Abstract:
A weighing scale and a load cell assembly therefor, the weighing scale including: (a) a weighing platform; (b) a base; and (c) a load cell arrangement including: (i) a load cell body, disposed below the platform and above the base, the body secured to the platform at a first position along a length of the body, and secured to the base at a second position along the length, the load cell body having a first cutout window transversely disposed through the body, the window adapted such that a downward force exerted on a top face of the weighing platform distorts the window to form a distorted window; and (ii) at least one strain-sensing gage, mounted on at least a first surface of the load cell body, the strain-sensing gage adapted to measure a strain in the first surface; and (d) an at least a one-dimensional flexure arrangement having at least a second cutout window transversely disposed through the body, the second cutout window shaped and positioned to at least partially absorb an impact delivered to a top surface of the load cell body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application draws priority from UK Patent Application Serial No. GB1207656.8, filed May 2, 2012, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
       FIELD AND BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to load cell assemblies and weighing devices employing such load cell assemblies, and more particularly, to impact-absorbent load cell assemblies and weighing devices that are largely impervious to shock forces acting thereupon. 
         [0003]    Load cells are employed extensively in weighing scales because of their accuracy in measuring weights. Such load cells, or transducers, may have a metallic body having a generally rectangular perimeter. Opposing surfaces of the perimeter may carry surface-mounted, resistor strain gauges, interconnected to form an electrical bridge. The central portion of the body may have a rigidly-designed opening beneath the strain gauges to define a desired bending curve in the body of the load cell. The body of the load cell is adapted and disposed to provide cantilevered support for the weighing platform. Thus, when a weight is applied to the weighing platform, temporary deformations in the load cell body are translated into electrical signals that are accurately and reproducibly responsive to the weight. 
         [0004]    When the weight on the platform is removed, the metallic load cell body is designed to return to an original, unstressed condition. However, excessive shock forces applied to the body via the weighing platform may permanently distort the load cell body, compromising thereby the accuracy of the bridge-circuit strain gauges. 
       SUMMARY OF THE INVENTION 
       [0005]    According to teachings of the present invention there is provided a weighing scale including: (a) a weighing platform; (b) a base; and (c) a load cell arrangement including: (i) a load cell body, disposed below the platform and above the base, the body secured to the platform at a first position along a length of the body, and secured to the base at a second position along the length, the load cell body having a first cutout window transversely disposed through the body, the window adapted such that a downward force exerted on a top face of the weighing platform distorts the window to form a distorted window; and (ii) at least one strain-sensing gage, mounted on at least a first surface of the load cell body, the strain-sensing gage adapted to measure a strain in the first surface; and (d) an at least a one-dimensional flexure arrangement having at least a second cutout window transversely disposed through the body, the second cutout window shaped and positioned to at least partially absorb an impact delivered to a top surface of the load cell body. 
         [0006]    According to further teachings of the present invention there is provided a load cell assembly, including: (a) a load cell arrangement including: (i) a load cell body having a first cutout window transversely disposed through the body, the window adapted such that a downward force exerted on a top face of the load cell body distorts the window to form a distorted window; and (ii) at least one strain-sensing gage, mounted on at least a first surface of the load cell body, the strain-sensing gage adapted to measure a strain in the first surface; and (b) an at least a one-dimensional flexure arrangement having at least a second cutout window transversely disposed through the body, the second cutout window shaped and positioned to at least partially absorb an impact delivered to a top surface of the load cell body. 
         [0007]    According to still further features in the described preferred embodiments, the load cell body is adapted and disposed to provide cantilevered support for the weighing platform. 
         [0008]    According to still further features in the described preferred embodiments, the at least one strain sensing gage is adapted to measure the strain at a location in the first surface that is above and/or below the distorted window. 
         [0009]    According to still further features in the described preferred embodiments, the first cutout window and the load cell body are adapted such that, when a weight is disposed on the platform, bending beams in a vicinity of the first cutout window achieve a substantially double bending position. 
         [0010]    According to still further features in the described preferred embodiments, the second cutout window is laterally disposed with respect to the first cutout window. 
         [0011]    According to still further features in the described preferred embodiments, the first cutout window and the flexure arrangement are dimensioned to satisfy an equation: 
         [0000]      ( H   1   +H   2 )/ H   3 &lt;0.50, 
         [0000]    wherein H 3  is a height of the first cutout window; H 2  is a height of a protrusion of the flexure arrangement below a bottom plane of the first cutout window, H 2  being ≧0; and H 1  is a height of a protrusion of the flexure arrangement above a top plane of the first cutout window, IL being ≧0. 
         [0012]    According to still further features in the described preferred embodiments, (H 1 +H 2 )/H 3  is at most 0.40, at most 0.30, at most 0.25, at most 0.20, at most 0.10, or at most 0.05. 
         [0013]    According to still further features in the described preferred embodiments, the first and second positions are longitudinally disposed at a distance of at least 20%, at least 30%, at least 40%, at least 50%, or at least 60% of a longitudinal length of the load cell body. 
         [0014]    According to still further features in the described preferred embodiments, the second cutout window is disposed in a proximal side of the load cell body, with respect to a free end of the load cell body. 
         [0015]    According to still further features in the described preferred embodiments, the second cutout window is shaped and disposed to inhibit, or at least mitigate, a permanent distortion of the load cell body, when the impact is severe. 
         [0016]    According to still further features in the described preferred embodiments, the second cutout window includes a plurality of windows. 
         [0017]    According to still further features in the described preferred embodiments, the second cutout window is disposed substantially parallel to the top surface and a bottom surface of the load cell body. 
         [0018]    According to still further features in the described preferred embodiments, the weighing scale further includes a dampening arrangement associated with the flexure arrangement. 
         [0019]    According to still further features in the described preferred embodiments, the dampening arrangement includes a vibration suppressing material filling the second cutout window. 
         [0020]    According to still further features in the described preferred embodiments, the dampening arrangement is adapted and disposed to dampen an amplitude of an electrical signal associated with the strain in the first surface. 
         [0021]    According to still further features in the described preferred embodiments, the dampening arrangement is adapted and disposed to dampen an amplitude of an electrical signal associated with the strain in the first surface, with respect to a strain produced by a load cell arrangement identical to the load cell arrangement, but being unconnected to the dampening arrangement. 
         [0022]    According to still further features in the described preferred embodiments, the dampening arrangement is adapted and disposed to dampen an amplitude of an electrical signal associated with the strain in the first surface, while being further adapted to reduce a settling time associated with the impact. 
         [0023]    According to still further features in the described preferred embodiments, the vibration suppressing material has a Shore A hardness below 85, below 80, below 75, or below 70. 
         [0024]    According to still further features in the described preferred embodiments, the vibration suppressing material has a Shore A hardness in a range between 35 and 75, between 40 and 70, between 45 and 70, between 50 and 70, between 55 and 70, or between 55 and 65. 
         [0025]    According to still further features in the described preferred embodiments, the vibration suppressing material has a Shore A hardness of at least 30, at least 35, at least 40, or at least 45. 
         [0026]    According to still further features in the described preferred embodiments, the vibration suppressing material has a modulus of elasticity of at most 10·10 9  Pa, at most 7·10 9  Pa, at most 5·10 9  Pa, or at most 2·10 9  Pa. 
         [0027]    According to still further features in the described preferred embodiments, the modulus of elasticity of the vibration suppressing material is at least 0.5·10 6  Pa, at least 1·10 6  Pa, at least 210 6  Pa, at least 3·10 6  Pa, at least 5·10 6  Pa, or at least 8·10 6  Pa. 
         [0028]    According to still further features in the described preferred embodiments, the vibration suppressing material has a modulus of elasticity within a range of 0.5·10 6  Pa to 10·10 9  Pa, 0.75·10 6  Pa to 10·10 9  Pa, 1·10 6  Pa to 10·10 9  Pa, 3·10 6  Pa to 10·10 9  Pa, 5·10 6  Pa to 5·10 9  Pa, or 1·10 6  Pa to 10·10 6  Pa. 
         [0029]    According to still further features in the described preferred embodiments, the weighing scale is a scanner-type weighing scale. 
         [0030]    According to still further features in the described preferred embodiments, the flexure arrangement is disposed, from an impact absorption standpoint, before, and in series with, the load cell arrangement, with respect to the impact delivered to the top of the load cell body. 
         [0031]    According to still further features in the described preferred embodiments, the flexure arrangement is disposed, from an impact absorption standpoint, at least partially in parallel with the load cell arrangement, with respect to the impact delivered to the top surface of the load cell body. 
         [0032]    According to still further features in the described preferred embodiments, the at least a one-dimensional flexure arrangement is a two-dimensional or an at least two-dimensional flexure arrangement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. Throughout the drawings, like-referenced characters are used to designate like elements. 
           [0034]    In the drawings: 
           [0035]      FIG. 1A  is a simplified perspective view of an exemplary load cell assembly according to one embodiment of the present invention. 
           [0036]      FIG. 1B  is a schematic side view of the load cell assembly of  FIG. 1A , with a partial cross-sectional view at the left end of the assembly; 
           [0037]      FIG. 1C  is a transverse cross-sectional view of the load cell assembly of  FIG. 1 a   , taken along the A-A plane shown in  FIG. 1B ; 
           [0038]      FIG. 1D  is a transverse cross-sectional view of the load cell assembly of  FIG. 1A , taken along the B-B plane shown in  FIG. 1B ; 
           [0039]      FIG. 1E  is a schematic top view of the load cell assembly of  FIG. 1A ; 
           [0040]      FIG. 1F  is a conventional schematic diagram of the strain gage electronics; 
           [0041]      FIG. 2  is a schematic exemplary exploded view of a weighing module according to an embodiment of the present invention; 
           [0042]      FIG. 3A  is a perspective view showing a top and side of a double ended bending beam having an integral one-dimensional flexure; 
           [0043]      FIG. 3B  is a perspective view showing a bottom and side of the load cell assembly of  FIG. 3A ; 
           [0044]      FIG. 3C  is a perspective, partial, cut-open view of the load cell assembly of  FIG. 3A , showing the integral one-dimensional flexure; 
           [0045]      FIG. 4A  is a perspective view showing a top and side of a double ended bending beam having an integral two-dimensional flexure; 
           [0046]      FIG. 4B  is a perspective view showing a bottom and side of the load cell assembly of  FIG. 4A ; 
           [0047]      FIG. 4C  is a perspective, partial, cut-open view of the load cell assembly of  FIG. 4A , showing the integral two-dimensional flexure; and 
           [0048]      FIG. 5  is an exemplary static nodal stress plot showing the deflection of the flexure arrangement and the load cell arrangement in one embodiment of the load cell assembly of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0049]    The principles and operation of the shock-absorbent load cell according to the present invention may be better understood with reference to the drawings and the accompanying description. 
         [0050]    Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
         [0051]    Referring now to the drawings,  FIG. 1A  is a simplified perspective view of a load cell and flexure assembly  100  (also termed load cell assembly) according to one embodiment of the present invention.  FIG. 1B  provides a schematic side view of the load cell assembly of  FIG. 1A , with a partial cross-sectional view at the left end of the assembly. Transverse cross-sectional views are provided in  FIG. 1C  (along the A-A line) and  FIG. 1D  (along the B-B line). 
         [0052]    A load cell body  125  may be made from a block of load cell quality metal or alloy. Referring collectively to  FIGS. 1A-1D , at least one transverse cutout  110  is formed in a side of the load cell body, to form bending beams above and below the cutout. These beams are held in fixed parallel relationship by end blocks  112 ,  114  on both ends of the load cell body. Load cell arrangement  105  may include strain-sensing gages  120  adapted and positioned to measure the strains caused by a force applied to the top of the (free side of) load cell body  125 . When a vertical load acts on a free end (i.e., an end unsupported by the base, as shown in  FIG. 2 )  130  of load cell body  125 , the load cell body undergoes a slight deflection or distortion, which distortion is measurably sensed by strain gages  120 . 
         [0053]    The load cell body may also have a hole, threaded hole, or receiving element (not shown) for receiving or connecting to a base or base element of the weighing system. Towards free end  130  of the load cell body, a top face  102  of the load cell body may have one or more hole, threaded hole, or receiving element  104  for receiving or connecting to a platform of the weighing system. 
         [0054]    Load cell and flexure assembly  100  may also have at least one transverse cutout or “window”  150  formed in the side of the load cell body, in lateral position with respect to the transverse cutout(s) associated with the strain gages  120 . In  FIGS. 1A, 1B, and 1D  are shown three such windows, disposed one on top of the other. The windows may be of a substantially rectangular profile. The ends of the windows may have a rounded or hemi-circular profile, substantially as shown. 
         [0055]    Windows  150  may advantageously provide additional flexibility to the load cell body, and absorb excessive impact delivered to the body. Thus, windows  150  may form or partially form a flexure or shock-absorbing arrangement  175 . Thus, flexure or shock-absorbing arrangement  175  is integral with load cell body  125  (e.g., both are disposed within a monolithic load cell body such as a monolithic block of alloy, aluminum metal, or aluminum-containing alloy suitable for use as a load cell body), within load cell and flexure assembly  100 . 
         [0056]    Windows  150  may be disposed in the proximal side of the load cell body, with respect to the free end  130  of the load cell body. In other words, windows  150  may be disposed longitudinally in-between transverse cutout  110  and free end  130 . 
         [0057]    In a preferred embodiment, shown in  FIG. 1B , at least one of windows  150  may be filled, e.g., with an elastomer, to provide a dampening (vibration suppressing) mechanism  160  to load cell body  125 . Typically, all of windows  150  may be filled with a vibration suppressing material. This mechanism is especially important when an excessive impact is delivered to the body. Silicone and rubber may be suitable materials for filling the windows. 
         [0058]    The filling material may have a Shore A hardness below 80, and more typically, below 75, or below 70. The Shore A hardness may be at least 30, at least 35, at least 40, or at least 45. The Shore A hardness may be between 35 and 75, between 40 and 70, between 45 and 70, between 50 and 70, between 55 and 70, or between 55 and 65. 
         [0059]    The filling material may have a modulus of elasticity that is less than half that of aluminum. More typically, the modulus of elasticity of the elastomer is less than 10·10 9  Pa, less than 7·10 9  Pa, less than 5·10 9  Pa, or less than 2·10 9  Pa. The modulus of elasticity may be at least 0.5·10 6  Pa, at least 1·10 6  Pa, at least 210 6  Pa, at least 3·10 6  Pa, at least 5·10 6  Pa, or at least 8·10 6  Pa. The modulus of elasticity may be within the range of 0.5·10 6  Pa to 10·10 9  Pa, 0.75·10 6  Pa to 10·10 9  Pa, 1·10 6  Pa to 10·10 9  Pa, 3·10 6  Pa to 10·10 9  Pa, 5·10 6  Pa to 5·10 9  Pa, or 1·10 6  Pa to 10·10 6  Pa. 
         [0060]    The filling material may advantageously contact an entire, or substantially entire, perimeter of window  150 . The filling material may contain extremely small pockets of air. For example, the filler or filling material may have a sponge-like distribution of air pockets. 
         [0061]    In one embodiment, the shock absorber arrangement is adapted whereby the arrangement maintains or nearly maintains the profile or “footprint” of the load cell assembly. 
         [0062]    Referring back to  FIG. 1B , the height of transverse cutout  110  is defined as H 3 . The height of flexure arrangement  175  extending above the top of transverse cutout  110  is defined as H 1 , and the height of flexure arrangement  175  extending below the bottom of transverse cutout  110  is defined as H 2 . The minimum value of each of H 1  and H 2  is zero (i.e., H 1  and H 2  do not assume negative values). 
         [0063]    The inventor has found that it may be highly advantageous for the heights H 1 , H 2 , and H 3  to satisfy the relationship: 
         [0000]      ( H   1   +H   2 )/ H   3 &lt;0.50. 
         [0000]    It may be of further advantage for (H 1 +H 2 )/H 3  to be less than 0.40, less than 0.30, less than 0.25, less than 0.20, less than 0.15, less than 0.10, or less than 0.05. In some cases it may be of further advantage for (H 1 +H 2 )/H 3  to be substantially zero. 
         [0064]    This structural relationship may enable various low-profile scale modules, and may also enable facile retrofitting of the inventive load cell arrangement in existing weighing scales and weighing scale designs. 
         [0065]    The inventive load cell assemblies may be particularly suitable for scanner-type weighing scales. 
         [0066]      FIG. 1E  provides a schematic top view of the load cell assembly of  FIG. 1A , showing two strain sensing gages  120  disposed on a top surface of the load cell body. 
         [0067]      FIG. 1F  provides a conventional schematic diagram of the strain gage electronics, which may be used in, or with, the load cell assemblies and weighing modules of the present invention. The load cell system may further include a processing unit, such as a central processing unit (CPU). The processing unit may be configured to receive the load or strain signals (e.g., from 4 strain gages SG1-SG4) from each particular load cell and to produce a weight indication based on the load signals, as is known to those of ordinary skill in the art. 
         [0068]      FIG. 2  is a schematic exemplary exploded view of a weighing module  200  according to an embodiment of the present invention. Weighing module  200  may include a load cell assembly such as load cell assembly  100 , a weighing platform  260  disposed generally above load cell assembly  100 , and a weighing module base  270  disposed generally below load cell assembly  100 . Load cell assembly  100  may be secured to base  270  by means of an anchoring assembly  280 , which may include at least one fastener such as screws  282 . Base  270  may be equipped with a leg or more typically, a plurality of legs  272  adapted to make contact with a surface on which rests weighing module  200 . 
         [0069]    Load cell assembly  100  may be secured to weighing platform  260  by means of a securing arrangement  280 , which may include at least one fastener such as screws  262 , adapted to securely attach platform  260  to load cell assembly  100 . 
         [0070]      FIG. 3A  is a perspective view showing a top and side of a double ended bending beam assembly  300  having integral, one-dimensional flexures  375 A,  375 B disposed near each longitudinal end  330 A,  330 B of beam  300 . Flexure  375 A, by way of example, may be disposed longitudinally between transverse cutout  310 A associated therewith, and longitudinal end  330 A. 
         [0071]      FIG. 3B  provides a perspective view showing a bottom and side of the load cell assembly of  FIG. 3A . Referring collectively to  FIGS. 3A and 3B , double ended bending beam assembly  300  may be secured within a weighing module in a largely analogous manner to that shown in  FIG. 2 , and described hereinabove. Double ended bending beam assembly  300  may be secured to a weighing module base by means of an anchoring assembly, which may include at least one fastener such as screws or complementary fasteners adapted to securely fit in at least one receptacle such as screwholes  384 . Bending beam assembly  300  may be secured to a weighing platform (similar to weighing platform  260  shown in  FIG. 2 ) by means of a platform securing arrangement, which may include at least one fastener or complementary fastener such as screws, adapted to securely attach the platform to beam assembly  300  by means of at least one receptacle such as screwholes  364 . 
         [0072]    In this embodiment, screwholes  364  are disposed towards the ends of beam assembly  300 , with respect to each respective load cell, while screwholes  384  are disposed towards the center of beam assembly  300 , with respect to each respective load cell. 
         [0073]      FIG. 3C  provides a perspective, partial, cut-open view of the load cell and flexure assembly of  FIG. 3A , showing the integral one-dimensional flexure. 
         [0074]    In the embodiment provided in  FIGS. 3A-3C , beam assembly  300  may be adapted, when secured within a weighing module as described, such that a vertical impact (e.g., an object that is slammed down with great force onto the weighing platform) acts upon one-dimensional flexures  375 A,  375 B, while load cell arrangements  305  remain largely or substantially completely unaffected. Thus, flexures  375 A,  375 B may serve as a vertical shock-protection mechanism for the relatively delicate load cell arrangements  305 . Flexures  375 A,  375 B may be designed and adapted to exhibit, at a maximum load capacity for the load cell, a vertical deflection that is at most 3 times, at most 2 times, at most 1.5 times, at most 1.0 times, or at most 0.8 times, the vertical deflection exhibited by the load cell itself (without the flexure), at that maximum capacity. 
         [0075]    As described above, at least one of windows  150  may be filled, e.g., with an elastomer, to suppress vibration and reduce settling time. Typically, all of windows  150  may be filled with a vibration suppressing material. 
         [0076]      FIG. 4A  is a perspective view showing a top and side of a double ended bending beam having an integral two-dimensional flexure (the entire arrangement designated as assembly  400 ).  FIG. 4B  is a perspective view showing a bottom and side of assembly  400  of  FIG. 4A .  FIG. 4C  is a perspective, partial, cut-open view of assembly  400  of  FIG. 4A , showing the integral two-dimensional flexure. 
         [0077]    Referring collectively to  FIGS. 4A to 4C , the assembly  400  may be constructed, and may be adapted to operate in a substantially similar fashion to the double ended bending beam having an integral one-dimensional flexure described in detail hereinabove. 
         [0078]    However, the second dimension of the integral two-dimensional flexure, including top-oriented windows  490 , is adapted to serve as a horizontal shock-absorbing mechanism for the relatively delicate load cell arrangements  405 . In the exemplary embodiment provided in  FIGS. 4A to 4C , the second dimension of the integral two-dimensional flexure is particularly adapted to act on forces exerted in a direction M, generally perpendicular to the longitudinal or long dimension of assembly  400 . 
         [0079]      FIG. 5  is an exemplary static nodal stress plot showing the deflection of the flexure arrangement and the load cell arrangement in one embodiment of the load cell assembly of the present invention. It will be appreciated by those of skill in the art that the bending beams advantageously maintain a substantially double bending position. 
         [0080]    It will be appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. 
         [0081]    Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.