JPH0326467Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a device for detecting welded seams in plates, rods, pipes, etc.

(Prior Art) There are cases where it is necessary to automatically detect weld seams of plates, rods, pipes, etc. while feeding them. For example, spiral steel pipes are manufactured by coils made by joining strips together by welding, but after the pipe is manufactured, the portion of the pipe corresponding to the joint is cut and scrapped. Since this cutting is done automatically, the joint of the coil must be automatically detected while the coil is being unwound from the unwinding machine.

An eddy current type device is known as one type of weld seam detection device. In this method, an excitation coil and two detection coils are placed close to a material to be detected, such as a plate. An alternating current is supplied to the excitation coil to magnetize the material to be detected, and the impedance of the two detection coils is detected. If the material of the material to be detected is uniform, the impedance of both detection coils will be balanced, but if one detection coil is located at a weld seam, the impedance of both detection coils will be unbalanced due to eddy current loss, changes in magnetic resistance, etc. . Then, if the magnitude of the difference in impedance between the two detection coils exceeds a preset reference signal level, it is determined that there is a weld seam.

(Problems to be Solved by the Invention) In conventional devices, the level of the reference signal is determined and fixed in advance depending on the material of the object to be detected, the degree of amplification of the device, etc. Therefore,
If the material to be detected has irregularities due to scratches, adhesion of foreign matter, etc., and the signal due to the irregularities exceeds the level of the above-mentioned fixed reference signal, the irregularities will be erroneously determined as a weld seam.

This idea was made in order to solve the above-mentioned problems with conventional weld seam detection devices, and it is possible to distinguish between irregularities such as scratches and weld seams, and to create a weld seam detection device that detects only weld seams. This is what we are trying to provide.

(Means for Solving the Problems) The weld seam detection device of this invention includes a first detection coil, an excitation coil, and a second detection coil that are arranged adjacent to each other in sequence along the feeding direction of the detected material. , an oscillation circuit that supplies an alternating current to the excitation coil, a differential amplifier circuit that uses signals from the first detection coil and the second detection coil as input signals, and a differential amplifier circuit that uses the signal from the oscillation circuit as a reference signal. A detection circuit that synchronously detects signals from
and a comparison circuit that compares the signal level from the detection circuit with the reference signal level from the reference signal setting circuit. The reference signal from the reference signal setting circuit is variable at a level that allows discrimination between weld seams and surface irregularities of the detected material.

(Function) The excitation coil and the detection coil are arranged close to the surface of the material to be detected. Further, the two sets of detection coils are arranged along the moving direction of the detected material, that is, so that the weld seam passes sequentially from the upstream detection coil to the downstream detection coil via the excitation coil. An alternating current is supplied from an oscillation circuit to the excitation coil to magnetize the material to be detected. Two sets of detection coils detect reactions caused by eddy currents generated in the material to be detected. The fact that the difference between the output signals of both detection coils is 0 indicates that there is no weld seam in the detected material at the detection position. Furthermore, when a weld seam comes to one of the detection positions, a difference in impedance occurs between the two detection coils due to the difference in material between the detected material itself and the weld seam, and a signal of this difference is input to the detection circuit. Then, a comparison circuit compares the reference signal and the DC signal from the detection circuit to detect a weld seam.

If the surface of the material to be detected is uneven, the gap between the detection coil and the material to be detected changes at the uneven portion, resulting in a difference in impedance between the two detection coils, and the unevenness is incorrectly determined as a weld seam. The output signal due to the unevenness is smaller than the output signal due to the weld seam. In the device of this invention, the reference signal of the comparison circuit is variable, so the reference signal is set between the output signal level due to the weld seam and the output signal level due to the unevenness. Therefore, only weld seams are detected. The level of the reference signal depends on the material of the detected material,
It is set in advance in consideration of dimensions, excitation frequency, size of unevenness, etc.

(Embodiment) FIG. 1 shows an embodiment of this invention, and is a block diagram of a weld seam detection device.

The device is divided into a detection section 1 and a signal processing section 11.

The detection section 1 consists of a test coil 2. The test coil 2 has an excitation coil 3 in the center and detection coils 4 and 5 on both sides thereof. The test coil 2 is placed close to the surface of a material to be detected (in this case, a plate material used for manufacturing electric resistance welded steel pipes) M. Board material M
is sent at a constant speed (for example, 30 m/s) in the direction of arrow S.

An oscillation circuit 12 of a signal processing section 11 is connected to the excitation coil 3 via an output amplification circuit 13. The excitation coil 3 is supplied with a low frequency (for example, 3KHz) alternating current from an oscillation circuit 12 . The plate M is AC magnetized by the excitation coil 3, and eddy current is generated.

