C of the ultrasonic wave propagating in the resin material varies depending on the type and temperature of the resin material, the value can be generally changed. Set a value according to the type and size of the resin material and start measurement.

[0005] Now, in order to control the thickness of the resin material, which is a manufactured product, and to suppress the yield of the product and the basic unit of material,
It is necessary to measure the thickness as close to the extrusion die as possible. However, the temperature of the resin material to be measured is high near the extrusion die, and the temperature is not constant due to the drawing speed and the cooling time.

Generally, the sound speed C of an ultrasonic wave in a resin material greatly depends on the temperature. Therefore, if the temperature is unstable, there is a problem that the measurement accuracy of the thickness is reduced.

In order to solve such inconveniences, a method for measuring the surface temperature of a resin material to be measured has been proposed (Japanese Patent Laid-Open No. 58-186010).

For example, as shown in FIG. 7, a vertical ultrasonic probe 2 is attached to an outer peripheral surface of a resin material 1 to be measured, which is made of a polyethylene tube, and an ultrasonic transceiver is attached to the ultrasonic probe 2. 3 transmits a pulse signal to the ultrasonic probe 2, detects an echo signal a from the ultrasonic probe 2 with the ultrasonic transmitter / receiver 3, and detects a surface of the echo signal a with the propagation time detector 4. The round trip propagation time Δt indicated by the time difference between the reflected echo b ₁ and the bottom surface reflected echo b ₂ is obtained. The detected propagation time Δt is input to the thickness calculator 5.

On the other hand, the temperature detector 6 measures the surface temperature T _S of the resin material 1 and sends it to the sound speed correction unit 7. The sound speed correction unit 7 corrects the sound speed C with the input surface temperature T _S ,
The corrected sound velocity C is sent to the thickness calculator 5. The thickness calculation unit 5 calculates the thickness d of the resin material 1 using the corrected sound velocity C and the above-described equation (1).

[0010] However, in the method shown in FIG. 7, for the case the thickness of the resin material 1 is thick there is a large temperature distribution in the thickness direction of the resin material, thereby representing the temperature of the entire resin material at the surface temperature T _S It is difficult. Therefore, the calculation accuracy of the calculated thickness d of the resin material 1 does not improve much.

Further, in order to solve such inconvenience, Japanese Patent Application Laid-Open No. 61-251707 discloses a method of obtaining a temperature distribution in a thickness direction in a resin material to be measured by using an operating parameter, and from this temperature distribution, The average temperature Tm is obtained, and the thickness d of the resin material is calculated by the aforementioned equation (1) using the sound speed C at that time.

The operating parameters are the surface temperature of the resin material at the measuring position, the extrusion temperature of the material, the nominal thickness, the cooling time, the residence time, and the like. Then, the temperature distribution in the thickness direction in the resin material is estimated based on these.

[0013]

However, the following problems still need to be solved in a method of obtaining a temperature distribution using the operating parameters and further obtaining an average temperature Tm.

In other words, when the thickness of the part to be measured is large, such as a resin tube, where the resin material to be measured is thick, and the thickness is measured immediately after cooling immediately after the extrusion dies, the cooling inside the resin tube is difficult. Although the vicinity of the outer peripheral surface is solid phase, the vicinity of the inner peripheral surface is still liquid phase.

Since the sound speed of the ultrasonic wave propagating in the resin material is greatly different between the case where the ultrasonic wave propagates in the solid phase and the case where the ultrasonic wave propagates in the liquid phase, even if the thickness d is measured at the sound speed C corresponding to the average temperature Tm, The measurement accuracy cannot be increased to some extent.

FIG. 8 is a graph showing the temperature characteristics of the sound speed of an ultrasonic wave propagating in a resin material. As shown in the figure, it can be understood that the temperature T decreases and the sound velocity C sharply changes near the melting point where the solid phase changes from the liquid phase. If the temperature T changes only within the solid phase, the sound speed C is almost linear with respect to the temperature. If the resin material is a solid phase, the thickness can be obtained using the sound speed C at the average temperature Tm. No problem.

However, when the resin material also contains a liquid phase, for example, if the average temperature is about 100 ° C., the thickness is determined using the sound velocity of the solid phase according to the above-mentioned prescription. Is very slow, which has a great effect on the propagation time of the ultrasonic wave, and the actual average sound speed does not become the sound speed corresponding to the average temperature. The reason for this is that the propagation time Δt of the ultrasonic wave is exactly the sound speed C
This is because the reciprocal of (x) is expressed in an integrated form.

[0018]

(Equation 1)

As described above, in each of the above-described measuring methods, there is a problem that, in the measurement of the thickness of the resin material, if the resin material to be measured contains a liquid phase, the measurement accuracy is greatly reduced.

The present invention has been made in view of such circumstances, and by determining the sound velocity distribution in the thickness direction, even if the resin material to be measured contains a liquid phase, the thickness of the resin material can be reduced. It is an object of the present invention to provide a resin material thickness measuring method and a resin material thickness measuring device capable of measuring with high accuracy.

[0021]

The present invention is applied to a resin material thickness measuring method for measuring the thickness of a resin material containing a solid phase and a liquid phase using ultrasonic waves. In order to solve the above-mentioned problems, in the method for measuring the thickness of the resin material of the present invention, the propagation time of the ultrasonic wave reciprocating in the thickness direction of the resin material is measured, and the temperature distribution in the thickness direction of the resin material is determined from the operation parameters. Calculate the sound velocity distribution in the thickness direction of the resin material from the temperature distribution in the thickness direction and the temperature characteristics of the sound velocity in the resin material, calculate the average sound velocity of the sound velocity distribution in the thickness direction, and calculate the average sound velocity The thickness of the resin material is calculated from the measured propagation time.

Further, another invention is applied to a resin material thickness measuring device for measuring the thickness of a resin material containing a solid phase and a liquid phase by using ultrasonic waves.

In order to solve the above-mentioned problems, the apparatus for measuring the thickness of a resin material according to the present invention measures the propagation time of the ultrasonic wave applied to the resin material in which the ultrasonic wave travels back and forth in the thickness direction of the resin material. Means, temperature distribution calculation means for calculating the temperature distribution in the thickness direction of the resin material from the operation parameters,
A sonic temperature characteristic storage unit that stores the temperature characteristics of the sound velocity of the ultrasonic wave propagating through the resin material; and a resin based on the temperature distribution in the thickness direction calculated by the temperature distribution calculation unit and the temperature characteristics of the sound velocity read from the sonic temperature characteristic storage unit. A sound velocity distribution calculating means for calculating a sound velocity distribution in the thickness direction of the material; an average sound velocity calculating means for calculating an average sound velocity of the sound velocity distribution in the thickness direction calculated by the sound velocity distribution calculating means; and an average sound velocity calculating means. Thickness calculating means for calculating the thickness of the resin material based on the average sound speed and the propagation time measured by the propagation time measuring means.

In the resin material thickness measuring method and the resin material thickness measuring apparatus configured as described above, the temperature distribution in the thickness direction of the resin material is calculated from the operation parameters. The operation parameters are, as described above, the surface temperature of the resin material at the measurement position, the extrusion temperature of the material, the nominal thickness, the cooling time, the residence time, and the like. Further, the sound velocity at each position in the thickness direction of the resin material can be accurately obtained from the temperature distribution and the temperature characteristics of the sound velocity.

Therefore, by accumulating the sound velocities at the respective positions in the thickness direction and dividing the accumulated value by the nominal thickness, the average sound speed in the entire thickness direction of the resin material can be obtained. The thickness of the resin material is calculated from the average sound speed and the measured propagation time.

As described above, since the average sound velocity in the entire thickness direction of the resin material is determined with high accuracy, the final thickness of the resin material is calculated with high accuracy.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a resin material thickness measuring apparatus to which a resin material thickness measuring method according to an embodiment is applied. The resin material thickness measuring apparatus of this embodiment is installed, for example, at a position near an extrusion die on a polyethylene pipe production line.

