JPS6255100B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a so-called rotating probe type flaw detector that detects flaws while rotating an ultrasonic or eddy current probe along the outer periphery of a test material. This invention relates to a signal transmitting/receiving device between.
Note that the present invention can be implemented not only for signal transmission and reception of ultrasonic flaw detection, but also for signal transmission and reception of eddy current flaw detection, etc.; however, in order to simplify the explanation below, ultrasonic flaw detection will be exemplified and explained.

In order to perform ultrasonic flaw detection on long rolled products with a circular cross section, such as pipes or round bars, the probe is rotated at high speed along the outer periphery of the material to be tested, while the material is axially rotated. So-called rotating probe type flaw detectors, which detect flaws over the entire length of the test material by propelling it forward and scanning the outer circumference of the test material in a spiral manner, are often used in steel mills and rolling mills. This flaw detector uses a rotary probe holder equipped with a multi-channel probe to rotate around the outer circumference of the material being tested at high speed, allowing for fast flaw detection and extremely high-efficiency inspection. It is used as an important non-destructive testing device in manufacturing factories.

Although this flaw detector is suitable for high-efficiency flaw detection, it requires a signal transmission device to transmit and receive flaw detection signals between the probe attached to the probe holder on the rotating part and the fixed part. It is no exaggeration to say that the overall performance of a rotating probe type flaw detector is influenced by the function and performance of this signal transmission device.

In conventional rotary probe flaw detectors, the most widely used signal transmission devices from the earliest flaw detectors to the present are slip rings and brushes. When considering the problem of signal transmission, devices using slip rings and brushes are the most elementary and basic devices, and in order to understand the present invention, we will briefly explain the slip rings and brush signal transmission devices. I think it is necessary.

Figure 1 shows a slip ring as a signal transmission device.
An overview of the structure of a rotating probe type flaw detector using a brush is shown below. 1 is a steel pipe to be inspected and is guided by a guide 2 and transported in the direction of the arrow through a rotating probe type flaw detector. The rotor 3 of the probe rotating type flaw detector is supported by bearings 4a and 4b at both ends of the rotor.
Timing pulley 5 fitted to the end of the rotor shaft
The drive motor 7 is engaged with the drive motor 7 via the timing belt 6 that meshes with the timing belt 6, and rotates at high speed. rotor 3
A probe holder 9 is attached to the face plate 8 on the end surface of the rotor 3 at the other end of the rotor 3, and the probe holder 9 has a plurality of probes 10a, 10b, .
is installed. Coaxial cable 1 from this probe
1a, 11b, . . . are connected by connectors 12a, 12b, . On the other hand, the connectors 12a, 12b... of the face plate 8 and the rotor 3
A slip ring 14a ₁ arranged on the outer periphery of the cylindrical part,
14a ₂ , 14b ₁ , 14b ₂ , 14c ₁ , 14c ₂ . . . are connected. Here, the slip ring _14a2 is connected to the shield of the coaxial cable, and the slip ring _14a1 is connected to the center conductor, that is, the probe 10a is connected to the slip ring 1.
4a ₁ and 14a ₂ , the probe 10b is similarly attached to the slip rings 14b ₁ and 14b _{2, and the probe 10b is similarly attached to the slip rings 14b 1 and 14b 2} .
c is connected to slip rings 14c ₁ , 14c ₂ . . . .

FIG. 2 shows the transportation of the brush part, where the brush 15 is loosely fitted into the brush holder 16 and held by the coil spring 17.
is crimped onto the slip ring. The coil spring 17 is compressed by the cap 18. cap 18
The lead wire 19 from the brush 15 is drawn out through a hole provided in the center of the brush 15.

In the conventional signal transmission device using a slip ring and a brush as described above, transmission is essentially through sliding contact between the slip ring and the brush, so contact noise and wear are unavoidable. The speed is limited, and material selection is required depending on the conditions of use.Adjacent channels are electrostatically coupled due to capacitance, resulting in cross talk between channels.Dirty slip rings may cause brush contact. There were problems such as the need for sophisticated maintenance of slip rings and brushes due to unstable conditions.

As a signal transmission means to solve these problems, an electromagnetic coupling signal transmission device that transmits signals in a non-contact manner has been put into practical use. As an example of this device, its structure is shown in FIG. In FIG. 3, the slip ring and brush portions of FIG. 1 are replaced with an electromagnetic coupling signal transmission device, so explanations of the same contents as in FIG. 1 will be omitted.

