Stem load determining system

Abstract

A stem load determining system comprises a method and apparatus for determining the load developed on a threaded stem, including a valve stem driven by a valve operator. An integral component of the apparatus is a stem strain transducer uniquely designed to girp a threaded stem to define a guage length on the threaded stem and to detect and measure deformation of the stem at the guage length when subjected to a compressive or tensile load.

We claim: . .1. An apparatus for monitoring the axial deformation in a stem or other symmetrical object which is subjected to a load, said apparatus comprising: 
     
        forces..!.2. . .Apparatus of claim 1,.!. .Iadd.An apparatus for monitoring the axial deformation in a stem or other symmetrical object which is subjected to a load, said apparatus comprising: first gripping member positioned along the object;   second gripping member cooperating with said first gripping member to releasably and tightly grip the object between them;   third gripping member positioned along the object at a position axially displaced from said first gripping member;   fourth gripping member cooperating with said third gripping member to releasably and tightly grip the object between them;   wherein said first and third gripping members are capable of relative movement to one another in each of the axial, radial and angular directions in response to forces acting on the object, and wherein said second and fourth gripping members are capable of independent relative movement relative to one another in each of the axial, radial and angular directions in response to forces acting on the object;   first movement detecting means for detecting the axial component of the relative movement between said first and third gripping members and for generating an electrical signal representative of said axial component .Iaddend.wherein said first movement detecting means comprises, at least: a first striking surface mounted to said first gripping member. .;.!..Iadd., .Iaddend.and   a first LVDT comprising a base element mounted to said third gripping member and a core element supported by and protruding from said base element, said core element being movable relative .Iadd.to .Iaddend.the LVDT base element in response to relative axial movement between said first and third gripping members to generate said electrical signal representative of said axial component of the relative movement between said first and third gripping members. .;.!..Iadd., .Iaddend.   said LVDT core element contacting said first striking surface in a manner so as to move relative to said first striking surface in response to radial and angular deformation of the object and to move with said first striking surface in response to axial deformation of the object; . .and.!.     .Iadd.second movement detecting means for detecting the axial component of the relative movement between said second and fourth gripping members and for generating an electrical signal representative of said axial component of movement between said second and fourth gripping members .Iaddend.wherein said second movement detecting means comprises, at least: a second striking surface mounted to said second gripping member. .;.!..Iadd., .Iaddend.and   a second LVDT comprising a base element mounted to said fourth gripping member and a core element supported by and protruding from said base element, said core element being movable relative to the base element of said second LVDT in response to relative axial movement between said second and fourth gripping members to generate said electrical signal representative of said axial component of the relative movement between said second and fourth gripping members. .;.!..Iadd., .Iaddend.   said LVDT core element of said second LVDT contacting said second striking surface in a manner so as to move relative to said second striking surface in response to radial and angular deformation of the object and to move with said second striking surface in response to axial deformation of the object.Iadd.;     means for combining said signal from first movement detecting means and said signal from said second movement detecting means in a predetermined manner, thus providing a signal representative of the axial deformation of the object; and   said first movement detecting means and said second movement detecting means each being so comprised as to not inhibit said independent relative movement of said gripping members in each of the radial and angular directions, whereby freedom of movement is available between the first and third gripping members and between the second and fourth gripping members for at least some distance in each of the axial, radial and angular directions and whereby axial deformation of the object is measurable while the object is experiencing any and all of axial, bending and torsional   
     
     
        forces..Iaddend.3. Apparatus of claim 2, wherein said core element of said first LVDT contacts said first striking surface at a location which is displaced 180 degrees about the centerline of the object from the location at which said core element of said second LVDT contacts said second striking surface, and wherein said contact locations are spaced 
     
     
        equidistant from the centerline of the object. 4. Apparatus of claim . .1.!. .Iadd.2.Iaddend., further comprising interconnect means interconnecting said first and second gripping members for drawing said first and second gripping members toward oneanother and tightly against said object; and second interconnect means interconnecting said third and fourth gripping members for drawing said first and second gripping members toward oneanother and tightly against said shaft. . .5. Apparatus of claim 1, wherein said first movement detecting means comprises, at least: a strike element mounted to said first gripping member and movable with said first gripping member;   a contact assembly supported by said third gripping member, at least a reactive portion of said contact assembly being positioned for engagement by said strike element and being movable relative to said third gripping member within an axial plane parallel to the axis of the object in response to axial movement of said strike element; and   signal means responsive to the relative movement between said reactive portion and said third gripping member for generating an electrical signal representative of the axial component of said relative movement between said reactive portion and said third gripping member, wherein relative movement between said first and third gripping members effects movement of said reactive portion in response to movement of said strike element, which in turn effects generation of said electrical signal; and wherein said second movement detecting means comprises, at least:     a strike element mounted to said second gripping member and movable with said second gripping member;   a contact assembly supported by said fourth gripping member, at least a reactive portion of said contact assembly being positioned for engagement by said strike element and being movable relative to said fourth gripping member within an axial plane parallel to the axis of the object in response to axial movement of said strike element; and   signal means responsive to the relative movement between said reactive portion and said fourth gripping member for generating an electrical signal representative of the axial component of said relative movement between said reactive portion and said fourth gripping member, wherein relative movement between said second and fourth gripping members effects movement of said reactive portion in response to movement of said strike   
     
     
        element, which in turn effects generation of said electrical signal..!.6. . .Apparatus of claim 5,.!. .Iadd.An apparatus for monitoring the axial deformation in a stem or other symmetrical object which is subjected to a load, said apparatus comprising: first gripping member positioned along the object;   second gripping member cooperating with said first gripping member to releasably and tightly grip the object between them;   third gripping member positioned along the object at a position axially displaces from said first gripping member;   fourth gripping member cooperating with said third gripping member to releasably and tightly grip the object between them;   wherein said first and third gripping members are capable of relative movement to one another in each of the axial, radial and angular directions in response to forces acting on the object, and wherein said second and fourth gripping members are capable of independent relative movement relative to one another in each of the axial, radial and angular directions in response to forces acting on the object;   first movement detecting means for detecting the axial component of the relative movement between said first and third gripping members and for generating an electrical signal representative of said axial component wherein said first movement detecting means comprises, at least: a strike element mounted to said first gripping member and movable with said first gripping member,   a contact assembly supported by said third gripping member, at least a reactive portion of said contact assembly being positioned for engagement by said strike element and being movable relative to said third gripping member within an axial plane parallel to the axis of the object in response to axial movement of said strike element, and   signal means responsive to the relative movement between said reactive portion and said third gripping member for generating an electrical signal representative of the axial component of said relative movement between said reactive portion and said third gripping member, wherein relative movement between said first and third gripping members effects movement of said reactive portion in response to movement of said strike element which in turn effects generation of said electrical signal;     second movement detecting means for detecting the axial component of the relative movement between said second and fourth gripping members and for generating an electrical signal representative of said axial component of movement between said second and fourth gripping members wherein said second movement detecting means comprises, at least: a strike element mounted to said second gripping member and movable with said second gripping member,   a contact assembly supported by said fourth gripping member, at least a reactive portion of said contact assembly being positioned for engagement by said strike element and being movable relative to said fourth gripping member within an axial plane parallel to the axis of the object in response to axial movement of said strike element, and   signal means responsive to the relative movement between said reactive portion and said fourth gripping member for generating an electrical signal representative of the axial component of said relative movement between said reactive portion and said fourth gripping member, wherein relative movement between said second and fourth gripping members effects movement of said reactive portion in response to movement of said strike element, which in turn effects generation of said electrical signal;     means for combining said signal from first movement detecting means and said signal from said second movement detecting means in a predetermined manner, thus providing a signal representative of the axial deformation of the object;   said first movement detecting means and said second movement detecting means each being so comprised as to not inhibit said independent relative movement of said gripping members in each of the radial and angular directions, whereby freedom of movement is available between the first and third gripping members and between the second and fourth gripping members for at least some distance in each of the axial, radial and angular directions and whereby axial deformation of the object is measurable while the object is experiencing any and all of axial, bending and torsional forces; and.Iaddend.   wherein each said reactive portion is substantially non-responsive to angular movement of the respective said strike element about the object axis.