JP2001521170A - Device for detecting defects in plastic ribbons, parts or tubes by ultrasonic signals - Google Patents

Abstract

The present invention relates to an apparatus for detecting defects in a continuously moving plastic ribbon, section or tube by means of an ultrasonic signal. The measuring head, which introduces the ultrasonic signal into the plastic and receives the reflected signal, is either fixedly arranged over the width of the ribbon to this end or distributed around the tube. The mathematical combination of the signals in the subtraction and addition stages can successfully reduce the number of signals important in the evaluation.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention detects defects in a continuously moving plastic ribbon or tube by means of ultrasonic signals introduced into the plastic from a measuring head which is fixedly arranged around the circumference of the tube or over the width of the ribbon. The reflected signal is received by the measuring head and transmitted to an evaluation unit.

Prior art devices of the type specified for tubes (US Pat. No. 4,740,146)
In, since a few measuring heads are arranged fixedly in a relatively large area, they cover the tube wall only with a few strips extending in the direction in which the tube passes. Such a device is suitable for measuring wall thickness, since the change in peripheral thickness is usually not confined to a narrow longitudinal strip but extends over a rather large peripheral area. However, such devices are not suitable for detecting defects, since defects are often exclusively confined to very small locations.

[0003] However, the testing of the tube wall over its entire circumference is based on a different prior art device (DE 40 33 443) having a measuring head extending around the entire circumference of the tube.
Al). However, driving and guiding such a measuring head involves very expensive equipment. With the use of such a measuring head, there is also the fact that for a continuously moving tube only a spiral path can be covered. In this case, too, there may be areas that are not covered.

In another prior art device (US-PS 5,431,054) for the detection of defects in continuously moving stretched products, a number of receivers are equipped with an ultrasonic transmitter and Involved. The ultrasonic transmitter and receiver are arranged in a single line in the direction in which the stretched product moves. In order to be able to cover the stretched product over its entire surface, the relevant movement in the peripheral direction must be performed in addition to the linear movement of the stretched product in the direction in which it moves . However, such a combination has a single transmit and receive measuring head that moves around the tube or laterally in the direction of ribbon movement, or has more fixed around the tube or laterally in the direction of ribbon movement. It is expensive in itself in comparison with a device for detecting defects having a transmitted and received measuring head.

[0005] In one prior art device for ultrasound testing, which also has only one ultrasound transmitter and a number of receivers associated therewith, more particularly in the medical field (US
-PS 4,680,966), the signals received in parallel are output to various difference stages and then to an addition stage. This prior art discloses how to perform a spatial arrangement of the receiver in connection with the determination of a defect over the entire area of the object to be measured, such as a continuously moving ribbon or tube. Absent.

It is an object of the present invention to thoroughly test the material of a continuously moving ribbon, section or tube,
It is another object to provide an apparatus for completely detecting defects.

[0007] The problem is that since the measuring heads are arranged one after the other and laterally in the direction of movement of the ribbon or tube, the measuring head completely covers the ribbon / tube and the evaluation unit The reflection signals emitted from the individual measuring heads are combined with one another for the same length of unit of the ribbon / tube, so that a device of the type specified by the form in which only defects are dealt with is solved. Is done. More specifically, individual sensors can be combined into many sections or blocks. Further, according to one aspect of the invention, the step of difference and / or the step of summation is related to a signal of an adjacent measuring head, the indication of an error is related to each difference step, and In this connection plane, the stages of difference with error indication and the stage of summation are associated with each summation stage associated with an adjacent measuring head.

According to the invention, a number of ultrasonic signals are output from the individual measuring heads to the evaluation unit for the same length of unit of the ribbon / part / tube. A large number of signals can be reduced to a few, either by combining signals by subtraction or addition from each other.
Is reduced to This allows the evaluation unit to output results that can be immediately investigated for subsequent processing / follow-up devices / operators. In this measurement method, the invention starts with the recognition that the signals received from the two measurement heads are generally identical only if no defect is detected. If a defect is detected, it appears in one of two signals,
By subtracting the two signals, the defect is clearly recognizable. However, for the rare case where the defect signal is not indicated by subtraction, because each two reflected signals relate to similar defect locations, the defect indication is more than or several times rather than just one other signal. It can be generated by combining each signal with the further signal. More particularly, defects can be detected by the formation of a difference between the output signals of the signals combined in pairs by addition. With such coupling, it is practically impossible for all the combined signals to contain the same defect location. The combination of the signals by subtraction and addition can be repeated several times in order to obtain as few indicated signals as possible. In combining, for example, in signal subtraction, the indication is output on a separate combining surface only if the output signal is not zero.

However, in the present invention, not only the defect location of the ribbon / portion / tube but also the thickness can be detected. In this case, the combination is performed by summing the signals. The wall thickness can then be determined in a conventional manner from the summed signals. Embodiments according to the invention are described below in more detail with reference to the drawings.

