Patent Publication Number: US-10782268-B2

Title: Automated ultrasonic inspection of adhesively-bonded joints and inspection method therefor

Description:
RELATED APPLICATION 
     This application is a Non-Provisional Patent Application, and claims the benefit and priority of U.S. Provisional Patent Application No. 62/458,250, filed on Feb. 13, 2017. The entire content and disclosure of such an application are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The subject matter disclosed herein relates to inspection techniques for adhesively bonded joints. 
     The automotive industry is increasingly moving away from tack welded and/or line-welded joints in favor of adhesively-bonded joints. Such joints can be highly reliable, less susceptible to corrosion over time, offer improved acoustic performance, and/or can be practiced on a fiscal par with welded joints. While such bonded joints provide certain structural benefits, inspection thereof can be labor intensive and, as such, can mitigate the fiscal benefits derived from adhesive bonding. 
     Non-destructive testing of bonded joints can produce a lower amount of material scrap and, as such, can optimize the fiscal gains achievable by adhesive bonding. One such non-destructive method employs an ultrasonic inspection probe disposed over a bonded surface to detect anomalies in the underlying bond-line. The ultrasonic inspection probe is pressed against the surface, i.e., manually manipulated, to introduce an acoustic pulse into the structure. The probe can measure the acoustic impedance in the structure (i.e., the speed of sound in the structure) as a function of the material density. Changes in density, from one material to another, or from one medium to another, effect reflections back to the source, i.e., the inspection pad, which may be imaged by a signal processor. Typical deficiencies/anomalies can include voids, discontinuities, and/or differences in density with respect to the cured composite adhesive of the bond-line. 
     In practice, such probes may not provide a full picture of the bond-line and generally are presented slowly and deliberately, manually against the surface to ensure that the data obtained by the probe is accurate. If an operator suspects that the pad did not properly image an area of the bond-line, i.e., due to the contour of the part which may be affecting the resultant output, he/she may present the pad at a slightly different orientation. This may be done to determine whether the output changes, e.g., improves/degrades the output by (i) skewing the angle of the probe, or (ii) pitching/rolling the pad five (5) or ten (10) degrees from the previous scan. Additionally, rotary encoders can be integrated with the housing of the probe which have the effect of resisting the motion of the probe. That is, such rotary encoders produce friction drag which can further slow the speed of inspection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are, therefore, not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Differences between otherwise like parts may cause to those parts to be indicated with different numerals. Different parts are indicated with different numerals. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which: 
         FIG. 1  is an broken-away, perspective view of a flexible ultrasonic pad of the type employed in the teachings of the disclosure, which flexible pad is disposed in a housing which traps a bonded joint between the ultrasonic pad and a path pulse generator. 
         FIG. 2  is a schematic of a robotic inspection system in accordance with the teachings of the present disclosure wherein a robotic arm assembly provides a gimbal mount for supporting a flexible ultrasonic transducer operative to inspect the bond-line of a bonded part. 
         FIG. 3  depicts schematic views of the robotic inspection system taken substantially along line  3 - 3  of  FIG. 2  showing the robotic arm assembly and the flexible ultrasonic transducer in two positions along the contoured surface/edge of the bonded part. 
         FIG. 4  depicts the underside surface of the flexible ultrasonic transducer taken substantially along line  4 - 4  of  FIG. 3 , which ultrasonic transducer is segmented into a plurality of finite transducer elements for the purpose of: (i) performing inspection subroutines dedicated to evaluation of the bond-line, and (ii) determining contour variations of the bond-line. 
         FIG. 5  depicts an enlarged view of the bond-line for joining the components or layers of the bonded part and a cone of pulsed ultrasonic energy transmitted by a single transducer element. 
         FIG. 6  is a schematic illustration of an acceptance criterion used for determining the efficacy of a bond-line for joining the components of a bonded part. 
     
