Patent Publication Number: US-7910841-B2

Title: Weighing scale with level compensating foot assembly

Description:
This application is a continuation of U.S. patent application Ser. No. 11/215,826, filed Aug. 30, 2005, now U.S. Pat. No. 7,151,232, which is a continuation of U.S. patent application Ser. No. 10/695,216, filed Oct. 28, 2003, now U.S. Pat. No. 6,936,776, which is a continuation of U.S. patent application Ser. No. 10/213,289, filed Aug. 6, 2002, now U.S. Pat. No. 6,639,158, and entitled “Weighing Scale with Level Compensating Foot Assembly”. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to electronic type platform weighing systems, and more particularly to a free-standing scale having an improved base member for aligning parts of the scale. 
     BACKGROUND OF THE INVENTION 
     There are many different types of electronic weighing scales in use today. One popular type of electronic weighing scale is constructed with a platform for receiving the load to be weighed and a set of levers, pivots, flexures, and torque tubes to mechanically combine the forces applied to the platform by the load. The combined forces are then applied to a single electronic load cell to yield the weight of the load. The load cell is typically constructed with a mechanically-deformable sensor plate which operates as a force transducer. The sensor plate includes one or more sensor elements that serve to convert the mechanical bending forces of the sensor plate into electrical signals. When a load is applied to such a load cell, the sensor elements produce electrical signals which are proportional to the load applied to the load cell. 
     Many load cells utilize a measurement beam which carries all or a part of the load to be measured and thus deforms as a function of the weight of the load. Load cell measurement beams are typically either of two types, bending beams or shear beams. Bending beams undergo bending strains that vary as a function of the weight of the load applied to the beams, while shear beams undergo shear strains that vary as a function of the weight of the load applied to the beams. Strain measuring devices, such as strain gauges or the like, are normally mounted on the beams to measure the magnitude of the load induced bending strains in bending beams or the load induced shear strains in shear beams. 
     The accuracy of load cells employing bending beams and shear beams is highly dependent on the manner in which the beams are supported and/or how the loads are coupled to the beams. Ideally, changes in the load induced deformation of the beam, i.e., the bending strain or shear strain, should be solely a function of changes in the weight of the load. If the structure that either supports the beam or couples the load to the beam applies rotational moments or twisting torques to the beam, then the deformation of the beam will not be a true indication of the weight of the load. 
     Not only should the beam be supported and/or loaded in a manner that does not apply rotational moments or twisting torques to the beam, but the beam supporting or loading structure should not restrain the beam from the load induced deformations that are to be measured. For example, for a beam that is freely supported at each end, i.e., a non-cantilever beam, the support structure should allow the ends of the beam to freely pivot. 
     The location at which the beam is supported and/or the location where the load is applied to the beam can also affect the accuracy of load cells using measurement beams. In particular, it is important that the beams be symmetrically supported and loaded so that the weight induced deformation of the beam is symmetrical. 
     The foregoing problems in the art can exist in any weighing scale that employs measurement beams, and can be especially exasperated by the placement of the scale on an uneven support surface. As a result of supporting the weighing scale on an even surface there can be large variations in both the direction and the location that the load is applied to the bending beams and shear beams through the support structure. 
     In the past, attempts have been made to ensure the proper direction and location of beam support and loading by either using complex and costly mechanical coupling mechanisms or by attempting to electrically compensate for the inaccuracies. For example, in U.S. Pat. No. 4,554,987, a scale assembly is provided that includes a platform which is supported by a plurality of force transmitting assemblies. The force transmitting assemblies and platform cooperate to automatically center the platform relative to an enclosing structure and to align the force transmitting assemblies and platform. The automatic centering of the platform and aligning of the force transmitting assemblies is accomplished by moving the platform back and forth in sideways directions against stops which limit motion of the platform. Centering the platform and aligning the force transmitting assemblies is claimed to be effective to eliminate sideward force components on load cells. 
     In U.S. Pat. No. 6,177,638, a portable load scale is disclosed for use in rugged terrain or at locations without suitable support pads. The load scale includes a support deck affixed to a base platform through a plural number of load cells. The base platform is constructed to provide ramp members joined by longitudinal runner assemblies to form a rigid, non-flexing assembly having a central gap and gaps between pairs of ramp members to reduce the standard rectangular footprint by approximately thirty percent. The runner assemblies are constructed so that the bottom of the support deck is separated from the top of the base plate of the runner assemblies by a distance of several inches. The load cells are mounted onto the underside of the support deck and joined to the base platform by ball bushings such that the load cells can pivot in any or about all axis directions relative to the base platform to relieve stresses induced by uneven terrain. 
     None of the prior art weighing systems have proved to be wholly satisfactory, especially when the weighing system is also to be portable, light weight, and of a size that is appropriate for table top applications. There remains a need for an improved structure that supports the beams, or couples the load to the beams, to reduce or prevent the application of unwanted rotational moments or twisting torques to the beam system, so that the deformation of the beam will be a true indication of the weight of the load. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the invention, a weighing scale comprises a platform operatively coupled to a plurality of foot assemblies. Each foot assembly comprises a base having a bottom surface for contacting a portion of a floor, a retaining member arranged in spaced relation to the base; and a plurality of deformable compensation beams projecting outward from a portion of the base to support the retaining member. A plurality of force transfer beams are arranged to operatively interconnect to the plurality of foot assemblies. A mounting portion is coupled to a bottom surface of the platform and associated with each of the plurality of foot assemblies. In response to a force applied to a top surface of the platform, the force is translated to the mounting portion engaging the bottom surface without the platform contacting the force transfer beams, to cause a downward force to be applied to the foot assemblies. The deformable beams tend to locate the applied force at a central position where the foot assemblies engage the force transfer beams. 
     In another embodiment, a foot assembly for a weighing scale comprises a base, a ring arranged in coaxial spaced relation to the base; and a plurality of deformable compensation beams projecting outwardly from a portion of the base so as to support the ring. 
     In another embodiment of the invention, a weighing scale is provided including a platform coupled to a mounting tray, where the mounting tray has a plurality of apertures. A weight determination assembly is positioned between the platform and the mounting tray. A plurality of force transfer beams are arranged within the mounting tray so as to substantially support the platform and the mounting tray such that the mounting tray is isolated from a support surface. In this way, forces that are applied to the weighing scale by the placement of a load on the platform are transferred to the plurality of force transfer beams, without direct interaction between the mounting tray and the support surface. A plurality of foot assemblies are positioned within the apertures and operatively interconnected to the plurality of force transfer beams. Each of the foot assemblies includes a base having a plurality of compensation beams that project radially outwardly so as to support a ring that is coupled to the mounting tray. In this way, if a support surface onto which the weighing scale is placed is canted at some angle, the compensation beams twist and/or bend so as to take up and compensate for any unwanted rotational moments or twisting torques. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be more fully disclosed in, or rendered obvious by, the following detailed description of the preferred embodiments of the invention, which are to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
         FIG. 1  is a front elevational view of a weighing scale formed in accordance with the present invention; 
         FIG. 2  is a perspective view of the weighing scale shown in  FIG. 1 , with the platform removed for clarity of illustration; 
         FIG. 3  is a partially broken away, exploded perspective view of a foot assembly and primary beam formed in accordance with the present invention; 
         FIG. 4  is a partially broken away, perspective view of the foot assembly shown in  FIG. 3 , assembled in accordance with the present invention; 
         FIG. 5  is a partially broken away, exploded perspective view of a foot assembly and secondary beam formed in accordance with the present invention; 
         FIG. 6  is a partially broken away, perspective view of the foot assembly shown in  FIG. 5 , assembled in accordance with the present invention; 
         FIG. 7  is a cross-sectional view of the assembled foot assembly shown in  FIG. 4 , as taken along the lines  7 - 7  in  FIG. 4 ; 
         FIG. 8  is a cross-sectional view of the foot assembly shown in  FIGS. 4 and 7 , as taken along the lines  8 - 8  in  FIG. 7 ; 
         FIG. 9  is a cross-sectional view of the assembled foot assembly shown in  FIG. 6 , as taken along the lines  9 - 9  in  FIG. 6 ; 
         FIG. 10  is a cross-sectional view of the foot assembly shown in  FIGS. 6 and 9 , as taken along the lines  10 - 10  in  FIG. 9 ; and 
         FIG. 11  is a cross-sectional view similar to that shown in  FIG. 10 , but illustrating the affect of an uneven support surface on the foot assembly of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This description of preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawing figures are not necessarily to scale and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected or interconnected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. In the claims, means-plus-function clauses are intended to cover the structures described, suggested, or rendered obvious by the written description or drawings for performing the recited function, including not only structural equivalents but also equivalent structures. 
     Referring to  FIGS. 1 and 2 , a scale  10  formed in accordance with the present invention includes a platform  12 , a mounting tray  14 , a force transfer assembly  16 , a weight determination assembly  18 , and a display  20 . More particularly, platform  12  is sized and shaped so as to be positioned in overlying relation to mounting tray  14 . Platform  12  and mounting tray  14  are often rectilinearly shaped, and are normally formed from either metal or a stiff polymer. Other shapes are also possible for use with the present invention. Platform  12  and mounting tray  14  are coupled to one another along a peripheral edge  21  in a conventional manner, e.g., mechanical fasteners, welds, adhesive bonding, or the like. A receiving surface of platform  12 , upon which a load may be placed, is often covered by a vinyl or plastic sheet  23  so as to provide a non-slip surface. 
     Mounting tray  14  is typically molded from a suitable engineering polymer, or formed (i.e., stamped or drawn from a suitable metal sheet) so as to have an annular wall  24  supporting peripheral edge  21 , and surrounding a central, channeled surface  25  ( FIG. 2 ). A plurality of apertures  27  are defined through portions of central surface  25  in spaced apart relation to one another. For example, when scale  10  comprises a rectilinear shape, apertures  27  are located in the corners of mounting tray  14 . A vertically oriented slot  30  is defined within the portion of wall  24  that is adjacent to a respective one of each of plurality of apertures  27 . A plurality of recessed channels  29  are also formed in central surface  25  of mounting tray  14 . Plurality of recessed channels  29  are sized and arranged in central surface  25  so as to receive and locate portions of force transfer assembly  16 , weight determination assembly  18 , and display  20 . 
     Referring to  FIGS. 2-4 , force transfer assembly  16  includes a pair of primary beams  36 , a pair of secondary beams  38 , and a plurality of foot assemblies  40 . More particularly, each primary beam  36  is formed from a substantially flat strip of metal often having a length that is larger than its width, and a width that is larger than its thickness, e.g. a thin, elongate plate. Primary beams  36  each include a foot engagement end  42  and a sensor engagement end  44 . Each foot engagement end  42  includes a substantially “V” shaped pier-notch  48 , a substantially “V” shaped tray-notch  50 , a cam lock  51  and at least one platform support pad  52  ( FIGS. 3 and 4 ). Pier-notch  48  and tray-notch  50  open onto different edges of foot engagement end  42 . Primary beams  36  are arranged within channels  29  of central surface  25  such that sensor engagement ends  44  are located adjacent to one another and to weight determination assembly  18  ( FIG. 2 ). Each sensor engagement end  44  is adapted to operatively engage a portion of weight determination assembly  18 . In this arrangement, foot engagement ends  42  are positioned in spaced apart relation to one another, and each overtop of a respective aperture  27 . A coupling hole  57  is defined through a portion of each primary beam  36  in spaced relation to both foot engagement end  42  and sensor engagement end  44 . 
     Secondary beams  38  are also formed from a substantially flat strip of metal having a length that is larger than its width, and a width that is larger than its thickness, e.g. a thin, elongate plate. Each secondary beam  38  includes a foot engagement end  62  and a coupling end  64 . Secondary beams  38  are generally shorter than primary beams  36 , and are arranged within channels  29  of central surface  25  such that coupling ends  64  are located within coupling hole  57  of an adjacent primary beam  36 . Each foot engagement end  62  includes a substantially “V” shaped pier-notch notch  68 , a substantially “V” shaped tray-notch  70 , a cam lock  71  and a pair of platform support pads  72   a ,  72   b  ( FIGS. 5 and 6 ). Pier-notch  68  and tray-notch  70  open onto different edges of foot engagement end  62 . Each coupling end  64  is sized and shaped to be received within coupling hole  57  of an adjacent primary beam  36 . A biasing spring  77  is positioned on central surface  25  directly below each secondary beam  38  so as to bias each coupling end  64  against a portion of the interior surface of primary beam  36  that defines coupling hole  57 . In this arrangement, foot engagement ends  62  are positioned in spaced apart relation to one another, and each overtop of a respective aperture  27 . 
     Referring to  FIGS. 3-9 , each foot assembly  40  includes a base  80 , an annular clamp-ring  82 , a plurality of resilient beams  84 , and a pier  86 . More particularly, base  80 , annular clamp-ring  82 , and beams  84  are preferably formed as an integral unit (e.g., by injection molding) from one of the well known polymer materials that are suitable for use in structures requiring mechanical strength and integrity, e.g., polyhalo-olefins, polyamides, polyolefins, polystyrenes, polyvinyls, polyacrylates, polymethacrylates, polyesters, polydienes, polyoxides, polyamides and polysulfides and their blends, copolymers and substituted derivatives thereof. 
     Base  80  often comprises a cylinder defined by a cylindrical wall  90  having a partial top wall  92  and central blind openings  94 , 95  ( FIGS. 3 and 7 ). Annular clamp-ring  82  is arranged in coaxial spaced relation to a top portion  93  of cylindrical wall  90 , and includes at least two through-holes  96  and at least two recesses  98  that are arranged in circumferentially spaced relation to one another, e.g., at 90.degree. intervals around the circumference of the annular ring. 
     Plurality of resilient beams  84  are arranged in circumferentially spaced relation to one another, e.g., at 90.degree. intervals around the circumference of annular clamp-ring  82 . Each beam  84  has a first end  100  that is fixedly clamped (e.g., integrally molded, or the like) to top portion  93  of cylindrical wall  90  and a second end  102  that is fixedly clamped to an inner surface  99  of annular clamp-ring  82 . In this way, each beam  84  projects radially outwardly or away from top portion  93 . 
     Advantageously, each second end  102  is fixedly clamped at a location on inner surface  99  of annular clamp-ring  82  that is circumferentially spaced away from the location on top portion  93  of cylindrical wall  90  at which first end  100  is fixedly clamped to top portion  93  of base  80 . The locations on annular clamp-ring  82  at which each second end  102  is fixedly clamped to inner surface  99  correspond to either one of through-holes  96  or one of recesses  98 . In order to facilitate this arrangement, resilient beams  84  often have a compound curve contour, i.e., having curved sections defined by separate and spaced apart centers, e.g., as in the letter “S” or the mathematical symbol for an integral sign “.intg.”. Of course, while a beam  84  having a compound curve contour is preferable, other shapes and profiles of beam are possible for use with the present invention. In any case, it is the combination of the resilient spring properties of beams  84  and the transversely off-set positioning of their fixed first and second ends that provides for a high degree of compensation when unwanted rotational moments and twisting torques are applied to foot assemblies  40 . 
     Referring again to  FIGS. 3-6 , pier  86  is preferably formed from a metal, and includes a leg  110  that projects downwardly from a plate  112 . A central slot  114  is defined in plate  112 , with knife-edge support  116  formed in plate  112  at the bottom of slot  114 . A pad  120  is often positioned within blind opening  95  of base  80  in coaxially aligned relation to leg  110  so as to provide for a non-slip engagement with a support surface  125  ( FIGS. 6-8 ). 
     Referring once again to  FIG. 2 , weight determination assembly  18  and display  20  are of the type often used in the weighing scale arts. For example, the load cell having a bossed sensor plate taught in U.S. Pat. No. 6,417,466, hereby incorporated herein by reference, provides a weight determination assembly  18  that is adequate for use with the present invention. Briefly, such a weight determination assembly includes a sensor plate for use in a load cell comprising a planar first surface, a planar second surface opposite the first surface which includes a depression formed therein defining a flexure area. A load cavity is formed in the second surface having a conical receptacle end for receiving a strut. Sensors  126  are disposed over the flexure area for generating a signal in response to a load applied to the loading cavity, via interaction with sensor engagement ends  44  of primary beams  36 . The signal is communicated to display  20  via conductors  127 . In this way, the strut has a first conical projection end coupled to the conical receptacle end of the loading cavity and a second end coupled to a foot member such that the strut mechanically floats therebetween for providing the applied load at a substantially central position at the load cavity. Weight determination assembly  18  may be mounted on a channel support  128  forming part of mounting tray  14 . Display  20  may comprise a known mechanical, electromechanical or electronic numerical display panel of the types that are well known in the art for presenting analog or digital numerical data, e.g., a rotary dial, LED, or LCD panels or the like. 
