Patent Publication Number: US-11650185-B2

Title: System and method for passive normalization of a probe

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to wheel probes for inspecting a structure, and, more particularly, to a system and method for passive normalization of an ultrasonic dry coupled wheel probe as the probe inspects a structure. 
     BACKGROUND OF THE DISCLOSURE 
     In various technical fields, such as the oil and gas industry, pipelines and other structures are inspected using sensors. In ultrasonic testing (UT), such sensors utilize ultrasonic waves to penetrate the surface of structures. UT-based sensors are known for providing a non-destructive testing technique for such inspections of structures. For example, when inspecting a steel structure such as a steel pipe, a UT-based sensor traverses the surface of the structure to measure the thickness of the steel to determine whether the thickness has reduced below a certain critical limit due to erosion. By periodically performing such non-destructive and surface penetrating inspections, the steel structure can be evaluated to avoid leaks, failures, and unplanned shutdowns of the pipe during operation. 
     UT-based sensors can be directional sensors, such as ultrasonic dry coupled wheel probes. Such wheel probes are capable of traversing any type of surface, such as a flat surface or a curved surface of a pipe. The wheel probes can be incorporated into a crawler-type device which moves upon the surface of the structure being inspected. However, such directional sensors require normalization of the sensors in order to ensure that the generated ultrasonic waves from the probe are directed normal, that is, perpendicular to the surface under test. Such normal emissions permit the reflection of the ultrasonic waves from the structure to be redirected back to the sensor. A slight inclination of the direction of the emission of the ultrasonic waves can cause the loss of the reflected signal. Accordingly, recalibration of known probes with sensors is often required as the probes traverse surfaces having different curvatures. 
     One technique to recalibrate a probe is to use an actuator for actively normalizing the probe towards a given surface. However, such actuators increase the size and cost of the probe or the crawler in which the probe is mounted. In addition, such actuators must be activated every time for different curvatures of the surface under test. It is in respect of these problems in the art that the present disclosure is directed. 
     SUMMARY OF THE DISCLOSURE 
     According to an embodiment consistent with the present disclosure, a system and method passively normalize an ultrasonic dry coupled wheel probe as the probe traverses a surface of a structure to inspect the structure, such as a flat structure or a curved pipe. At least a pair of arms are configured to passively maintain normalization of the probe in a detection direction normal to the surface. 
     In an embodiment, an assembly configured to hold a probe adjacent to a test surface. The assembly comprises a first connector, first and second arms, a pair of first mounting members, a pair of first wheels, and a holder. The first arm is pivotably coupled to the first connector at a first end thereof. The first arm extends in a forward direction and extends in a normal direction perpendicular to the forward direction and normal to the test surface. Similarly, the second arm is pivotably coupled to the first connector at a first end thereof. The second arm extends in a rearward direction opposite to the forward direction and extending in the normal direction. 
     In a more particular embodiment, each of the pair of first mounting members is coupled to a respective second end of the first and second arms, each of the pair of first wheels is coupled to a respective first mounting member, the holder is coupled to the first connector and is configured to hold the probe, the pivotable coupling of the first and second arms to the first connector passively normalizes a detection direction of the probe as the probe traverses the test surface, or a combination of these further arrangements can be used in a given embodiment. 
     In additional, particular embodiments, the first connector can include a first pinion gear, the pair of first wheels can be casters, the holder can be coupled to a rotating shaft of the probe and can be configured to allow the probe to rotate around the rotating shaft, a first resilient member can connect to each of the first and second arms and the first resilient member can be configured to bias the first and second arms towards each other, the first and second arms can pivot with a first degree of freedom in the forward and rearward directions, respectively, or a combination of these further arrangements can be used in a given embodiment, including with any of the embodiments described above 
     In an alternative embodiment, the assembly includes a second connector, third and fourth arms, a pair of second mounting members, and a pair of second wheels. The third arm is pivotably coupled to the second connector. The third arm extends in a right direction and extends in the normal direction. Similarly, a fourth arm is pivotably coupled to the second connector. The fourth arm extends in a left direction opposite to the right direction and extends in the normal direction. Each of the pair of second mounting members is coupled to a respective second end of the third and fourth arms. Each of the pair of second wheels is coupled to a respective second mounting member. Each of the right and left directions is perpendicular to both of the forward direction and the normal direction. The third and fourth arms pivot with a second degree of freedom in the right and left directions, respectively. 
     In another embodiment, a system is configured to traverse a test surface. The system includes a housing, a drive wheel rotatably coupled to the housing and configured to traverse the test surface, and an assembly disposed within the housing. The assembly comprises a first connector, first and second arms, a pair of first mounting members, a pair of first wheels, and a holder. The first arm is pivotably coupled to the first connector at a first end thereof. The first arm extends in a forward direction and extends in a normal direction perpendicular to the forward direction and normal to the test surface. Similarly, the second arm is pivotably coupled to the first connector at a first end thereof. The second arm extends in a rearward direction opposite to the forward direction and extending in the normal direction. The pivotable coupling of the first and second arms to the first connector passively normalizes a detection direction of the probe towards the test surface as the system with the probe traverses the test surface in response to rotation of the drive wheel. 
     In more particular embodiments, a system as described above can include a linear motion guide configured to guide the assembly linearly relative to the housing. The system can further include a compression-based resilient member disposed between a top surface of the assembly and an interior surface of the housing. The pair of first wheels can be casters. The holder can be coupled to a rotating shaft of the probe and configured to allow the probe to rotate around the rotating shaft. A first resilient member can be connected to each of the first and second arms. The first resilient member can be configured to bias the first and second arms towards each other. A given embodiment can include any one or more of the foregoing further features, connections and arrangements. 
     In a further embodiment, a method is configured to inspect a test surface. The method comprises providing a housing having a drive wheel rotatably coupled to the housing and configured to traverse the test surface, and providing an assembly disposed within the housing. The assembly includes a first connector, a first arm, a second arm, a pair of first mounting members, a pair of first wheels, and a holder. The first arm is pivotably coupled to the first connector at a first end thereof. The first arm extends in a forward direction and extends in a normal direction perpendicular to the forward direction and normal to the test surface. Similarly, a second arm is pivotably coupled to the second connector at a first end thereof. The second arm extends in a rearward direction opposite to the forward direction and extends in the normal direction. Each of the pair of first mounting members is coupled to a respective second end of the first and second arms. Each of the pair of first wheels is coupled to a respective first mounting member. The holder is coupled to the first connector and is configured to hold a probe adjacent to the test surface. 
     The method according to this disclosure further comprises traversing the test surface by operation of the drive wheel, pivoting the first and second arms, and passively normalizing a detection direction of the probe within the holder towards the test surface as the probe inspects the test surface. In more particular embodiments, the method can further include biasing the first and second arms towards each other by a first resilient member. 
     Any combinations of the various embodiments and implementations disclosed herein can be used in a further embodiment, consistent with the disclosure. These and other aspects and features can be appreciated from the following description of certain embodiments presented herein in accordance with the disclosure and the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a side schematic view of a crawler system having a passive normalization assembly traversing a curved surface, according to an embodiment. 
         FIG.  2    is a side schematic view of the crawler system of  FIG.  1    traversing a flat surface, according to the embodiment. 
         FIG.  3    is a top rear side perspective view of the passive normalization assembly, according to the embodiment. 
         FIG.  4    is a side plan view of the passive normalization assembly of  FIG.  3   , according to the embodiment. 
         FIG.  5    is a top rear side perspective view of a portion of the passive normalization assembly with parts separated, according to the embodiment. 
         FIG.  6    is a top rear side perspective view of the portion of the passive normalization assembly of  FIG.  5    with parts assembled, according to the embodiment. 
         FIG.  7    is a side plan view of the passive normalization assembly of  FIG.  3    in a frame in a first configuration, according to the embodiment. 
         FIG.  8    is a side plan view of the passive normalization assembly of  FIG.  3    in a frame in a second configuration, according to the embodiment. 
         FIG.  9    is a side plan view of the passive normalization assembly of  FIG.  3    in a frame in a third configuration, according to the embodiment. 
         FIG.  10    is a rear plan view of a passive normalization assembly in a frame, according to an alternative embodiment. 