On the outer periphery of the cylindrical portion of the rotor 3, disks 20 of electromagnetic coupling coils made of glass fiber epoxy substrates are arranged in a number corresponding to the number of channels. The disk 20 has an annular shape as shown in FIG.
A single conductor 21 is carved as a 1-turn coil along the outer edge of the 1-turn coil.
Pull it out to the inner edge of the ring as shown in 2a and 22b. Conductive wire 21 on disk 20 and both end drawers 2
2a and 22b are fabricated by etching the above-mentioned patterns from a glass fiber epoxy substrate with copper foil attached. A ferrite core 23 is arranged so as to surround a conductor 21 of a one-turn coil. A slit 24 is machined in one part of the ferrite core 23, and a slit 2
4 are inserted so that the disc 20 is sandwiched therebetween. A coil 25 of several turns is wound around the ferrite core 23. Further, although not shown, an electromagnetic shield plate is inserted between each disc to prevent crosstalk between adjacent channels.

If the pulser/receiver of the flaw detector 26 is connected to the coil 25 with the above configuration, a pulse is induced in the one-turn coil via the ferrite by the excitation pulse from the pulser during transmission, and this pulse causes the probe to Drive 10. In the case of reception, the reception signal from the probe is transmitted from the one-turn coil to the coil 25 via the ferrite, contrary to the transmission, and is transmitted to the receiver of the flaw detector.

The above-mentioned electromagnetic coupling type signal transmission device can effectively transmit and receive flaw detection signals between rotating parts and fixed parts without contact, and eliminates the problems of noise, wear, and maximum circumferential speed that were problems in signal transmission using slip rings and brushes. It is an excellent transmission device that has no limitations and solves maintenance management problems, and is effectively put into practical use in applications where the problems described below do not pose a problem.

This electromagnetic coupling type signal transmission device has a large coupling loss because it is a one-turn coil coupling, and although it depends on the design conditions, a disk with a diameter of about 400 mm has a diameter of 2M.
There is about 30 dB attenuation compared to when transmitting and receiving by connecting the probe directly to the flaw detector at Hz or 5 MHz, and it is necessary to equip the probe with a resonant coil to compensate for this attenuation. Due to these reasons, the flaw detection waveform is broader than that of direct connection, and although it is practical at 2MHz and 5MHz, even though there are the above problems, at higher frequencies, such as
At 10MHz, the attenuation is large and exceeds 40dB, making it impractical in high frequency ranges.

The above problem is that when performing ultrasonic flaw detection of steel pipes using a rotating probe type flaw detector, in normal ultrasonic flaw detection of steel pipes, flaws on the inner and outer surfaces in the axial direction of the pipe, and flaws on the inner and outer surfaces in the circumferential direction are detected using oblique angles. Since 2MHz or 5MHz is commonly used for flaw detection, there is no problem in using an electromagnetic coupling signal transmission device for flaw detection. There are many requests for ultrasonic measurement of pipe wall thickness in conjunction with oblique defect detection in the pipe circumferential direction. To measure pipe wall thickness using ultrasonic waves, ultrasonic waves are incident perpendicularly to the wall thickness direction.
The wall thickness is measured by measuring the ultrasonic propagation time between echoes of multiple reflections occurring on the inner and outer surfaces of the pipe, so echo separation becomes a problem, requiring the use of a high frequency of 10 MHz or more, and the waveform in the signal transmission system. Avoiding broadness is an absolute necessity. For this reason, it can be seen that the above-mentioned electromagnetic coupling type signal transmission device cannot be used for measuring pipe wall thickness using ultrasonic waves.

The present invention provides a signal transmission device that can be used in the area of pipe wall thickness measurement using ultrasonic waves, which cannot be used with the signal transmission device using the electromagnetic coupling method described above. It is desirable to implement the electromagnetic coupling method in combination with the signal transmission device according to the present invention in the pipe wall thickness measurement system.

The signal transmission device of the present invention uses electrostatic coupling, and the structure of the present invention makes it possible to implement such a system using electrostatic coupling. In Fig. 5, instead of directly connecting the terminals 26a, 26b of the ultrasonic flaw detector 26 and the probe 10, a capacitance is used as a transmission path between the two to detect the transmission characteristics. It is a connection diagram when experimenting the relationship between capacitance and flaw detection sensitivity. That is, the steel pipe 1 is vertically inspected by the probe 10 while immersed in water. Coaxial cable 28 of probe 10
Capacitors 27a and 27b are connected between the external connection coaxial cable 29 and the external connection coaxial cable 29. 27a is for the center conductor of the coaxial cable, and 27b is for the shield. The external connection coaxial cable 29 is connected to terminals 26a and 26b of the transmitting/receiving section of the flaw detector 26.