Resin material 10 to be measured, such as a polyethylene tube
When a pulse signal is applied from an ultrasonic transmitter / receiver 13, a vertical ultrasonic probe 12 disposed at a small interval on the outer peripheral surface 10a of the device 10 transmits an ultrasonic wave 11 to the resin material 10. With the surface (outer peripheral surface 10a) and the bottom surface (inner peripheral surface 1a).
Each reflected wave reflected in 0b) is transmitted to the ultrasonic transceiver 13 as an echo signal a.

The ultrasonic transceiver 13 transmits a pulse signal to the ultrasonic probe 12, receives an echo signal a from the ultrasonic probe 12, and transmits the echo signal a to the propagation time calculator 14. The propagation time calculator 14 calculates the input echo signal a
The round trip propagation time Δt indicated by the time difference between the surface (outer surface 10 a) reflected echo b ₁ and the bottom surface (inner surface 10 b) reflected echo b ₂ is calculated and sent to the next thickness calculator 15.

The surface thermometer 16 measures the surface temperature at the position where the thickness of the resin material 10 to be measured is measured and sends it to the operation parameter input unit 18. Further, the cooling time counter 17a measures a cooling time indicated by a time required for the resin material 10 to be extruded from the extrusion die to reach the thickness measurement position, and sends it to the operation parameter input unit 18. Specifically, the cooling time is determined by the transport speed of the resin material 10.

Further, the residence time counter 17b measures the residence time of the resin material 10 in the extrusion die and sends it to the operation parameter input unit 18. A nominal thickness (target thickness) d _S set by the operator is input to the operation parameter input unit 18. The operation parameter input unit 18 uses the input surface temperature, cooling time, residence time, and nominal thickness d _S as operation parameters, for example, in a one-second cycle, and calculates the temperature distribution calculation unit 1.
Send to 9

The temperature distribution calculating section 19 calculates a temperature distribution T (x) in the thickness direction of the resin material 10 to be measured shown in FIG. Here, the variable x is a distance in the thickness direction from the surface of the resin material 10. Specifically, the temperature distribution T (x) can be easily calculated by a heat conduction calculation. For example, the thermal conductivity of the resin material 10,
With the specific heat, density, extrusion temperature, and heat transfer coefficient during cooling as initial values, the temperature distribution when the cooling time elapses may be obtained by solving the heat conduction equation by a difference method or the like. Temperature distribution calculator 1
Reference numeral 9 sends the temperature distribution T (x) in the thickness direction of the resin material 10 shown in FIG.

The temperature characteristic C (T) of the sound velocity of the ultrasonic wave propagating in the resin material 10 to be measured shown in FIG. Specifically, as shown in FIG. 8, an S-shaped waveform whose characteristics change greatly near the melting point is shown. Therefore, this temperature characteristic C (T) is represented by, for example, a fifth-order polynomial as shown in Expression (3). And so on.

C (T) = a ₁ T + a ₂ T ² + a ₃ T ³ + a ₄ T ⁴ + a ₅ T ⁵ (3) a ₁ , a ₂ , a ₃ , a ₄ , a _5. Since each of the coefficients a _{1 to} a ₅ greatly changes according to the value, the temperature characteristic C (T) of the sound speed is stored and held for each resin material 10 to be measured.

The sound velocity distribution calculating unit 20 stores the temperature distribution T (x) in the thickness direction of the resin material 10 shown in FIG.
From the temperature characteristic C (T) shown in FIG. 8 stored in the table, a sound velocity distribution C (x) showing the distribution of sound velocity at each position x in the thickness direction of the resin material 10 as shown in FIG. 3 is calculated. . The sound velocity distribution calculation unit 20 calculates the calculated sound velocity distribution C in one second cycles.
(X) is sent to the average sound speed calculation unit 22.

The average sound speed calculation unit 22 calculates the average sound speed in a one-second cycle as shown in (4)
The average sound speed Cm in the thickness direction of the resin material 10 having the nominal thickness d _S is calculated using the equation.

[0037]

(Equation 2)

The average sound velocity calculating section 22 sends the calculated average sound velocity Cm in the thickness direction to the thickness calculating section 15 at one-second intervals.

