Abstract:
A platform less center of mass measurement system employs independently positionable load cell units whose locations can be identified and combined with load cell measurements to compute a center amass for arbitrarily shaped large structures without the need for precise or predetermined locating of the load cell units on a platform or the like.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application 62/081,345 filed Nov. 18, 2014 and hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an electronic apparatus for measuring center of gravity (center of mass) and in particular an apparatus for this purpose suitable for use in the field. 
         [0003]    The measurement of center of gravity of large structures or mechanisms is often desired, for example, in determining the stability of the structure or mechanism particularly under different configurations or with movement, or determining the appropriate lifting point the structure or mechanism. Generally, it is understood that maintaining the center of gravity above the support point of the structure is required for stability of the structure and that hoisting a structure from a point above the center of gravity provides improved balance and reduced problems of rotation. 
         [0004]    Generally, it is understood that a two-dimensional center of gravity measurement may be made by supporting the structure or mechanism on one or more weight measuring sensors such as load cells. The measured wave at each sensor, and the precise relative location of the sensors with respect to the supported structure together define “moments” from which center of gravity may be determined. 
         [0005]    This technique may be implemented using a platform on which the structure or mechanism may be placed. The platform may incorporate precisely located weight sensors and appropriate processing equipment to calculate center of gravity. 
         [0006]    Such center of gravity measuring techniques are relatively difficult for structures or mechanisms that cannot be easily moved or placed on a platform. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a system for measuring center of gravity of large structures or mechanisms employing multiple, freely locatable sensor supports that may be installed to measure the mechanism or structure in place. Importantly, system automatically locates the position of each installed sensor after installation to calculate the necessary moments and center of gravity. The result is a highly portable system that may measure center of gravity on arbitrarily large structures or machines in the field and away from special ramps or measuring systems. 
         [0008]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a simplified perspective view of multiple sensor stands of the present invention positioned to measure the center of gravity of a structure and showing a base station providing a central reference point used in one embodiment of the invention and the wireless processing system for calculating the center of mass; 
           [0010]      FIG. 2  is a detailed diagram of one sensor stand showing a functional block diagram of its associated electronics; 
           [0011]      FIG. 3  is a top plan view of the sensor stands located using an optical system; 
           [0012]      FIG. 4  is a side elevational view of one sensor stand at base station used for ultrasonic location of the sensor stands; 
           [0013]      FIG. 5  is a fragmentary elevational view of two sensor stands supporting an object to be measured showing corrections for skew and tilt; 
           [0014]      FIG. 6  is a cross-sectional view through the upper end of the sensor stand showing a swivel Mount for the load cell; and 
           [0015]      FIG. 7  is a flowchart of a program executed on one or more of the electronic computers of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Referring to  FIGS. 1 and 2 , a center of gravity calculating system  10  per one embodiment of the present invention may work to determine an areal center of gravity  11  of a large structure or mechanism providing an object to be measured  12 . In that measurement, object to be measured  12  is supported at arbitrary points on multiple (at least three) sensor stands  14 . Generally, the location of the sensor stands  14  is largely arbitrary provided that the object to be measured  12  may be stably supported within a load range of the sensor stand  14 . Specifically, each sensor stand  14  may be positioned independent of the location of the other sensor stands  14 . An arbitrary number of sensor stands  14  may be employed. 
         [0017]    Each sensor stands  14  may include a base pad  16  for supporting the sensor stand  14  in an arbitrary field location. Desirably the base pad  16  is large enough to prevent substantial downward movement of the sensor stand  14  under load, for example, when the sensor stand  14  is supported on earth or pavement given the anticipated weight of the object to be measured  12  and the number of sensor stands  14 . In one embodiment, the base pad  16  may be a disk, for example of quarter inch steel having a diameter of at least one foot. The base pad  16  further is sized to resist torque on the sensor stand  14  caused by expected imbalances of the object to be measured  12  as it is raised on the sensor stands  14 . 
         [0018]    Extending up from the base pad  16  may be a sensor column  18  which may, in one embodiment, be implemented in the form of a hydraulic jack having a base portion  20  and a telescoping piston portion  22  that may be extended from the base portion under great mechanical advantage by mechanical movement of an operator  24 , in this case, a pump operator. Alternatively a screw-type jack may be used, in which case the operator is a shaft allowing rotation of the jackscrew. Movement of the operator  24  elevates or lowers the load cell  26  with respect to the base pad  16  and resists subsequent change in that position by forces applied to the load cell  26  up to the capacity of the load cell  26 . The base portion  20  is attached to the base pad  16  and the upper surface of the telescoping piston portion  22  holds a load cell  26  that may contact the under surface of the object to be measured  12 . 
         [0019]    Referring momentarily to  FIG. 6 , the load cell  26  may be attached to the upper surface of the telescoping piston portion  22  through a swivel joint  27  that allows a top face  29  of a load cell  26  to swivel so that its surface is generally normal to a load vector  31  applied to the load cell  26 . Alternatively, the load cell  26  may be rigidly attached to the telescoping piston portion  22 . Generally, it is contemplated that the load cell  26  will be able to provide measurements of no less than 500 pounds and will typically have a load capacity of at least two tons. 
         [0020]    Also attached to the telescoping piston portion  22 , at a known location with respect to the load cell  26 , is a location identifier  28  which allows determination of the location of each sensor stand  14 . The location identifier  28  allows the location of the load stand  14  by any of a variety of mechanisms including GPS, optical and ultrasonic techniques. 
         [0021]    The load cell  26  and in some cases the location identifier  28  may communicate, for example, by flexible conductors  30  with a processing unit  32 . The processing unit  32  generally includes a microcontroller  34  having one or more processors  36  and a memory  38  holding a stored program executable by the processors  36  whose operation will be described below. The processing unit  32  may communicate with load cell processing circuitry  40  of a type known in the art which receive signals from the load cell  26  provides to the processing unit  32  a force measurement from the load cell  26  being a general downward force along the axis of the sensor column  18 . The processing unit  32  may also communicate with an output display  33  visible to a user as will be discussed below. 
         [0022]    The microcontroller  34  may also communicate with remote location determining circuitry  42 , for example, communicating via conductor  30  with the location identifier  28 , Generally, the location determining circuitry  42  may be distributed among the tablet computer  46  and the processing unit  32 . In one embodiment, the location identifier  28  may be a GPS/Real-Time Kinematic (RTK) antenna and the location determining circuitry  42  will be the circuitry associated with this location technique. The microcontroller  34  may also communicate with a wireless data circuit  44  such as a Bluetooth LE transmitter/receiver or standard Wi-Fi transceiver of types known in the art The microcontroller  34  may also communicate with a three axis accelerometer  25  or other tilt measuring device indicating an angle of an axis  15  generally normal to the upper face of the load cell  26  and extending between the load cell  26  and the base pad  16 , with respect to gravity. 
         [0023]    The wireless data circuit  44  permits communication with a remote computer/human machine interface, for example, a tablet computer  46  or the like. The wireless data circuit  44  in other embodiments may also provide for data communication between the sensor stands  14 . As is understood in the art, the tablet computer  46  may include a battery operated computer system having at least one processor as well as memory holding with a stored program executable by the processor. The tablet computer  46  may also provide for a touchscreen surface providing an interface to the user as will be understood in the art and various radio transceivers including Bluetooth, Wi-Fi, and GPS. 
         [0024]    The GPS/RTK antenna of location identifier  28  may receive GPS signals  50  from one or more GPS satellites  52  and a carrier wave signal  54  from a stationary base station  56 , the latter also part of the center of gravity calculating system  10 . As will be understood in the art, the GPS signal  50  and the carrier wave signal  54  from the base station  56  combine to allow each of the sensor stands  14  to accurately determine the location of the location identifier  28  (and hence by reference the load cell  26 ). While standard civilian. GPS provides accuracy of approximately 3 meters, inadequate for this purpose, GPS RTK using carrier phase tracking can provide accuracy on the order of several millimeters relative to the base station  56 . This information plus the force reading from the load cell  26  may be transmitted via the wireless data circuit  44  to the tablet computer  46  for calculation of center of gravity  11  independent of the install positions of the sensor stands  14 . Alternatively the signal from the base station  56  may be sent directly to the tablet computer  46  to provide this accuracy enhancing calculation. 
         [0025]    Each of the components of the processing unit  32  may be powered by a battery  37  for complete portability. Ideally each of the sensor stands  14  may he easily moved by a single individual and installed, possibly by the same individual holding and using the tablet computer  46 . Ideally, the sensor stands  14  may weigh less than 100 pounds and desirably less than 50 pounds. 
         [0026]    Referring now to  FIG. 3 , as an alternative to GPS or for use in augmenting GPS, each sensor stand  14  may provide an optical fiducial, for example, a cube corner or other reflector that allows laser position identification using a central optical rangefinder  21  that may determine range and bearing for each of the sensor stands  14  with respect to a known position of the optical rangefinder  21  determined, for example, using GPS. In this case, the optical rangefinder  21  may use a conventional laser rangefinder as is used in surveying techniques for high accuracy location of the sensor stands  14 . Alternatively, the optical rangefinder  21  may be a camera system, for example, identifying retro reflectors or fiducial marks on each of the sensor stands  14  and determining their location by trilateralization. 
         [0027]    Referring now to  FIG. 4 , as an alternative to GPS or use for augmenting GPS, each sensor stand  14  may provide for an ultrasonic transducer array  39  having an ultrasonic transducers and receivers at various locations around the base portion  20 . This ultrasonic transducer array  39  may communicate with a corresponding array  39  on a beacon  41  having a known location, for example, determined by GPS of an internal GPS transceiver system. An angle and distance of the beacon  41  from each of the sensor stands  14  may be determined, for example, by a round-trip travel of an ultrasonic signal between the sensor stands  14  and the beacon  41  and an angle of that signal determined, for example, by phase shift between the received ultrasonic signal from the arrays  39 . Alternatively, each of the sensor stands  14  and the beacon  41  may simply calculate relative separation distances and a mesh discovered that triangulates any two specific locations. 
         [0028]    In operation, each sensor stand  14  may be placed beneath a load bearing surface of the object to be measured  12  and the operator  24  activated either manually or by a battery pump system controllable from the tablet computer  46 , to raise the telescoping piston portion  22  to begin supporting the object to be measured  12 . During this time signals from the load cell  26  may be monitored to prevent exceeding the capacity of the sensor stand  14  and to provide an even load sharing among the sensor stands  14 . For this purpose, the tablet computer  46  may monitor a load signal from each sensor stand  14  and provide information to be displayed on display  33  indicating whether additional height should be provided to increase the load on the given load cell  26  or the height should be reduced to relieve load from that load cell  26 . 
         [0029]    Additional sensor stands  14  may be installed with a similar operation and during this time the tablet computer  46  may provide guidance to the operator to balance the load appropriately among sensor stands  14  and to level the object to be measured  12  into its attitude at which the center of gravity  11  is to be determined. Often this will mean a leveling of the height of each load cell  26  which may be determined from the location determining circuitry  42  provided to the user of the tablet computer  42 . 
         [0030]    Referring now to  FIG. 5 , the load signal transmitted to the tablet computer  46  may provide a measurement of the load vector  60  applied along axis  15  together with an indication of the gravitational vector  62  such as may be used to determine a weight at the point of contact between the sensor stand  14  and an object  12  being weighed. The load cell  26  may provide for three orthogonal axes of load measurement which may also be provided to the tablet computer  46  or used internally, for example, to activate the display  33  to instruct the user to adjust the sensor stand  14  to receive a force directly along axis  15  or alternatively to calculate a more complete load vector without concern about skew of the load force with respect to the axis  15  simply by making a vector sum of each of the load measurements along three different axes. 
         [0031]    Once the sensor stands  14  are position to fully support the object to be measured  12 , a center of gravity calculation may be performed by establishing moments between the base station  56  and each of the sensor stands  14  and combining those moments to deduce a center gravity  11  according to calculations well known in the art. 
         [0032]    The tablet computers  46  may also provide for a location system (including location identifier  28  and location determining circuitry  42 ) enabling the tablet computer  46  to be moved to the location of the center gravity  11  with appropriate visual feedback displays on the tablet computer  42  (for example arrows and distance measurements) allowing the operator to quickly locate center of gravity  11  and to mark it or to align other structures such as a hoist with that center of gravity. 
         [0033]    While the invention contemplates the use of GPS RTK in one embodiment, it will be appreciated that other methods of automatic location of the sensor stands  14  may be used including, for example, ultrasonic range finding. In such an ultrasonic system, each sensor stand  14 , one of the time may simultaneously transmit an ultrasonic pulse and radio signal pulse to determine an acoustic delay between the given sensor stand  14  and each of the other sensor stands  14  receiving those two pulses. Repeating this process for each sensor stand  14  provides a geometric network that uniquely identifies the relative location of each sensor stand  14  relative to the others. 
         [0034]    Alternatively, the base station  56  may be replaced with a laser rangefinder system locating each of the sensor stands  14  by ranging imaging markers (such as corner cube retro reflectors) operating as the location sensors  28 . Here angle and range establish the relative locations of each sensor stand  14 . Alternatively laser range finding may be performed at multiple locations of the laser rangefinder or time of flight measurements. 
         [0035]    An image-based system may also be employed where video images of unique markers forming location sensors  28  on each of the sensor stands  14  (for example, taken with a camera incorporated into the tablet computer  46 ) may be made of different angles of the camera to determine the location of the sensor stands  14  by triangulation. The multiple camera angles may be precisely located using the same triangulation method in which pre-positioned camera markers (for example supporting tripods) are pre-positioned and located visually in the same process. It will be appreciated that in some of these embodiments the location determining circuitry  42  may be positioned outside of the sensor stands  14 . 
         [0036]    It will be understood that the present invention may not only determined center of gravity  11  but may also make total weight measurements of the object to be measured  12  by summing together the values from each load cell  26 . In addition the system may be used for load balancing measurements in which movable elements of the object to be measured  12  are adjusted to position the center gravity in a particular location. This may be done interactively by seeing how the center of gravity II moves during adjustment of the movable elements. The tablet computer  46  may output a center gravity  11  with absolute location of the center of gravity as well as the time and date of the measurement. 
         [0037]    Although wireless communication is preferred for communication between the various components it will be appreciated that cabling may also be employed. 
         [0038]    Referring now to  FIG. 7 , a method of using the invention as indicated by process block  70  begins with a location of the sensor stands  14  on the ground to support the object to be weighed  12 . In cases where the sensor stands  14  have been leveled and then calibrated, this step checks to see if the sensor stand has been moved since that calibration. If so the operator may be notified to provide new calibration if desired. At process block  72 , the sensor stands  14  are adjusted to improve their load sharing and positioning as discussed above. 
         [0039]    At process block  74 , load values from each sensor stand  14  are obtained together with their positions either directly from the sensor stands  14  or indirectly using beacons  21 ,  41  and the like as have been discussed. At this point, the altitude and location of the sensor stands  14  may be determined and the weight adjusted according to known changes in the gravitational constant with altitude and location. 
         [0040]    At process block  76  an output may be generated that is human readable indicating the center of mass and its absolute position. The center of mass value may be used, for example, to allow the tablet computer  46  to be maneuvered to the position of the center of mass to allow its marking, using the same positioning techniques used to identify the position of the sensor stands  14  on the tablet computer  46 . Process block  76  may include an error handling routine in situations where the present system is used primarily for weighing objects. In these cases, the tablet computer  42 , for example, may receive an indication as to Whether the weighed object has changed. If not, the weight is obtained by combining the weight values of each of the sensor stands  14  per a typical scale system and also computing the center of gravity. lf the center of gravity has changed by a predetermined amount (for example, compared against historical values) for certain weighed objects that tend to sustain a constant center of gravity (for example, tanks silos etc., failure of one load cell  26  may be imputed from an extreme center of gravity change. In this case, a previous center of gravity calculation may be used to extrapolate the weight value for the failed load cell by first identifying the failed load cell, for example, from historical data and then solving for the weight value of the failed load cell using the center of gravity value from a previous measurement. This would allow avoiding scrapping or re-weighing materials in the event of a load cell failure. 
         [0041]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0042]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0043]    References to “a microprocessor” and “a processor” or “the microprocessor” and “the processor,” can be understood to include one or more microprocessors that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices. Furthermore, references to memory, unless otherwise specified, can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor-controlled device, external to the processor-controlled device, and can be accessed via a wired or wireless network. 
         [0044]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of dements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.