JPS62191745A - Apparatus for detecting surface flaw - Google Patents

Abstract

PURPOSE:To obtain a highly reliable flaw detector receiving no effect of noise, by taking synchronism between the timing of the noise removing processing of a noise removing circuit and the frequency of the AC power source of a surface heater. CONSTITUTION:A noise removing circuit 5 and a synchronous circuit 6 are provided to a flaw detector having a surface heater 2 heating the surface of a material 1 to be inspected, an infrared detector 3 detecting infrared rays emitted from the surface of the heated material 1 to be inspected and a signal processor 4 processing the output signal of the detector 3 to detect a flaw. The circuit 5 is provided between the detector 3 and the processor 4 and the synchronism between the timing of the noise removing processing of the circuit 5 and both of or either one of power source frequencies of the input commercial power source and output high frequency power source of the heater 2 is taken by the circuit 6. By this method, harmful power source noise is superposed to the output signal of the detector 3 and comes to a flaw judge level or more to prevent the generation of erroneous judgement.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention can be applied, for example, to a line for producing steel products.
The present invention relates to a surface defect detection device for detecting defects existing on the surface of these steel products.

[Conventional technology]

FIG. 5 is shown in, for example, Japanese Unexamined Patent Publication No. 57-111437. FIG. 2 is a diagram showing a conventional surface defect detection device.

In the figure, (1) is the material to be tested such as a slab, (2) is a surface heater for heating the surface of the material to be tested (1), and (31 is the radiation emitted from the surface of the material to be tested (1). An infrared scanner detects infrared rays while scanning them, and (4) is an image processor that processes a video signal from the infrared scanner (3).

Next, I will explain one work. For example, when the surface of the test material (1) is heated with a surface heater (2) such as an induction heating device, concave scratches (cracks) and convex m
It is known that the temperature of a defective part (such as a bald spot) is higher than that of the surrounding part because the heat conduction state and thermal radiation state are different from those of a healthy part without a defect.

Therefore, the surface of the specimen (1) after surface heating is scanned and imaged with an infrared scanner (3), and the signal is processed with an image processor (4) to detect the high temperature part.

It becomes possible to detect defective parts.

The above is the operating principle of the conventional example shown in FIG.

[Problem that the invention seeks to solve]

Generally, most of the surface heaters (2) utilize electrical energy, and in this case, a commercial AC power source is usually used as the power source. These alternating current power supplies require large currents to generate thermal energy, and this current often generates spike noise synchronized with the frequency of the alternating current power supply, disrupting the normal operation of the image processor (4). It may interfere with operation.

For example, when transformers and inductors are used in the surface heater (2), inrush currents due to the hysteresis of the cores of these transformers and inductors occur in synchronization with the timing when the polarity of the current changes. Can be a source of noise. In addition, when an induction heater is used as the surface heater (2), a high-frequency current is required for induction heating, and a circuit 5 for generating this high-frequency current 5 For example, a chopper circuit using a thyristor is used to control the polarity of the high-frequency current. Generates noise synchronized with the changing timing.

FIG. 2 is a diagram showing an example of the relationship between the current waveform of the power supply and the video signal of the infrared scanner (3). In the figure, (al
is the current waveform of the power supply, (b) is the video signal of the infrared scanner (3), (C) is the defect judgment level used as a comparison value for the video signal (video signal etc. in 41), and t
l, t2. t5. t4 is the time when the polarity of the current waveform fa) changes, N1. N2. N3. N4 is time 1. , 12.13
．． Noise waveform that adds 1 tatami to the video signal (bl) in synchronization with 1°.

Δt is the current waveform (delay time from the time when the polarity of at changes until noise occurs), and F is the waveform corresponding to the defective part in the video signal (b).For example, in the waveform example shown in Fig. 2, When the video signal (video signal, etc.) reaches a defect determination level (c1 or higher), it is determined that there is a defect.The infrared scanner (3) used is of a type in which the video signal increases at the defective part. Therefore, the part F is determined to be a defective part.In this example, the noise N is synchronized with the time when the polarity of the source current waveform (a) changes.
, r N21 N3+ NA is superimposed on the video signal (bl, of which N2 and N4 are higher than the determination level (c1), so the N2.N4 part is also determined to be defective, resulting in an erroneous detection.

As described above, conventional surface defect detection devices are affected by noise synchronized with the power frequency of a commercial power source or a high-frequency power source, significantly impairing the reliability of defect detection.

This invention was made to improve the above-mentioned problems, and aims to provide a highly reliable surface defect detection device that is not affected by noise.

[Means for resolving inter-concession]

The surface defect detection device according to the present invention includes a noise removal circuit provided between an infrared scanner and a signal processor, and synchronizes the timing of the noise removal processing of the noise removal circuit with the cross-current power frequency of the surface heater. A synchronization circuit is provided to take the following.

[Effect]

The synchronous circuit in this invention synchronizes the timing of the noise removal process of the noise removal circuit and the AC ii [frequency of the surface heater. Since this is done to coincide with the generation timing, it is possible to reliably remove noise caused by the AC power source of the 9 surface heaters.

〔Example〕

Hereinafter, one embodiment of the present invention will be described using FIG. 9. In Figure 1, (1) is the material to be tested such as slag, (2
) is a surface heater for heating the surface of the material to be inspected, and (3) is an infrared detector that detects while scanning the infrared beam emitted from the surface of the material to be inspected (1).

(4) is a signal processor for processing the output signal of the infrared detector (3), and (5) is a noise removal circuit for removing noise superimposed on the output signal of the infrared detector (3).

(61 is a synchronization circuit for synchronizing the surface heater (21) and the noise removal circuit (5).

A support that is not shown in FIG. 1 or supports the surface heater (2) and the infrared detector (3) in the actual device.

A display for displaying the processing output of the signal processor (4).

It also includes a device that provides a power source to these devices, and an operating section for configuring each part.

Next, the operation will be explained. When the surface of the test material +1+ is heated with the surface heater (2), the defective areas on the surface of the test material (1) will have a higher temperature than the healthy areas, and will generate and send out infrared rays with a shorter wavelength than the healthy areas. . This infrared rays are scanned and imaged by an infrared detector (3), passed through a noise removal circuit (51), and processed by a signal processor (4) to detect the high temperature area of the surface of the material to be inspected (1), that is, the infrared wavelength. Detect short parts of as defects.

Now, the synchronous circuit (61 is a circuit that generates a gate signal at the timing shown in FIG. 3. In the figure,
(a) is the current waveform of the power supply, (b) is the infrared detector (3)
The output signal of (d) is the goo 1 generated by the synchronous circuit (6).
No. 4 (e) is the signal waveform after noise removal by the noise removal circuit (5). The gate signal (d) is generated at time t, t2. when the polarity of the power supply current (a) changes. t5. t
Starting from l, after a certain period of time t has elapsed,
This is a signal that has a gate with a constant time twO width. t and tw, the gate is just noise N11 N21 N,
, is adjusted in advance to match the time when N4 occurs, and the noise generated in synchronization with the source current (a) has the characteristic of repeatedly occurring at the power supply frequency or twice its frequency. There is no possibility that the gate of signal (d) deviates from the noise generation timing.

The noise removal circuit (5) inputting the gate signal (dl) detects the gate signal (out of the output signal (b) of the infrared detector (31)
In order to prevent the signal at the gate portion of di from being transmitted to the signal processor (6), a signal in which the portion of the gate signal corresponding to the gate becomes a zero signal, such as the signal tel, is output. Since the surface defect detection device shown in the embodiment is configured as described above, harmful power supply noise is superimposed on the output signal of the infrared detector (3), and when this noise exceeds the defect determination level, the noise This prevents the product from being mistakenly judged as a defect.

Highly reliable flaw detection can be performed.

Now, the timing relationship of the signals in the embodiment of FIG. 1 will be shown. In Fig. 3, an example is shown in which the signal at the defective part F increases, but depending on the type of infrared detector (31), the signal decreases at the defective part, and in this case, the infrared detector (31) It is necessary to determine that there is a defect when the signal level of the output signal 31 (bl) becomes smaller than the defect determination level.In this case, the noise removal circuit (5) outputs a zero signal at the gate section. rather than
Why not output a signal larger than the defect detection level?

You can get exactly the same effect. Also, in Figure 3,
Noise N,, N2. superimposed on signal (b). N...
Although it is supposed to remove all the noise of N4.

The point is that it is good to remove harmful noise9.For example, N2
．． A gate signal (dl is generated by a synchronous circuit (
61 may also be output.

Furthermore, t is the starting point of gate generation of gate signal (d).
l, t2. button tl In Figure 3, the power supply current (a
), but this is not necessarily the time when the polarity of the source current (a) changes, but this does not necessarily have to be the case. Any point is fine as long as you choose .Also, as long as there are no large fluctuations in the load impedance, the power supply current (instead of a+!
You may use the voltage. If the cause of noise is related to the voltage waveform, the power supply voltage should be used instead.

Now, FIG. 4 shows another embodiment of the operation of the synchronous circuit (6) of the embodiment shown in FIG. In this embodiment, a sample hold circuit is used as the noise removal circuit (5), and an induction heating method, for example, is used as the surface heater (2) using a high frequency power source. Synchronous circuit (
6) synchronizes the frequency of the high frequency power supply and the sampling frequency of the sample hold circuit, that is, the noise removal circuit (5).

In the figure, (f) is a synchronization signal output from the synchronization circuit (6).

(gl is the high frequency power supply current generated based on the synchronization signal.

(hl is the output signal of the infrared detector (3), and (i) is the output signal of the noise removal circuit (5). As mentioned above, the noise removal circuit (5) is a sample and hold circuit.

Since the timing is the timing when noise occurs due to the power supply current waveform, the signal (il) output from the noise removal circuit (5) as a result of being sampled and held is a waveform that is not affected by noise at all. In this embodiment, the synchronous signal (f) generated by the synchronous circuit (61)
The high frequency power supply frequency is determined based on As long as there is a synchronization circuit (6) for sample-holding while avoiding timing and a noise removal circuit (5), the desired effect of the present invention can be obtained.

Two embodiments of the surface defect detection apparatus having the configuration shown in FIG. 1 have been described above, but the examples are not limited to these examples. In addition to gate circuits and sample-hold circuits, example type a can also be considered as the noise removing means of the noise removing circuit (51), and the combination of these noise removing circuits (5) and the surface heater (2) It goes without saying that the effects of the present invention can be brought out by providing a synchronization circuit for synchronizing the two.

Furthermore, although the embodiment shown in FIG. 1 deals with plate-shaped specimens such as slabs, it is also possible to use plate-shaped specimens.

It goes without saying that the present invention is effective regardless of the shape of the target material to be tested.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a surface defect detection device according to an embodiment of the present invention, FIGS. 2, 3, and 4 are diagrams showing signal relationships, and FIG. 5 is a diagram showing a conventional surface defect detection device. It is. In the figure, (1) is the test sample, +21 is the surface heater, (3) is the infrared detector, (4) is the signal processor, and (5) is the infrared detector.
is a noise removal circuit, and (6) is a synchronous circuit. In addition, in FIG. 9, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A surface heater that heats the surface of the material to be inspected; an infrared detector that detects infrared rays emitted from the surface of the material to be inspected heated by the surface heater; and a signal processed by the output signal of the infrared detector to detect defects. In a surface defect detection apparatus having a signal processor that performs detection, a noise removal circuit is provided between the infrared detector and the signal processor, and the timing of noise removal processing of the noise removal circuit and the surface heater 1. A surface defect detection device comprising a synchronization circuit for synchronizing the power frequency of both or either of an input commercial power source and an output high-frequency power source.