Patent Publication Number: US-11035744-B2

Title: Non-contact magnetostrictive sensor alignment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation and claims priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 16/454,514, filed on Jun. 27, 2019, which is a continuation of and claims priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 15/606,605, filed on May 26, 2017, and granted as U.S. Pat. No. 10,337,934, the contents of each is hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     Sensor alignment systems and methods are provided, and in particular systems and methods are provided for aligning a magnetostricive sensor. 
     BACKGROUND 
     Ferromagnetic materials can have magnetostrictive properties that can cause the materials to change shape in the presence of an applied magnetic field. The inverse can also be true. When a stress is applied to a conductive material, magnetic properties of the material, such as magnetic permeability, can change. A magnetostrictive sensor can sense the changes in magnetic permeability and, because the changes can be proportional to the amount of stresses applied to the conductive material, the resulting measurement can be used to calculate the amount of stress. 
     The changes in the magnetic permeability arising from an application of stress to the conductive material, however, can be small, making accurate measurement difficult. Some magnetostrictive sensors can be manually aligned and a gap is set by a gauge. Such alignment can result in different air gaps being defined between each detector pole of the sensor. 
     SUMMARY 
     A sensor system for mounting a sensor assembly relative to a target object to be tested is provided herein. In one embodiment, a sensor system is provided and can include a sensor assembly. The sensor system can also include a control and processing module coupled to the sensor assembly and configured to process signals generated by the sensor assembly. The sensor system can also include a mounting assembly configured to receive the sensor assembly and to position the sensor assembly relative to a surface of a target. The mounting assembly can include a retaining element configured to translate along a first axis. 
     In one or more embodiments, the mounting assembly can include an extension arm coupled to the sensor assembly and a rigid support coupled to the extension arm. The sensor assembly can further include a proximity sensor configured to determine a size of a gap formed between the proximity sensor and the target. The control and processing module can processes the raw stress signals and generates a corrected stress signal based on the determined size of the gap. 
     In one or more embodiments, the sensor assembly can include a housing and a sensor head disposed within the housing. The housing can include a proximal end and a distal end. The proximal end of the housing can be formed from one of stainless steel and aluminum and/or the distal end of the housing can be formed from one of a ceramic and a polymer. 
     In one or more embodiments, the sensor head can include a drive element and at least one detection element. The control and processing module can provide an alternating current input drive signal to the drive element to cause a magnetic flux to be generated in a central arm of the sensor assembly. The control and processing module can receive raw stress signals generated by the at least one detection element based on the at least one detection element detecting the magnetic flux generated in the central arm of the sensor assembly. The at least one detection element can generate the raw stress signals after the magnetic flux has passed through a gap formed between the at least one detection element and the target. A magnitude of the raw stress signals can correspond to a stress state of the target and/or a size of the gap. 
     In one or more embodiments, the sensor assembly can be adjusted with respect to a pitch axis of the sensor assembly, a yaw axis of the sensor assembly, and/or a roll axis of the sensor assembly, via the mounting assembly. In one or more embodiments, the mounting assembly can further includes an adjustment assembly coupled to the retaining element and a frame assembly coupled to the adjustment assembly. The frame assembly can include a first member coupled to the adjustment assembly, a second member pivotally coupled to the first member about a second axis extending transverse to the first axis, and a third member pivotally coupled to the second member about a third axis extending transverse to the first and second axes. Pivotal movement of the first member relative to the second member can cause rotation of the retaining element about the second axis, and further wherein pivotal movement of the second member relative to the third member is configured to cause rotation of the retaining element about the third axis. 
     In one or more embodiments, the adjustment assembly can include a movable member configured to couple the adjustment assembly with the retaining element and a frame to which the movable member is coupled. The movable member and the frame can be coupled to a rotatable adjuster configured to slidably position the moveable member. The rotatable adjuster can be adjusted to cause the sensor assembly to move proximally or distally with respect to an axis that is parallel to a surface of the target. 
     In one or more embodiments, the retaining element can be formed as a clamp configured to releasably engage the sensor assembly received within a central bore of the retaining element. The retaining element can include first and second pairs of arms extending from the clamp at an opening of the clamp. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view of one embodiment of a sensor system; 
         FIG. 1B  is an enlarged perspective view of a sensor assembly of the sensor system shown in  FIG. 1A ; 
         FIG. 1C  is a perspective view of one embodiment of a sensor head; 
         FIG. 2A  is a perspective view of one embodiment of a sensor mounting assembly; 
         FIG. 2B  is an exploded perspective view of sensor assembly shown in  FIG. 2A ; 
         FIG. 2C  is a top view of the sensor mounting assembly shown in  FIG. 2A ; 
         FIG. 2D  is another perspective view of the sensor mounting assembly shown in  FIG. 2A ; 
         FIG. 2E  is a right side view of the sensor assembly shown in  FIG. 2A ; and 
         FIG. 2F  is a back side view of the sensor assembly shown in  FIG. 2A . 
         FIG. 3A  is a side view of one embodiment sensor head of a sensor assembly; and 
         FIG. 3B  is a top view of the sensor head shown in  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems, devices, and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the systems, devices, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. Further, in the present disclosure, like-named components of the embodiments generally have similar features, and thus within a particular embodiment each feature of each like-named component is not necessarily fully elaborated upon. 
     Systems, methods, and devices for positioning, orienting, and/or aligning a stress sensor relative to a structure to be tested are discussed herein. It can be desirable to monitor certain components, such as a shaft of a turbine, to ensure that it is functioning within an appropriate operating range. One way to monitor such components is to use a stress sensor to sense stress within the material. In order to minimize measurement error, the stress sensor can be properly aligned relative to the component prior to taking a stress measurement. For example, when the stress sensor is properly aligned, a change in a size of a gap between the sensor and a surface of a target can result in approximately equal changes in raw stress signals output from a number detection elements that the stress sensor can have, where the raw stress signals can correspond to values of stress in the target. Accordingly, it can be beneficial to use a sensor mounting assembly that allows the stress sensor to be positioned appropriately such that accurate stress measurements can be obtained. Otherwise, if the size of the gap changes, raw stress signals from each of the number detection element can change by significantly different amounts, which can result an inaccurate stress measurements. 
       FIG. 1A  illustrates an exemplary embodiment of a sensor system  100  that can be used to detect stress, such as torque, bending, and/or axial loading, applied to a target. In general, the sensor system  100  can include a sensor assembly  102  which can be received within a sensor mounting assembly  150  or mounting bracket, and positioned proximate to a surface  126  of a target  110  such as, e.g., a rotatable shaft, to be tested. As an example, the target  110  can rotate about axis A 1 , as indicated by arrow B 1 . The sensor mounting assembly  150  can facilitate adjusting and/or maintaining the position of the sensor assembly  102  relative to the target  110 . As illustrated in  FIG. 1A , the mounting assembly  150  can be coupled to an extension arm  155 , which can be coupled to a rigid support  159 . The mounting assembly  150  can facilitate proper alignment of the sensor assembly  102  relative to the target  110 , and it can maintain proper orientation and alignment of the sensor assembly  102  with regard to the target  110 . The sensor assembly  102  can send and receive signals to and from a control and processing module  106  for conducting measurements. The signals can be, e.g., voltage and/or current signals. 