[0010] Ultrasonic pulses are introduced into the tube R in order to allow the covering of the wall of a continuously moving plastic tube, for example the tube R arriving from the extruder, over its entire area. And a plurality of measuring heads 1, 2, 3,... Receiving the reflected signals S1, S2, S3, S4 of the ultrasonic pulse and transmitting them to the evaluation unit.
4 are arranged in a ring around the entire circumference of the tube R.

A typical reflected signal is the signals S 1 and S 2 shown in FIG. Due to these signals, the first reflection is a collision on the outer wall of the tube and the second reflection occurs on the inner wall of the tube after passing through the tube wall. These are the large swings of the two graphs. The second large runout is smaller than the first large runout because the signal is weakened as it passes through the tube wall. The two graphs also show two substantially smaller runouts due to the location of the defect. Substantially less runout in graph S1 indicates a defect in the central area of the tube wall, while substantially less runout in graph S2 indicates a defect in the inner wall of the tube. The reflected and defective signals at the inner wall of the tube are listed separately only for better clarity of the graph. In effect, the sum of the two signals is obtained.
The two signals S1, S2 are subtracted for evaluation. The result obtained is the signal S
= S1-S2, which comprises only defective locations, as shown at the bottom of FIG. This considerably simplifies the evaluation compared to the individual evaluation of the signals S1, S2.

The electronic evaluation unit shown in FIG. 3 is preferably used for combining the signals S1, S2 and also the signals S3, S4. The reflected signals S1, S2, S3, S4 emitted by the measuring heads 1, 2, 3, 4 are output at the same time to an evaluation unit where they are connected to each other on different planes. At the stage of M1 [-], a difference is formed between the signals S1 and S2. If the defect signal is included in the signal S1 or S2, the output signal of the M1 [-] stage is not zero. The monitor circuit T1 forms, for example, a trigger shape and outputs a corresponding alarm signal in case of a defect. The addition of the signals S1 and S2 is performed in the M1 [+] stage. Signal S
1, the sum signal of S2 is output to both the step M [-] for the formation of the difference and the step M [+] for the addition at the next coupling plane.

[0013] The signals S3, S4 are coupled to each other in a corresponding manner. Thus, the signal S3
, S4 is performed in step M2 [-], and the formation of the sum of the signals S3, S4 is performed in step M2 [+]. The output signal of stage MS [-] is M2 [-
When the output signal of the step is not 0, the present invention is applied to a monitor circuit T2 which forms a trigger for outputting an alarm signal.

The output signal of the stage M2 [+] for summation is output on the one hand to the aforementioned stage M [-] for subtraction, and on the other hand the stage obtained with the two signals S1, S2. It is output to stage M [+] for summation with the output signal of M1 [+]. The monitor circuit T3 is concerned with the next coupling plane step M [-] described above and forms a trigger which outputs an alarm signal if the signal is not zero. The step M [+] for summation in the next joining plane outputs a signal in a further step for the formation of sums and differences in the next next joining step.

This double combination due to the formation of the sums and differences of the different signals, even if they are identical, cancel each other out when combined by subtraction, so that defects can be detected. To secure. For example, if the errors in signals S1 and S2 are the same, they appear amplified with the sum signal at the output of stage M1 [+]. Since they can also be predicted not to appear in the signals S3, S4, the signal of the defect is obtained by the shape of the difference of the sum of the steps M1 [+] and M2 [+].

Obviously, the evaluation unit can have many coupling surfaces, so that the operator (
The number of signals associated with the driver) is as small as possible. The output signal of the total stage M [+] at the last coupling surface is also a measurement of the wall thickness.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view through a tube wall part with four related measuring heads.

FIG. 2 is a diagram of various reflected signals and their combination.

FIG. 3 shows an evaluation unit for signal combination.

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Claims (2)

[Claims] 1. An apparatus for detecting defects in a continuously moving plastic ribbon or tube by means of ultrasonic signals introduced into the plastic from a measuring head fixedly arranged around the circumference of the tube or over the width of the ribbon. In the device, the reflected signal is received by the measuring head and output to the evaluation unit, since the measuring heads are arranged one by one and laterally in the direction of movement of the ribbon or tube. The measuring head completely covers the ribbon / tube and the evaluation unit combines the reflected signals emitted from the individual measuring heads with each other for the same length unit of the ribbon / tube. A device for detecting defects in ribbons or tubes, characterized in that only defects are reported. 2. The method according to claim 1, wherein the step of difference (M1 [-], M2 [-]) and / or the step of addition (M1 [+], M2 [+]) are performed by adjacent measuring heads (1, 2, 3, 4). ) Signal (S1, S2, S3, S4), the error indication (T) is associated with each difference step (M1 [-], M2 [-]), and the next coupling surface , The difference stage (M [−]) and the addition stage (M [+]) with the error indication (T) comprise the respective addition stages associated with the adjacent measuring heads (1, 2, 3, 4). (M1 [+], M2 [+
2. The apparatus for detecting defects according to claim 1, characterized in that: