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    44 ABSTRACT A method and a system for inspecting objects by means ofultrasound is provided, wherein reference signals are used asreferences for test signals in order to establish residual signalsindicating flaws in the objects. The said method comprisespositioning (103) a measuring device (11) comprising a pluralityof transducers (12) on the inspected object (20) and performing anumber of test signal acquisitions (103). Each acquisitionincludes using one transducer to induce an ultrasonic signal intothe test object, and using at least one other transducer to receivean ultrasonic test signal. The inspecting further comprisesdetermining (105, 205) the influence of contact surface variationsbetween each test signal and the reference signal; compensating(106, 206) the full test signal for the contact surface variations;and determining (109) a residual signal based on thecompensated test signal. The system comprises a computing device (30), and a measuringsystem (13) communicatively connected to the computing device(30). The measuring system (13) includes an ultrasound unit (19)and a measuring device (11) provided with a plurality oftransducers (12). The computing device (30) comprises acalibrator (303) configured to determine (105, 205) the influenceof contact surface variations, and compensate (106, 206) the testsignal for the contact surface variations. The computing device(30) also comprises a residual calculator (304) configured todetermine (109) the residual signal based on the compensatedtest signal and the reference signal. A computer program is also provided for enabling a computingdevice (30) to perform the method steps of the computing device.
    公开号:SE1450404A1
    申请号:SE1450404
    申请日:2014-04-03
    公开日:2015-10-04
    发明作者:Christophe Mattei
    申请人:Creo Dynamics Ab；
    IPC主号:
    专利说明:

    Method and Device for lnspection of Solids BACKGROUND OF THE INVENTION AND PRIOR ART The invention relates to nondestructive inspection of solidmaterials using ultrasonic waves. Especially, the invention relatesto a method for determining a residual between a reference signaland a test signal of an inspected solid material, and to a systemfor providing such a residual. An image of any defect of theinspected material can be calculated from the residual.
    Different methods for non-destructive inspection of fluid and solidmaterials using ultrasound techniques have been developed.Such methods include transmitting an ultrasonic signal into thematerial and measuring a resulting ultrasonic signal that hastravelled through the material at a measuring point, whichresulting ultrasonic signal for example has been reflected insidethe material before arriving at the measuring point. The analyzingof the resulting ultrasonic signal provides an image of the interiorof the material.
    Ultrasonic inspection of fluids may start from analysis of pressure.The arrival times of pressure wave echoes give an indication of adistance to a pressure altering structure in the fluid.
    The problem of inspecting solids is generally more difficult sincesolid materials may contain and transfer stress from bothcompression and shear. Solid materials therefore transfer energyin the form of shear waves as well as compression waves.Ultrasonic inspection of solids is often based on an analysis of astrain field in the material, which strain field may corresponds tocompression and shear in the material. The propagation speed ofshearing waves is different from the speed of propagation ofcompression waves, and the measurements and the analysis ofthe measured signal need to be performed in a more sophisticatedmanner than for fluids.
    One common method uses a short ultrasonic pulse and analysisof the response. One known way of analyzing the resultingmeasured ultrasonic signal from an inspected part of aconstruction is to compare the measured signal to a referencesignal obtained from a flawless part. Such a reference signal mayalso be provided from a FEl/I analysis (Finite Element Method) ofthe part. The comparison provides a residual signal, which issubsequently analyzed.
    Mathematical calculations of how ultrasonic signals from smallsources in such a part would produce measurable signals at themeasuring position is used to determine an indication of thedisturbances in the inspected part that may have produced theresidual signal.
    Thus, the calculations of a forward, or direct, problem of howsmall sources produce ultrasonic signals propagating through amaterial is used as a basis for solving the adjoint, or inverse,problem of what sources, i.e. defects, have produced the residualsignal.
    US 7,654,142 describes a method for obtaining an image of aninspected part. ln this method, a reference part is used, whichreference part is a flawless part. A first ultrasonic measurementis performed on the reference part, and a second ultrasonic scanis performed on the inspected part. The measuring probe ispositioned in the same relation to the reference part as theinspected part during the measurements, at the same heightabove a corresponding plane to be inspected. A subtraction isperformed between the measurements of the inspected part andthe reference part, and the topological energy at each position inthe part is determined.
    The method of US 7,654,142 determines a “cost function” thatcorrelates data obtained from the reference part and dataobtained from measuring the inspected part. ln this way an indication of the modifications, or defects, in the inspected part isobtained. ln more detail, the measuring probe includes a number of alignedtransducers. The transducers transmit an ultrasonic test signal,one transducer at a time, while the other transducers receives. Amatrix of all the received test signals are created, which receivedtest signals are compared to corresponding reference test signalsfrom the reference part. The frequency used for the ultrasonicsignals is not indicated, but each measuring results inmeasurements from a plane of the inspected part.
    The method of US 7,654,142 uses the topological energy forproviding an image of the inspected part. US 7,654,142 aims atsimplifying a previous method described in the article “Flawimaging with ultrasound: the time domain topological gradientmethod” by N. Dominguez et al (A1, see the reference list at theend of the description). Both methods are performed in the time-domain, but US 7,654,142 determines the topological energyinstead of the gradient for each position of the inspected part. lnmore detail, the field values of the reference part is subtractedfrom the measured values of the inspected part, thereafter thesubtracted residual signal is subjected to a time reversal byinverting the time scale. This time reversal is described in moredetail in the article “Flaw imaging...” and in a further article “Timedomain topological gradient and time reversal analogy: an inversemethod for ultrasonic target detection” (A2, see the referencelist).
    A problem for using the methods described in US 7,654,142 andthe articles A1 and A2 are to obtain an accurate measurement,i.e. how to avoid disturbances to the ultrasonic test signal whenapplying the ultrasonic test signal to the inspected part and toavoid disturbances when measuring the resulting signal. Theprocess suggested in article A2 is to use water as a transfermedium to transfer the ultrasonic test signal from the transducer into the inspected part for example, as referred to in the articleA2 by immersion of the inspected part in water.
    A known alternative to immerse the inspected part in water is todirect a beam of water onto the inspected part and use the waterbeam as a means for transferring the ultrasonic signal.
    A disadvantage of using water is that immersing parts in waterbaths or directing beams of water onto inspected parts makes thehandling of parts for inspection complicated, especially for largerparts and structures.
    An alternative to water immersion that may be used is attachingthe transmitting and measuring probes permanently to the surfaceof the inspected part. Such attachment may be done on a flawlesspart during manufacturing and subsequently used for regularinspections. ln this way, the distortion induced from the glue layerwill be the same and the measurement signal obtained during aninspection can be compared to an original test signal obtainedduring manufacturing so that the distortion from the glue layer willnot influence the difference between the original reference signaland the subsequent test signal. However, for many parts andconstructions it may not be suitable to leave measuring probesattached during use, and also the glue layer may be affectedduring use of such parts and constructions.
    Thus, there is a need for facilitating the measuring process, stillproviding accurate measurement signals, in order to determine areliable residual signal.
    SUMMARY OF THE INVENTIONAccording to a first aspect of the invention, the invention provides a method for inspecting objects by means of ultrasound, whereinreference signals are used as references for test signals in order to establish residual signals indicating flaws in the objects. Themethod of inspection comprises: - inspecting a test object at one or more positions, wherein theinspecting of one position comprises: - positioning a measuring device comprising a plurality oftransducers in a selected position on the inspected object, so thatthe ultrasonic transducers are in contact with the inspectedobject, - performing a number of test signal acquisitions at the selectedposition, each test signal acquisition comprising: - using one transducer of the plurality transducers as a sendingprobe to induce an ultrasonic signal into the test object, and usingat least on other transducer of the transducers as a receivingprobe to receive ultrasonic signals from the test object, so thatone test signal is obtained for each combination of sending probeand receiving probe. The inspecting of one position furthercomprises: - determining the influence of contact surface variations betweeneach test signal and corresponding reference signal; - compensating the full test signal for the contact surfacevanaüons;and - determining the residual signal based on the compensated testsignal for each combination.
    An advantage is that the method does not require any “a-priori”knowledge of how the wave of the test signal propagates in thestructure of the inspected object. The residual is determined fromthe reference signal and the compensated test signal and willindicate if a defect is present in the inspected object.
    A preferred embodiment includes extracting a direct signal portionof the test signal, and determining the contact surface variationsbased on the direct signal portion of the test signal and acorresponding direct signal portion of the reference signal.
    The compensating is performed for the full test signal. The fulltest signal includes the direct signal portion of the test signal anda reflected signal portion of the test signal.
    Preferably, the determining of the residual signal includesperforming a subtraction of the full reference signal and thecompensated full test signal.
    Preferably, the determining of contact surface variationscomprises identifying a time window for a direct signaltransmission of the combination of sending probe and receivingprobe, and using the direct signals of the test signal and thereference signal of said time window. The time window of thedirect signal from the sending probe to the receiving probe ofeach combination is a sub-portion of the total reception timeperiod of the full test signal. ln an embodiment, the determining of the contact surfacevariations comprises determining a phase shift between the testsignal and the reference signal, and the compensating includescompensating the full test signal for the determined phase shift.
    This can be seen as a way of aligning the acquired test signal andthe corresponding reference signal. ln an embodiment, the step determining of the contact surfacevariations also comprises determining an amplitude variationbetween the test signal and the reference signal, and thecompensating further includes normalizing the amplitude of thefull test signal and/or the reference signal in accordance with thedetermined amplitude variation. ln an embodiment, the determining of the contact surfacevariations includes determining a frequency varying filterequivalent for the contact surface, and the compensating includes compensating the full test signal on the basis of the determinedfilter equivalent. ln an embodiment, the inspecting includes evaluating the level ofthe residual. ln an embodiment, the evaluating of the residual level includescomparing a measure of the residual, or the residual, to athreshold, and indicating to an operator when the measure of theresidual exceeds the threshold. ln an embodiment, the inspecting includes obtaining the referencesignal from a reference zone of the inspected object, or from areference zone of a reference object. ln an alternative embodiment, the reference signal is obtainedfrom simulations, such as FEM simulations (Finite ElementMethod), in a computer model of the test object. ln an embodiment, the induced ultrasound signal has a frequencyof less than 1 MHz, preferably between 50 kHz and 500 kHz,especially between 100 and 250 kHz. Using a frequency lowerthan 1 MHz provides a spreading of the ultrasonic signal withinmany materials, and makes it possible to inspect a larger area, orinspection zone, at each position. These frequencies are suitablefor inspection using Lamb waves. Especially, the frequency canbe selected to provide Lamb waves propagating in an inspectedplate-like object. To create the Lamb waves, the frequency isselected based on the elastic properties of the material of theinspected object and on the thickness of the inspected plate-likeobject. The plate-like object will then act as a guide for thepropagation of the Lamb waves. By choosing such a frequency,the inspection is especially suitable for inspecting plate-likestructures such as aerospace structures. Thus, in preferredembodiments, the frequency is selected to create Lamb waves inthe inspected object. However, these frequencies are also suitable for other waves in solid objects of large dimensions, suchas a solid concrete construction having a non-plate shape.
    According to a second aspect, the invention also provides asystem for inspecting an object by means of ultrasound. Theinspection system comprises: - a computing device, and - a measuring system configured to acquire test signals from theinspected object, which the measuring system iscommunicatively connected to the computing device fortransferring the test signals from the measuring system to thecomputing device. The measuring system includes an ultrasoundunit and a measuring device provided with a plurality oftransducers, wherein each test signal is obtained by using one ofthe transducers as a sending probe and another one of thetransducers as a receiving probe. The computing device isconfigured to establish a residual by comparing each test signalwith a corresponding reference signal in order to detect flaws inthe inspected object. The inspection system is characterized inthat the computing device comprises a calibrator configured to: - determine the influence of contact surface variations betweeneach test signal and the corresponding reference signal by usinga direct signal portion ofthe test signal and a direct signal portionof reference signal, and - compensate the full test signal for the contact surface variations;and in that the computing device comprises: a residual calculator configured to determine the residual signalbased on the compensated test signal and the reference signal. ln an embodiment of this aspect, the calibrator is adapted todetermine the influence of contact surface variations bydetermining a phase shift between the test signal and thereference signal, and to compensate the full test signal for thedetermined phase shift. ln an embodiment of this aspect, the calibrator is further adaptedto determine the influence of contact surface variations bydetermining an amplitude difference between the test signal andthe reference signal, and to compensate the test signal byperforming an amplitude normalization of the full test signal andthe reference signal. ln an embodiment of this aspect, the calibrator is adapted todetermine the influence of contact surface variations bydetermining a frequency varying filter equivalent and tocompensate the full test signal on the basis of the determinedfilter equivalent. ln an embodiment of this aspect, the computing device furthercomprises: - a residual evaluator configured to compare a measure or theresidual to a threshold, and - an output configured for indicating to an operator when themeasure of the residual exceeds the threshold by means of themeasuring system or by means of a monitor. ln an embodiment of this aspect, the ultrasound unit is adaptedto provide ultrasound signals at a frequency of less than 1 MHz,preferably between 50 kHz and 500 kHz, especially between 100and 250 kHz. Especially, the frequency is selected to create Lambwaves in the inspected object. Thus, the ultrasound unit isadapted for frequencies that when induced by the transducer,which acts as sending probe, create Lamb waves in the inspectedobject.
    According to a third aspect, the invention also provides acomputer program product for determining a residual from testsignals acquired by means of ultrasound from an inspected objectand reference signals. The computer program product comprisesa computer program that when run on a computer enables thecomputer to perform the steps of: - extracting a direct signal portion of each test signal; - determining the influence of contact surface variations betweenthe direct portion of the test signal and a corresponding portionof the reference signal; - compensating each test signal for the contact surface variations;and - determining a residual signal based on the compensated testsignal and the corresponding reference signal. ln an embodiment of this aspect, the step of determining thecontact surface variations comprises determining a frequencyvarying filter equivalent for the contact surface, and the step ofcompensating includes compensating the test signal on the basisof the determined filter equivalent ln an embodiment of this aspect, the step of determining thecontact surface variations comprises determining a phase shiftbetween the test signal and the reference signal, and determiningan amplitude difference between the test signal and the referencesignal, and the step of compensating includes compensating thetest signal for the determined phase shift, and normalizing theamplitude of the test signal and/or the reference signal inaccordance with the determined amplitude variation.
    SHORT DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be described with reference tothe drawings wherein; Figure 1 illustrates measuring of a reference object in accordancewith an embodiment of the invention; Figure 2 illustrates measuring an inspected object in accordancewith an embodiment of the invention; Figure 3 illustrates measuring in a reference zone and inspectedzone of a test object in accordance with an embodiment of theinvenüon; 11 Figure 4 illustrates measuring in a reference zone and inspectedzone of a test object in accordance with an embodiment of theinvenüon; Figure 5A illustrates a reference signal and an acquired testsignal; Figure 5B illustrates a phase shift between the direct signalportion of the reference signal and the direct signal portion of theacquired test signal of figure 5A; Figure 6A illustrates a reference signal and an acquired testsignal having different phases and amplitudes; Figure 6B illustrates the phase shift and amplitude differencebetween the direct portion of the reference signal and the directportion of the acquired test signal of figure 6A; Figures 7A-7C illustrates an embodiment of a measuring systemin accordance with the invention; Figures 8A-8B illustrates an embodiment of a measuring devicein accordance with the invention during inspection; Figure2 9A-9B illustrates an embodiment of a measuring deviceand acquired test signals in accordance with the invention;Figure 1OA-1OC illustrates a phase shift between a referencesignal and a test signal in figure, an uncompensated residual infigure 1OB and a residual after calibration, in accordance with anembodiment of the invention, in figure 1OC; Figure 11 illustrates a method in accordance with an embodimentof the invention; Figure 12 illustrates a method in accordance with an embodimentof the invention; Figure 13 illustrates embodiments of a computer and software inaccordance with the invention.
    DESCRIPTION OF El/lBODll/IENTS With reference to figures 1-4 some main principles of a theoreticalbasis for the embodiments of the invention will be explained, soas to simplify implementation of the invention. 12 Figure 1 illustrates a reference zone 1 on a flawless referenceobject A. An ultrasonic sending probe 3 and an ultrasonicreceiving probe 4 are placed in the reference zone 1 of thereference object A. The sending probe 3 and the receiving probe4 are positioned in contact with the reference object A. Anultrasonic pulse signal, or excitation signal, induced by thesending probe 3 propagates in the object A in all directions. ltshould be noted that the sending probe 3 (and the sending probe7 in figure 2) should act as a point source and therefore shouldhave a diameter less than half the wavelength of the inducedsignal. Especially, a part of the excitation signal propagates to,and is received by the receiving probe 4. When a calibration isperformed, in accordance with the invention, the direct signalfrom the sending probe 3 to the receiving probe 4 can be used.The direct signal propagates through a zone located between thesending probe 3 and the receiving probe 4, which is illustrated asa calibration zone 2 in figure 1.
    Figure 2 illustrates an inspected zone 5 of an inspected object B,which has a defect 9 in its structure. A sending probe 7 and areceiving probe 8 are arranged in contact with the inspectedobject B in the inspected zone 5. For the purposes of calibration,the direct signal propagating in a calibration zone 6 between thesending probe 7 and the receiving probe 8 is used.
    The present invention provides a method of calibration using thedirect signals propagating through the calibration zones 2 and 6.This calibration method will be described mathematically in thefollowing.
    Referring to figure 1. The transfer of the direct signal, from thesending probe 3 to the receiving probe 4, through the calibrationzone 2 during calibration can be mathematically described in thetime domain as follows: m0) = SU) * hsü) * ffs * G 340) * kl * M0) 6G- 1 13 which in the frequency domain is equivalent to: R4(w) = S(w).H3(w).K3.G 34(w).K4.H4(w) eq. 2 wherein: r4 is the time domain signal received and measured by thereceiving probe 4; s is the excitation signal induced by the sending probe 3 in thereference zone 1 of reference object A; ha and h4 are the respective transfer function (i.e. the response)of the sending probe 3 and the receiving probe 4; ka and k4 are the respective filtering effect of the contact betweenthe sending probe 3 and the reference object A, and between thereceiving probe 4 and the reference object A; and G34 is the Green function that describes the propagation betweenthe sending probe 3 and the receiving probe 4 through thereference zone 1 of reference object A, i.e. through the calibrationzone 2; Referring to figure 2. The transfer from sending probe 7 toreceiving probe 9 of a direct signal through the calibration zone 6and a signal reflected by the defect 9 can be mathematicallydescribed in the time domain as follows: w) = so) * hm * k * G wc) * kg * m)+su) *fww wc 798w<8w18 eq. ß which in the frequency domain is equivalent to: R8(w) = S(w).H7(w).K7.G 78(w).K8.H8(w)+ S(w). H7(w). K7. G (w). Ks .H8(w) eq. 4 798 wherein: 14 rs is the time domain signal received and measured by thereceiving probe 8; s is the excitation signal induced by the sending probe 7 in theinspected zone 5 of the inspected object B; hv and ha are the respective transfer function (i.e. the response)of the sending probe 7 and the receiving probe 8; kr and ks are the respective filtering effect of the contact betweenthe sending probe 7 and the inspected object B, and between thereceiving probe 8 and the inspected object B; G78 is the Green function that describes the direct propagationbetween the sending probe 7 and the receiving probe 8 throughthe calibration zone 6 of the inspected object B; 6798 is the Green function that describes the reflected signal, i.e.the propagation from the sending probe 7 to the defect 9, theinteraction of the signal wave with the defect 9 and thepropagation from the defect 9 to the receiving probe 8.
    To extract the contribution of the defect, i.e. (3798 the same pairof probes (3, 4) should be used on the inspected object B as onthe reference object A. Also, the excitation signal s(t) used shouldbe the same. Thus, a pair of probes 3, 4 are used for a firstmeasurement in the reference zone 1 on the reference object Aand subsequently the same pair of probes 3, 4 are used in theinspected zone 5 on the inspected object B.
    The responses ha, and hv are the same, and the responses h4 andha are the same, so that: här) * Mt) = Mt) * har) = hhü) eq- 5 Also, the reference object A and the inspected object B areselected so that the propagation zones, i.e. the reference zone 1,the inspected zone 5, and especially the calibration zones 2 and 6 have the same, or at least very similar, material and geometry,so that: G34 =G7s = G eq. 6 The filtering effect from the contacts between the probes and thereference object A and inspected object B, respectively, can bedescribed as: Kn = Anefwn eq. 7 wherein A is a loss factor and Note, however, that a more general model of filtering effectsarising from the contacts between the probes and the objects willbe given in eq. 17.
    Referring to eq. 7, Kr * Ks can be written: K7K8 = A7A8e1'(<07+<0s) = A78 eiuvvs) eq_ 8 and Ks * K4 can be written: K3K4 = A3A4ej(<0s+<04) = A34 eiuvss) eq_ 9 When the calibration zones 2 and 6 are much smaller than theinspection zone 5 that includes the defect 9, the time domainsignal rs will not include any contribution from the signal reflectedby the defect 9 during an initial time period (or calibration time) Tc. This means that rs can be described by: rs(O = A78 effißvß) *hh(t) * G(t) *s(t) eq. 10aandrs(t>Tc)= A78 effiflvß) *hh(t) *G(t) *s(t)+A78 efWvß) *hh(t) * 6798 (t) *s(t) eq. 10b 16 ln the same way the time domain signal for the reference objectA does not include any contribution from a defect, so that r4(t) = A84 efWBU * hh(t) * G(t) *s(t) eq. 11 During the initial time period Tc the received signals r4 and rs willbe similar, and this may be used for determining the contribution6788 (t) of the defect 9 in the received signal after the initial timeperiod Tc. The received signals r4 and rs will, however, differ inrespect of the amplitudes A84, A78 and the phases probes in contact with the reference object A and the inspectedobject B, respectively (see eq. 7).
    The received signals r4(O A i A78A34 eq. 12 and using a cross-correlation of these received signalsr4(O A: 4178-4734 eq- 13Thus, the influence of the differences of the filtering effects, i.e.differences in the contact between each probe and the objects,can be determined from the measured signals, i.e. receivedsignals, of the initial time period Tc. This time period Tc may therefore be used for calibration, and referred to as a calibrationtime window. 17 Applying the normalization factor A (of eq. 12) and the phase shift(of eq. 13) to the received signal r4 (of eq. 11) in the referenceobject 1 gives: A e1'(4),«4(t) = :LAM eiüßsß e1'(<ß78-<034) * hhw * Gm *S(t)=34- = A78 effißvß) *hh(t) *G(t) *s(t) eq. 14As can be seen eq. 14 relates the received signal r4 of the reference object A to the received signal of the inspected objectB. ln order to determine a time signal that is only depending on thepresence and influence of the defect 9, the left hand and righthand sides of eq. 14 are subtracted from the left hand and righthand sides eq. 1OB, which describes the received signal rs in theinspected object B after the initial time period (t>Tc): r8(t) - A ef(^)r4(t) =+A78 ejßßß) * hh(f) * 6798 (f) *s(t) eq. 15 and thus r8(t) - A eKA) * r4(t) = residuaKt) eq. 16 lt should be noted that the residual is independent from the Greenfunctions G(t). Thus, the presence of a defect or flaw can bedetected from the residual without knowledge of how the wave ofthe signal propagates in the inspected object, i.e. withoutknowledge of any Green function G(t). lf there are no other reflections than the defect 9 during the totalinspection time period, then r4(t) will be null after the initial timeperiod Tc. However, normally there are other reflections as well.Since the influences of the difference of contact between theprobes and objects, as described by the amplitude normalizationA and the phase shift A, are determined from the received signalsr4 and rs during the initial time period Tc, the influence from thedefect 9 can be determined as described by eq. 15 since the otherreflections are the same in the reference zone 1 of the reference 18 object A and the inspected zone 5 of the inspected object B. lnthis way a residual (eq. 16) can be obtained, which will onlyindicate the defect 9.
    As an alternative, or complement, to using the model of thefiltering effect described in eq. 7, a more general filtering modelis provided. lt is suggested that a more general filtering modelthat also considers frequency dependency of the phase shift andamplitude variations during the initial time period Tc is used. lnthe frequency domain: Kn(w) = An(w)ej9””(“) eq. 17 Using the filter model of eq. 17, for the reference zone (see eq.2) during t R4(w) = S(w).H3(w).K3(w).G 34(w).K4(w).H4(w) eq. 18 The received signal Rs in the inspected zone during t R8(w) = S(w).H7(w).K7(w).G 78(w).K8(w).H8(w) eq. 19 Using eq. 5 ( h3(t) * h4(t) = h7(t) * h8(t)) Rs can be rewritten as: K7 (OÛ-Ks (00) R8(w) = S(w).H3(w).K3(w).G 34(w).K4(w).H4(w).K3(w)IK4(w) eq. 20thus:Rsw) = mo) eq. 21 'K3(w)-K4(w)wherein the contact filter CF(w) can be defined as:CF(w) = = Af(w)ei<ßf(w) eq 22 Ks (w)-K4(w) wherein f denotes filter. 19 To determine CF(w), the direct signals of R8(w) and R4(w),received during the calibration time t a) a frequency response estimate; b) a time domain correlation analysis for estimation of the finiteimpulse response (FlR); or c) a transfer function estimate.
    Such analysis can for example be made as presented in “Systemidentification, Theory for user, by L. Ljung, Prentice Hall” (A3).
    The residual can be determined from (compare eq. 16): residuaKt) = r8(t) - CF(t) * r4(t) eq. 23The residual is determined for the total inspection time period, i.e.also for t>Tc, by convolution.
    Once again, the residual is independent from the Green functionsG(t). The presence of a defect can, thus, be determined by onlyusing the test signal r8(t) and the reference signal r4(t).
    Thus, the general filter CF(t) is determined in the frequencydomain by means of the direct signals r4 and rs received duringthe initial time period Tc, and the general filter is subsequentlyapplied to the total reference signal r4 for subtraction from thereceived signal rs of the inspected zone, i.e. also for t>Tc, toprovide the residual.
    Figure 3 illustrates measurements in a reference zone 1 and aninspected zone 5 of the same solid material object C. ln this casethe reference zone 1 of the solid object C is used as a referencefor measurements of another zone, the inspected zone 5 of thesame solid object C. The reference zone 1 is flawless, whereas the inspected zone 5 comprises a defect 9. As with the referenceobject A and inspected object B of figures 1 and 2, the referencezone 1 and the inspected zone 5, of the same solid object C,should have the same material and geometry. The sameultrasonic probes 3, 4 are used in both the reference zone 1 andthe inspected zone 5; and consequently sending probe 3 is thesame as sending probe 7, and receiving probe 4 is the same asreceiving probe 8.
    Figures 1-3 illustrate two different alternatives. ln the firstalternative, separate objects are used for the measurements; onefirst object, i.e. reference object A, is used for providing thereference zone 1 when another second object, i.e. inspectedobject B, is inspected in the inspected zone 5. ln the secondalternative, of figure 3, the reference zone 1 is provided in theinspected object C, i.e. the same object that is also beinginspected in its zone of inspection, i.e. inspected zone 5.
    A third alternative is to create a computer model of an object tobe inspected, such as a CAD-model (“Computer Aided Design”),for providing a virtual reference zone for comparison ofsubsequent measurements of the real object, i.e. measurementsin an inspected zone 5 of the real object.
    Figure 4 illustrates a situation wherein the inspected object Dprovides a reference zone 1 and an inspected zone 5. ln thisobject D, a known feature 10 that will reflect ultrasonic signals ispresent in the reference zone 1 and in the inspected zone 5. Thedirect signals, of the calibration zone 2 of the reference zone 1and the calibration zone 6 of the inspected zone 5, will not beaffected by the feature 10 of the object D. This means that thesame measurements as referred to for figures 1, 2 and 3 can beused for a calibration, so that the effect of the differences ofcontact between the probes and the object can be determined. 21 The reference signal r4(t) will not be null after the calibration timedue to the echo from the known feature 10, but the influence of adefect 9 can be determined using eq. 16 or eq. 23.
    Using eq. 16, the direct signals received during the calibrationtime period Tc should be used for amplitude normalization andphase shift determination, e.g. by means of cross correlation, ofthe received signals r4(t) and r8(t) in the reference zone 1 and theinspected zone 5, respectively, so that the amplitude of thereceived reference signal r4(t) is normalized and the phasedifference is compensated for.
    Using eq. 23, the direct signals used during the calibration timeperiod TC should be used for determining the filtering effect ofthe contact surface, as described in eq. 17, and by means ofconvolution a calibration is performed for the full signals of r4(t)and Fsfl).
    The influence of the known feature 10 can be seen as A * ef(^)r4(t)(of eq. 15 and eq. 16) in the received signal r8(t) in the inspectedzone 5 for t>Tc, i.e. after the calibration time period. ln accordance with eq. 23, the known feature 10 can be seenCF(t)*r4(t) in the received signal r8(t) for t>Tc, i.e. after thecalibration time period, in the inspected zone 5.
    Figure 5A illustrates the received signals r4(t) and r8(t) beforeapplying the phase shift. ln this example, the amplitudes of r4(t)and r8(t) are equal. The residual will indicate the presence of thedefect 9 as can be seen by the differences of the two signals r4(t)and r8(t) that appear in the reflected signals received after thedirect signal. The amplitudes of these differences are howeversmall, so without performing a calibration, the contribution of thedefect 9 will be small compared to the overall energy of thesignals r4(t) and rs(t). 22 Figure 5B is a time window Tc of the direct signals beforeperforming a calibration, i.e. the received signals r4(t) and rs(t)during the calibration time periods. Figure 5B illustrates the phasedifference, or phase shift A, between the received signals r4(t) andr8(t). Without performing a calibration of these signals r4(t) andr8(t) in accordance with the present invention, the subtraction ofr4(t) and r8(t) would have resulted in large signals compared tothe signal reflected by the defect 9.
    Figure 6A illustrates an example wherein r4(t) and rs(t) havedifferent amplitudes. Figure 6A illustrate r4(t) and r8(t) beforeapplying the amplitude normalization and the phase shift. Theresidual will indicate the presence of the defect 9 as can be seenby the differences of the two signals r4(t) and rs(t) that appear inthe reflected signals received after the direct signal. Theamplitudes of these differences are however small, so withoutperforming a calibration, which includes amplitude normalizationand compensation ofthe phase shift, the contribution of the defect9 will be small compared to the overall energy of the signals.
    Figure 6B is a time window of the direct signals of figure 6A beforeperforming a calibration, i.e. the received signals r4(t) and rs(t)during the calibration time periods. Figure 6B illustrates the phasedifference, or phase shift A, between the received signals r4(t) andr8(t). Figure 6B also illustrates the amplitude difference, indicatedby A, between the received signals r4(t) and rs(t). Withoutperforming a calibration of these signals r4(t) and rs(t) inaccordance with the present invention, the subtraction of r4(t) andr8(t) would have resulted in large signals compared to the signalreflected by the defect 9.
    Figures 1OA-C illustrate how the use of a calibration inaccordance with the invention enables obtaining a residualwithout being influenced with the variations created by the contactbetween transducers and the surface of the inspected object. 23 Figure 10A illustrates the phase shift A, similar to figures 5A-B,of the direct signals r4(t) and r8(t). The received reference signalr4(t) includes a reflection from a known feature 10 of a referencezone 1, and the received test signal r8(t) includes a signalreflected from the known feature 10 and a signal reflected from adefect 9 in the inspected zone 5.
    Figure 1OB illustrates a residual, i.e. a test signal after subtractionof the reference baseline signal, that has been computed when acalibration has not been performed. As can be seen, the firstportion that includes the direct signal influences the residualsignificantly. Also, the signal reflected from the defect isinfluenced by the signal that is reflected from the known feature.
    Figure 1OC illustrates a residual after a calibration that includesdetermining, and compensating for, the phase shift A between thetest signal r8(t) and the reference baseline signal r4(t). Thesubtraction after phase compensation provides no contribution,or at least a very small contribution, from the direct signal to theresidual. Moreover, the subtraction after compensation does notprovide any contribution, or at least a very small contribution,from the signal reflected from the known feature. The reflectedsignal received after the direct signal, i.e. after the calibrationtime Tc, can be identified for further analysis. For example, theenergy of the residual in figure 1OC can be determined andcompared to a threshold so as to determine if the inspected objectcontains a defect. lf the residual shown in figure 1OB was subjected to a comparisonwith a threshold value for its energy content, the contribution ofthe defect would have been concealed by the contribution fromthe direct signal so that the existence of a defect could not havebeen determined. 24 Figures 7 to 9 illustrate embodiments for implementing theinvention. ln figures 1-4, the ultrasonic transducers wereillustrated as individual sending and receiving probes 3, 7 and 4,8, respectively. ln figures 7 to 9, ultrasonic transducers arearranged in a single measuring device 11 that keeps thetransducers 12 in a fixed geometric relation to each other.Measurements can be provided by moving the measuring device11 on an inspected object, inducing an ultrasonic pulse from onetransducer 12 acting as a sending probe 3, 7 and receiving testsignals in the other transducers 12 acting as receiving probes 4,8. During the measurements, every transducer 12 will actalternately as a sending probe 3, 7 and as a receiving probe 4, 8.
    Figure 7A illustrates a measuring system 13 for inspection of anobject 20, made of a solid material, in accordance with theinvention. The measuring system 13 comprises a measuringdevice 11 provided with transducers 12 capable of inducing andreceiving ultrasonic signals. The transducers 12 are fixedlymounted in the measuring device 11 and are arranged separatedfrom each other. The figure 7A illustrates an inspection process,wherein the measuring device 11 is positioned on the inspectedobject 20 with the transducers 12 placed in contact with theinspected object 20. The measuring system 13 comprises themeasuring device 11 and an ultrasound unit 19, which measuringdevice 11 and ultrasonic unit 19 are interconnected by cables 18.The ultrasound unit 19 is configured to generate voltage signalsto the measuring device 11, and receive voltage signals from themeasuring device 11. The transducers 12 provides theconversions between voltage and ultrasound. Each of thetransducers 12 is provided to apply an ultrasonic signal to the testobject 20 upon receiving a voltage signal from the ultrasound unit19. Each of the transducers 12 is provided to transmit a voltagesignal to the ultrasound unit 19 upon sensing an ultrasound signalin the inspected object 20. The measuring system 13 is configuredto obtain test signals from the inspected object 20 by applying anultrasonic signal by means of one of the transducers 12 and registering the voltage signals from at least one other transducer12 of the transducers 12. Especially, the measuring device 13applies a voltage signal to one transducer 12 acting as a sendingprobe 3, 7 and receives a respective voltage signal from each ofthe at least one other transducers 12 that acts as a receivingprobe 4, 8.
    The measuring system 13 is communicatively connected, asindicated by the broken line 21, to a computing device 30. Thecomputing device 30 comprises a computer 31 configured forreceiving the measurements and performing an analysis of themeasurements. The computing device 30 also comprises amonitor 32 for displaying the results to an operator. Thecomputing device 30 can suitably be configured to obtainreference signals, or alternatively, the computing device 30should be configured with stored reference signals obtainedpreviously, for example by means of FEM-simulations. Thecomputing device 30 is configured to retrieve the referencesignals, so called baseline signals, and configured to compare theobtained test signals with the baseline signals. The computingdevice 30 may preferably be configured with software for per-forming reference measurements and inspection measurements.The software should include computer executable instructions forperforming a reference measurement, obtaining a referencebaseline signal, and storing the baseline signal, as well asinstructions for performing inspection measurements, obtainingtest signals and comparing the test signals with the storedbaseline signals.
    When using the measuring system 13, a user position themeasuring device 11 at a predetermined position on the testobject 20, and the measuring device 11 acquires test signals inthat position. The acquired test signals are transferred to thecomputing device 30 that compares the acquired signals withbaseline signals for that position. From this comparison, the 26 computing device is adapted to perform a calibration anddetermine the residual, such as described by eq. 16 or eq. 23.
    The computing device 30 should be configured with, or configuredfor obtaining, baseline reference signals for each position thatshould be inspected. As indicated previously, these baselinereference signals can be provided by measuring on a referenceobject, measuring in a reference zone on the inspected test objector performing calculations from a FEM-model of the test object.
    Especially, the computing device 30 is adapted to compensate forvariations in the contact area, or zone, between each transducers12 and the inspected test object 20, i.e. the computing device 30is adapted to compensate for the effect of different contactinterfaces between the reference baseline signal and the testsignals of the measurements.
    To perform a compensation for different contact interfacesbetween the measurements of, or calculations of, the referencebaseline signal and measurements of the test signals, thecomputing device 30 may be adapted to compensate for thephase difference, or phase shift A, between the referencebaseline signal and the test signal from the inspected object 20as described by eq. 15 and eq. 16. Also, the computing device 30may be adapted to perform an amplitude compensation such asthe described amplitude normalization. ln many inspectionsituations it has been found that the influence from the variationsin amplitude, between reference measurements and inspectionmeasurement, is small compared to the influence of the phaseshift A. Therefore, it may not be necessary to performcompensation of the amplitude. ln other cases a more general model of the filtering effect arisingfrom the contact surfaces should be used in accordance with eq.16. The computing device 30 may be adapted for both types ofcompensation. The computing device 30 can suitable be adapted 27 to compensate for the phase shift A, check the residual todetermine if the compensation is adequate, e.g. check that theresidual during the initial time period is approximately null, andapply an amplitude normalization if the compensation is notadequate. The computing device 30 can be adapted tosubsequently deduce if the compensation of phase shift andamplitude normalization is adequate, e.g. by checking that theresidual during the initial time period is approximately null, andcompensate by means of the general filter model of eq. 16 if thecompensation is not good enough, e.g. if the residual is not smallenough.
    When test signals have been acquired for a first position of aninspected zone 5, the measuring device 11 is moved to a secondposition of the inspected zone 5. The measuring device 11 maybe moved continuously or step-wise. The measuring system 13 isconfigured to use short ultrasonic pulses, and test signals may beobtained at regular intervals during continuous movement of themeasuring device 11 in contact with the inspected object 20.
    The measuring system 13 is provided with transducers 12preferably adapted to induce ultrasonic signals at a low ultrasonicfrequency, i.e. below 1 MHz. ln many solid materials, such asmetals like aluminum, such low frequency ultrasonic signalsspread while propagating through the solid material. Ultrasonicsignal of between 5-10 MHz propagate in a more straight manner,and an advantage of using the low frequency ultrasonic signals ofless than 1 MHz is that these signals can spread into and cover alarger portion of the inspected object 20. Moreover, the lowfrequency ultrasonic signals can be used for inspecting morecomplicated structures, also at a distance beyond the variationsof the structure. The technique, using a reference signal e.g. asobtained from the inspected object or structure, for calibrationdoes not require any “a-priori” knowledge of how the wavepropagates in the structure under inspection,. That is to say thatno knowledge of G(t) in eq 10a, 10b and 11 is needed in order to 28 identify the presence of a defect. This makes possible theinspection of a complicated structure.
    The test object 20 inspected in figure 1 is a plate-like constructionseen from the side and includes beams 22 extending along thebottom side. Using the lower frequency ultrasonic signals, themeasuring device 11 may, as illustrated, be placed on an oppositeside of the test object 20 compared to the beams 22, and still beable to receive echoes of the ultrasonic test signals travelling intoand being reflected in the distal ends 22B, at the bottom surface,of theses beams 22. The beams 22 of the test object 20 may bearranged inside the test object 20, as indicated with the brokencontour line. ln such a case the beams 22 may not be easilyavailable for inspection, however, using an ultrasonic signalhaving a low frequency will provide information from the beams22. Low frequency signals will propagate into each beam 22 andreflected signals from the distal ends 22B of the beams 22 will bereceived by the measuring device 11.
    Figures 7B and 7C illustrates an embodiment of a measuringdevice 11 in more detail than figure 7A. Figure 7B illustrates thebottom side of the measuring device 11, which bottom side isprovided with an array of transducers 12, at positions a, b, c andd. The transducers 12 protrude slightly from the bottom side to bein contact with the test object 20 that is inspected. The measuringdevice 11 is provided with four cables 18, one for each transducer12, and each cable is connected between a respective one of thetransducers 12 in positions a-d and the ultrasonic unit 19. Eachcable 18 may include a pair of wires, one wire for transmitting andone wire for receiving voltage signals.
    Figure 7C illustrate the top side of the measuring device 11. Thetop side is provided with a user interface comprising a lightemitting unit 14, such as a lamp or LED, and a screen 15. Theuser interface may alternatively include either a light emitting unit14 or a screen 15. The user interface 14, 15 may suitable be used 29 for presenting information from the computing device 30 to theoperator of the measuring device 11. For example, the computingdevice 30 may be adapted for determining the size of thedetermined residual, such as calculating the energy content of theresidual signal, and comparing the size with a threshold value.The computing device 30 may also be adapted to transfer a signalto the measuring device 11 indicating a defect when the size ofthe residual is above the threshold value. As a consequence theuser interface 14, 15 of the measuring device 11 may thenindicate that the inspected object 20 has a defect by means of forexample flashing the light of emitting unit, or change color. Themeasuring device 11 may also, or alternatively, be equipped witha sound or vibration emitting unit for indicating a defect to theoperator.
    Figures 8A and 8B illustrate an embodiment of the measuringdevice 11 provided with an array of eight transducers 12. Themeasuring device 11 is illustrated during inspection of aninspected test object 20 having a known feature that reflects thetest signals, which known feature is exemplified as the internalbeam 22, indicated by broken lines, arranged on the oppositeside, i.e. underside, of the inspected object 20. The measuringdevice 11 is illustrated from above, having the transducers 12,illustrated by broken lines, located on its underside in contact withthe inspected object 20.
    Figure 8A illustrates a measurement wherein one transducer 12,at position p, acts as a sending probe 3, 7 and sends an ultrasonictest signal that is received by the neighboring transducers 12,acting as receiving probes, of the sendingtransducer12, i.e. thetransducers 12 located in positions o and q. The neighboringtransducers 12 receives a direct signal, and also a signalreflected from the beam 22.
    Figure 8B illustrates a situation wherein the inspected zone 5 ofthe inspected object 20 has a defect 27. The ultrasonic test signal from the sending transducer 12, which is located at position p andacts as a sending probe 7, is received by the neighboringtransducers 12, i.e. the transducers located in position o and qthat acts as receiving probes 8. The signal is received as a directsignal, a signal reflected by the beam 22 and a signal reflectedby the defect 27.
    The other transducers 12 of the array in figures 8A, 8B may alsoreceive the signal. However, since the direct signals to thesesignals will pass the neighboring transducers 12 in positions oand q respectively, it is preferred that the non-neighboringtransducers 12 are not used for measuring transmissions fromtheir non-neighboring transducer 12 of position p. Thus, it ispreferred that only signals from neighboring transducers 12 areused, so as to be able to perform a calibration by means of thedirect signals. Each end transducer 12 of the array will onlyreceive and obtain one test signal, whereas each other transducer12, i.e. each transducer 12 having two neighboring transducers12, will obtain two test signals, one from each neighboringtransducer 12.
    The situation of only using test signals from neighboringtransducers 12 is further illustrated in figures 9A and 9B. Figure9 is a side view illustrating a measuring device 11 provided withsix transducers 12 in an array, located at positions e-j,respectively. The measuring device 12 is positioned in contactwith one side of a test object 20 that is inspected. The test object20 has a feature or defect 23 at its opposite side that will influencethe test signal when these are reflected by the opposite sidesurface of the solid object.
    Figure 9B illustrates test signals arranged in a matrix format. Thecircled test signals are the ones that are used for themeasurements of the test object 20 of figure 9A. As illustrated infigure 9B, only the test signals received from neighboringtransducers 12 are used for the measurements. The transducer 31 12 at position e receives only the test signal from the transducer12 located at position f. The transducer 12 at position f receivesonly the test signals from its neighboring transducers 12 locatedat positions e and g, etc. The transducer 12 in the other end ofthe array, located at position j only receives the test signal fromone neighboring transducer 12 located at position i.
    Figure 11 illustrates a method for inspection an object 20 madein a solid material according to embodiments of the invention.Optional steps are indicated by broken lines.
    The method for inspecting begins with obtaining 100 a baselinereference signal. The obtaining 100 can preferably be done on areference zone 1 of a reference object or on a reference zone 1of the test object. An ultrasonic signal is induced in the referencezone 1 by at least one transducer 12 of the measuring device 11and received by at least one other transducer 12 of thetransducers. Preferably every transducer 12 induces anultrasonic signal, which ultrasonic signal is received by thetransducers 12 that neighbors that sending transducer 12. Onereference signal is obtained for each combination of sendingtransducer 12 and receiving transducer 12 that should be usedduring the subsequent inspection of the test object. Referencesignals are obtained for all positions corresponding to thepositions of the subsequent inspection.
    An alternative to measuring reference signals is to simulatetransmissions in a FEM model of the test object, i.e. simulatingtransmissions and receptions in the positions of the inspectedzone 5.
    The inspection of the test object begins by positioning 101 themeasuring device with the transducers 12 in contact with thesurface of an inspected zone 5 of the inspected object 20. 32 The inspecting may include measuring at several positions,wherein the inspecting includes moving the measuring device 11from position to position, in a continuous or step-wise fashion. Aresidual for each test signal of each position is determined.
    After the step of positioning, the inspecting continues withacquiring 103 test signals. Acquiring a test signal includesinducing an ultrasonic signal, such as a short pulse, by means ofone of the transducers 12 acting as a sending probe 7 andreceiving the ultrasonic signal by means of at least one othertransducer 12 acting as a receiving probe 8.
    The acquiring 103 includes establishing test signals for everytransducer 12 of the measuring device 11 acting as a sendingprobe 7.
    Preferably, each transducer 12 that neighbors the transducer 12that induces a test signal are used for receiving this test signal.The measurements of the transducers 12 may be controlled bynot registering signals from non-neighboring transducers 12.
    After acquiring the test signals, the method of inspectingcontinues with extracting 104 a direct signal portion of each testsignal. The extracting 104 preferably includes identifying a timewindow Tc for the direct signals of each pair of neighboringtransducers 12.
    The inspecting continues with determining 105 the influence ofthe contact surface variations between the reference signal andthe test signal. The determining 105 is based on the direct signalportions of the reference signal and the corresponding test signal.ln the embodiment of figure 11, the determining105 of the contactsurface influence is determined as a phase shift for each acquiredtest signal. The determining 105 includes comparing the directsignal portion of each test signal with the direct signal portion ofthe corresponding reference signal. 33 The determining 105 of the influence of the contact surfacevariations as a phase shift includes comparing the test signalreceived in the time window Tc with the reference signal of thetime window Tc. The comparing may be provided by performing across correlation analysis of the test signal and the referencebaseline signal, especially the signals of the calibration timewindow Tc.
    After establishing the phase shift, the inspecting continues withcompensating 106 for the phase shift. The compensating 106 ismade for the full test signal, so that it includes, not only the directsignal portion but also, the reflected signals, i.e. the portion ofthe test signal received after the time window Tc.
    The inspecting may include establishing the time window for theinspection of the inspected zone 5, which time window of theinspection is determined on the basis of the size of the inspectedzone 5. The full signals used should end when the time windowof the inspection ends.
    The inspecting method may continue with normalizing 107 theamplitude of the test signal in relation to the amplitude of thebaseline signal. The normalizing 107 of the amplitude isperformed by means of the direct signals of the time window Tc.However, for many applications the influence of the phase shift ismuch greater than the variation of the amplitude, and thereforethe inspecting may provide valid measurements performing onlycompensation 106 of the phase shift for the full signal, evenwithout normalizing 107 the amplitudes.
    After compensating 106 for the phase shift the residual isdetermined 109. lf an amplitude normalization 107 has beenmade, the determining 109 of the residual is performed after thenormalization 107. 34 The determining 109 of the residual includes comparing the fulltest signal to the full baseline signal. Especially, performing asubtraction of the compensated full test signal and the fullbaseline signal in accordance with eq. 15 and eq. 16.
    The inspecting preferably also includes evaluation 110 of theresidual, at least an evaluation of the size of the residual. A sizeof the residual can be established by determining a measure ofthe energy of the residual or a measure of the amplitude, such asa mean or maximum amplitude. The size of the residual may becompared to a threshold value. The evaluation preferablyincludes comparing the residual, or the measure of the residual,to a threshold and presenting the result of the evaluation to theoperator, especially indicating to the operator if the residual, orthe measure of the residual, exceeds a threshold value. Thus,preferably the computing system 30 performs the evaluation andtransmits an indication of a defect to the measuring device 11,which indicates by means ofthe user interface 14, 15 that a defecthas been detected in the inspected zone 5 of the test object 20.
    Figure 12 illustrates a method for inspection an object 20 madein a solid material according to embodiments of the invention. Themethod for inspecting an object 20 of solid material of figure 12is similar to the method of figure 11. However, this method offigure 12 includes a different step of determining 205 theinfluence of the contact surface variations and a different step ofcompensating 206 the test signal.
    The inspecting method of figure 12 may start with a step ofobtaining 100 a reference signal. The method of figure 12continues with the steps of positioning 101 the measuring device,acquiring 103 the test signals and extracting 104 the direct signalportion of each acquired test signal.
    The method of inspecting in figure 12 continues with a step ofdetermining 205 the influence of contact surface variations between the reference signal and the test signal. This determining205 is performed by viewing the contact surface variations,preferably in the frequency domain, as a filter. Thus a filterequivalent, in accordance with eq. 17, corresponding to thecontact surface variations is established by means of any of thepreviously identified methods of a) performing a frequencyresponse estimate; b) performing a time domain correlationanalysis and c) performing a transfer function estimate.
    After determining 205 the influence of the contact surfacevariation for each of the direct signals, a compensation 206 ofeach full test signal is performed based on the respective filterequivalent.
    As in the inspecting method of figure 11, the inspecting methodof figure 12 includes the step of determining 109 the residual andmay include the step of evaluating 110 the residual.
    The computer 31 will be illustrated in more detail with referenceto figure 13. The computer 31 comprises hardware, such as aprocessor and memory, and software for handling data when anoperator inspects an object 20. Thus, the computer has beenadapted for performing functions in accordance with theinspecting methods described in figures 11 and 12 and themeasuring system 13 as illustrated in figure 1. Figure 13 is asimplified illustration for showing main features of the computer31. The hardware and software can be describes as functionalunits for performing steps of the methods of figure 11 and 12.
    The functional units include an ultrasonic controller 301, ameasuring unit 302, a calibrator 303, a residual calculator 304,an evaluator 305, and an output 306. The ultrasonic controller 301comprises means for controlling the ultrasonic unit 19 provided toto transmit signals to and receive signals from the measuringsystem 13. The output 306 comprises means for returning aresult, such as an indication of a defect, to the measuring device 36 11, and for providing information to the operator by means of themonitor 32. The measuring unit 302 is configured for receivingmeasurements and storing these, and is adapted for receivingand storing both test signals and reference signals to perform thesteps of obtaining 100 a reference signal and acquiring 103 testsignals.
    The calibrator 303 is configured to extract 104 the direct signalportion of the test signal, determine 105, 205 the influence of thevariations of the contact surfaces and compensate 106, 107, 206the full test signal before the residual is determined by theresidual calculator 304. The calibrator 303 may be adapted bothfor comparing the test signal with a measured reference signal aswell as comparing the test signal with a pre-stored referencesignal. The calibrator 303 may be adapted to - determine 105 the influence of the contact surface as a phaseshift and amplitude variation, - compensate 106 the full signal for the phase shift, - compensate 107 the full signal for the amplitude variation; as well as to - determine 205 the influence of the contact surface as afrequency dependent filter, and - compensate 206 the full test signal based on the determinedfilter equivalent.
    The residual calculator 304 is configured to subtract thecalibrated test signal from the reference signal in order to providea residual for further calculations.
    The residual evaluator 305 is adapted to determine a measure ofthe residual signal such as an energy content and may preferablyalso be adapted for solving the adjoint problem to provide anillustration of the inspected object 20 on the monitor 32 by meansof the output 306. 37 The functional units 301-306 may be implemented in a computer31 by means of a computer program 307, illustrated as acomputer disc, which computer program 307, when run on thecomputer 31, enables the computer 31 to perform the functionsdescribed above.
    A method and a system for inspecting objects by means ofultrasound has been provided, wherein reference signals areused as references for test signals in order to establish residualsignals indicating flaws in the objects.
    The said method comprises positioning (103) a measuring device(11) comprising a plurality of transducers (12) on the inspectedobject (20) and performing a number of test signal acquisitions(103). Each acquisition includes using one transducer to inducean ultrasonic signal into the test object, and using at least oneother transducer to receive an ultrasonic test signal. Theinspecting further comprises determining (105, 205) the influenceof contact surface variations between each test signal and thereference signal; compensating (106, 206) the full test signal forthe contact surface variations; and determining (109) a residualsignal based on the compensated test signal.
    The system comprises a computing device (30), and a measuringsystem (13) communicatively connected to the computing device(30). The measuring system (13) includes an ultrasound unit (19)and a measuring device (11) provided with a plurality oftransducers (12). The computing device (30) comprises acalibrator (303) configured to determine (105, 205) the influenceof contact surface variations, and compensate (106, 206) the testsignal for the contact surface variations. The computing device(30) also comprises a residual calculator (304) configured todetermine (109) the residual signal based on the compensatedtest signal and the reference signal. 38 A computer program has also been provided for enabling acomputing device (30) to perform the method steps of thecomputing device.
    All embodiments have been provided for facilitating enabling theinvention and are examples only, the scope of the invention isonly limited by the claims.
    List of references A1 “Flaw imaging with ultrasound: the time domaintopological gradient method” by N. Dominguez et al,AIP Conference Proceedings, 2005, pages 859-866.(http://dx.doi.org/10.1063/1.1916764) A2 “Time domain topological gradient and time reversalanalogy: an inverse method for ultrasonic targetdetection” by N. Dominguez et al, Wave Motion, Vol.42, No. 1. June 2005, pages 31-52.(http://dx.doi.org/10.1016/j.wavemoti.2004.09.005) A3 “System identification, Theory for user”, by L. Ljung,Prentice Hall, 1998.
    权利要求:
    Claims (18)
    [1] 1. A method for inspecting objects by means ofultrasound, wherein reference signals are used as references fortest signals in order to establish residual signals indicating flawsin the objects, said method comprising: - inspecting a test object at one or more positions, the inspectingof one position comprises: - positioning (103) a measuring device (11) comprising a pluralityof transducers (12) in a selected position on the inspected object(20), so that the ultrasonic transducers (12) are in contact withthe inspected object (20), - performing a number of test signal acquisitions (103) at theselected position, each test signal acquisition (103) comprising:- using one transducer of the plurality transducers (12) as asending probe (7) to induce an ultrasonic signal into the testobject, and using at least one other transducer of the transducersas a receiving probe (8) to receive ultrasonic signals from the testobject (20), so that one test signal is obtained for eachcombination of sending probe (7) and receiving probe (8); said inspecting of one position further comprising: - determining (105, 205) the influence of contact surfacevariations between each test signal and corresponding referencesignal; - compensating (106, 206) the full test signal for the contactsurface variations; and - determining (109) a residual signal based on the compensatedtest signal for each combination.
    [2] 2. The method of claim 1, including extracting (104) adirect signal portion of the test signal, and wherein thedetermining (105, 205) of the contact surface variations is basedon the direct signal portion of the test signal and a correspondingdirect signal portion of the reference signal.
    [3] 3. The method of claim 1 or 2, wherein the step ofdetermining (105) the contact surface variations comprisesdetermining a phase shift (A) between the test signal and thereference signal, and wherein compensating (106) includescompensating the full test signal for the determined phase shift (A)-
    [4] 4. The method of claim 3, wherein the step of determining(105) the contact surface variations comprises determining anamplitude variation between the test signal and the referencesignal, and wherein the method further includes normalizing (107)the amplitude of the full test signal and/or the reference signal inaccordance with the determined amplitude variation.
    [5] 5. The method of claim 1 or 2, wherein determining (205)the contact surface variations includes determining a frequencyvarying filter equivalent for the contact surface, and wherein thecompensating (206) includes compensating the full test signal onthe basis of the determined filter equivalent.
    [6] 6. The method of any of claims 1 to 5, including evaluating(110) the level of the residual.
    [7] 7. The method of claim 6, wherein the evaluating (110)includes comparing the residual, or a measure of the residual, toa threshold, and indicating to an operator when the measure ofthe residual exceeds the threshold.
    [8] 8. The method according to any of claims 1 to 7, includingobtaining (100) the reference signal from a reference zone (1) ofthe inspected object (20), or from a reference zone (1) of areference object (A).
    [9] 9. The method according to any of claims 1 to 8, whereinthe induced ultrasound signal has a frequency of less than 1 l/lHz, 41 preferably between 50 kHz and 500 kHz, especially between 100and 250 kHz.
    [10] 10. A system for inspecting an object (20) using ultrasoundcomprising: - a computing device (30), and - a measuring system (13) configured to acquire test signals fromthe inspected object (20), which measuring system (13) iscommunicatively connected to the computing device (30) fortransferring the test signals from the measuring system (13) tothe computing device (30), wherein said measuring system (13) includes an ultrasound unit (19) anda measuring device (11) provided with a plurality of transducers(12), wherein each test signal is obtained by using one of thetransducers (12) as a sending probe (3, 7) and another one of thetransducers (12) as a receiving probe (4, 7), and said computing device (30) is configured to establish a residualby comparing each test signal with a corresponding referencesignal in order to detect flaws in the inspected object (20),characterized in that the computing device (30) comprises: a calibrator (303) configured to - determine (105, 205) the influence of contact surface variationsbetween each test signal and the corresponding reference signalby using a direct signal portion of the test signal and a directsignal portion of reference signal, and - compensate (106, 206) the full test signal for the contact surfacevanaüons;and a residual calculator (304) configured to determine (109) theresidual signal based on the compensated test signal and thereference signal.
    [11] 11. A system for inspecting an object (20) according toclaim 10, wherein the calibrator (303) is adapted to determine(105) the influence of contact surface variations by determining aphase shift (A) between the test signal and the reference signal, 42 and compensate (106) the full test signal for the determinedphase shift (A).
    [12] 12. A system for inspecting an object (20) according toclaim 11, wherein the calibrator (303) is further adapted todetermine (105) the influence of contact surface variations bydetermining (105) an amplitude difference between the test signaland the reference signal, and to compensate (107) the test signalby performing an amplitude normalization of the full test signaland the reference signal.
    [13] 13. A system for inspecting an object (20) according to anyof claims 10 to 12, wherein the calibrator (303) is adapted todetermine (105) the influence of contact surface variations bydetermining a frequency varying filter equivalent and compensate(206) the full test signal on the basis of the determined filterequivalent.
    [14] 14. A system for inspecting an object (20) according to anyof claims 10 to 13, wherein the computing device furthercomprises - a residual evaluator (305) configured to compare a measure orthe residual to a threshold, and - an output (306) configured for indicating to an operator whenthe measure of the residual exceeds the threshold by means ofthe measuring system (13) or by means of a monitor (32).
    [15] 15. A system for inspecting an object (20) according to anyof claims 10 to 14, wherein the ultrasound unit (19) is adapted toprovide ultrasound signals at a frequency of less than 1 l/lHz.
    [16] 16. A computer program product (307) for determining aresidual from test signals acquired by means of ultrasound froman inspected object (20) and reference signals, which computerprogram product (307) comprises a computer program that when 43 run on a computer (31) enables the computer (31) to perform thesteps of: - extracting (104) a direct signal portion of each test signal; - determining (105, 205) the influence of contact surfacevariations between the direct portion of the test signal and acorresponding portion of the reference signal; - compensating (106, 107, 206) each test signal for the contactsurface variations; and - determining (109) a residual signal based on the compensatedtest signal and the corresponding reference signal.
    [17] 17. A computer program product (307) according to claim16, wherein the step of determining (105) the contact surfacevariations comprises determining a frequency varying filterequivalent for the contact surface, and wherein the compensating(206) includes compensating the test signal on the basis of thedetermined filter equivalent
    [18] 18. A computer program product (307) according to claim16, wherein the step of determining (105) the contact surfacevariations comprises determining a phase shift (A) between thetest signal and the reference signal, and determining anamplitude difference between the test signal and the referencesignal, and wherein the step of compensating (106, 107) includescompensating (106) the test signal for the determined phase shift(A), and normalizing (107) the amplitude of the test signal and/orthe reference signal in accordance with the determined amplitudevariation.
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    同族专利:
    公开号 | 公开日
    US20170023527A1|2017-01-26|
    SE537991C2|2016-01-19|
    WO2015152795A1|2015-10-08|
    EP3126825A1|2017-02-08|
    EP3126825A4|2018-01-24|
    US10627369B2|2020-04-21|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US4252022A|1978-11-17|1981-02-24|Westinghouse Electric Corp.|Detection, characterization and studying of flaws in work by acoustic imaging|
    US5033304A|1989-04-27|1991-07-23|Industrial Quality, Inc.|Method and apparatus for laser ultrasonic characterization of coated fibers|
    US5280724A|1989-06-22|1994-01-25|Nissan Motor Co., Ltd.|Ultrasonic inspection method for detecting defects in solid objects|
    JPH05188043A|1992-01-14|1993-07-27|Tokimec Inc|Ultrasonic flaw detecting device|
    US5563848A|1994-09-08|1996-10-08|Monash University|Object detector for detecting buried objects|
    FR2891367B1|2005-09-28|2007-12-14|Airbus France Sas|METHOD OF IMAGING BY CALCULATING TOPOLOGICAL ENERGY|
    US20070144263A1|2005-12-27|2007-06-28|Caterpillar Inc.|Apparatus for non-destructive evaluation of a workpiece including a uniform contact apparatus|
    EP2232123B1|2008-01-11|2014-09-17|PII Limited|Pipeline inspection apparatus and method using two different ultrasound wavemodes|
    SE533385C2|2009-03-27|2010-09-14|Atlas Copco Tools Ab|Ultrasonic measurement method and apparatus|JP6602449B1|2018-12-05|2019-11-06|株式会社日立パワーソリューションズ|Ultrasonic inspection method, ultrasonic inspection apparatus and ultrasonic inspection program|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    SE1450404A|SE537991C2|2014-04-03|2014-04-03|Method and apparatus for inspection of ultrasonic structures|SE1450404A| SE537991C2|2014-04-03|2014-04-03|Method and apparatus for inspection of ultrasonic structures|
    EP15772469.1A| EP3126825A4|2014-04-03|2015-03-26|Method and device for inspection of solids by means of ultrasound|
    US15/301,440| US10627369B2|2014-04-03|2015-03-26|Method and device for inspection of solids by means of ultrasound|
    PCT/SE2015/050367| WO2015152795A1|2014-04-03|2015-03-26|Method and device for inspection of solids by means of ultrasound|
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