FIG. 6 shows data obtained by measuring attenuation values for various capacitance values when connecting capacitance with respect to direct connection in the case of 25 MHz and 10 MHz in the above connection.

From the data in Figure 6, at 10MHz, the capacitance values of 27a and 27b in Figure 5 are each 2000pF.
If it is above, it can be seen that even if the capacitance value changes somewhat, the fluctuation in flaw detection sensitivity is extremely small. According to experiments, no change in waveform was observed at 200 pF or more compared to when the probe was directly coupled. Generally, the relationship between the capacitance C (F) between parallel plane electrodes, the electrode area A (m ² ), and the inter-electrode distance d (m) is given by the following equation.

C=8.854×10 ^-2 ×A/d……(1) The rotor diameter of a normal probe rotating type flaw detector varies depending on the maximum diameter of the applicable test material, but for example, the rotor diameter is 3″ outer diameter.
76.2 mm, it becomes approximately 250 mm, and considering a doughnut-shaped electrode as shown in FIG. 7, the inner diameter D ₁ of the electrode disk is considered to be approximately 250 mm. Assuming the electrode width W50mm and effective diameter DE300mm,
The electrode area is 471 cm ² . Assuming a capacitance of 2000 pF and inserting 471 cm ² into the area of the above equation (1) to find the distance d between the electrodes, d = 0.2 x 10 ^-3 m = 0.2 mm is obtained.

The distance between the electrode plates determined by the above calculation is 0.2 mm
The gap between the rotating annular electrode and the stationary electrode is
It is impossible to maintain the fixed electrode at 0.2 mm by spatially fixing the fixed electrode, but in the present invention, a micro gap is created using air pressure between the fixed electrode and the rotating annular electrode, so that the fixed electrode can be held in a non-contact state. It was constructed so that it could be maintained.
The structure and operation of the present invention will be explained in detail below.

FIG. 8 is a diagram explaining the gist of an embodiment of the present invention. The rotating annular electrode 31 is attached to the rotor 3 via an insulating plate 30 and rotates in the direction indicated by the arrow in FIG. The fixed part side electrode 3 faces the rotating annular electrode 31.
As shown in FIG. 9, the fixed part side electrode 32 is secured to a fixed plate by plate springs 33a, 33b, 33c, 33d... equally distributed on the circumference of the fixed part side electrode 32. 35 and is spring-pressed to the rotating annular electrode 31. In addition, leaf springs 33a, 33b, 33
There are air hole nipples 34a, 34b, 34c, 34d... in the middle of each arrangement position of c, 33d..., and the air hole nipples are emptied by flexible vinyl pipes or rubber pipes (not shown). supply pressure.

In this embodiment with the above configuration, the fixed side electrode 32 is spring-pressed to the rotating annular electrode 31.
Air hole nipples 34a, 34b, 34c, 34d
Air pressure supplied from the fixed side electrode 32 opens between the contact surfaces of the rotating annular electrode 31 and blows out to the fixed side electrode 3.
2 is held in a floating state similar to a thrust air bearing. Both opposing surfaces of the stationary electrode 32 and rotating annular electrode 31 must be finished with a flatness of approximately 0.05 mm, and at the same time, one of the opposing surfaces must be coated with a thin insulating resin, such as tetrafluoroethylene resin. By applying a fluororesin coating treatment, even if partial contact occurs, it is possible to prevent direct contact between the two electrodes, and a wear-resistant lubricant film can prevent excessive wear due to contact between the two electrodes. desirable. Note that the gap between the electrodes can be adjusted by adjusting the supplied air pressure.

In the above embodiment, a method of supplying air pressure to the stationary electrode from the outside was shown, but the rotor rotation speed of the rotating probe type flaw detector is extremely high due to its performance, e.g.
Since it is normally used at 3000 rpm, it is also possible to automatically generate air pressure as the rotor rotates, and use this air pressure to obtain the same effect as in the above embodiment. .

That is, FIGS. 10 and 11 show the structure of a rotating annular electrode for automatically generating air pressure. In the figure, the rotating annular electrode 31 rotates at high speed in the direction of the arrow. The rotating annular electrode 31 has a plurality of air fins 36a, 36b, 36c, 36d... arranged at equal positions around the entire circumference.
is provided. Air fins 36a, 36b, 36
When rotated at high speed in the direction of rotation shown by the arrow in FIG. 10, the blades c, 36d, . That is, FIG. 11 shows a sectional view along the circumference of the air fin 36a of FIG. 10. When the air fin 36a moves at high speed as indicated by the solid line arrow, it generates an air flow as indicated by the dotted line arrow, so if there is a stationary electrode close to the back side of the rotating annular electrode 31, air pressure is generated on both opposing surfaces. This produces the same pneumatic effect as the embodiment described above. In this case, since it is the rotating annular electrode 31 that automatically supplies air pressure to the gap between both electrodes, the stationary side electrode is as shown at 32 in FIG. 12, excluding the pneumatic nipples 34a, 34b, etc. in FIG. 9. The structure is as follows. Note that the opposing surfaces of both electrodes always slide when the rotor is at excessively low rotational speed when starting or stopping the rotor, so as in the previous example, one of the opposing surfaces is coated with tetrafluoroethylene resin. It is necessary to perform film processing, and the distance between the electrodes is adjusted by adjusting the spring pressure applied to the fixed electrode.

The signal transmission device using capacitive coupling explained above is
This is a technical solution by providing electrode spacing to ensure the capacitance required for signal transmission, and it is possible to transmit and receive flaw detection signals at a frequency of 10 MHz using a signal transmission device using capacitive coupling as in the present invention. , and enables waveform transmission that is no different from direct probe connection, and the technical effects are significant.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of a conventional rotating probe flaw detector using a slip-ring brush, Figure 2 is a structural diagram of the brush section shown in the previous figure, and Figure 3 is the slip-ring brush shown in Figure 1. Fig. 4 is a diagram showing the rotational configuration of the electromagnetic coupling in Fig. 3; Fig. 5 is a circuit diagram of the capacitive coupling according to the present invention; Fig. 6 5 is the measurement data of the attenuation value of the ultrasonic transmission waveform with respect to the connection capacitance when the circuit is connected as shown in FIG. 5, FIG. 7 is the disc-shaped ring electrode of the capacitive coupling according to the present invention, and FIG. A configuration diagram showing an embodiment of the present invention, FIG. 9 is a configuration diagram of a rotating annular electrode and a fixed part side electrode of the invention, FIGS. 10 and 11 are configuration diagrams of a rotating annular electrode having air fins, FIG. 12 is a facing view of a rotating annular electrode having air fins and a fixed part side electrode. 10... Probe, 28, 29... Coaxial cable, 31... Rotating annular electrode, 32... Fixed part side electrode, 33a, 33b, 33c, 33d... Leaf spring, 34a, 34b, 34c, 34d ...Air hole nipple, 36a, 36b, 36c, 36d...
Air Finn.

Claims (1)

[Scope of Claims] 1. A disc-shaped disc provided on the rotor for transmitting and receiving signals between the probe attached to the rotor side of a rotating probe type flaw detector and the fixed part side, and the receiving part. A fixed part side electrode is disposed opposite to the rotating ring electrode, and the fixed part side electrode is pressed against the rotating ring electrode by a spring so that both surfaces are in contact with each other, and one or both of the surfaces is coated with fluorine. A signal transmission device for a rotating probe type flaw detector that uses capacitive coupling to maintain insulation between both electrodes through resin coating treatment. 2. In order to send and receive signals between the probe attached to the rotor side of the rotating probe type flaw detector and the fixed part side, and the receiving part, there is a disc-shaped rotating ring electrode installed on the rotor. Opposing fixed part side electrodes are arranged, the fixed part side electrodes are pressed against the rotating annular electrode by a spring so that both surfaces are in contact with each other, and one or both of the two surfaces are treated with a fluororesin coating to make both electrodes A plurality of air holes are provided at circumferential positions of the electrode on the fixed part side, and a plurality of air holes are provided at circumferential positions of the electrode on the fixed part side. A signal transmission device for a rotating probe type flaw detector using capacitive coupling, which provides a required electrode spacing between the two electrodes by applying air pressure. 3 In order to send and receive signals between the probe attached to the rotor side of the rotating probe type flaw detector and the fixed part side, and the receiving part, there is a disc-shaped rotating ring electrode installed on the rotor. Opposing fixed part side electrodes are disposed, and the fixed part side electrodes are pressed against the rotating annular electrode by a spring so that both surfaces are in contact with each other, and one or both of the two surfaces are treated with a fluororesin coating to make both electrodes By arranging a plurality of air fins at circumferential positions of the rotating annular electrode, the air pressure caused by the high speed rotation of the rotor is transferred between the rotating annular electrode and the fixed part side electrode. A signal transmission device for a rotary probe type flaw detector that uses capacitive coupling to provide a predetermined electrode spacing between the two electrodes.