The detection coils 4 and 5 are connected to input amplification circuits 15 and 16 of the signal processing section 11, respectively. Furthermore, the input amplifier circuits 15 and 16 are connected to a differential amplifier circuit 19 via phase circuits 17 and 18, respectively. An induced voltage is generated in the detection coils 4 and 5 by the eddy current, and the two induced voltages are amplified by input amplifiers 15 and 16, and then the difference between the two voltages is amplified by a differential amplifier circuit 19. Phase circuit 17, 18
is used to adjust the balance (phase) of both detection coils 4 and 5.

When both the detection coils 4 and 5 do not detect the weld seam W or the unevenness D, the impedances of both the detection coils 4 and 5 are balanced and the output from the differential amplifier circuit 19 becomes zero. Furthermore, when either of the detection coils 4 and 5 detects the weld seam W or the unevenness D, the differential amplifier circuit 19 outputs a signal at a level corresponding to the weld seam W or the unevenness D.

The differential amplifier circuit 19 is connected to a detection circuit 22 via a band amplifier circuit 20 and a changeover switch 21. The band amplification circuit 20 amplifies only the alternating current of a specific frequency (3 KHz in this case), cuts out other frequency components, and inputs them to the detection circuit 22. Further, the oscillation circuit 12 is connected to the detection circuit 22 via an amplifier circuit 14 and a changeover switch 21.

When the changeover switch 21 is switched to the other side, the detection circuit 22
The output waveform of is always in the + direction.

The signal from the differential amplifier circuit 19 is synchronously detected in the detection circuit 22 based on the reference signal from the oscillation circuit 12. The detection circuit 22 outputs a DC component (amplitude is
(varies at 3KHz) is output.

The detection circuit 22 is connected to a band amplification circuit 23. The band amplification circuit 23 removes a specific frequency (3KHz) and outputs a signal with constant amplitude.

A display circuit 24 and a comparison circuit 25 are connected to the output side of the band amplification circuit 23. Display circuit 2
4 displays the output signal from the band amplification circuit 23 using an LED or the like.

The reference signal level of the comparison circuit 25 is determined by the setting circuit 26.
It is variable depending on As shown in FIG. 2, the level of the output signal A due to the unevenness is smaller than the level of the output signal B due to the weld seam. Therefore, by setting the level of the reference signal R to an intermediate level between the output signals A and B, only the output signal B due to the weld seam can be extracted. The level of the reference signal R is set in advance by the setting circuit 26 according to the material, size, excitation frequency, size of unevenness, etc. of the material to be detected.

An output circuit 27 is connected to the comparison circuit 25 . The output circuit 27 includes a relay excitation circuit, etc.
Outputs control signals to control devices, drive devices, etc.

(Effect of the invention) In the weld seam detection device of this invention, the level of the reference signal of the comparison circuit for determining a weld seam is variable. By setting the level of the reference signal between the output signal level of the weld seam and the output signal level due to the unevenness, only the weld seam can be detected. Therefore, it is possible to accurately detect the weld seam without erroneously determining that the unevenness is a weld seam. Furthermore, since the level of the reference signal of the comparison circuit is simply made variable, the device can be constructed easily and economically, and existing devices can be easily modified to the device of the present invention.

Note that this invention is not limited to the above embodiment. For example, the material to be detected may be a rod or a tube instead of a plate. In this case, a through-type or interpolated type test coil is used.

[Brief explanation of the drawing]

FIG. 1 shows an example of the weld seam detection device of this invention, and is a block diagram showing the configuration of the device, and FIG. 2 is a diagram showing the level of the output signal due to the weld seam and irregularities. 1...detection section, 3...excitation coil, 4, 5...
Detection coil, 11...Signal processing section, 12...Oscillation circuit, 13-16...Amplification circuit, 17, 18...
Phase circuit, 19... Differential amplifier circuit, 20, 23...
... Bandwidth amplifier circuit, 22 ... Detection circuit, 25 ... Comparison circuit, 26 ... Setting circuit.

Claims (1)

[Scope of utility model registration request] A first detection coil, an excitation coil, and a second detection coil arranged adjacent to each other in sequence along the feeding direction of the detected material, an oscillation circuit that supplies an alternating current to the excitation coil, the first detection coil, and Refer to the differential amplifier circuit that uses the signal from the second detection coil as an input signal, the detection circuit that synchronously detects the signal from the differential amplifier circuit using the signal from the oscillation circuit as a reference signal, and the signal level from the detection circuit. , comprising a comparison circuit for comparing the level of the reference signal from the signal setting circuit, and characterized in that the reference circuit from the reference signal setting circuit is variable at a level that allows discrimination between weld seams and surface irregularities of the detected material. Weld seam detection device.