The thickness calculating section 15 calculates the object to be measured in a one-second cycle from the propagation time Δt inputted from the propagation time calculating section 14 and the average sound velocity Cm inputted from the average sound velocity calculating section 22 by using equation (5). The thickness d of the resin material 10 is calculated and sent to the output unit 23.

D = Cm ・ Δt / 2
(5) The output unit 23 sends out the calculated thickness d as a measurement result in a one-second cycle, for example, to a control computer of a manufacturing line.

In the resin material thickness measuring apparatus thus configured, the temperature distribution T (x) in the thickness direction of the resin material is calculated from the operating parameters, and the temperature distribution T (x) and the temperature characteristic C of the sound velocity are calculated. From (T), the sound velocity C (x) at each position x in the thickness direction of the resin material 10 can be accurately obtained. Therefore, as shown in the equation (4), by accumulating each sound speed C (x) at each position x in the thickness direction and dividing the accumulated value by the nominal thickness d _S , the average sound speed Cm in the entire thickness direction is obtained. The average sound velocity Cm and the propagation time Δt are used to determine the resin material 10
Is calculated.

As described above, even if a solid phase and a liquid phase exist in the resin material 10, the average sound velocity Cm in the entire thickness direction of the resin material 11 can be determined with high accuracy. d is calculated with high accuracy.

Although the nominal thickness d _S is used to calculate the temperature distribution T (x), since the nominal thickness d _S is the control target thickness in the production line, the measured resin material 10 Should be approximately equal to this nominal thickness d _S. Therefore, this nominal thickness d _S is _converted to the temperature distribution T (x).
Does not increase the measurement error.

Next, specific characteristics of the resin material thickness measuring apparatus thus configured will be described with reference to actual measurement diagrams.

FIG. 4 shows the temperature distribution T (x) in the thickness direction of the resin material under various experimental conditions used for confirmation. Here, it is a temperature distribution when a polyethylene pipe having a nominal thickness d _s = 10 mm and an initial temperature of 200 ° C. is cooled from the outside. Here, it is assumed that the thickness does not change.

First, the case where the resin material having a cooling time of 400 seconds is all solid phase will be verified.

In the conventional thickness measurement procedure, the average temperature is 65.8 ° C. according to the temperature distribution T (x) in FIG. The sound speed C at this time is 2265.m from the temperature characteristic C (T) in FIG.
3 m / s. Assuming that the propagation time is Δt = 8.849 μs, the thickness is determined to be d = 10.02 mm. On the other hand, in the method of the embodiment of the present invention, a sound velocity distribution C (x) in the thickness direction of the resin material is obtained as shown in FIG. From the sound velocity distribution C (x) in FIG. 5, the average sound velocity Cm when the cooling time is 400 seconds in which the resin material is all solid phases is 2265.3.
m / s, which is equal to the result of the conventional method described above.

Next, the case where the cooling time, which is the region where the liquid phase is contained in the resin material, is 150 seconds will be verified.

In the conventional thickness measurement procedure, the average temperature is 116.3 ° C. according to the temperature distribution T (x) in FIG.
The sound speed at this time is 1856 according to the temperature characteristic C (T) in FIG.
m / s. In this case, the propagation time is Δt = 13.10.
When 4 μs is set, the thickness becomes d = 12.16 mm, which is much larger than the thickness d = 10.02 mm in the case of the solid phase.

On the other hand, in the method of the embodiment of the present invention, the average sound speed Cm when the liquid phase is contained in the resin material having a cooling time of 150 seconds from the sound speed distribution C (x) in FIG.
It was 9 m / s, and the thickness was determined to be d = 10.80 mm. The error was smaller than that of the thickness d = 10.02 mm in the case of a solid phase, and high accuracy was obtained.

FIG. 6 is a diagram showing the measurement error in each method when the thickness d is measured by the conventional method and the method according to the embodiment of the present invention at various cooling times. In FIG. 6,
In the area where the cooling time is short and the liquid phase begins to be included,
Although a large error occurs in the conventional method, measurement can be performed with a small error according to the embodiment of the present invention.

The present invention is not limited to the above embodiment. For example, the thickness d of the resin material 10 is set to (1)
Equation (2) can be used instead of the equation. In this case, it is sufficient to perform numerical integration to solve equation (2), calculate the propagation time for several thicknesses, and search for the thickness whose value is equal to the measured value of the propagation time. I just need.

[0053]

As described above, in the method for measuring the thickness of a resin material and the apparatus for measuring the thickness of a resin material according to the present invention, the sound velocity distribution in the thickness direction is obtained from the temperature distribution in the thickness direction and the temperature characteristics of the sound velocity. The average sound speed of the ultrasonic wave propagating in the resin material is calculated from the sound speed distribution.

Therefore, even if the liquid phase is contained in the resin material to be measured, the thickness of the resin material can be measured with high accuracy. As a result, a resin material having a uniform thickness can be manufactured on a manufacturing line in which the thickness measuring device is incorporated. Also, since the measurement position can be set near the extrusion die,
The yield of the produced resin material can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a resin material thickness measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a temperature distribution diagram calculated by a temperature distribution calculation unit in the resin material thickness measuring apparatus of the embodiment.

FIG. 3 is a sound velocity distribution diagram calculated by a sound velocity distribution calculating unit in the resin material thickness measuring apparatus of the embodiment.

FIG. 4 is a temperature distribution diagram in a thickness direction of a resin material with cooling time as a parameter.

FIG. 5 is a sound velocity distribution diagram in a thickness direction of a resin material with cooling time as a parameter.

FIG. 6 is a schematic diagram showing a difference in the degree of occurrence of an error between the resin material thickness measurement method of the embodiment and a conventional thickness measurement method.

FIG. 7 is a block diagram showing a schematic configuration of a conventional resin material thickness measuring apparatus.

FIG. 8 is a diagram showing temperature characteristics of ultrasonic waves propagated in a resin material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Resin material 12 ... Ultrasonic probe 13 ... Ultrasonic transceiver 14 ... Propagation time calculation part 15 ... Thickness calculation part 16 ... Surface thermometer 17a ... Cooling time counter 17b ... Residence time counter 18 ... Operation parameter input part 19 ... temperature distribution calculation unit 20 ... sound velocity distribution calculation unit 21 ... sound velocity temperature characteristic calculation unit 22 ... average sound velocity calculation unit 23 ... output unit

Claims (2)

[Claims] 1. A method for measuring the thickness of a resin material including a solid phase and a liquid phase by using ultrasonic waves, wherein a propagation time of the ultrasonic waves reciprocating in a thickness direction of the resin material is measured. Calculating the temperature distribution in the thickness direction of the resin material from the operating parameters; calculating the sound velocity distribution in the thickness direction of the resin material from the temperature distribution in the thickness direction and the temperature characteristic of the sound velocity in the resin material; Calculate the average sound speed of the sound speed distribution in the direction,
A method for measuring the thickness of a resin material, wherein the thickness of the resin material is calculated from the average sound speed and the measured propagation time. 2. A resin thickness measuring apparatus for measuring the thickness of a resin material containing a solid phase and a liquid phase using ultrasonic waves, wherein the ultrasonic waves applied to the resin material are oriented in the thickness direction of the resin material. Propagation time measurement means for measuring the propagation time of reciprocation, temperature distribution calculation means for calculating the temperature distribution in the thickness direction of the resin material from operation parameters, and temperature characteristics of sound speed of ultrasonic waves propagating through the resin material are stored. A sound speed temperature characteristic storage unit, and a sound speed distribution for calculating a thickness direction sound speed distribution of the resin material from the thickness direction temperature distribution calculated by the temperature distribution calculation unit and the sound speed temperature characteristic read from the sound speed temperature characteristic storage unit. Calculating means; average sound velocity calculating means for calculating an average sound velocity of the sound velocity distribution in the thickness direction calculated by the sound velocity distribution calculating means; average sound velocity calculated by the average sound velocity calculating means; and the propagation time measuring means. A thickness calculating means for calculating the thickness of the resin material with the propagation time measured in the step (c).