     Scale  10  is assembled and functions in the following manner. Each foot assembly  40  is first positioned for placement within mounting tray  14  such that base  80  is arranged in confronting coaxially relation with an aperture  27 . Once in this position, base  80  is moved toward and into aperture  27  until annular clamp-ring  82  engages the portion of central surface  25  that defines the perimeter of aperture  27 . As this occurs, mounting studs  140  slip into each of through-holes  96 . Mounting studs  140  are then bent over thereby clamping annular clamp-ring  82  securely to mounting tray  14 . As a result of this construction, recesses  98  are arranged in parallel aligned relation to slot  30 . Once in this position, a pier  86  may be positioned within each foot assembly  40  by positioning leg  110  in confronting coaxial relation with central blind opening  94 . Pier  86  is then moved toward base  80  until leg  110  engages the bottom of central blind opening  94 . In this position, slot  114  is arranged in parallel aligned relation with slot  30  in wall  24  and recesses  98  in annular clamp-ring  82 . 
     Force transfer assembly  16  is assembled to foot assemblies  40  and mounting tray  14  by first inserting each coupling end  64  of each secondary beam  38  into it&#39;s corresponding coupling hole  57  of a primary beam  36 . Once in this position, the combined primary and secondary beams are arranged in spaced confronting relation to channels  29  such that foot engagement ends  42  and  62  are positioned in confronting relation to piers  86  of foot assemblies  40  ( FIGS. 3 and 5 ). Once in this position, primary and secondary beams  36 , 38  are moved toward foot assemblies  40  such that pier-notches  48 , 68  enter slots  114  of piers  86 , while at the same time, cam locks  51 , 71  enter slots  30  in wall  24  of mounting tray  14 . When pier-notches  48 , 68  fully engage knife-edge  116  of piers  86 , tray-notches  50 , 70  are seated against the edge of wall  24  that defines the terminal edge of each slot  30 . 
     As a result of this construction, mounting tray  14  is isolated from support surface  125  via foot assemblies  40  and foot engagement ends  42 , 62 . In other words, mounting tray  14  is supported by the engagement of tray-notches  50 , 70  with the edge of wall  24  that defines the terminal edge of each slot  30 . Primary beams  36  and secondary beams  38  are in turn supported upon each knife-edge  116  located within pier-notches  86 . Thus, mounting tray  14  is isolated from support surface  125 , i.e., it does not directly contact support surface  125 . In this way, forces applied to weighing scale  10  by the placement of a load on platform  12  are transferred to force transfer assembly  16 , via foot assemblies  40 , without direction interaction between the underside of mounting tray  14  and support surface  125 . 
     Referring once again to  FIG. 2 , when foot engagement ends  42 , 62  are fully assembled to foot assemblies  40 , sensor engagement ends  44  of primary bending beams  36  are disposed in operative engagement with the deflector area of the sensor plate within weight determination assembly  18 . With all of the foregoing components in place, platform  12  may be secured to mounting tray  14  such that a portion of the underside of platform  12  engages each of platform support pads  52  and  72   a  or  72   b.    
     In operation, when a load is placed on plastic sheet  23  of platform  12 , the force is transferred to force transfer assembly  16 , via all four of support pads  52 , 72 , to weight determination assembly  18 . Referring to  FIG. 11 , if support surface  125  is canted at some angle.alpha., resilient beams  84  twist and/or bend so as to take up and compensate for the resultant unwanted rotational moments or twisting torques being applied to primary beam  36  or secondary beam  38 . In this way, knife edge support  116  is maintained in aligned contact with it&#39;s respective pier-notches  48 , 68  so as to prevent changes in the load induced deformation of primary beams  36  and secondary beams  38 . In this way, the load induced deformation of primary beams  36  and secondary beams  38  is solely a function of the changes in the weight of the load applied to platform  12 . In other words, foot assemblies  40  in combination with primary beams  36  and secondary beams  38  couple the load to the beams without significant affect from rotational moments or twisting torques that are applied to foot assemblies. 
     It is to be understood that the present invention is by no means limited only to the particular constructions herein disclosed and shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims.