Six degree-of-freedom load cell body

Abstract

To provide a load cell body and a machine.SOLUTION: A load cell body is configured to be used with a specimen, and the load cell body comprises a first component, a second component, and a flexure mechanism disposed between the first component and the second component. The flexure mechanism comprises a pair of convergent flexure assemblies, each of which has a flexure axis plane. The flexure axis planes intersect at a line, and the mid-point of the line defines the origin of a coordinate system. The specimen is configured to be positioned such that the center of the specimen is located at the origin. In another aspect, a machine comprises a platform, a crosshead, and a load cell body. The load cell body is disposed on the platform, and the specimen is configured to contact the load cell body.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] background The following discussion is provided merely as general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The present disclosure relates to a transducer formed as a load cell body with appropriate sensors for transmitting and measuring linear forces along and moments about up to three orthogonal axes. Transducers or load cells for determining forces along and about orthogonal axes are known. Two such load cells are disclosed in commonly owned U.S. Patent Nos. 4,640,138 and 4,821,582, both of which are incorporated herein by reference. [Background technology]

[0002] U.S. Patent No. 4,640,138 illustrates a multi-axis load-sensing transducer having a central member and a peripheral member joined by a pair of axially spaced arms. The arms are integral with the central member and connected to an outer member by flexible straps, the ends of which are fixed to the outer member. Each arm is fixed to the center of a corresponding strap. Load is sensed as a function of bending of the arms.

[0003] U.S. Patent No. 4,821,582 shows a load transducer for measuring linear forces in three axes and moments about two of those axes. The transducer has an inner structure and an outer structure connected by a load-sensitive arm or shear beam. The outer end of the arm is connected to an outer link which provides stiffness when the inner structure is loaded in a direction along an axis perpendicular to the plane of the arm. [Prior art document] [Patent documents] [Patent Document 1] U.S. Patent No. 4,640,138 [Patent Document 2] U.S. Patent No. 4,821,582 [Patent Document 3] U.S. Patent No. 10,545,062 Summary of the Invention

[0004] overview In one embodiment, a load cell body is configured for use with a test specimen, the load cell body comprising a first member, a second member, and a flexure mechanism disposed between the first member and the second member. The flexure mechanism comprises a pair of focused flexure assemblies, each of the focused flexure assemblies having a flexure axis plane. The flexure axis planes intersect with a line, the midpoint of which defines the origin of a coordinate system. The test specimen is configured to be positioned such that the center of the test specimen is located at the origin.

[0005] In another aspect, a machine is configured for use with a test specimen. The machine includes a platform, a crosshead, and a load cell body. The test specimen is configured to be received between the platform and the crosshead. The load cell body is disposed on the platform, and the test specimen is configured to contact the load cell body. The load cell body includes a pair of focused flexure assemblies, each of the focused flexure assemblies having a flexure axis plane. The flexure axis planes intersect with a line, the midpoint of which defines an origin of a coordinate system. The test specimen is configured to be positioned such that a center of the test specimen is located at the origin.

[0006] This summary is provided to introduce concepts in a simplified form that are further described in the detailed description below. This summary is not intended to identify key or essential features of the disclosed or claimed subject matter, nor is it intended to describe each disclosed embodiment or every implementation of the disclosed or claimed subject matter. In particular, features disclosed herein with respect to one embodiment may be equally applicable to other embodiments. Moreover, this summary is not intended to be used as an aid in determining the scope of the claimed subject matter. Many other novel advantages, features, and relationships will become apparent as this description proceeds. The following figures and description more particularly exemplify illustrative embodiments.

[0007] BRIEF DESCRIPTION OF THE DRAWINGS The disclosed subject matter will be further described with reference to the accompanying drawings, in which like structures or system elements are referenced with like reference numerals throughout the several drawings, and all descriptions are applicable to like and similar structures throughout the several embodiments, unless otherwise specified. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of an exemplary multi-axis elastomeric testing system having a load transducer cell and a bushing specimen mounted thereon.

[0009] [Diagram 2] FIG. 1 is a perspective view of a bushing specimen showing its typical orientation in a testing system.

[0010] [Diagram 3] FIG. 2 is a front right perspective view of an exemplary load cell.

[0011] [Figure 4] FIG. 1 is a perspective end view of an exemplary load cell showing the orientation of focused flexure arms.

[0012] [Diagram 5] FIG. 1 is a front view of an exemplary load cell.

[0013] [Figure 6] FIG. 4 is an enlarged portion of FIG. 3 showing an exemplary sensor labeled on the load cell body.

[0014] [Figure 7] FIG. 7 is a perspective cross-sectional view taken along line 7-7 in FIG. 3.

[0015] [Figure 8] FIG. 8 is a perspective cross-sectional view taken along line 8-8 in FIG. 3.

[0016] [Figure 9] FIG. 1 illustrates a typical strain gauge bridge circuit used for sensing loads, where the gauges are selected based on the column or beam associated with the particular desired force and moment measurements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] While the above-mentioned drawings show one or more embodiments of the load transducer, other embodiments are contemplated. This disclosure is presented by way of representation of the disclosed subject matter, not by way of limitation. It is to be understood that numerous other variations and embodiments may be devised by those skilled in the art that fall within the principles of the present disclosure.

[0018] The figures may not be drawn to scale. In particular, some features may be enlarged relative to other features for clarity. Furthermore, when terms such as upper, lower, top, bottom, side, right, left, vertical, horizontal, etc. are used, it should be understood that they are used only to facilitate understanding of the description. It is contemplated that structures may be in other orientations.

[0019] The terms used herein are intended to describe the embodiments, and the terms are not intended to be limiting. Unless otherwise indicated, ordinal numbers (e.g., first, second, third, etc.) are used to distinguish or identify different elements or steps within a group of elements or steps, and do not impose any serial or numerical limitations on the elements or steps of the embodiment. For example, the "first", "second", and "third" elements or steps do not necessarily have to appear in that order, and the embodiment is not necessarily limited to three elements or steps. Unless otherwise indicated, designations such as "left", "right", "front", "rear", "top", "bottom", "forward", "back", "clockwise", "counterclockwise", "up", "down", or other similar terms such as "upper", "lower", "rear", "front", "vertical", "horizontal", "proximal", "distal", "middle", etc. are used for convenience and do not, for example, imply any particular fixed position, orientation, or direction. Instead, such designations are used to reflect, for example, relative positions, orientations, or directions. The singular forms "a", "an" and "the" include the plural forms unless the context clearly indicates otherwise.

[0020] Detailed Description 1 is a front perspective view of an exemplary testing system 30 including the disclosed load cell 10 for detecting a force applied to a test specimen 32 held in a fixture 34. A suitable machine 36 for use in the testing system 30 is a Model 836 Multi-axial Elastomer Test System available from MTS Systems, Inc. of Eden Prairie, Minnesota. However, it should be understood that other test machines may be used with the system 30. The illustrated MTS Model 836 test machine 36 is designed to perform durability testing of the elastomeric specimen 32 and operates in all six degrees of freedom. The MTS Model 83 includes sensors for each of the actuators 42, 44, 46.

[0021] While the illustrated test specimen 32 is configured as a suspension bushing, it is understood that the test machine 36 with the disclosed load cell 10 can be used with other components, including but not limited to elastomeric components. The test machine 36 and load cell 10 are configured to withstand high load capacities and wide frequency bands to meet a wide range of testing requirements, including elastomeric components for vehicle ride and operation. The illustrated system 30 can be used with the load cell 10 in addition to or in place of sensors in the actuators to provide optimized results, as described further herein.

[0022] 2 shows a typical orientation of a test specimen 32 as oriented in a testing machine 36. The coordinate system 12 represents the linear force (F x , F y , F z ) and rotational moment (M x , M y , M z ) orientation. The exemplary testing system 30 uses a test machine 36 with the disclosed load cell 10 to test a test specimen 32, which may or may not include an adapter or fixture 34. The fixture 34 holds the test specimen 32 in the proper orientation relative to the load cell 10. The load cell 10, fixture 34 and test specimen 32 are positioned between a platform 38 and a crosshead 40. In the present disclosure, forces and moments are measured with respect to a stationary Cartesian coordinate system 12 that includes mutually orthogonal X, Y and Z axes.

[0023] In the exemplary system 30, forces are applied to the test specimen 32 by multiple actuators, and these forces are detected by the load cells 10. In the illustrated machine 36, a single actuator 42 is actuated via a support 42a in a reciprocating (back and forth) direction F X In the exemplary embodiment, two actuators 44 (via struts 44a) provide a force in a reciprocating direction F ZAdditionally, in the exemplary embodiment of the machine 36, three actuators 46 (located at the center and at each end of the crosshead 40) apply a force (via supports 46a) in a reciprocating direction F. Y Give power to.

[0024] The controller of the test machine 36 can individually command each actuator 42, 44, 46. Thus, for example, if two Z actuators 44 differentially move the left and right portions of the crosshead 40, a moment about Y (M Y ) can be applied to the test specimen 32. When the three Y actuators 46 differentially move the left, right, or upper part of the crosshead 40, a moment (M Z ) and / or moment about X (M X ) can be applied to the test specimen 32.

[0025] 3-8 show various views of an exemplary load cell 10 suitable for use in the system 30. In an exemplary embodiment, the load cell 10 comprises a one-piece body 14 preferably formed from a solid block or mass of material. Suitable materials include ductile metals such as steel or titanium. Machined from a single piece of material, the one-piece body 14 reduces hysteresis during operation, improves repeatability, and provides a good low-force response. The one-piece machined construction of the body 14 also improves durability by eliminating welds, brazes, adhesives, and bolted joints. The one-piece machined body 14 provides a small package size with high stiffness in all directions.

[0026] The monolithic construction of the body 14 eliminates creep, hysteresis and damping from bolted joints. These effects are eliminated by the nearly slip-free, highly rigid machined joints. Additionally, the focused flexure assembly 48 is X F related to the measurement of Y This eliminates the large overturning moment from the XThis allows for extremely sensitive measurement of forces, which is five times higher than can be achieved with conventional methods. Furthermore, the compact and stiff design of the load cell 10 with minimal series paths allows the load cell to have a high natural frequency, eliminating dynamic errors in the force and moment measurements. The combination of stiffness with parasitic load tuning minimizes compound load errors across the entire calibration space.

[0027] As shown in Figures 3 and 4, in an exemplary embodiment, the two axial planes 49 of the focusing flexure assembly 48 intersect in a line (straight line). The midpoint of that line defines the center or origin of the control coordinate system 12. The origin of the coordinate system 12 is also directly above the center of the body 14 in the XY plane (Z direction). In the testing system 30, the center of the test specimen 32 is placed at this focal origin by the fixture or adapter 34. Thus, while the coordinate system 12 is depicted in many of the drawings to show the orientation of the structures shown, its origin is properly located at the center of the test specimen 32 positioned at the intersection of the planes of the flexure axes 49 of the focusing flexure assembly 48 as shown in Figures 2 to 4.

[0028] In an exemplary embodiment of the transducer or load cell 10, the body 14 includes a plurality of sensors 50. In an exemplary embodiment, the transducer 10 provides six measurements including moment and axial measurements in three major axes (X, Y, and Z) with very little cross talk or the measurement in one axis being influenced by the load in another axis, a result achieved by the isolation provided by the use of flexible bending beams at the supports of the linked load bearing members.

[0029] In the exemplary embodiment, the body 14 is configured in the form of a frame or cage having a cavity 64 within the boundaries of the first member 20, the second member 24, the two opposing converging flexure assemblies 48, and the two opposing end wall flexure assemblies 58. In the exemplary embodiment, the components 20, 24, 48, 58 are integral with one another and formed from a single, unitary body. However, in alternative embodiments, the components 20, 24, 48, 58, or portions thereof, may be manufactured as separate elements.

[0030] In the exemplary embodiment, as shown in Figures 3-8, a first member 20 is connected to a second member 24 via a flexure mechanism 22. In the exemplary embodiment, each of the first member 20 and second member 24 includes a substantially planar load surface 16, 18, respectively. In application of the load cell 10, forces transmitted between the connected components via the load surfaces 16, 18 are sensed and measured by a sensor 50 disposed on the flexure mechanism 22 of the transducer body 14.

[0031] When equipped with appropriate sensing devices 50, the load cell 10 can sense forces and moments in up to six degrees of freedom. In a preferred embodiment, the first member 20 moves relative to the second member 24 and is supported on the second member 24 by the flexure mechanism 22 while the second member 24 is grounded or otherwise fixed relative to the set of axes 12. This is only one embodiment, and if desired, the first member 20 can be fixed relative to the set of axes 12 while the second member 24 moves relative to the first member 20.

[0032] In an exemplary embodiment, the flexure mechanism 22 comprises two opposing focused flexure assemblies 48 and two opposing end wall flexure assemblies 58. In an exemplary embodiment of the focused flexure assemblies 48, two upper hinges 26 and two lower hinges 28 extend along the length of the body 14 (parallel to the x-axis). In an exemplary embodiment, each of the linear hinges 26, 28 is configured as a thinned portion of the body 14 between two curved machined grooves 27. In an exemplary embodiment, each of the grooves 27 is radially symmetrically positioned about the axial plane 49 of the focused flexure assembly 48. This results in equal strain transmission through the flexure ends and makes the center of the flexure assembly 48 more stable and constant. Thus, the flexure assembly 48 responds to loads without nonlinear effects, thus eliminating nonlinear crosstalk from the measurements.

[0033] 6, each focusing flexure assembly 48 includes an opening 52 that extends through the focusing flexure assembly 48 and leads to a cavity 64. In the exemplary embodiment, each focusing flexure assembly 48 includes a pair of posts 54 and a pair of beams 56. In the exemplary embodiment, each end wall flexure assembly 58 includes an opening 62 that includes a beam 66. The posts 54 and beams 56, 66 are labeled with the principle forces that the sensor 50 thereon is designed to measure, as described further below.

[0034] The load cell 10 includes a transducer body 14 with a sensor 50 mounted thereon, which allows for the measurement of forces and moments at high and low frequencies to characterize the performance of an elastomeric test specimen 32, such as a bushing, over a wide frequency range. It also provides a transducer output for acceleration compensation. The use of a focused flexure assembly 48 allows for high fidelity, low noise force and moment measurements at large offsets while maintaining a high natural frequency. This construction allows the focused flexure assembly 48 to have a high sensitivity, high stiffness load path to provide low noise measurement signals over a wide dynamic range.

[0035] The sensors 50 can be based on strain measurements and / or can be, for example, piezoelectric transducers. Some measurement outputs are fatigue or wear characteristics of the elastomeric test specimen 32, and the frequency content and transmissibility of the elastomer in six degrees of freedom.

[0036] The environment of the test system 30 can be quite harsh, with high loads and large moments on the arm relative to the size of the load cell 10. The load cell 10 attenuates thermal loads from the test specimen 32 as high frequency dynamic loads. Even in harsh environmental conditions, the load cell 10 maintains thermal stability, high natural frequency, high output, low noise, long life, low crosstalk, and low static measurement error. In an exemplary embodiment, the transducer body 14 is made of steel selected for its endurance limit. If the applied stress is below this limit, the body will have a useful life with no calculable termination with respect to fatigue. The use of steel also provides a higher modulus of elasticity than other materials, resulting in a space-efficient stiff beam with low associated loads.

[0037] In an exemplary embodiment, the load cell 10 measures six degrees of freedom through load separation. In general overview, the load cell 10 includes a pair of focused flexure assemblies 48 having pairs of posts 54 and beams 56 carrying sensors 50 thereon. The focused flexure assemblies 48 receive applied forces at a focused point above the load cell 10. Separating the degrees of freedom along a coordinate system allows for improved measurement performance relative to natural frequencies with low noise, high power, low static measurement error, and low thermal error. X Load, F Y Load, F Z Load, M Y Load and some M Z The load is deflected through the focusing flexure assembly 48 so that the post 54 is Y , F Z , and M Y This allows the measurement of F Y M released from the tipping moment, which is the load multiplied by the height above the load cell center coordinate system XWithout this function, the sensor output is M X Measurements of this signal will be undetectable due to noise.

[0038] In an exemplary embodiment, each focused flexure assembly 48 comprises two "Push-Pull" (PP) beams 56 and two "Axial-Poisson" (P / A) posts 54. The two PP beams 56 on one focused flexure assembly 48 are considered as a pair. The pair of PP beams generates a signal by having one PP beam 56 react in compression and the other PP beam 56 react in tension. Thus, sensors 50, such as strain gauges 72, located on these beams 56 experience compressive and tensile strains. This causes a change in resistance, which produces a signal output in the Wheatstone bridge.

[0039] A pair of PP beams 56 provide a stiff load path along the X-axis, thereby reducing the load on the F X and M. Z The two sets of PP beams 56 are offset (along the y-axis) on two focusing flexure assemblies 48 positioned on opposite sides of the transducer body 14, so that the moment M Z These PP beams 56 are compliant in the other four degrees of freedom by utilizing the lateral compliance from the bending beam. Increasing the length of these PP beams 56 reduces the orthogonal stiffness by the cube of the length. However, the axial stiffness is simply a function of the cross-sectional area divided by the length, so it is possible to obtain a high axial stiffness while keeping the orthogonal stiffness low. This allows for a high natural frequency along the length of the beam 56 while the loads associated with the other degrees of freedom remain low, reducing the thermal drift and stresses induced by the other degrees of freedom.

[0040] Another set of PP beams 66 are located within the end wall flexure assembly 58. These PP beams 66 take the same form as "push-pull" beams, and have high axial stiffness and low transverse stiffness. Thus, F Y Load, M XLoad and M Z However, due to the high stiffness of the focusing flexure assembly 48 in the Y direction, F Y The majority of the load is diverted through the focused flexure assembly 48, and this set of beams 66 is Y However, since the body flexure assembly 48 does not have any rotational stiffness about X (due in large part to the hinges 26, 28), M X The load passes through the beams 66. These beams 66 have no rotational stiffness, but do have axial stiffness. Additionally, the beams 66 are located below (in the Z direction) the origin of the measurement coordinate system 12 (located above the load cell 10 as shown in FIG. 4), thereby allowing the beams 66 to react to the moment with an axial load. Additionally, the two sets of beams 66 on opposite end wall flexure assemblies 58 are offset in the X direction, so that these beams 66 are able to react to the moment M Z The height of these beams 66 is M Z Reduces crosstalk from M X Helps to increase output.

[0041] Two sets of PP beams 66 are M Z Load is received. M Z The loads can be quite large for measurements on a PP beam 66. In this configuration, the beam is stiffened by a factor of M in proportion to its relative stiffness. Z The load can be shared between the beams. X Output and M X The output will be relatively sensitive compared to expectations.

[0042] In the exemplary embodiment, two sets of PP beams 56 are disposed in the focusing flexure assembly 48, and another two sets of PP beams 66 are disposed in the end wall flexure assembly 58. In the exemplary embodiment, each of the PP beams 56 and 66 has a strain gauge 72 positioned on each of the upper and lower surfaces. These four sets of PP beams 56, 66 are ZThis results in four bridge outputs that are summed and differen- tiated to measure the force. It is possible to take only the outputs from two sets of PP beams, but this can lead to thermal drift issues due to the parallel paths that the internal force loops will take when either end of the load cell 10 experiences thermal deflection. Therefore, by taking all four bridge outputs and assigning appropriate gains, these internal force loops can be countered to create stability.

[0043] Two opposing focusing flexure assemblies 48 carry four P / A pillars 54 that are loaded in the axial direction 49 of each pillar due to the high axial stiffness of the pillars and compliance in the other degrees of freedom. The P / A pillars 54 are wider than the PP beams 56, 66 to provide stiffness in the loading direction perpendicular to the axial direction 49 of the pillars 54 and perpendicular to the X direction, so that the focusing flexure assemblies 48 do not distort under load and do not exhibit nonlinearity or low mode resonance. The P / A pillars 54 are subjected to axial strain that is measured by axial and Poisson gauges.

[0044] 6, in an exemplary embodiment, the sensor 50 in the pillar 54 comprises an axial gauge 68 arranged in the direction of the axial strain, and a Poisson gauge 70 arranged perpendicular to the axis of the pillar 54 that measures the Poisson strain from the material due to maintaining a constant volume under deformation proportional to the Poisson's ratio of the sensor material. The axial strain exceeds the Poisson strain due to the Poisson's ratio of the material used for the sensor body 14. By taking all the outputs from the P / A pillars 54 and summing them, F Z The force can be measured by subtracting the force of the bridge in the front and rear of the X-direction. Y The difference between the left and right bridges in the Y direction is F Y All of these outputs are passed through an amplifier or some signal conditioning and converted to engineering units through a conversion function.

[0045] In an exemplary embodiment, the load cell 10 utilizes a set of eight Wheatstone bridges. These bridges are summed and subtracted to generate an output for a calibration function that converts to engineering units. In an exemplary embodiment, each set of two PP beams 56 has four gauges 72 and forms a bridge, and thus the two sets of PP beams 56 on the two focused flexure assemblies 48 form two bridges. In an exemplary embodiment, each set of two PP beams 66 has four gauges 72 and forms a bridge, and thus the two sets of PP beams 66 on the two end wall flexure assemblies 58 form another two bridges. In an exemplary embodiment, each P / A column 54 has two axial gauges 68 and two Poisson gauges 70 and forms a bridge, and thus the four P / A columns 54 on the two focused flexure assemblies 48 form another four bridges.

[0046] When an applied load is asymmetric on load surface 16 relative to load surface 18, the acceleration of the active portion of load cell 10 is measured. Algorithms are used which correct for resonances in the measurement system to remove these errors from the load measurement. Further details regarding the calculations used with the load transducers are provided in the following commonly owned U.S. patents, U.S. Pat. No. 4,640,138, entitled "Multiple Axis Load Sensitive Transducer," U.S. Pat. No. 4,821,582, entitled "Load Transducer," and U.S. Pat. No. 10,545,062, entitled "Multi Axis Load Cell Body," which are incorporated herein by reference.

[0047] It should be noted that the geometry of the columns 54 and beams 56, 66 can take a number of different forms when viewed in cross section. For example, the columns can have a constant area in cross section, or the columns can be tapered as shown, which can reduce the stress gradients through the columns or beams induced by off-axis loads and bending due to end effects. The load-bearing capabilities of the columns and beams can also be tailored depending on the force to be measured.

[0048] In an exemplary embodiment of the transducer body 14, temperature control features may be provided in one or both of the first member 20 and the second member 24. In an exemplary embodiment, one or more of the members 20, 24 include passages through which a cooling fluid, such as water, is pumped. Thus, the upper and lower temperature control members 20, 24 of the load cell 10 faithfully control the temperature of the load cell such that thermal equilibrium occurs between the first member 20 and the second member 24. By eliminating thermal gradients in the load cell 10, no thermal errors are introduced. In contrast, the presence of thermal gradients in the load cell creates strain states in the beams and columns, and thermal warping creates offsets that vary with load.

[0049] In the disclosed load cell 10, all degree of freedom bridges are isolated from each other by reducing the orthogonal stiffness of each beam and column so that the associated loads are nearly eliminated. Each end of the beam and column is designed with sufficient cantilever stiffness to ensure that the beam and column are in double cantilever bending rather than just cantilever bending so that the beam has a well-defined inflection point rather than a moving center as exists in a cantilever beam. Thus, the disclosed structure produces very low crosstalk in a load cell 10 with high orthogonal output and therefore very stable load measurement capabilities.

[0050] The load cell 10 works with both AC and DC components of the load. It measures low frequency quasi-static loads while maintaining a high natural frequency to measure dynamic loads. The geometry of the transducer body 14 allows for a high level of flexural isolation, and the tuned beam and column positions provide low crosstalk, low thermal errors, and low noise in the measurement device.

[0051] FIG. 9 shows a typical strain gauge bridge circuit used to sense loads, where the gauges are selected in relation to the columns or beams associated with the particular desired force and moment measurements. "C" indicates a compression gauge and "T" indicates a tension gauge. To obtain a signal representative of the force acting on the transducer, multiple strain gauge bridges are formed using strain gauges in selected bridge arms, represented by resistors R1 through R4, which correspond to C1, T1, C2, and T2 in FIG. 9, respectively. Individual bridge outputs provide signals indicative of various forces, from which moments about two of the coordinate axes (e.g., X and Z) can be determined, and separate bridges can be used to determine moments about the remaining axis (e.g., Y).

[0052] In an exemplary embodiment, tension gauges are on opposing arms of the bridge and compression gauges are also on opposing arms of the bridge. The unitary (one-piece) construction of the body 14 in which the sensors 50 / gauges 68, 70, 72 are located, including the focused flexure assembly 48 and end wall flexure assembly 58, allows the loads to be isolated from one another minimizing cross-coupling and reducing hysteresis and other operational problems.

[0053] Exemplary, non-limiting embodiments of a load cell 10 comprising a body 14 carrying a sensor 50 are described. In the exemplary embodiment, the load cell body 14 is configured for use with a test specimen 32, the load cell body 14 comprising a first member 20, a second member 24, and a flexure mechanism 22 disposed between the first member 20 and the second member 24. In the exemplary embodiment, the flexure mechanism 22 comprises a pair of focused flexure assemblies 48, each of which has a flexure axis 49, the flexure axis planes 49 of the pair of focused flexure assemblies 48 intersecting at a focal line, the midpoint of the line defining the origin of the coordinate system 12. In the exemplary embodiment, the test specimen 32 is configured to be positioned such that the center of the test specimen 32 is located at the origin.

[0054] In an exemplary embodiment, the coordinate system 12 includes mutually orthogonal X-, Y-, and Z-axes, and at least one of the focused flexure assemblies 48 includes hinges 26, 28 extending parallel to the X-axis. In an exemplary embodiment, at least one of the focused flexure assemblies 48 includes a first post 54 extending parallel to the flexure axis 48 and a first beam 56 extending parallel to the X-axis. In an exemplary embodiment, a sensor 50 is disposed on at least one of the first post 54 and the first beam 56. In an exemplary embodiment, the sensor 50 includes a strain gauge 72 disposed on the first beam 56. In an exemplary embodiment, the sensor 50 includes an axial gauge 68 disposed on the first post 54 and aligned with the flexure axis 49. In an exemplary embodiment, the sensor 50 includes a Poisson gauge 70 disposed on the first post 54 and orthogonal to the axial gauge 68.

[0055] In the exemplary embodiment, the flexure mechanism 22 includes a pair of end wall flexure assemblies 58, each of which is positioned at an end of a pair of focusing flexure assemblies 48. In the exemplary embodiment, at least one of the end wall flexure assemblies 58 includes a first beam 66 extending parallel to the Y-axis. In the exemplary embodiment, the sensor 50 is disposed on the first beam 66. In the exemplary embodiment, the sensor 50 includes a pair of strain gauges 72 disposed on two opposing sides of the first beam 66.

[0056] In an exemplary embodiment, the flexure mechanism 22 includes at least two pairs of posts 54 and four pairs of beams 56, 66. In an exemplary embodiment, each of the posts 54 extends parallel to the flexure axis 49. In an exemplary embodiment, each of the beams 56, 66 extends parallel to the X-axis or parallel to the Y-axis. In an exemplary embodiment, two opposing pairs 56, 66 of the four pairs of beams are disposed at equal distances from the origin of the coordinate system 12. In an exemplary embodiment, the two opposing pairs of beams 56 are disposed on a pair of converging flexure assemblies 48. In an exemplary embodiment, the two opposing pairs of beams 66 are disposed on a pair of end wall flexure assemblies 58. In an exemplary embodiment, the first member 20, the second member 24, and the flexure mechanism 22 are integrally formed from a single unitary mass that defines the interior cavity 64.

[0057] Although the subject matter has been described in language specific to structural features and / or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above, as has been determined by a court. Rather, the specific features and acts described above are disclosed as exemplary forms for implementing the claims. Furthermore, features disclosed with respect to one embodiment may be included in another embodiment, and vice versa. All references cited in this disclosure are incorporated herein by reference.

Claims

1. 1. A load cell body configured for use with a test specimen, comprising: A first member; A second member; and a flexure mechanism disposed between the first member and the second member, a pair of focusing flexure assemblies, each of the focusing flexure assemblies having a flexure axis plane, the flexure axis planes intersecting each other at a line, the midpoint of the line defining an origin of a coordinate system, and the test specimen configured to be positioned such that a center of the test specimen is located at the origin. A deflection mechanism; A load cell body comprising:

2. 2. The load cell body of claim 1, wherein the coordinate system includes mutually orthogonal X, Y, and Z axes, and at least one of the focused flexure assemblies comprises a hinge extending parallel to the X axis.

3. 2. The load cell body of claim 1, wherein the coordinate system includes mutually orthogonal X-, Y-, and Z-axes, and at least one of the focused flexure assemblies comprises a first post extending parallel to the flexure axis plane and a first beam extending parallel to the X-axis.

4. 4. The load cell body of claim 3, comprising a sensor disposed on at least one of the first pillar and the first beam, the sensor preferably comprising a strain gauge disposed on the first beam and optionally an axial gauge disposed on the first pillar and aligned parallel to the flexure axis plane or a Poisson gauge disposed on the first pillar and perpendicular to the flexure axis plane.

5. 5. A load cell body as claimed in any one of claims 1 to 4, wherein the flexure mechanism comprises a pair of flexure end wall assemblies, each of which is positioned at an end of the pair of converging flexure assemblies, preferably wherein the coordinate system includes mutually orthogonal X-, Y- and Z-axes, and at least one of the flexure end wall assemblies comprises a first beam extending parallel to the Y-axis.

6. 5. The load cell body of claim 4, further comprising a sensor disposed on the first beam, preferably the sensor comprising a pair of strain gauges disposed on two opposing sides of the first beam.

7. The coordinate system includes mutually orthogonal X-axis, Y-axis, and Z-axis, and the flexure mechanism is two pairs of struts, each of said struts extending parallel to a respective flexure axis plane; Four pairs of beams, each of the beams extending parallel to the X-axis or parallel to the Y-axis; The load cell body according to claim 1 , comprising at least

8. 8. The load cell body of claim 7, wherein two opposing pairs of beams of the four pairs of beams are disposed at equal distances from each other from the origin of the coordinate system, and preferably the two opposing pairs of beams are disposed on the pair of focused flexure assemblies.

9. the flexure mechanism comprises a pair of flexure end wall assemblies, each of the flexure end wall assemblies positioned at an end of the pair of converging flexure assemblies; the two pairs of opposing beams are disposed on the pair of flexible end wall assemblies; The load cell body according to claim 8.

10. 10. The load cell body of claim 1, wherein the first member, the second member, and the flexure mechanism are integrally formed from a single unitary mass having an internal cavity.

11. 1. A machine configured for use with a test strip, comprising: a platform and a crosshead, the test specimen being configured to be received between the platform and the crosshead; a load cell body disposed on the platform, the test specimen being configured to contact the load cell body, the load cell body comprising: a pair of focusing flexure assemblies, each of the focusing flexure assemblies having a flexure axis plane, the flexure axis planes intersecting each other at a line, the midpoint of the line defining an origin of a coordinate system, and the test specimen configured to be positioned such that a center of the test specimen is located at the origin. A load cell body comprising: A machine equipped with:

12. 12. The machine of claim 11, wherein the coordinate system includes mutually orthogonal X, Y, and Z axes, the machine comprising an actuator configured to apply a force to the test specimen along the X axis.

13. The machine of claim 11 , wherein the coordinate system includes mutually orthogonal X, Y, and Z axes, and the machine comprises an actuator configured to apply a force to the test specimen along the Y axis.

14. The machine of claim 11 , wherein the coordinate system includes mutually orthogonal X, Y, and Z axes, and the machine comprises an actuator configured to apply a force to the test specimen along the Z axis.

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