         FIG.  11    is a top rear side perspective view of the passive normalization assembly in the frame shown in  FIG.  10   , according to the alternative embodiment. 
         FIG.  12    is a flowchart of operation of the system having the passive normalization assembly of  FIGS.  1 - 11   . 
         FIGS.  13 - 19    are side schematic views of alternative embodiments of the crawler of  FIGS.  1 - 2    illustrating symmetry-preserving mechanisms. 
     
    
    
     It is noted that the drawings are illustrative and are not necessarily to scale. 
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE DISCLOSURE 
     Example embodiments consistent with the teachings included in the present disclosure are directed to a system and method which passively normalize an ultrasonic dry coupled wheel probe as the probe traverses a surface of a structure to inspect the structure, such as a flat structure or a curved pipe. At least a pair of arms are configured to passively maintain normalization of the probe in a detection direction normal to the surface. 
     As shown in  FIGS.  1 - 9    in one embodiment, a system  10  is configured as a crawler device having a probe  12 . The system  10  traverses a test surface  14  of a structure  16 . The probe  12  is adjacent to the test surface  14  and inspects the structure  16 . The probe  12  can be a wheel probe. For example, the probe  12  can be an ultrasonic dry coupled wheel probe. Alternatively, other types of probes can be used as the probe  12 . As shown in  FIG.  1   , the system  10  traverses a curved surface  14 . As shown in  FIG.  2   , the system  10  traverses a substantially flat surface  18  of a structure  20 . 
     As shown in  FIGS.  1 - 2   , the system  10  includes a housing  22 , a drive wheel  24 , and an assembly  26 . The drive wheel  24  is rotatably coupled to the housing  22 . The drive wheel  24  is configured to traverse the test surface  14 ,  18 . The assembly  26  is disposed within the housing  22 . The system  10  can further include a linear motion guide  28  configured to guide the assembly  26  linearly relative to the housing  22 , for example, in a vertical direction  30 . The linear motion guide  28  can be affixed within the housing  22 . The system  10  can further include a compression-based resilient member  32  disposed between a top surface  34  of the assembly  26  and an interior surface  36  of the housing  22 , with one surface braced against the top surface  34  or structures that are fixedly attached to the housing  22 . The interior surface  36  can be an undersurface of the linear motion guide  28 . The compression-based resilient member  32  can allow the assembly  26  to move upward and downward against the restoring force of the resilient member. The resilient member  32  provides a pushing force downwards on the assembly  26 . The pushing force ensures the probe  12  maintains contact with the surface  14 ,  18  as the system  10  moves along the surface  14 ,  18  regardless of changes in the topology of the surface being traversed. The resilient member  32  can also prevent the assembly  26  from hitting against the interior surface  36  as the assembly  26  moves linearly relative to the housing  22 . In an alternative embodiment, the resilient member  32  can be a piston-cylinder device filled with compressed gas or vacuum which is arranged to provide a restoring force as described above. 
     Referring to  FIGS.  3 - 6   , the assembly  26  includes a rightward set of components  40 - 46 ,  54 - 58  which form a rightward portion of the assembly  26 , as shown in particular in  FIG.  6   . Similarly, a leftward set of components of the assembly  26  are mirror images of the rightward set of components  40 - 46 ,  54 - 58 . Accordingly, the leftward set of components, once assembled, form a leftward portion of the assembly  26 , which is a mirror image of the rightward portion of the assembly  26  shown in  FIG.  6   . The rightward and leftward portions are then assembled to form the overall assembly  26 , as shown in  FIG.  3   . The rightward and leftward portions can be fastened together at the mounting members  46 ,  48 , described below, using any known fastening mechanism. 
     Referring to the rightward portion shown in  FIGS.  3 - 6   , which is a mirror image of the leftward portion, the assembly  26  comprises a first connector  40 , a first arm  42 , a second arm  44 , a pair of first mounting members  46 ,  48 , a pair of first wheels  50 ,  52 , and a holder  54 . The first arm  42  is pivotably coupled to the first connector  40  at a first end  56  thereof. As shown in  FIG.  3   , the first arm  42  extends in a forward direction, and extends in a normal direction perpendicular to the forward direction and normal to the test surface  14 ,  18 . Similarly, the second arm  44  is pivotably coupled to the first connector  40  at a first end  58  thereof. The second arm  44  extends in a rearward direction opposite to the forward direction and extending in the normal direction. The pivotable coupling of the first arm  42  and the second arm  44  to the first connector  40  passively normalizes a detection direction of the probe  12  towards the test surface  14 ,  18  as the system  10  with the probe  12  traverses the test surface  14 ,  18  in response to rotation of the drive wheel  24 . 
