TECHNICAL FIELD 
     The present invention relates to a method and device for load measurement, and, more specifically, to an axial load measurement on a mechanical control device having a rotating shaft, for example, a valve actuator for fluid flow control devices. The load measurement may be used to derive a torque measurement. 
     BACKGROUND 
     Fluid flow control devices include devices for both liquids and gases. Valve actuators for fluid flow control devices are known and may be mechanically operated. For example, the valve actuator may be manually driven, operated by fluid pressure in which the shaft is connected directly or indirectly to a fluid operated piston, or be driven by an electro-hydraulic or electro-fluid means. Conventional valve actuators comprise an electrically driven input shaft, which may be rotatable at relatively high speeds with relatively low torque. The input shaft may, through reducing gears such as a worm gear or a helical screw thread and nut, rotate a relatively high torque, low speed output shaft. 
     It may be desirable to determine the torque generated by the output shaft. For example, when a valve is fully closed and seated, the torque required to open the valve may be considerably higher. Consistently monitoring the torque may indicate if a valve is wearing out or sticking. Trending patterns in the torque measurements may enable predictive maintenance. Override shut-off features may be provided if a torque exceeds a predetermined allowable level. 
     Measurement of the axial force on the input shaft may be used to determine the torque delivered by the output shaft. The axial load multiplied by the worm gear pitch radius is the torque delivered by the output shaft. 
     Conventional devices for measuring the end thrust or torque of a rotating shaft are known and include a thrust-torque transducer described in U.S. Pat. No. 4,182,168 to Desch. The thrust-torque transducer includes a LVDT (Linear Voltage Differential Transformer) having a movable core axially aligned with, secured to, and rotatable with the shaft, and producing an output signal corresponding to thrust or torque. However, in order to provide for operation of the transducer in both clockwise and counterclockwise rotations of the shaft, the Desch thrust-torque transducer requires presetting of a diaphragm of a thrust bearing. The Desch thrust-torque transducer does not detect any misalignment of the axial load on the shaft. 
     Another conventional device for indicating loading on a shaft is described in U.S. Pat. No. 5,503,045 to Riester. An increased load on a worm causes axial shifting of a worm shaft and an accompanying deformation of a membranous disc mounted on the worm shaft. One side of the disc is formed with a circumferentially extending, annular recess. The central portion of the disc is fixed against axial displacement relative to the worm shaft by an axial bearing situated on one side of the disc and a bushing which is disposed on the opposite side of the disc. A strain measuring strip on another side of the disc generates changes in measurements with displacement of the worm shaft. The device of Riester does not provide a method for detection of any misalignment of the load on the shaft. 
     Therefore, it would be advantageous to develop a technique for measuring the torque generated by an output shaft using the axial displacement of an input shaft, and detecting any misalignment of the load on the input shaft. 
     DISCLOSURE OF THE INVENTION 
     The present invention, in a number of representative embodiments, provides a load measurement method and device which may be used to determine a load including, but not limited to, the load on a rotating shaft. A mechanical control device having a rotating shaft, for example, a valve actuator for fluid flow control devices, may include a load measurement device of the present invention. 
     In accordance with one embodiment of the present invention, a mechanical control device includes a shaft configured for rotation, a beam operatively connected to the shaft and configured to deform under axial displacement of the shaft, and a sensor coupled with the at least one beam and configured to produce an output signal proportional to the axial displacement of the shaft. The beam may have a substantially uniform cross-section through substantially its entire length. 
     The mechanical control device may additionally include bearings for translating the axial displacement of the shaft to the beam. The bearings may include a first annular bearing disposed about the shaft and contacting a first surface of the beam, and a second annular bearing disposed about the shaft and contacting a second, opposing surface of the beam. Additionally included in the mechanical control device may be an annular body encircling the shaft, with the beam extending outwardly from the shaft toward the annular body. A portion of the beam may be fixed to the annular body. A housing may be fixed to the annular body, and configured for axial movement of the shaft relative to the housing. 
     The output signal of the sensor of the mechanical control device may identify any misalignment of the worm shaft. The sensor may include at least one strain gauge. The beam of the mechanical control device may include a metal, and may also include an array of discrete beams arranged in a spoke formation about the shaft. 
     In accordance with another embodiment of the present invention, a load sensor for measuring the axial load on a rotatable shaft includes at least one deflection beam having a first end portion thereof retained between two bearings, each bearing operatively connected to the rotatable shaft for translating axial movement of the shaft to the at least one deflection beam (as a deflection), and a sensor operatively connected to the at least one deflection beam and configured for measuring the deflection of the at least one deflection beam. 
     The sensor may comprise at least one stain gauge and the at least one deflection beam may comprise a discrete metal segment having a substantially uniform width and thickness therethrough. The at least one deflection beam may include a second end portion fixed to a housing for the load sensor, the housing being configured to enable relative axial displacement of the rotating shaft with respect thereto. 
     The load sensor may additionally include an annular body encircling the rotatable shaft. The at least one deflection beam may include an array of deflection beams arranged in a spoke formation about the shaft, extending outwardly from the shaft toward the annular body, wherein a second portion of each deflection beam is fixed to the annular body. A housing may be fixed to the annular body, the shaft being configured for axial movement relative to the housing. Each deflection beam of the array of deflection beams may include a sensor operatively connected thereto, each sensor being in communication with an output device, which relates any misalignment of the worm shaft. 
     In yet another aspect, the present invention includes a method of measuring a torque delivered to a valve. A rotatable shaft may include two bearings operatively coupled to the rotatable shaft. The method includes providing at least one beam disposed between the two bearings on a first end and coupled to a fixed housing on a second end, rotating a worm gear with the shaft, the worm gear being operatively coupled with a worm wheel and shaft driving the valve, and transmitting the torque delivered to the valve into axial movement of the rotatable shaft. The method additionally includes deflecting the at least one beam with the axial movement of the shaft, which is translated to the beam with the axial displacement of the two bearings, sensing the deflection of the at least one beam, determining an axial load on the shaft using the deflection of the at least one beam, and determining the torque delivered to a valve using the axial load on the shaft and a radius of the worm gear. 
     In particular embodiments of the invention, providing at least one beam may comprise providing a beam of a substantially uniform width and thickness therethrough, or alternatively may comprise providing an array of beams arranged in a spoke formation about the rotatable shaft. Sensing the deflection of the at least one beam may comprise independently sensing the deflection of each beam of the array of beams. 
     The features, advantages, and alternative aspects of the present invention will be apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention can be more readily ascertained from the following description of the invention when read in conjunction with the accompanying drawings in which: 
         FIG. 1A  is a cross-sectional view of a mechanical control device and torque measurement device of the present invention; 
         FIG. 1B  is a perspective view of the mechanical control device and torque measurement device of  FIG. 1A   
         FIG. 2  is a view of one embodiment of a plate of a torque measurement device of the present invention; 
         FIG. 3  is a view of another embodiment of a plate of a torque measurement device of the present invention; 
         FIG. 4  is a perspective view of the plate of  FIG. 3  installed in a representative load measurement device of the present invention; 
         FIG. 5  is a perspective view of another embodiment of a load measurement device of the present invention; and 
         FIG. 6  is a view of yet another embodiment of a plate of a torque measurement device of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some representative embodiments. Similarly, other embodiments of the invention may be devised that do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims, are to be embraced thereby. 
       FIG. 1A  illustrates a cross-section of an embodiment of a mechanical control device  10  including a torque measuring device  20  of the present invention. The mechanical control device  10  may comprise a valve actuator and may be operated, by way of example, manually, by a motor, or by fluid pressure. The mechanical control device  10  comprises a rotor  150 , which drives the worm shaft  30  coupled to a worm gear  40 . The worm gear  40  drives and is operatively connected to an output shaft  45 . As the worm shaft  30  is rotated to drive the worm gear  40 , the force required to drive the worm gear  40  and output shaft  45  may cause an axial displacement of the worm shaft  30  relative to a housing  120  of the mechanical control device  10 . The axial movement may be registered with a plate  60 . A portion of the plate  60  may be fixed to the housing  120 , preventing axial movement thereof. Another portion of the plate  60  may deflect with the axial displacement of the worm shaft  30 , transferred by a ball bearing  74 ,  76 . 
     The deflection of the plate  60  may cause a significant strain therein, which may, in turn, be measured using a sensor  80  (see  FIG. 2 ). The sensor  80  may have an output that may be translated into the axial load on the worm shaft  30 . The axial load, when multiplied by the worm gear pitch radius, is the torque delivered by the worm gear  40  to the output shaft  45 . The axial movement of the worm shaft  30  may occur in either direction, depending on the direction of rotation of the worm shaft  30  and subsequent rotation of the output shaft  45 . An output device  170  may be provided to display information such as, by way of example, the strain of the plate  60 , the axial load of the worm shaft  30 , and/or the torque on the output shaft  45 . 
     The worm shaft  30  shown in  FIG. 1A  rotates within a sleeve  90  on bearings  70 ,  74 , and  76 , which, by way of example, can include ball bearings. A perspective view is shown in  FIG. 1B . Driving the worm gear  40 , which in turn drives the output shaft  45 , applies an axial load on the worm shaft  30 . The axial load forces the worm shaft  30  to displace axially. The worm shaft  30  may be displaced in two opposing axial directions, shown by arrows  1  and  2 , and the plate  60  may be deflected toward two different positions. During rotation, the worm shaft  30  may be displaced to the left, as shown by arrow  1 . The axial load may be transferred to the plate  60  via the rotor  150 . An attachment element  140  secures the worm shaft  30  to the rotor  150 . The attachment element  140  may comprise, for example, a bolt or a screw. The worm shaft  30  pulls on the attachment element  140 . The attachment element  140  causes the rotor  150  to axially displace with the worm shaft  30  and the rotor  150  presses against the bearing  76 . The bearing  76  pushes on the plate  60 , causing the plate to deflect toward a first flexed position. An inner race  76   a  of the bearing  76  is flush with, and rotates with, the worm shaft  30 . An outer race  76   b  of the bearing  76  contacts and pushes on the plate  60 . The plate  60  does not rotate since the outer circumference of the plate  60  is fixed to the housing  120  with attachment elements  130 . A sensor  80  may determine the strain on the plate  60  to determine the axial load on the worm shaft  30 . 
     Alternatively, the worm shaft  30  may rotate in the opposite direction, turning the output shaft  45  in the opposite direction. The worm shaft  30  is thus axially loaded to the right, in the direction of arrow  2 . The worm shaft  30  is displaced to the right and a shoulder  100  of the worm shaft  30  may press against the bearing  70 . The shoulder  100  comprises a radial face of the worm shaft  30  at a junction of a portion of the worm shaft  30  having a smaller diameter and a portion of the worm shaft  30  having a larger diameter. The bearing  70  presses against the sleeve  90 , causing matching axial displacement of the worm shaft  30  and the sleeve  90 . The sleeve  90  and the bearing  74  thus undergo substantially the same axial displacement as the worm shaft  30 , forcing the bearing  74  against the plate  60 , and causing the plate to deflect toward the second flexed position. An inner race  74   a  of the bearing  74  is flush with, and rotates with, the worm shaft  30 . An outer race  74   b  of the bearing  74  contacts the sleeve  90  and the plate  60 , transmitting the axial load thereto. The first flexed position of the plate  60  may correspond to a closing force being applied to the valve (not shown) via the mechanical control device  10 , and the second flexed position may correspond to an opening force being applied to the valve, or vice versa, depending on the direction of the threads of the worm shaft  30  and the configuration of the valve in communication with the valve actuator. 
     The sleeve  90 , as depicted, does not rotate with the worm shaft  30 . However, it is understood that a sleeve which rotates in conjunction with the worm shaft  30  is within the scope of the present invention. In addition, it is within the scope of the present invention to include a second sleeve about the worm shaft  30 , between the rotor  150  and the bearing  76 . Thus, a sleeve (and not the rotor  150 ) may transmit the axial load to the plate  60  from the worm shaft  30  when experiencing an applied load in the direction of arrow  1 . 
     An axial bearing may be positioned between the rotor  150  and the device operating the mechanical control device  10 , such as a motor, enabling the rotor  150  to move axially relative to the operating device. Thus, any outside axial forces on the operating device may also be absorbed with the axial bearing and do not affect the measurement of the axial load. 
       FIG. 2  depicts a plate  60   a  according to a particular embodiment of the present invention. The plate  60   a  is substantially planar, comprising an annular body  62   a  and an array of four discrete inwardly protruding beams  65   a . Each beam  65   a  may have a substantially rectangular cross-section may be disposed at a right angle to each adjacent beam  65   a . The annular body  62   a  and the inwardly protruding beams  65   a  may be contiguous, formed from a single piece of material, such as, for example, a metal disc. For example, the plate  60   a  may be formed by stamping, forging, or laser cutting. Alternatively, the beams  65   a  may be attached to the annular body  62   a , such as with an adhesive or an attachment element. The beams  65   a  may be formed of the same material as the annular body  62   a  or can be formed from a different material. By way of example, suitable materials for the annular body  62   a  and beams  65   a  include a metal, such as copper, aluminum, steel, stainless steel, or a polymer. The inwardly protruding beams  65   a  may be removable and replaceable. 
     The inwardly protruding beams  65   a  provide a passageway  110  for the worm shaft  30  (not shown in  FIG. 2 ) to extend therethrough. The inwardly protruding beams  65   a  may be arranged in a spoke formation within the central opening of the annular body  62   a . However, the beams  65   a  need not join at the center of the annular body  62   a  central opening; rather, the center may comprise the open passageway  110 . The ends of the beams  65   a  distal from the annular body  62   a  are free to displace under the load of the axial displacement of the worm shaft  30 , transferred by the bearings  74 ,  76 . (See  FIG. 1A .) Each beam  65   a  may have a substantially uniform thickness t and width w along the length l of the beam  65   a.    
       FIG. 2  depicts (with shading) the strain under deflection on the annular body  62   a  and each beam  65   a  of the plate  60   a . The darkly shaded portions represent the portions under the greatest strain, and the lighter shaded areas show the portions under less strain. The plate  60   a  is depicted with four apertures  50  through the annular body  62   a , enabling the plate  60   a  to be secured to a housing  120  (see  FIG. 1A ) of the mechanical control device  10 . Attachment elements  130 , for example, bolts, pins, or screws, may be used to secure the plate  60   a . The plate  60   a  may be secured by methods other than attachment elements, such as, for example, by brazing or welding. 
     During use, the motor may turn the worm shaft  30 , which rotates the output shaft  45 . The force causing the output shaft  45  to turn causes an axial movement of the worm shaft  30 . The sleeve  90  on the worm shaft  30  also moves axially, pushing the bearings  74  against each beam  65   a  of the array. Each beam  65   a  flexes with the portion of the beam  65   a  that is in contact with the bearing being displaced with the axial movement of the shaft. The annular body  62   a  of the plate  60   a  is fixed to the housing and is not displaced. Thus, each beam  65   a  deflects or flexes, causing a strain therein. The strain within each beam  65   a  may be measured using a sensor  80 . Each beam  65   a  may include a sensor  80  or, alternatively, only one beam may include a sensor  80 . 
     Including a sensor  80  on a plurality of beams  65   a  of the array of beams enables independent measurements of the stress and/or strain on each of the plurality of beams  65   a . Each beam  65   a  of the array of beams  65   a  is discrete and the array may surround the worm shaft  30 . Each beam  65   a  may undergo the axial displacement of the worm shaft  30  at separate locations about the circumference of the worm shaft  30 . Thus, if the worm shaft  30  bends or assumes any other misalignment of the axial load, the sensors  80  on each beam  65   a  may sense different measurements. Comparing the measurements further enables a determination of any misalignment of the axial load on the worm shaft  30 . The sensors may be configured to cancel out any misalignment and to provide a signal corresponding to a reading incorporating any misalignment. Alternatively, a separate signal may be provided, warning of the misalignment. 
       FIG. 3  depicts another embodiment of a plate  60   b  according to the present invention. The plate  60   b  comprises a substantially planar annular body  62   b  having four discrete inwardly protruding beams  65   b . Each beam  65   b  may have a substantially rectangular cross-section and may be disposed at a right angle to each adjacent beam  65   b . Corners  66   b  at the junction of the annular body  62   b  and inwardly protruding beams  65   b  are chamfered. The chamfering may reduce the stress on the plate  60   b  at the corners  66   b . The inwardly protruding beams provide a passageway  110  for the worm shaft  30  (not shown in  FIG. 3 ) to extend therethrough. The plate  60   b  shows the stress under deflection of the annular body  62   b  and each beam  65   b  with shading. The darkly shaded portions represent the portions under the greatest stress, and the lightly shaded area shows the portions under less stress. The plate  60   b  is depicted with four apertures  50 , enabling the plate  60   b  to be secured to a housing  120  (see  FIG. 1A ) of the mechanical control device  10 . Attachment elements  130 , for example, bolts or screws, may be used to secure the plate  60   b.    
       FIG. 4  is a perspective view of the plate of  FIG. 3  installed in a load measurement device  20   b  of the present invention. The rotor  150  protrudes from the center of the plate  60   b . A portion of the worm shaft  30  is encased within the rotor  150  and secured thereto with attachment element  140 . The bearing  76  encircles the worm shaft  30 . A distal end of the rotor abuts the bearing  76 , transmitting any axial load in the direction of arrow  1  (see  FIG. 1A ) thereto. The outside race  76   b  of the bearing contacts the surface of each beam  65   b  on a first portion distal from the annular body  62   b . Each beam  65   b  may include a second portion secured to the annular body  62   b , which does not undergo displacement since the annular body  62   b  is fixed to the housing  120 . The first portions of the beams  65   b  displace with the bearing  76 , while the second portions of the beams  65   b  are secured to the fixed annular body  62   b . Thus, the beams  65   b  deflect or flex, which places the beam under a strain. The strain may be measured with a sensor  80 , such as a strain gage. 
       FIG. 5  is a perspective view of a load measurement device  20   c  according to a particular embodiment of the invention. Plate  60   c  comprises an array of three discrete beams  65   c  disposed in a spaced-apart configuration, each beam  65   c  extending outwardly from the worm shaft  30 . Although the present embodiment is shown with three beams  65   c , it is understood that any number of beams  65   c  can be used. Each discrete beam may be secured to the housing  120  with an attachment element  160 . Each beam  65   c  may have a sensor  80  mounted thereon or, alternatively, only one or two of the beams  65   c  may include a sensor  80 . The sensor  80  may include a plurality of sensors disposed in a plurality of locations on the beam  65   c . In one embodiment, the sensors  80  may be located in the areas of maximum strain. The beams  65   c  do not contact the worm shaft  30 , however, any axial load applied to the worm shaft  30  may be transferred to the beams  65   c  via the bearing  74 . The beams  65   c  do not completely encircle the worm shaft  30 , rather, each beam  65   c  is separately spaced. 
     The beams  65   c  need not be secured to an annular body, such as the beams  65   a  and  65   b  depicted in  FIGS. 3 ,  4 , and  5 . The beams  65   c  may each comprise an elongated body, having a substantially uniform cross-section therethrough. A first portion of each beam  65   c  may be free to axially displace with the worm shaft  30 , under the axial load transferred by bearing  74 . A second portion of each beam  65   c , at an opposite end longitudinally from the first portion, may be secured to the housing  120  with an attachment element  160 . The worm shaft  30  may be axially displaced relative to the housing  120  under the axial load. The first portion of each beam  65   c  may be displaced relative to the housing  120  with the worm shaft  30 . The second portion of each beam  65   c  can be secured to the housing and can be prevented from being displaced. Thus, each beam  65   c  may deflect, causing strain therein. The strain may be measured with the sensor  80 . 
     A plate  60  may include any number of beams  65   a - 65   c . For example, the plate  60   b  depicted in  FIG. 4  includes an array of four beams  65   b , and the plate  60   c  depicted in  FIG. 5  includes an array of three beams  65   c . Additionally, a plate having only a single beam is within the scope of the present invention. 
     Measuring the direct reaction forces on internal components of a mechanical control device, such as the axial load on a worm shaft  30 , is an accurate method of determining the torque that the mechanical control device is delivering to an output shaft. This measurement is independent of gear efficiency, gear speed, motor torque, and motor applied line power. A beam  65   a ,  65   b ,  65   c  of a load measurement device  20 ,  20   b ,  20   c  of the present invention may be formed so that the deflection caused by the axial load on the worm shaft  30  creates enough strain to obtain an electronic signal with the sensor  80 , but not enough to cause a permanent strain or deflection to the beam  65   a ,  65   b ,  65   c . The worm gear  40 , driven by the worm shaft  30 , may be a shell type or may be integral to the worm shaft  30 . 
       FIG. 6  depicts a plate  60   d  according to a particular embodiment of the present invention. The plate  60   d  is annular, having a passageway  110   d  for the worm shaft  30  (not shown in  FIG. 6 ) to extend therethrough. The annular plate  60   d  may be contiguous, formed from a single piece of material, such as, for example, a metal disc. For example, the plate  60   d  may be formed by stamping, forging, or laser cutting. By way of example, suitable materials for the plate  60   d  include a metal, such as copper, aluminum, steel, stainless steel or a polymer. The plate  60   d  may include apertures  50  therethrough, enabling the plate  60   d  to be secured to a housing  120  (see  FIG. 1A ) of the mechanical control device  10 . A sensor  80  may be positioned in an area of maximum strain on the plate  60   d , near an aperture  80 . 
     Although the foregoing description contains many specifics, these are not to be construed as limiting the scope of the present invention, but merely as providing certain representative embodiments. Similarly, other embodiments of the invention can be devised which do not depart from the spirit or scope of the present invention. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims, are encompassed by the present invention.
A device for axial load measurement on a mechanical control device ( 10) having rotating shaft ( 30) maybe used to derive a torque measurement. A mechanical control device ( 10) may comprise a valve actuator for fluid flow control devices. The load measurement device may include a beam ( 65 a) operatively connected to a rotatable shaft and configured to deform under axial displacement of the shaft. A sensor ( 80) maybe coupled with the at least one beam ( 65 a) and configured to produce an output signal related to the axial displacement of the shaft. The beam may be retained between two bearings ( 74) of the rotatable shaft at a first end, and fixed to the housing ( 120) of the mechanical control device at a second end. The first end of the beam ( 65 a) may displace axially with the rotatable shaft. The beam ( 65 a) may comprise a discrete segment of a uniform width and thickness.