     While the mounting assembly  150  disclosed herein can be used with various sensor assemblies,  FIGS. 1B-1C  illustrate one exemplary embodiment of a sensor assembly  102 . The sensor assembly is described in more detail in U.S. application Ser. No. 15/598,062 entitled “Non-Contact Magnetostrictive Sensor with Gap Compensation Field,” filed on May 17, 2017, is incorporated by reference herein in its entirety. As shown in  FIG. 1B , the sensor assembly  102  can include a housing  103  having a proximal portion  105  and a distal portion  107 . In some embodiments, the proximal portion  105  can be made out of, e.g., stainless steel, aluminum, or another metal, and the distal portion  107  can be made out of a non-conductive material such as, e.g., a ceramic or a moldable, machinable, polymer. The sensor assembly  102  can include a sensor head disposed within the housing  103 . The sensor head can include a drive element and at least one detection element that can be disposed within the distal portion  107  of the housing  103 . 
     The sensor assembly is shown in more detail in  FIG. 1C . As shown, the sensor assembly  102  includes a sensor head  104  having a support  112  with four support bars  114   a ,  114   b ,  114   c ,  114   d  that extend radially outward from a central axis Z 1 . The support bars  114   a ,  114   b ,  114   c ,  114   d  can have detection arms  116   a ,  116   b ,  116   c ,  116   d  that extend distally therefrom toward the target  110 . In some embodiments, the number of support bars and/or detection arms may be greater than or fewer than four in some embodiments. A first pair of detection elements  122   a ,  122   c  can extend along and define an axis X 1 , and a second pair of detection elements  122   d ,  122   b  can extend along and define an axis Y 1 , which can extend orthogonal to the first axis. The support  112  can also include a central arm  118  that extends distally toward the target  110  along the central axis Z 1 . The sensor head  104  can further include the drive subsystem having a drive element  120  located on the central arm  118  of the support  112 , and detection elements  122   a ,  122   b ,  122   c ,  122   d  located on the detection arms  116   a ,  116   b ,  116   c ,  116   d.    
     As explained in the above mentioned application, the drive element can receive an input drive signal from the control and processing module  106  to generate a magnetic flux. The magnetic flux can travel from the drive element  120  through the target  110 , and it can be detected by the first and second pair of detection elements. The detection elements  122   a ,  122   b ,  122   c ,  122   d  can then generate a raw stress signal based on the detected magnetic flux. The raw stress signals can be delivered to the control and processing module  106 , and can be used to determine values of stress within the target  110 . 
     The values of the raw stress signals can be sensitive to the alignment and positioning of the sensor assembly  102 , and/or sensor head, relative to the target  110 . Therefore, it can be beneficial to align the sensor assembly  102 , and/or the sensor head, relative to the target. In an exemplary embodiment, a mounting assembly is provided to allow the sensor assembly to be adjustable about multiple axis to adjust a pitch, yaw, and/or roll of the sensor assembly. The mounting assembly can also allow a distance between the sensor assembly  102  and the target  110  to be adjusted. In certain exemplary embodiments, the mounting assembly is configured to allow a pitch of the sensor assembly to be adjusted about an axis X 1  aligned with the first pair of detection elements  122   a ,  122   c , and/or to allow a roll of the sensor assembly to be adjusted about an axis Y 1  aligned with the second pair of detection elements  122   d ,  122   b , as indicated by arrows P 1  and R 1  in  FIGS. 1B and 1C . The mounting assembly can also be configured to allow a yaw of the sensor assembly  102  to be adjusted by rotating the sensor assembly  102  about axis Z 1 , as indicated by arrow Yaw 1  in  FIGS. 1B-1C . 
       FIGS. 2A-2F  show one exemplary embodiment of a sensor mounting assembly  250 , also referred to as a mounting bracket, that can be used to position, orient, and/or align a sensor assembly, such as sensor assembly  102 . In general, the mounting assembly  250  can include at least one of a retaining element  252  that can releasably engage the sensor assembly, an adjustment assembly  254 , and a mounting frame  251 . The mounting frame  251  can include a first member  256 , a second member  258 , and a third member  260 . 
     As shown in  FIGS. 2A-2D , the retaining element  252  can be in the form of a substantially C-shaped clamp having a central bore  266  about defining an axis Z 2 . First and second pairs of spaced-apart arms  253   a ,  253   b  and  253   c ,  253   d  can extend outward from each end of the C-shaped clamp. The arms  253   a ,  253   b ,  253   c ,  253   d  can include threaded bores  255   a ,  255   b ,  255   c ,  255   d  for receiving fasteners  268   a ,  268   b , such as threaded bolts for example, for drawing the arms  253   a ,  253   b ,  253   c ,  253   d  together to engage a sensor assembly within the central bore  266  of the clamp. In use, the sensor assembly can be positioned within the central bore  266  of the retaining element  252 , and a yaw of the sensor assembly can be adjusted by rotating the sensor assembly about axis Z 2 , as indicated by Yaw 2 , until a desired alignment with respect to axes X 2 , Y 2  is achieved. In an embodiment, the fasteners  268   a ,  268   b  can be threaded into the bores  255   a ,  255   b  and  255   c ,  255   d  to cause the retaining element  252  to clamp onto and frictionally engaging the sensor housing within the central bore  266 . The coupling elements  268   a ,  268   b  can also be loosened to allow the sensor assembly to be removed from the retaining element, as desired. 
     As indicated above, the mounting assembly  250  can also include an adjustment assembly  254 , which can be configured to allow slidable movement of the retaining element  252 , and thus the sensor housing, along axis Z 2 , to thereby adjust a distance between the sensor assembly and a structure. The adjustment mechanism  254  can include a movable member  272  that can mate to the retaining element  252 , and frame  276  having the movable member  272  slidably coupled thereto. A rotatable adjuster  274  can be coupled between the frame  276  and the movable member  272  for causing sliding movement of the movable member  272 . In an exemplary embodiment, a spindle  278 , shown in  FIG. 2D , can extend through the frame  276  and can be mated to the movable member  272 . The spindle  278  can be threadably coupled with the rotatable adjuster  274  such that rotation of the rotatable adjuster  274 , indicated by arrow T 2 , can cause the spindle  278  to translate proximally and distally relative to the rotatable adjuster  274 , thereby causing the movable member  272  to move proximally or distally relative to the frame  276 . Accordingly, as the movable member  272  moves proximally or distally along axis Z 2 , the retaining element  252  and sensor housing can move proximally or distally. In some embodiments, other adjustment assemblies, such as a linear actuator, can be used in place of the adjustment assembly  254 . 
     As further shown in  FIGS. 2A-2B , the mounting assembly  250  can also include the mounting frame  251  having the first member  256 , the second member  258 , and the third member  260 . The first member  256  can generally be the shape of a rectangular prism. The second member  258  can have first and second arms  258   a ,  258   b  that can be coupled at their ends such that they form approximately a 90° angle between them. Similarly, the third member  260  can include first and second arms  260   a ,  260   b  that can be coupled at their ends such that they form approximately a 90° angle between them. The arms  258   a ,  258   b ,  260   a ,  260   b  of the second and third members  258 ,  260  can also be shaped as rectangular prisms. The shape of the first member  256 , second member  258 , and third member  260  may vary in different embodiments. 
     As illustrated in  FIG. 2C , the first member  256  can have an inner surface  257   a  that is mated to the frame  276  of the adjustment mechanism  254 . The first member  256  can have an outer surface  257   b  that is adjacent to an inner surface  259   a  of the first arm  258   a  of the second member  258 . A pivotal connection can be formed between the first and second members  256 ,  258  such that a first pivot  262  is formed along axis Y 2 . As illustrated in  FIGS. 2B-2C , the first pivot  262  can be formed by a first pivot coupling  280  that can extend through a first pivot bore  261  in the first member  256  and a second pivot bore  263  in the second member  258 . The first pivot coupling  280  can be, e.g., a dowel pin. The first pivot bore  261  can extend from the inner surface  257   a  of the first member  256  to the outer surface  257   b  of the first member  256 . The second pivot bore  263  can extend from the inner surface  259   a  of the first arm  258   a  of the second member  258  to an outer surface  259   b  of the first arm  258   a  of the second member  258 . The first pivot coupling  280  can include a spiral groove  281  cut along its length to relieve trapped air and facilitate easy insertion into first and second pivot bores  261 ,  263 . The first pivot  262  allows the first member  256  to rotate, or pivot, relative to the second member  258  about axis Y 2 , as indicated by arrow R 2 , to adjust a roll of the sensor assembly. 
     In some embodiments, the amount of rotation of the first member  256  relative to the second member  258  can be limited. As shown in  FIGS. 2B and 2E , the first member  256  can include another bore  282  that can align with an elongated slot  284  in the first arm  258   a  of the second member  258 . The bore  282  can extend from the inner surface  257   a  of the first member  256  to the outer surface  257   b  of the first member. The elongated slot  284  can extend from the inner surface  259   a  of the first arm  258   a  of the second member  258  to the outer surface  259   b  of the first arm  258   a  of the second member. The bore  282  and the elongated slot  284  can receive an elongate member  283 , such as a bolt, that can extend from the inner surface  257   a  of the first member  256  to the outer surface  259   b  of the second member  258 . The elongated slot  284  can have a radius of curvature that can be approximately equal to a distance from axis Y 2  to a central axis of the bore  282 . Therefore, when the elongate member  283  is inserted therethrough, rotation of the first member can be limited by radial travel of the elongate member  283  between ends  284   a ,  284   b  of the elongated slot  284 . A distance between the ends  284   a ,  284   b  of the elongated slot  284  can be determined based on a desired amount of angular rotation of the first member  256  relative to the second member  258 , and the distance from axis Y 2  to the central axis of bore  282 . In some embodiments, the elongate member  283  can be retained within the bore  282  and the elongated slot  284  by a coupling element  285 . The coupling element  285  can be, e.g., a nut. When a desired amount of rotation about axis Y 2 , or roll, is achieved, the coupling element  285  can be tightened to secure the position of the first member  256  relative to the second member  258 . 
     In a similar manner to the pivot coupling between the first member  256  and the second member  258 , the second member  258  can be pivotally coupled to the third member  260 . In one embodiment, an outer surface  259   d  of the second arm  258   b  of the second member  258  can be adjacent to an inner surface  265   a  of the first arm  260   a  of the third member  260 . The second pivot  264  can be formed by a second pivot coupling  286  that can extend through a third pivot bore  288  in the second member  258  and a fourth pivot bore  290  in the third member  260 . The second pivot coupling  286  can be, e.g., a dowel pin. The third pivot bore  288  can extend from the inner surface  259   c  of the second arm  258   b  of the second member  258  to the outer surface  259   d  of the second arm  258   b  of the second member  258 . The fourth pivot bore  290  can extend from the inner surface  265   a  of the first arm  260   a  of the third member  260  to an outer surface  265   b  of the first arm  260   a  of the third member  260 . The second pivot coupling  286  can include a spiral groove  287  cut along its length to relieve trapped air and facilitate easy insertion into third and fourth pivot bores  288 ,  290 . The second pivot  264  allows the second member  258  to rotate, or pivot, relative to the third member  260  about axis X 2 , as indicated by arrow P 2 , to adjust a pitch of the sensor assembly. 
     In some embodiments the amount of rotation of the second member  258  relative to the third member  260  can be limited in a manner similar to that described above with regard to rotation of the first member  256 . As shown in  FIGS. 2B and 2F , the second arm  258   b  of the second member  258  can include another bore  292  that can align with an elongated slot  294  in the first arm  260   a  of the third member  260 . The bore  292  can extend from the inner surface  259   c  of the second arm  258   b  of the second member  258  to the outer surface  259   d  of the second arm  258   b  of the second member  258 . The elongated slot  294  can extend from the inner surface  265   a  of the first arm  260   a  of the third member  260  to the outer surface  265   b  of the first arm  260   a  of the third member. The bore  292  and the elongated slot  294  can receive an elongate member  293  that can be, e.g., a bolt, that can extend from the inner surface  259   c  of the second arm  258   b  of the second member  258  to the outer surface  265   b  of the first arm  260   a  of the second member  260 . The elongated slot  294  can have a radius of curvature that can be approximately equal to a distance from axis X 2  to a central axis of the bore  292 . Therefore, when the elongate member  293  is inserted therethrough, rotation of the second member  258  can be limited by radial travel of the elongate member  293  between ends  294   a ,  294   b  of the elongated slot  294 . A distance between the ends  294   a ,  294   b  of the elongated slot  294  can be determined based on a desired amount of angular rotation of the second member  258  relative to the third member  260 , and the distance from axis X 2  to the central axis of bore  292 . In some embodiments, the elongate member  293  can be retained within the bore  292  and the elongated slot  294  by a coupling element  295 . The coupling element  295  can be, e.g., a nut. The coupling element  295  can be, e.g., a nut. When a desired amount of rotation about axis X 2 , or pitch, is achieved, the coupling element  295  can be tightened to secure the position of the second member  258  relative to the third member  260 . 
     In order to mate the mounting assembly  250  to a support structure, the second arm  260   b  of the third member  260  can include bores  296   a ,  296   b ,  296   c  on a proximal facing surface  265   d . The bores  296   a ,  296   b ,  296   c  can be threaded and can be used to couple the mounting assembly  250  to an extension arm and/or a rigid support. 
     In use, the mounting assembly  250  can facilitate proper positioning of a sensor head relative to a target. As shown in  FIG. 3A , the sensor head  104  can be positioned above a surface  126  of a target  110 , with a gap G 1  between a distal end  128  of the central arm  118  and the surface  126  of the target  110 . Similarly, each of the detection arms  116   a ,  116   b ,  116   c ,  116   d  can have corresponding gaps G 1   a , G 1   b , G 1   c , G 1   d  between distal ends of the arms and the surface  126  of the target  110 , in the direction parallel to the Z 1  axis, as illustrated in  FIGS. 1C and 3A . The control and processing module  106  can deliver an input drive signal to the drive element  120  such that a magnetic flux  140 , corresponding to a magnetic field, can be generated in the central arm  118  of the support  112 . The input drive signal can be, e.g., an alternating current (AC) signal. The magnetic flux  140  can travel from the central arm  118 , through the gap G 1 , through the target  110 , through the detection arms  116   a ,  116   b ,  116   c ,  116   d  and back to the central arm  118  to form magnetic loops. As the magnetic flux  140  travels through the detection arms  116   a ,  116   b ,  116   c ,  116   d  the detection elements  122   a ,  122   b ,  122   c ,  122   d  can detect the magnetic flux  140 , and generate raw stress signals which can be delivered to the control and processing module  106 . Magnetic properties, such as magnetic permeability, of the target  110  can change as a result of a change in stress within target  110 . Therefore, changes in the detected magnetic flux  140  can correspond to changes in the stress within target  110 . The raw stress signals can correspond to magnitudes of stress within the target  110  and can be used to calculate values of stress within the target  110 . 
     Although changes in the detected magnetic flux  140  can correspond to changes in the stress state of the target  110 , the detected magnetic flux  140  can also be sensitive to the position and orientation of the sensor relative to the surface  126  of the target  110 . As one example, the raw stress signals, corresponding to the detected magnetic flux  140 , can be a function of a stress state of the target  110  as well as the size of gap G 1 . Accordingly, in some embodiments, a proximity sensor element can be used to determine the size of gap G 1  so that the raw stress signals can be corrected based on the size of the gap G 1 , and a corrected stress signal can be determined. 
     The raw stress signals can also vary with a size of gaps G 1   a , G 1   b , G 1   c , G 1   d  between distal ends of detection arms  116   a ,  116   b ,  116   c ,  116   d  and the surface  126  of the target  110 . As an example, for a given gap G 1 , gaps G 1   a , G 1   b , shown in  FIG. 3A , can have different sizes. In one embodiment, as the size of gap G 1   a  is increased, the value of the raw stress signal from the detection element  122   a  can decrease. For example, in one embodiment, as the size of gap G 1   a  is increased, the value of the raw stress signal from the detection element  122   a  decreases. Since the raw stress signals can be dependent on the position and orientation of the sensor assembly  102  relative to the target, it can be desirable to align the sensor assembly relative to the target  110  using a mounting assembly such as mounting assembly  250 . Such an alignment may help to ensure that approximately equal changes in the size of gaps G 1   a , G 1   b , G 1   c , G 1   d  can result in approximately equal changes in the raw stress signals from the detection elements  122   a ,  122   b ,  122   c ,  122   d.    
     Accordingly, initially the sensor assembly  102  can be mechanically aligned using, e.g, a v-block, to achieve an initial alignment between the sensor assembly  102  and the target  110 . In some instances, to achieve a more sensitive alignment, the sensor assembly  102  can be inserted into the central bore  266  of the retaining element  252  and rotated about axis Z 1  to adjust a yaw of the sensor assembly, as indicated by Yaw 1 , shown in  FIGS. 1C and 3B . In some embodiments, axis Z 1  can correspond to axis Z 2 , as described with regard to mounting assembly  250 . The yaw of the sensor assembly  102  can be adjusted such that axes X 1 , Y 1  align with axes X 2 , Y 2  as described above. In other embodiments, the yaw of the sensor assembly can be adjusted such that axes X 1 ′, Y 1 ′, align with axes X 2 , Y 2 , where axes X 1 ′, Y 1 ′ can be offset from axes X 1 , Y 1  by approximately 45°. In some embodiments, axis X 1 , Y 1  can be approximately orthogonal to each other. Similarly, axes X 1 ′, Y 1 ′ can be approximately orthogonal to each other. The sensor assembly  102  can then be secured within the retaining element  252  as described above. When the sensor assembly is in secured within the mounting assembly  250 , the input drive signal can be delivered to the drive element  120 , and raw stress signals can be measured by detection elements  122   a ,  122   b ,  122   c ,  122   d.    
     A pitch and roll of the sensor assembly  102  can be adjusted independently by rotating the sensor assembly about axes X 1 , Y 1 , as indicated by arrows P 1 , R 1 . In other words, the bracket can allow the user to adjust sensor pitch while keeping sensor roll substantially unchanged, and vice versa. For example, the second member  258  of the mounting assembly  250  can be rotated relative to the third member  260  at the second pivot  264  to adjust the pitch of the sensor assembly  102 . Adjusting the pitch of the sensor assembly can change the relative sizes of gaps G 1   b , G 1   d . For example, by increasing the size of gap G 1   b , the gap G 1   d  can decrease by a corresponding amount while keeping G 1   a  and G 1   c  nominally unchanged. Therefore, detection element  122   b  can be moved in the proximal direction away from the surface  126  of the target  110 , and detection element  122   d  can be moved in the distal direction toward the surface  126  of the target  110 . Alternatively, the size of gap G 1   b  can be decreased, and the size of gap G 1   d  can be increase by a corresponding amount. Therefore, detection element  122   b  can be moved in the distal direction toward the surface  126  of the target  110 , and detection element  122   d  can be moved in the proximal direction away from the surface  126  of the target  110 . 