    
    
     SUMMARY OF THE DISCLOSURE 
     The subject matter disclosed herein relates to inspection techniques for adhesively bonded joints, and more specifically, to an automated ultrasonic inspection system and method for determining and ensuring the integrity/strength of bonded joints. In light of the current technology, a need, therefore, exists for an inspection probe which produces reliable inspection data of a scanned bond-line, resolves inaccuracies associated with the bond-line data, eliminates the requirement for rotary encoders and rapidly develops/determines a pass/fail criteria for acceptance/rejection of bond-line data. 
     In one embodiment, an inspection system is provided for determining the efficacy of a bond-line, comprising: a robotic arm assembly capable of linear translation and rotational displacement about multiple axis, a flexible ultrasonic transducer mounted to the robotic arm assembly and having an array of transducer elements, each element configured to transmit and receive ultrasonic energy indicative of the efficacy of the bond-line within the bonded part; and a signal processor, responsive to ultrasonic impedance signals issued by the ultrasonic transducer and to position signals issued by position encoders of the robotic arm assembly. The signal processor is operative to: (i) calculate an amplitude value from each impedance signal, (ii) average the maximum amplitude values associated with each of the transducer elements, (iii) compare the maximum amplitude values to a bond-line threshold, and (iv) determine whether the bond-line threshold is greater than a defect threshold value. 
     In another embodiment, an inspection system is provided for determining the efficacy and veracity of a bond-line, comprising: a robotic arm assembly providing a gimbal mount for enabling linear and rotary translation about multiple axes; an ultrasonic transducer affixed to the gimbal mount of the robotic arm assembly and comprising a planar array of transducer elements, each transducer element capable of transmitting and receiving reflected ultrasonic energy indicative of changes in acoustic impedance within the bond-line, the reflected energy providing original bond-line data indicative of the efficacy of the bond-line; and select transducer elements additionally transmitting and receiving ultrasonic energy for producing orientation data indicative of the orientation of the planar array relative to the contour of the bonded joint. The bond-line and orientation data are processed to determine whether additional bond-line data ought to be collected and analyzed to determine the veracity of the original bond-line data. 
     DETAILED DESCRIPTION 
     An exemplary embodiment of the disclosure describes an ultrasonic inspection system for determining the efficacy of a bond-line for joining structural components. The ultrasonic inspection system is described in the context of a three-dimensional robotic arm assembly capable of linear and rotary motion about multiple axes of the robotic arm assembly. The robotic arm assembly is operative to displace an ultrasonic inspection probe over the bond-line of the structural components. 
     An inspection probe having a linear array of ultrasonic elements is described, however, it will be appreciated that other inspection probe assemblies may be employed within the spirit and scope of the appended claims. Commonly-owned, co-pending, U.S. patent application Ser. No. 15/068169 entitled “Ultrasonic Inspection Probe Assembly” describes a flexible ultrasonic transducer located between a backing block and a face layer. The flexible ultrasonic transducer array is located in an opening of a compliant frame which flexes to fit the shape of a curved or contoured surface during inspection. After inspection, both the transducer and frame retain their original shape. 
       FIG. 1  depicts an inspection probe assembly  10  of the type described in the preceding paragraph. The inspection probe assembly  10  includes a flexible array of ultrasonic transducer elements which conform to geometric changes in contour within prescribed limits. In the described embodiment, the flexible array conforms to relatively small variations in contour, i.e., relatively shallow angles. The inspection probe assembly  10  shown in  FIG. 1  is manually manipulated over the surface of a bonded part  12  and includes a path pulse generator  14  for measuring the location of the inspection probe assembly  10  along the surface  16  of the bonded part  12 . Operationally, the ultrasonic transducer array transmits ultrasonic energy into the bond-line (not shown in  FIG. 1 ) and receives/records reflected ultrasonic energy indicative of changes in acoustic impedance within the bond-line. 
