APPARATUS FOR CONTROL AND/OR MEASURING OF OBJECTS

Abstract: Device for measuring and/or control of objects such as bodies, billets, wire, etc. with respect to changes, for example defects, comprising at least one transducer with associated signal processing means, the transducer moving relative to the object. Characteristic of the device is that signals, completely or partially originating from the same part of the object, are time-delayed, by means of the signal processing, relative to each other and thereafter combined in such a way that at least one undesired signal, for example a disturbance, can be suppressed in a better way. By the time-lag delay, relatively simple signals can be converted into more complex ones, whereby the possibilities of signal processing can be improved. This can be utilized, especially in e.g. eddy current transducers, for simulating a balanced (differential) transducer starting from a simple so-called absolute transducer. The time-lag delay is accomplished, for example, with the aid of an analog shift register or the like.

Description: Apparatus for oontroi and/or measuring of objects The present invention can be regarded as a device but may also, due to its fundamental nature, if desired, be regard¬ ed as and defined as a method. The invention relates to a device for measuring and/or control, for example, testing, of materials such as bodies, liquids, powders, billets, tubes, rods, wire, etc. with respect to changes/irregularities, as for example defects and so on, in or on the material. The invention is intended to be used within technical fields such as eddy curr.ent testing, ultrasonic testing, leakage flux testing-, and so on, "that is, NDT techniques normally occurring in industry. For simplicity, the description will be restricted, in the following, to the eddy current field in spite of the fact that the invention has a considerably wider and more gener¬ al field of application, which is thus to be understood in the following. The majority of the measuring and/or control devices avail¬ able on the market can be described as transducers with subsequent signal processing and output circuits. The signals which are obtained from these transducers are often very difficult to signal process in an efficient manner because of their shape and duration. As an example, the detected transducer signal may consist of a simple half-period pulse, which is difficult to separate from un- desired signals which, unfortunately, are present too often. The present invention discloses a simple and fundamentally refined method of drastically improving the signal process¬ ing possibilities by utilizing time lag/signal delay of one or several signals which directly or indirectly is/are de¬ rived from the transducer. O PI A patent application o f a complementary kind is disc losed in Swedish patent app licat ion No . 781 3344-4. Swedish patents Nos . 7507857-6 and 761 3708- 2 can b e impro ved to a considerab le extent with res pect to per formanc e by ut i- lizin g th e present in vent ion . The invention, which aims to provide a solution to the prob ¬ lems mentioned above and other problems associated there ¬ with, will be described in the following. A device accord¬ ing the invention can be described as a device for control and/or measurement of materials with respect to changes/ irregularities in/on the material, said device comprising at least one scanning member/tτansducer for scanning/sensing the material or a part thereof, and at least one signal processing part/Oircuit, for example electronic equipment, directly or indirectly associated with said member, for signal processing of signals derived from the transducer, utilizing at least one signal-delay function/circuit, for example a shift register and characterized in that at least two signals, mutually time-delayed, directly or indirectly originating from the same change/irregularity, are combined, for example weighted and summed in such a way that the - change/irregularity can be detected in a better way. The term "combined" also comprises the case where, for ex¬ ample, the signals A and B in Figure 1, in addition to being mutually time-delayed, are signal-processed individually or together via, for example, a filter. This very fact, that is, using signal delay and active filters, has proved very efficient in practice, since in that way the filter charac¬ teristic suppresses undesired signals considerably whereas, for example, the defect is emphasized. In other words, there is a great variety of possibilities of performing the signal processing. In practice, transducers are often designed as absolute or OMPI differential (balanced) transducers. The absolute trans¬ ducers have special advantages with regard to measuring practice but normally provide a half-period pulse when, for example, a defect passes the transducer, as opposed to the differential transducers which then provides a complete full-period pulse, which is much more simple to signal- process. Characteristic of the present invention is that with, for example, the absolute transducer as a starting point, a signal of a differential nature is simulated, while at the same time retaining the advantages of the absolute transducer. This means that with one simple transducer, the advantages of both transducer types can be utilized, which is a great advantage from the point of view of measuring practice. As an example, a simple but very practicable variant of the present invention is shown in greatly simplified form in Figure 1. Figure 2 shows the signals A, B and C, which refer to points A, B and C in Figure 1 and are derived from the transducer and thereby also wholly or partially from the object. Figure 1 , which thus is a simplified block diagram, shows the transducer (1) moving over, for example, a hot billet surface (2) in which there is a defect/crack (10) that is to be detected/measured. From the transducer, signals are emitted to a subsequent signal processing block (4), com¬ prising certain signal-processing circuits as, for example, an amplifier (5), a delay circuit (6), a summation circuit (7, 8) and a filter (9). When the transducer moves over the billet surface, or when the billet or the transducer vibrates, the distance between the transducer and the billet surface often varies. This gives rise to undesired disturbing signals which considerably deteriorate the possibilities of detection. Signal A in Figure 1 may, for example, be an amplified, rectified and prefiltered carrier frequency signal from the transducer, the appearance of which may be according to Figure 2 (A). The lou-f_..--. ■ ■ ncy O PI ' - m *° , inclination (14) is due to the curving of the billet sur¬ face (2), whereas the more high-frequency pulse superimpo- sition (11) is related to the defect (10). By delaying the signal A in the signal-delay circuit (6) in Figure 1, the signal B is obtained, the appearance of which is clear from Figure 2. As can be seen, signal B has reversed pola¬ rity and is delayed by the time t ,. If the signals A and B are summed, as in Figure 1 , by means of, for example, a summational amplifier (7, 8), the signal C is obtained, which is shown at the bottom of Fig¬ ure 2 (C). It can now be seen that the fault signal (11) and (12), respectively, originating from the defect has been combined so that a complete sine period (13) has been superimposed on the signal C. On the other hand, the low- frequency signal components in A (14) and B (15), respec¬ tively, have been greatly suppressed. In this way, the chances of an efficient separation/filtering of the fault signal have been significantly increased. In Figure 1, the signal C is further filtered in a filter (9), which is adjusted to the frequency • contents of the. fault signal (13) . It should be pointed out here that the time-lag delay (t .) of the delay circuit (6) has an optimum value related to the appearance and duration of the fault pulse. The advantages of the invention described here in relation to only ordinary active filters reside in the fact that the filter effect is not connected to the Q-factors, etc. of filters, which deteriorate the pulse response. Within the scope of the invention, the optimum location of the signal delay may, of course, vary in dependence on the desired function, application and construction. Also, the invention is applicable to the suppression of a highly varying range of undesired signals, etc. provided the frequency contents are suitable. It is also possible to extend the number of delay circuits and thereby obtain a greater number of signals to combine, thus to a corre- sponding degree improving the measuring and detection possi¬ bilities. An example of how the present device/invention can be com¬ bined in practice with other inventions to achieve a com¬ bined good result will be clear from the following. A measuring device, the measuring principle of which is based on Swedish patents Nos. 7507857-6 and -7613708-2, comprises an automatic balancing function according to Swedish patent application 7813344-4, and is signal- processed in accordance with the present invention. Taken together this provides a sophisticated and efficient measuring and/or control device, in which inventions, which are independent per se, together form a totality, for ex¬ ample a system function, which in turn is able to provide, for example, billet-treating machines (e.g. grinding machines) with information as to defects, etc. on the surface of the billet. Figure 2 shows that especially signals/signal components, which have a. small differential coefficient in relation to the fault signal (11), are particularly adapted to be supp- ressed. This can also be expressed such that low-frequency signals are well suited to be suppressed/attenuated. As the signal-delay element, a plurality of circuits may be used. Both digital and analog shift registers are, of course, very suitable, but also computers can be used. In certain cases it may be suitable to realize the whole device, or parts thereof, with the aid of a computer, for example, or some other type of programmable electronic equipment. Especially when employing eddy current tech¬ nique (0FP) for detecting, for example, defects in differ- Λ eπt materials, the device has a given field of application since, for example, the transducer design can be simplified while at the same time the performance is improved. By varying the time-lag delay (t .) of the delay circuit, the device can be made selective for different types of defects. A large field of application of the invention is the detec¬ tion of cracks on so-called hot billets, where the varying distance of the transducer to the surface of the billet is often a disturbing problem but which can be effectively overcome by means of the invention. Finally, some clarifying remarks. By object are meant, for example, bodies, liquids, gases, powders, billets, wire, etc. By c ange/irregularity are meant, for example, defects (such as cracks), dimensional changes, speed variations, material changes, etc. By signals referring to the same part, for example point of measuring, on or in the object are meant, for example, signals which during the relative movement of the trans¬ ducer across the surface of the object, for each point in time, refer to/originate from that part/point of the object which the transducer is currently scanning (at the respec¬ tive point in time). By combined signals is meant, for example, that signals are weighted, summed, subtracted, the quotient thereof formed, and so on, according to the current need for obtai¬ ning the desired function and result. At the same time as the present invention makes it possible to simulate the signal shape and properties of the differ- O PΪ ential transducer starting from the use of a simple abso¬ lute transducer, it can, of course, be claimed that the function obtained by way of the delay technique is to be compared to an advanced filter. By undesired signal is meant, for example, a signal or a part thereof (e.g. a vector) which is to be suppressed. A typical example of such a signal is a disturbing (varied) position signal, a so-called "lift-off" signal. The invention can be varied in many ways within the scope of the following claims.

Claims: CLAIMS 1. A device far control and/or measurement, for example testing, of objects, preferably sheet, tube, wire, rod and billets, with regard to changes, for example cracks in or on the object, said device comprising at least one transducer (1), for example a coil, for scanning the surface (2) of the object, or a part thereof, and at least one signal-processing electronic system (4), directly or indirectly belonging to said transducer, for signal processing of signals (A) which are derived from the transducer including the object, utili¬ zing at least one signal-delay function, for example a shift register (6), c h a r a c t e r i z e d in that at least two signals (A, B) of the same origin, time-delayed relative to each other, are combined in such a way that signal com¬ ponents (14, 15) originating from a varying distance between the transducer and the object, of a relatively low frequency content, substantially cancel each other (C), as opposed to signal components (11, 12) originating from a change (10), the combination of which results in a more formed signal (13) because of higher frequency contents and a suitably selected time-lag delay (t,), whereby the change can be controlled and/or measured, for example detected, in a better way. 2. A device according to the preceding claims, c h a r ¬ a c t e r i z e d in that at least one analog shift regis¬ ter is used as a signal-delay element. 3. A device according to one or more of the preceding claims, c h a r a c t e r i z e d in that the functions incorporated in the device are realized, wholly or partially, via or with the aid of programmable electronic equipment, as a computer. 4. A device according to one or more of the preceding claims, c h a r a c t e r i z e d in that the device, or a part thereof, is based on the use of so-called eddy curr¬ ent technique. 5. A device according to one or more of the preceding claims, c h a r a c t e r i z e d in that the time-lay delay in at least one of the signal-delay functions/circuits is varied, for example for separating different types of changes. 6. A device according to one or more of the preceding claims, c h a r a c t e r i z e d in that the device is used for detecting defects, for example cracks, on hot, for example continuously cast, billets.

Inventors: TOERNBLOM BENGT, TOERNBLOM, BENGT
Applicants: TOERNBLOMS KVALITETSKONTROLL, TOERNBLOMS KVALITETSKONTROLL AB
Application year: 1983
Main classification: G01N21
IPC codes: G01N27