     Similarly, the roll of the sensor assembly can be adjusted by rotating the first member  256  of the sensor assembly  250  relative to the second member  258 . Adjusting the roll of the sensor assembly can change the relative sizes of gaps G 1   a , G 1   c . For example, by increasing the size of gap G 1   a , the size of gap G 1   c  can decrease by a corresponding amount. Therefore, detection element  122   a  can be moved in the proximal direction away from the surface  126  of the target  110 , and detection element  122   c  can be moved in the distal direction toward the surface  126  of the target  110 . Alternatively, the size of gap G 1   a  can be decreased, and the size of gap G 1   c  can be increase by a corresponding amount while keeping G 1   b  and G 1   d  nominally unchanged. Therefore, detection element  122   a  can be moved in the distal direction toward the surface  126  of the target  110 , and detection element  122   c  can be moved in the proximal direction away from the surface  126  of the target  110 . Therefore, pitch and roll of the stress sensor can be adjusted independently. Holding one axis fixed while rotating about another means that pitch and roll can be changed independently. This can greatly decrease the time necessary to install and align the stress sensor. The pitch and roll of the sensor assembly can be maintained by securing the positions of the elongate members  283 ,  293  in curved slots  284 ,  294 , using coupling elements  285 ,  295 , as described above. 
     Additionally, the sensor assembly  102  can be moved in the proximal and distal directions by adjusting the position of the retaining element  252 . For example, the adjuster  274  of the mounting assembly  250  can be rotated to move the sensor assembly  102  proximally or distally along axis Z 1  relative to the surface  126  of the target  110 , thereby changing the sizes of gaps G 1 , G 1   a , G 1   b , G 1   c , G 1   d , by a uniform amount. 
     Between each pitch and roll adjustment, raw stress signals can be measured. The sensor can be moved proximally or distally and raw stress signals can be measured again. The process can be repeated until changes in raw stress signals from each of the detection elements  122   a ,  122   b ,  122   c ,  122   d  are approximately equal when the sensor assembly  102  is moved proximally or distally over a given range. 
     In the descriptions above and in the claims, phrases such as “at least one of” or “one or more of” may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     The subject matter described herein can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed in this specification and structural equivalents thereof, or in combinations of them. The subject matter described herein can be implemented as one or more computer program products, such as one or more computer programs tangibly embodied in an information carrier (e.g., in a machine-readable storage device), or embodied in a propagated signal, for execution by, or to control the operation of, data processing apparatus (e.g., a programmable processor, a computer, or multiple computers). A computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. 
     The processes and logic flows described in this specification, including the method steps of the subject matter described herein, can be performed by one or more programmable processors executing one or more computer programs to perform functions of the subject matter described herein by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus of the subject matter described herein can be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processor of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, (e.g., EPROM, EEPROM, and flash memory devices); magnetic disks, (e.g., internal hard disks or removable disks); magneto-optical disks; and optical disks (e.g., CD and DVD disks). The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
     To provide for interaction with a user, the subject matter described herein can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, (e.g., a mouse or a trackball), by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well. For example, feedback provided to the user can be any form of sensory feedback, (e.g., visual feedback, auditory feedback, or tactile feedback), and input from the user can be received in any form, including acoustic, speech, or tactile input. 
     The techniques described herein can be implemented using one or more modules. As used herein, the term “module” refers to computing software, firmware, hardware, and/or various combinations thereof. At a minimum, however, modules are not to be interpreted as software that is not implemented on hardware, firmware, or recorded on a non-transitory processor readable recordable storage medium (i.e., modules are not software per se). Indeed “module” is to be interpreted to always include at least some physical, non-transitory hardware such as a part of a processor or computer. Two different modules can share the same physical hardware (e.g., two different modules can use the same processor and network interface). The modules described herein can be combined, integrated, separated, and/or duplicated to support various applications. Also, a function described herein as being performed at a particular module can be performed at one or more other modules and/or by one or more other devices instead of or in addition to the function performed at the particular module. Further, the modules can be implemented across multiple devices and/or other components local or remote to one another. Additionally, the modules can be moved from one device and added to another device, and/or can be included in both devices.