     At least one fastener  60 ,  62  pivotably couples the first ends  56 ,  58  to the first connector  40 , respectively. Each fastener  60 ,  62  defines a respective pivot point of the arms  42 ,  44  on the first connector  40 . The fasteners  60 ,  62  can also include pinion gears in a pinion gear assembly. The first ends  56 ,  58  of the arms  42 ,  44  are coupled together at the pinion gear assembly. The pinion gear assembly can be rigidly attached to the holder  54 , described below, to allow the holder  54  to rotate along with the arms  42 ,  44 , as shown in  FIGS.  7 - 9   . Such rotation of the holder  54  adjusts the angle of normalization of the probe  12 . Accordingly, when both of the wheels  50 ,  52  are on the same horizontal surface  18 , such as shown in  FIGS.  2  and  4   , the holder  54  has a vertical or normal orientation to the surface  18 . When the wheels  50 ,  52  are tilted upward or downward due to the curvature of the surface, such as the surface  14  in  FIG.  1   , the holder  54  has the same tilt angle as the wheels  50 ,  52  since the holder  54  is rigidly coupled to the arms  42 ,  44  by the pinion gear assembly at the first connector  40 . 
     The pair of first wheels  50 ,  52  can be casters held by the mounting members  46 ,  48 , respectively, at second ends  47 ,  49  of the arms  42 ,  44 , respectively. Alternatively, other known types of wheels can be held by the mounting members  46 ,  48 , such that the wheels are free to rotate and to roll on the test surfaces  14 ,  18 . The configuration of the arms  42 ,  44  and the respective first wheels  50 ,  52  as casters balance the assembly  26 . Such balancing provides a symmetry-preserving mechanism. As the diameter of the structure  16 ,  20  changes, and so the curvature of the surface  14 ,  18  changes, respectively, the preservation of symmetry allows the wheels  50 ,  52  to stay in contact with the surface  14 ,  18 . In addition, the symmetry of the arms  42 ,  44  and the wheels  50 ,  52  also preserves the perpendicularity of the assembly  26  to the surface  14 ,  18 , and so the probe  12  stays normal to the surface  14 ,  18 . 
     The holder  54  can be coupled to a rotating shaft  64  of the probe  12  and configured to allow the probe  12  to rotate around the rotating shaft  64 . As shown in  FIG.  4   , an optional first resilient member  66  can be connected to each of the arms  42 ,  44  at fasteners  68 ,  70  on each respective arm  42 ,  44 . The first resilient member  66  can be a spring, such as a tension spring. The first resilient member  66  can be configured to bias the arms  42 ,  44  towards each other. 
     As shown in  FIGS.  1 - 2  and  7 - 9   , the assembly  26  of  FIGS.  3 - 6    can be mounted in a frame  72  having a top member  74  upon which the resilient member  32  is disposed. The frame  72  can also include a guidance slot  76 . The guidance slot  76  permits the first connector  40  to move within a limited curved path which defines the location of the pivot point of the arms  42 ,  44 . A center line from a midpoint of the first connector  40  to a center of the shaft  64  substantially defines the normal direction. 
     In operation, as the wheels  50 ,  52  traverse the surface  14 ,  18 , the arms  42 ,  44  pivot about their respective pivot points on the first connector  40 , defined by the fasteners  60 ,  62 . The arms  42 ,  44  flex in a symmetrical manner toward or away from the center line, which passively normalizes the detection direction of the probe  12  to be substantially parallel to the normal direction. 
     In an alternative embodiment shown in  FIGS.  10 - 11   , the system  10  further includes an assembly  80  having a second connector  82 , a third arm  84 , a fourth arm  86 , a pair of second mounting members  88 ,  90 , and a pair of second wheels  92 ,  94 . The third arm  84  is pivotably coupled to the second connector  82  at a first end  91 . The third arm  84  extends in a right direction and extends in the normal direction. Similarly, the fourth arm  86  is pivotably coupled to the second connector  82  at a second end  93 . The fourth arm  86  extends in a left direction opposite to the right direction and extends in the normal direction. Each of the pair of second mounting members  88 ,  90  is coupled to a respective second end  96 ,  98  of the arms  84 ,  86 . Each of the pair of second wheels  92 ,  94  is coupled to a respective second mounting member  88 ,  90 . Each of the right and left directions is perpendicular to both of the forward direction and the normal direction, as shown in  FIG.  11   . The arms  84 ,  86  pivot with a second degree of freedom in the right and left directions, respectively. 
     In another embodiment, a method  100  includes providing, in step  110 , a housing  22  having a drive wheel  24  rotatably coupled to the housing  22 . The method  100  also includes providing, in step  120 , an assembly  26  disposed within the housing  22  with pivoting arms  42 ,  44  and a holder  54  holding a probe  12  adjacent to a test surface  14 ,  18 . The method  100  then has at least the probe  12  traverse the test surface  14 ,  18  in step  130 . The method  100  then pivots the arms  42 ,  44  in step  140  in response to changes in curvature of the test surfaces  14 ,  18 . The method  100  then passively normalizes the detection direction of the probe  12 , in step  150 , towards the test surface  14 ,  18  as the probe  12  inspects the test surface  14 ,  18 . 
     Portions of the methods described herein can be performed by software or firmware in machine readable form on a tangible (e.g., non-transitory) storage medium. For example, the software or firmware can be in the form of a computer program including computer program code adapted to cause the system and assembly to perform various actions described herein when the program is run on a computer or suitable hardware device, and where the computer program can be embodied on a computer readable medium. Examples of tangible storage media include computer storage devices having computer-readable media such as disks, thumb drives, flash memory, and the like, and do not include propagated signals. Propagated signals can be present in a tangible storage media. The software can be suitable for execution on a parallel processor or a serial processor such that various actions described herein can be carried out in any suitable order, or simultaneously. 
       FIGS.  13 - 19    illustrate alternative embodiments of the system  10  of  FIGS.  1 - 2   , utilizing symmetry-preserving mechanisms in the housing  22 . Each of the symmetry-preserving mechanisms in  FIGS.  13 - 19    utilize one or more of a resilient member, a linkage, a magnet, and, optionally, gravity (when the system is situated on top of a structure) to balance the wheels  50 ,  52  on either side of the probe  12  whether the system  10  is on a curved surface  14  or a flat surface  18 . The configuration of the wheels  50 ,  52  on the surface  14 ,  18  changes such that movement of the wheel  50  in a first direction relative to the probe  12  is mirrored by movement of the wheel  52  in a second direction relative to the probe  12 , with the second direction mirroring the first direction about an axis of the probe  12 . The axis of the probe passes through the shaft  64 . The axis is illustrated by the dotted lines in  FIGS.  7 - 9   . Such mirrored movement of the wheels  50 ,  52 , caused by each symmetry-preserving mechanism, maintains the probe  12  in continuous contact with the respective surface  14 ,  18 . As shown in  FIGS.  13 - 17   , the continuous contact can be maintained by a push-down compression mechanism, such as a resilient member in the form of a spring. As shown in  FIGS.  18 - 19   , the continuous contact can be maintained by a magnet. 
     The symmetry-preserving mechanisms described herein maintain the symmetry of the wheels  50 ,  52  and their arms  42 ,  44  independent of gravity. However, depending on the orientation of the surfaces  14 ,  18 , gravity can provide additional symmetry-preserving forces on the wheels  50 ,  52  and arms  42 ,  44 . In addition, the symmetry-preserving mechanisms described herein dynamically adjust the configuration of the wheels  50 ,  52  as the wheels  50 ,  52  move along the surfaces  14 ,  18  having different curvatures. Such dynamic adjustment passively normalizes the probe  12  without actuators. Accordingly, the symmetry-preserving mechanisms described herein are less costly to implement than known normalization systems. 
     Referring in greater detail to the embodiments in  FIGS.  13 - 19   , the system in  FIG.  13    has a mechanism  200  configured to have the wheels  50 ,  52  move in symmetrical linear paths  205 ,  206  due to and symmetrical linkages. The system in  FIG.  14    has a mechanism  210  configured to have the wheels  50 ,  52  move in symmetrical diagonal paths  215 ,  216  due to symmetrical linkages. The system in  FIG.  15    has a mechanism  220  configured to have the wheels  50 ,  52  move in symmetrical arc paths  225 ,  226  due to symmetrical linkages with pivot points. The system in  FIG.  16    has a mechanism  230  similar to the mechanism  200  in  FIG.  13   . The mechanism  230  has the wheels  50 ,  52  move in symmetrical linear paths  231 ,  232  due to symmetrical resilient linkages using a dedicated linear guide  233 ,  234  for each wheel  50 ,  52 , respectively. The wheels  50 ,  52  are connected to each other by a translational link  235  between the wheels  50 ,  52 . Resilient members  236 ,  237  are provided between the translational link  235  and the housing  22 . The resilient members  236 ,  237  can be compression springs. The system in  FIG.  17    has a mechanism  240  similar to the system  10  in  FIGS.  1 - 2    using swing arms  42 ,  44 , with the wheels  50 ,  52  moving in symmetrical arc paths due to symmetrical links  241 ,  242 . However, compared to the mechanism in  FIGS.  1 - 2   , the mechanism  240  in  FIG.  17    includes a coupling between the arms  42 ,  44  using links  241 ,  242 , respectively, and grounded revolute joints  243 ,  244 , respectively, with a tension spring  245  between the arms  42 ,  44 . 
     The systems in  FIGS.  18 - 19    use magnets to maintain strong contact between the probe  12  and the surfaces  14 ,  18 . The wheels  50 ,  52  move in symmetrical arc paths due to magnetic forces on the linkages attached to the wheels  50 ,  52 . The system in  FIG.  18    has a mechanism  250  with two fixed magnetic disks on the shaft  64  of the probe  12 , on either lateral side of the probe  12 .  FIG.  18    illustrates the magnetic disk  255  on a rightward side of the probe  12 . One of the two poles S, N on each magnetic disk  255  provides a magnetic force to align the pole with the surface  14 ,  18 . For example, as shown in  FIG.  18   , the north pole N of the magnetic disk  255  is aligned with the surface  14 ,  18 . Alternatively, the system in  FIG.  19    has a mechanism  260  with a static ring magnet  265  mounted rigidly to the shaft  64 . The wheel  266  of the probe  12  sits inside a hole  267  in the ring magnet  265 , with the ring magnet  265  surrounding a lower part of the wheel  266  of the probe  12 . The ring magnet  265  creates a magnetic pulling force for the probe  12  to maintain the probe  12  in continuous contact with the surface  14 ,  18 . In an example embodiment, the ring magnet  265  is diametrically magnetized, with the north pole disposed laterally to the right and the south pole disposed laterally to the left in  FIG.  19   . In another example embodiment, the ring magnet  265  can be axially magnetized, with the north pole disposed upward along the normal direction, and the south pole disposed downward along the normal direction. 
     It is to be further understood that like or similar numerals in the drawings represent like or similar elements through the several figures, and that not all components or steps described and illustrated with reference to the figures are required for all embodiments or arrangements. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “contains”, “containing”, “includes”, “including,” “comprises”, and/or “comprising,” and variations thereof, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Terms of orientation are used herein merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized these terms could be used with reference to an operator or user. Accordingly, no limitations are implied or to be inferred. In addition, the use of ordinal numbers (e.g., first, second, third) is for distinction and not counting. For example, the use of “third” does not imply there is a corresponding “first” or “second.” Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     While the disclosure has described several exemplary embodiments, it will be understood by those skilled in the art that various changes can be made, and equivalents can be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation, or material to embodiments of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, or to the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 
     The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes can be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the invention encompassed by the present disclosure, which is defined by the set of recitations in the following claims and by structures and functions or steps which are equivalent to these recitations.