     As mentioned in the background, manual manipulation of such inspection probe assemblies  10 , in some cases especially those which employ rotary encoders  14  for position acquisition, can slow the process of data acquisition. As such, the use of such inspection probe assembly  10  can be impractical for high volume production such as may be required in the automobile industry. Notwithstanding such drawbacks and/or deficiencies, such manually-manipulated inspection probe assembly  10  can offer the advantage of being able to immediately and instantaneously, or close thereto, collect additional inspection data which either validates or corrects the original bond-line data. That is, by further manual manipulation, the planar array of ultrasonic elements may be oriented at a slightly different angle or orientation such that the bond-line data may be seen from a slightly different vantage point or angle. This vantage point may validate or correct the efficacy of the bond-line such that it may now be deemed acceptable for passing certain predetermined bond-line criteria, i.e., eliminating the number of rejected parts and the expense associated therewith. 
     As will be discussed in greater detail hereinafter, the disclosure can employ algorithms which enable the flexible transducer to be manipulated by a robotic arm assembly which may not have the intrinsic or inherent “feel” such as that provided by a hand-held or manually operated transducer pads. More specifically, the algorithms employed by the present disclosure enables the flexible transducer to be manipulated by a high rate of production robotic arm assembly/machine while, at the same time, providing the dexterity and feel attainable by manually manipulated inspection probe assemblies  10 . 
     In  FIG. 2 , the ultrasonic inspection assembly  20  includes a robotic arm assembly  22 , a flexible ultrasonic transducer or transducer array  30  gimbal mounted to the robotic arm assembly  22 , and a signal processor  40 , responsive to position signals to control the position of the robotic arm assembly  24  and to ultrasonic impedance signals issued by the ultrasonic transducer  30 , to record/compare/contrast acquired bond-line data to stored values of a predetermined, bond-line threshold such that defect values may be issued which are indicative of an accepted or rejected component bond-line (the bond-line threshold and defect values associated with the difference between the bond-line threshold and the acquired bond-line data will be discussed in greater detail below). 
     In  FIGS. 2 and 3 , the robotic arm assembly  22  may include a variety of linear and rotary actuators and transducers operative to effect displacement of the robotic arm assembly  22  about multiple axes  26 . The linear and rotary actuators include position encoders to provide position feedback to the controller or signal processor  40  relative to a mounting table  28 , and to the bonded part  12  which is affixed to the mounting table  28 . That is, since the position of the robotic arm assembly  22  can be known in three dimensional space, i.e., by a laser alignment or a theodolite 3-D positioning system, the position of the ultrasonic transducer  30 , which is gimbal mounted to the robotic arm assembly  22 , can also known relative to the bonded part  12  and to the underlying bond-line thereof. 
     In  FIGS. 3 and 4 , the ultrasonic transducer  30  is gimbal mounted to the robotic arm assembly  22 , positioned over the bond-line, and displaced along the bond-line to acquire bond-line data. In the described embodiment, the ultrasonic transducer  30  is mounted within a rectangular housing  42  having a plurality to spring-biased, spherical rolling elements  44  disposed at each of the four-corners of the rectangular housing  42 . The rolling elements  44  ensure that that the transducer  30  and the housing  42  slide without resistance across the surface  16  of the bonded part  12 . In the described embodiment, the housing  42  includes a bore hole  46  at each corner thereof, which bore hole has an axis transverse to the direction of translational motion of the housing  42 . Each bore hole  46  receives a coil spring  48  for biasing a spherical ball  44  against the surface  16  of the bonded part  12 . 
     In  FIGS. 3, 4 and 5 , the ultrasonic transducer  30  includes an array of transducer elements  101 - 235  ( FIG. 4 ) to inspect the bond-line by transmitting an ultrasonic pulse  50  of high frequency RF energy through the bond-line  54 . The pulses  50  issued by each of the transducer elements  101 - 235  travel through the layers  52 ,  54 ,  56  of the bonded part  12  which may include a first layer  52  of sheet metal bonded to a second layer  56  of sheet metal by a bond-line  54  of thermoplastic/thermoset epoxy resin. Any change in density or reflective index, effecting a change in the speed of sound, i.e., also known as the acoustic impedance of the material, traveling through the layers  52 ,  54 ,  56 , produces an echo, or reflection, at the interface  58  of the materials  52 ,  54 ,  56 . 
     To ensure that transducer elements  101 - 235  of the ultrasonic transducer  30  are intimately in contact with the surface  16  of the bonded part  12 , it may be necessary to inject or spray a fluid conductive medium  59  therebetween. The conductive medium  59  ensures that the ultrasonic waves of the transducer  30  transmit directly into the surface  16  of the bonded part  12 . The conductive medium  59  may comprise various combinations of propylene glycol, glycerine, phenoxyethanol, carbapol R 940 polymer and water. 
     The reflected pulse is best heard/calculated when the reflection is orthogonal to an interface. However, inasmuch as the plane of the transducer elements  101 - 235  may vary relative to the plane of the surface  16 , i.e., due to contour variations of the surface  16 , the transducer elements  101 - 235  may not be receiving an optimum return. 
     In  FIGS. 4 and 5 , the disclosure provides information concerning the orientation of the ultrasonic transducer array  30  which may affect the efficacy of the return by using select transducer elements. That is, select transducer elements around the periphery of the array, e.g., elements  101 ,  115 ,  221 , and  235 , and at the center of the array, e.g., element  168 , may be used to calculate the distance that each such element  101 ,  115 ,  168 ,  221 , and  235  is separated from the surface  16 . These transducer elements  101 ,  115 ,  168 ,  221 , and  235  may pulse and receive a surface return, to determine a distance dimension from the surface  16 . By calculating the distance that each element  101 ,  115 ,  168 ,  221 , and  235  is from the surface, the angular orientation of the transducer  30  relative to the surface  16  can be calculated. If it is determined that a better return may be obtained by conically pulsing the elements, i.e., at a cone angle of about +/−5 degrees, then a forward or aft pulse or “shot”  50  may be taken by the other elements  101 - 114 ,  116 - 167 ,  169 - 219 , and  221 - 234 . While the direction of the pulse  50  may be performed electronically, it will also be appreciated that the “shot”  50  may be achieved by pitching the transducer  30  forward/aft, or rolling the transducer  30  to one side or to the other by the gimbal mount of the robotic arm assembly  22 . Whether the pulse or “shot”  50  is performed electronically or physically, such action can be taken to obtain a better return or picture, similar to the way that an operator manipulates the hand-held probe  10  shown in  FIG. 1 . Consequently, by using some of the elements  101 ,  115 ,  168 ,  221 , and  235  to obtain orientation data and other elements  101 - 114 ,  116 - 167 ,  169 - 219 , and  221 - 234  to obtain bond-line data, a more complete or optimum picture of the bond-line is obtained. 
     In operation, the signal processor  40  is responsive to the position signals of the robotic arm assembly  22  and the ultrasonic impedance signals of the flexible ultrasonic transducer  30 . More specifically, and referring to  FIGS. 5 and 6 , each transducer element  30  transmits a pulse  50  ( FIG. 5 ) and receives an impedance or return signal  60 . The signal processor  40  is operative to: (i) determine an amplitude value for each of the impedance signals  60  returned to each of the transducer elements  101 - 235 , (ii) sum/scale the maximum amplitude values  62 ,  64  returned to each of the transducer elements  101 - 235 , (iii) compare the actual amplitude values  62 ,  64  to a bond-line threshold  70  and issuing a difference signal indicative thereof, and/or (iv) determine whether the bond-difference signal is greater than a defect threshold. 
     These relationships are expressed below in equations (1.0) and (2.0). With respect to step (i), the amplitude value is obtained from the acoustic impedance signals  60  returned to each of the transducer elements  101 - 235 . In step (ii), the maximum amplitude values  62 ,  64  are summed/scaled by multiplying each by a normalizing factor between the start times t 1 , t 2  to obtain an image value pursuant to equation (1.0) below. 
     
       
         
           
             
               
                 
                   
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     Next, if the summation of the values returned by the Image (x.y) is greater than a bond threshold  70 , i.e., a predetermined threshold established by the specific bonded component, and, if this bond-line threshold  70  exceeds a defect threshold, i.e., another empirically established threshold based on other parameters such as the strength required by the bond-line, then the bond-line criteria is met and the part is accepted (see equation (2.0) below.) 
     
       
         
           
             
               
                 
                   
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     To the extent that the claims recite the phrase “at least one of” in reference to a plurality of elements, this is intended to mean at least one or more of the listed elements, and is not limited to at least one of each element. For example, “at least one of an element A, element B, and element C,” is intended to indicate element A alone, or element B alone, or element C alone, or any combination thereof. “At least one of element A, element B, and element C” is not intended to be limited to at least one of an element A, at least one of an element B, and at least one of an element C. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.