CN114514415A

CN114514415A - Planar load sensor assembly

Info

Publication number: CN114514415A
Application number: CN202080054390.4A
Authority: CN
Inventors: M·塔拉克海莫维奇
Original assignee: SHEKEL SCALES (2008) Ltd
Current assignee: SHEKEL SCALES (2008) Ltd
Priority date: 2019-06-26
Filing date: 2020-06-19
Publication date: 2022-05-17
Also published as: EP3990874A4; EP3990874A1; WO2020261075A1; IL289191A; AU2020307463A1; GB201909216D0

Abstract

An assembly, comprising: a load cell body having a continuous cutout window, each cutout window formed by a pair of cutout lines and connected by a cutout base, a second window laterally bounded by the first window; a measuring beam disposed generally along an edge of the body, each measuring beam defined by a respective line of the first pair of cut lines; a first arrangement and a second arrangement, each arrangement having a pair of flexure beams connected by a first base and a second base, respectively; a load element extending from the second base; and a strain gauge attached to the beam, and a lateral flexure arrangement.

Description

Planar load sensor assembly

This application claims priority from uk application No. 1909216.2 filed on 26.6.2019, which is hereby incorporated by reference as if fully set forth herein for all purposes.

Technical field and background

The present invention relates to weight measuring devices and, more particularly, to a planar weighing device employing a load cell assembly with an integral flexure.

Load cells are widely used in weighing scales due to their accuracy in measuring weight. Such a load sensor or transducer may have a metal body with a substantially rectangular face. The opposite surface of the load cell may carry surface mounted electrical resistance strain gauges that are interconnected to form an electrical bridge. The central portion of the body may have a rigidly designed opening below the strain gauge in order to define a desired bending curve in the body of the load cell. The body of the load cell is adapted and arranged to provide cantilevered support to the weighing platform. Thus, when a weight is applied to the weighing platform, the temporary deformation of the load cell body is converted into an electrical signal that responds accurately and reproducibly to the weight. When the weight on the platform is removed, the metal body of the load cell is designed to return to the original, unstressed state.

Planar load sensors are known in the art, for example, as disclosed in U.S. patent No. 5,510,581, which is incorporated by reference herein for all purposes as if fully set forth herein. A planar load cell may have a characteristic low amplitude signal. Spurious noise can also be a major problem. For these and other reasons, high precision weight measurement can present significant challenges.

The inventors have discovered various deficiencies in planar load cell assemblies. Including deficiencies in weighing accuracy and off-center load sensitivity.

Disclosure of Invention

According to aspects of the present invention, there is provided a planar load cell assembly, comprising: at least one load cell arrangement disposed on a single metallic load cell body having a main axis, a central longitudinal axis, and a transverse axis disposed transverse to the main axis and the central longitudinal axis, a wide dimension of the load cell body being disposed perpendicular to the main axis; each of the load cell arrangements comprises: (a) a first continuous slit window passing through the width dimension and formed by a first pair of slit lines disposed generally along or parallel to the central longitudinal axis and connected by a first slit base; (b) a pair of measuring beams disposed along opposite edges of the load cell body and generally parallel to the central longitudinal axis, each of the measuring beams being longitudinally defined by a respective cut line of a first pair of cut lines, each of the pair of cut lines disposed generally along or parallel to the central longitudinal axis; (c) at least one strain gauge fixedly attached to a surface of a measurement beam of the measurement beams; (d) a load member longitudinally defined by an innermost pair of cut lines and extending from an innermost flexure base, the transverse axis passing through the load member, the load member adapted to receive a vertical load; and at least one of the following structural limitations: (i) a hinge disposed in the metal load sensor body, the hinge having a transverse orientation relative to the primary axis and the central longitudinal axis; (ii) at least one transverse flexure beam disposed in the metallic load cell body, the hinge having a transverse orientation relative to the primary axis and the central longitudinal axis; and (iii) a lateral flexure arrangement disposed within the first continuous slit window.

According to still further features in the described preferred embodiments the angle of departure from the transverse axis of the transverse orientation is in a range of 0 ° to 70 °, 0 ° to 60 °, 0 ° to 45 °, 0 ° to 40 °, 0 ° to 35 °, 0 ° to 30 °, 0 ° to 25 °, or 0 ° to 20 °.

According to still further features in the described preferred embodiments, the lateral flexure arrangement is configured to mechanically bridge or connect between the load element and a spring arrangement of the load cell arrangement.

According to aspects of the present invention, there is provided a planar load cell assembly, comprising: at least one load cell arrangement disposed on a single metallic load cell body having a main axis, a central longitudinal axis, and a transverse axis disposed transverse to the main axis and the central longitudinal axis, a wide dimension of the load cell body being disposed perpendicular to the main axis; each of the load cell arrangements comprises: (a) at least a first pair of incision lines including an outermost pair of incision lines disposed generally along or generally parallel to the central longitudinal axis and passing through the wide dimension, the outermost pair of incision lines communicating with each other through a first cross-cut base to form a first continuous incision window passing through the wide dimension; (b) a pair of measurement beams disposed along opposite edges of the load cell body and generally parallel to the central longitudinal axis, each of the measurement beams being longitudinally defined by a respective one of the outermost pair of cut lines, (c) at least one strain gauge fixedly attached to a surface of a measurement beam of the measurement beams; (d) a load element defined by an [ optionally innermost ] cutout arrangement, the transverse axis passing through the load element, the load element adapted to receive a vertical load; and (e) a lateral flexure arrangement.

According to still further features in the described preferred embodiments, a double ended load cell assembly is disclosed having two load cell arrangements disposed on a single metallic load cell body, each of the load cell arrangements conforming to any of the planar load cell assemblies described above and/or any of the planar load cell assemblies described below.

According to still further features in the described preferred embodiments, the metal-loaded sensor body is made of a magnesium alloy, wherein a magnesium content of the magnesium alloy is optionally in a range of 85% to 98%, 88% to 98%, 90% to 98%, or 92% to 98% by weight or by volume.

According to still further features in the described preferred embodiments, the magnesium alloy is selected or adapted such that its modulus of elasticity (E) is lower than the modulus of elasticity of the load cell grade aluminum alloy 2023.

According to still further features in the described preferred embodiments, the load element, the second pair of deflection beams, the first pair of deflection beams, and the pair of gauging beams are mechanically arranged in series such that a load arranged on the load element acts on the second pair of deflection beams before acting on the first pair of deflection beams and acts on the first pair of deflection beams before acting on the pair of gauging beams.

Drawings

The invention will now be 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. Like reference characters are used to refer to like elements throughout.

In the figure:

FIG. 1 is a block diagram illustrating a series connection between a load beam and a gage beam of a load via a flexure arrangement having at least two flexures within a spring arrangement of a load cell assembly according to an embodiment of the present invention;

FIG. 2 is a conventional schematic of strain gauge electronics;

FIG. 3 is a schematic top view of a planar load cell arrangement according to an embodiment of the present invention;

FIG. 3A is a schematic top view of a planar load cell body according to an embodiment of the present invention;

FIG. 4 is an exemplary displacement graph illustrating the flexure arrangement and deflection of the load cell body of FIG. 3A in response to a moment (Mz) along the transverse (Z) axis;

fig. 5A-5E provide schematic top views of various planar load cell bodies according to embodiments of the present invention;

FIG. 6 is a block diagram of a weigh scale or load cell assembly according to an embodiment of the present invention;

FIG. 7 is an exploded perspective view of a planar weigh scale or load cell assembly according to an embodiment of the present invention;

FIG. 8 is an exploded perspective view of a planar weigh scale or load cell assembly having a base plate in accordance with an embodiment of the present invention;

FIGS. 9A and 9B are top views of a planar load cell assembly of the present inventor (not yet disclosed);

FIG. 9C is a top view of a planar load cell assembly according to the present invention; and is

Fig. 9D is a schematic top view of the planar load cell assembly of fig. 9C in accordance with the present invention.

Detailed Description

The principles and operation of a thin or planar load cell assembly according to the present invention may be better understood with reference to the drawings and the accompanying description.

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.

A thin load cell may have a characteristic low amplitude signal. Given the limitations of the total weight to be measured and the inherent sensitivity of the load cell, the performance of such devices may suffer due to high signal-to-noise ratios and unacceptable settling times. Various embodiments of the present invention solve, or at least significantly reduce, the parasitic noise problem associated with typical thin load cells and enable high precision weight measurements.

Fig. 1 is a block diagram schematically illustrating the operation of a spring arrangement in a load or operating mode according to aspects of the present invention. The loading of the spring arrangement is achieved by placing the load on or under the load beam, depending on whether the load beam is anchored on the weighing platform or on the weighing base. As used herein and in the appended claims, a load beam may also be referred to as a "load element" or "load-receiving element" or "load-supporting element" of a load cell assembly (depending on the configuration). The spring arrangement may comprise, in addition to the gauging beam, a flexure arrangement (comprising at least one flexure element) operatively connected in series with the gauging beam. The flexure arrangement may be operatively connected at a first end to the load beam and at a second or opposite end to a free or compliant end of the at least one measure beam.

As substantially shown, the flexure arrangement has n flexures (n being an integer) operatively connected in series, a first of the flexures being operatively connected to the load beam, and a final flexure of the n flexures being operatively connected in series to a second flexure that is in turn operatively connected to a first flexure of an assembly of m flexures (m being an integer) operatively connected in series. The final flexure of the m flexures is operatively connected in series to a measurement beam of the spring arrangement. Associated with the measuring beam is at least one strain gauge which generates weighing information about the load.

At least two of such flexure arrangements arranged in parallel may be necessary to properly arrange the load element substantially in a horizontal position (i.e., perpendicular to the load). In some embodiments, a single flexure disposed between the load beam and the measurement beam may be sufficient, particularly when extreme precision is not required. This single flexure load cell arrangement may also exhibit increased cross-talk with other load cell arrangements (a weighing assembly may typically have 4 such load cell arrangements for a single weighing platform). Overload capability may also be compromised for a given nominal capacity relative to a load cell arrangement having multiple flexures disposed in series between the load-receiving beam and the measuring beam. Such reduced overload capability may be manifested as less durability and/or shorter product life relative to a load cell arrangement having multiple flexures disposed in series. However, the overall performance of the single flexure arrangement may be comparable to conventional weighing apparatus and load cell arrangements. In any case, for this case, m + n is-1.

When there is no intermediate longitudinal flexure (i.e., m + n-2), the inventors have found that the arrangement is more compromised by cross-talk with other load cell arrangements, and that overload capability may be further compromised.

Furthermore, the inventors have found that planar load cells may exhibit poor or insufficient flexibility for lateral rotation when no intermediate longitudinal flexure is present.

The inventors have surprisingly found that by connecting the load receiving element or end to the measuring beam via a transverse (arranged transversely with respect to the longitudinal plane of the load cell body) flexure arrangement, the overload protection is significantly enhanced.

Such planar load cells may be made from sheet metal, typically having a thickness of 1.5mm to 10 mm. Typical materials of construction include aluminum and aluminum alloys for smaller capacities (e.g., 2024 aluminum T3) and steel for larger capacities (e.g., 17-4PH steel H900). Magnesium alloys that are typically targeted for ultra-low, low and medium power (e.g., E675) may also be employed.

Fabrication may be accomplished using various techniques known in the art.

The inventors have found that the sensitivity of a planar load cell to various parasitic moments can be significantly reduced by increasing the rotational flexibility of the load receiving element in the transverse plane.

The inventors have found that by connecting the load receiving element or end portion to the weighing beams via at least one lateral flexure arrangement, the planar load sensor may exhibit significantly increased lateral flexibility, thereby reducing parasitic moments. Furthermore, as briefly described above, such increased lateral flexibility may significantly contribute to the vertical displacement achieved by the load cell, thereby increasing the overload capability of the load cell.

Typically, there are 4 strain gauges per load beam. FIG. 2 provides a conventional schematic illustration of strain gauge electronics that may be used in or with the load cell assembly and weighing module of the present invention. The strain gauges may be configured in a Wheatstone (Wheatstone) bridge configuration, which is well known to those skilled in the art. The load sensor system may also include a processing unit, such as a Central Processing Unit (CPU). The processing unit may be configured to receive a load or strain signal from each particular load sensor (e.g., from 4 strain gauges SG1-SG4) and generate a weight indication based on the load signal, as known to one of ordinary skill in the art.

Referring now to fig. 3, fig. 3 is a schematic top view of a planar load cell assembly 100 according to one embodiment of the present invention;

the load cell body 125 of the planar load cell assembly 100 may be made of a mass of metal or alloy that is the texture of the load cell. Particularly advantageous embodiments using specific magnesium alloys will be described below.

The load cell body 125 may be secured to the weighing assembly by one or more mounting holes or elements 142. The first generally continuous cutout window 116 passes vertically through the bottom surface 112 from the top surface 110 through the wide dimension (i.e., the other 2 dimensions relative to the three-dimensional cartesian coordinate system) of the load cell body 125. The first continuous cutout window 116 may be generally C-shaped or U-shaped, and may have an arm or pair of

cutout lines

118a, 118b that extend generally parallel to the central longitudinal axis 102 of the load cell body 125 and are connected or made continuous by a cutout or cutout base 118C. Both the central longitudinal axis 102 and the transverse axis 104 disposed transverse to the central longitudinal axis extend generally parallel to the wide dimension of the load cell body 125. Both of which may be oriented in a generally perpendicular manner with respect to the main axis 114. The thickness of the load cell body 125 perpendicular to the main axis 114 is typically in the range 1.5mm to 10mm or 2mm to 10mm and is labeled as W_LCB。

The

long sides

105a and 105b of the load cell body 125 extend generally along or generally parallel to the central longitudinal axis 102.

As shown, the gauging beams or

spring elements

107a and 107b are each disposed away from the cut-out

lines

118a and 118b relative to the transverse axis 104 between the respective cut-out

lines

118a and 118b and the respective

long sides

105a and 105b of the load cell body 125. When the planar load cell assembly 100 is disposed in a vertical load position, the free end of each of the

beams

107a and 107b may be held in a fixed relationship substantially perpendicular to the vertical load by an end block 124 disposed at the free end 123 of the load cell body 125.

The second generally continuous cutout window 126 also passes vertically through the wide dimension of the load cell body 125 from the top surface 110 through the bottom surface 112. The second cutout window 126 may be generally C-shaped or U-shaped, and may have an arm or pair of

cutout lines

128a, 128b that extend generally parallel to the central longitudinal axis 102 and are connected or continuous by a cutout line or cutout base 128C. The second cutout window 126 may be surrounded on three sides by the first cutout window 116 (such that the second cutout window is laterally bounded by the first continuous cutout window). The second cutout window 126 may be oriented 180 ° (i.e., substantially opposite) relative to the first cutout window 116.

The load cell body 125 has a first flexure arrangement having a first pair of

flexure beams

117a, 117b disposed along opposite sides of the central longitudinal axis 102 and distal and parallel to the central longitudinal axis 102. The first pair of

flexure beams

117a, 117b may be longitudinally disposed between the first and second pair of cut lines and mechanically connected or coupled by the first flexure base 119.

As shown, the load cell body 125 has a second flexure arrangement 126, which may optionally be generally longitudinal. The second flexure arrangement may have a second pair of

flexure beams

127a, 127b disposed along opposite sides of the central longitudinal axis 102, and distal to and optionally substantially parallel to the central longitudinal axis 102. A second pair of

flexure beams

127a, 127b may be longitudinally disposed between the first and second pair of cut lines and mechanically connected or coupled by a second flexure base 129.

The lateral flexure arrangement 136 may be disposed within the first (outermost) cutout window 116 and, more typically, also within the second (or innermost) cutout window 126. In general, the lateral flexure arrangement 136 may be provided to mechanically bridge or connect between the load element 137 and the spring arrangement, for example to mechanically bridge or connect to or through the second flexure base 129 and/or the first flexure base 119.

The lateral flexure arrangement 136 may include at least one lateral flexure beam, such as

lateral flexure beams

138a, 138b, and 138 c. Such beams may be disposed on either or both sides of a load zone or load contact zone 140, as will be described in further detail below.

As used herein in the specification and in the claims section that follows, the term "transverse flexure beam" is used as will be understood by those skilled in the art. For the avoidance of doubt, such a transverse flexure beam may be a flexure beam disposed at an angle relative to the transverse axis such that the beam has a transverse component (e.g., related to the cosine of the angle of departure of the transverse axis). Typically, the angle of departure from the transverse axis of the transverse flexure beam is in the range of 0 ° to 70 °, 0 ° to 60 °, 0 ° to 45 °, 0 ° to 40 °, 0 ° to 35 °, 0 ° to 30 °, 0 ° to 25 °, or 0 ° to 20 °.

Transverse flexure beams

138a, 138b, and 138c may be formed from one or

more cutout structures

179a, 179a having comb-like cutout lines including

cutout backbone lines

180a, 180b and one or more transverse cutout lines 181a, substantially as shown. Typically, the angle of departure from the transverse axis of such a transverse cut line is in the range of 0 ° to 70 °, 0 ° to 60 °, 0 ° to 45 °, 0 ° to 40 °, 0 ° to 35 °, 0 ° to 30 °, 0 ° to 25 °, or 0 ° to 20 °.

The

cutout structures

179a, 179a may be spaced apart and dimensioned such that the lateral flexure arrangement 136 has a labyrinth or labyrinth-like lateral flexure beam structure.

More generally, the lateral flexure beams may be arranged and dimensioned to form a lateral hinge having a lateral characteristic or component. Typically, the angle of departure from the transverse axis of such a transverse hinge is in the range of 0 ° to 70 °, 0 ° to 60 °, 0 ° to 45 °, 0 ° to 40 °, 0 ° to 35 °, 0 ° to 30 °, 0 ° to 25 °, or 0 ° to 20 °.

Characterizing transverse Beam Length (L)_tb) Dimensionless parameter (D)_tb) Can be defined as follows:

D_tb＝L_tb/W_Lcb

wherein W_LcbIs the width of the load cell body in the lateral direction. The inventors have found that the length of such beams in the transverse direction may be such that D_tbIs at least 0.03 or at least 0.05, and more typically, at least 0.07, at least 0.10, at least 0.12, at least 0.15, or at least 0.20.

In some embodiments, D_tbIn the range of 0.03 to 0.60, 0.03 to 0.50, 0.05 to 0.60, 0.05 to 0.50, 0.05 to 0.40, 0.07 to 0.60, 0.07 to 0.50, 0.10 to 0.60, 0.10 to 0.50, 0.12 to 0.60, 0.12 to 0.50, 0.12 to 0.40, 0.15 to 0.60, 0.15 to 0.50, or 0.15 to 0.40.

The various cut lines described above can generally have a width (Wco) of 0.2mm to 5mm, and more typically, 0.2mm to 2.5mm, 0.2mm to 2.0mm, 0.2mm to 1.5mm, 0.2mm to 1.0mm, 0.2mm to 0.7mm, 0.2mm to 0.5mm, 0.3mm to 5mm, 0.3mm to 2.5mm, 0.3mm to 2.0mm, 0.3mm to 1.5mm, 0.3mm to 1.0mm, 0.3mm to 0.7mm, 0.3mm to 0.6mm, or 0.3mm to 0.5 mm.

In some embodiments, W_COAnd W_LCBRatio of (W)_CO/W_LCB) Is at most 0.5, at most 0.4, at most 0.3, at most 0.25, at most 0.2, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, or at most 0.05.

In some embodiments, W_COAnd W_LCBRatio of (W)_CO/W_LCB) In the range of 0.03 to 0.5, 0.03 to 0.4, 0.03 to 0.3, 0.03 to 0.2, 0.03 to 0.15, 0.03 to 0.10, 0.04 to 0.5, 0.04 to 0.4, 0.04 to 0.3, 0.04 to 0.2, 0.04 to 0.15, 0.04 to 0.10, 0.05 to 0.5, 0.05 to 0.4, 0.05 to 0.3, 0.05 to 0.2, 0.05 to 0.15, or 0.05 to 0.10. The load element 137 may also include a load zone or load contact zone 140, and the load zone or load contact zone 140 may be a thread of a bore (e.g., a thread for receiving a thread)A load, e.g., for receiving or connecting to an upper weighing platform, or for supporting a load, e.g., a base, legs, or support (disposed below the load cell body 125) of a weighing system (described with respect to fig. 11). A load zone or load contact zone 140 may be positioned at the intersection of the central longitudinal axis 102 and the lateral axis 104.

In the exemplary embodiment provided in fig. 3, the first and second flexure arrangements may form a generally longitudinal flexure arrangement 180, the flexure arrangement 180 being mechanically disposed between the load element 137 and the measurement beams or

spring elements

107a and 107 b.

At least one strain gauge, such as a strain (or "strain sensing") gauge 120, may be fixedly attached to a surface (typically a top or bottom surface) of each of the

measurement beams

107a and 107 b. The strain gage 120 may be adapted and positioned to measure strain caused by a force applied to the top of the "free" or "adaptive" side 123 of the load cell body 125. When a vertical load is applied to the free end (i.e., the end not supported by the base) 123 of the load cell body 125, the load cell body 125 undergoes a slight deflection or distortion in which the bending beam assumes a double bending configuration having at least partial, and typically predominantly or substantially double bending behavior. The distortion is measurably sensed by strain gauge 120.

Thus, it can be seen that the planar load cell assembly 100 is a special case of a load cell assembly having the load beam and spring arrangement of fig. 1. In this case, the number of intermediate flexures is 2, so m and n are both equal to zero. Additionally, the intermediate flexures are intermediate flexure beam pairs connected by flexure bases. Similarly, a first end of the measuring beam is connected by a fixed end of the load cell body 125, while the opposite end is connected by an adaptive end 124 of the load cell body 125.

Load cell body 125 can be made from a mass of metal or alloy that is the texture of the load cell. For example, aluminum loaded sensor texture is a conventional and suitable material. In some embodiments, the alloy may advantageously be a magnesium alloy, typically comprising at least 85%, at least 90%, and in some cases at least 92%, at least 95%, or at least 98% magnesium by weight or by volume. The magnesium alloy should preferably be selected to have a modulus of elasticity (E) that is lower than that of aluminum, and preferably, significantly lower than that of aluminum.

The flexure arrangement and measurement beams of the planar load cell assembly should be sized and configured such that the broadside of load element 137 is approximately 90 ° (within ± 5 °, within ± 3 °, or within ± 2 °, within ± 1.5 °, within ± 1.0 °, within ± 0.5 °, within ± 0.3 °, within ± 0.25 °, within ± 0.20 °, within ± 0.15 °, within ± 0.12 °, or within ± 0.10 °) relative to the vertical or loaded direction under a "full load capacity" or a "nominal capacity" of the load cell when subjected to a load in an operational mode. The closer this arrangement is to 90 °, the higher the weighing accuracy.

As used herein in the specification and in the claims section that follows, the term "nominal capacity" or the like, as known in the art, refers to a load that affects 1 microstrain (0.1% of strain) over the length of the measurement beam.

Alternatively, where the thin load cell assembly is disposed in an operational or weighing mode, and where a load is disposed on the load element to achieve a nominal load capacity, the angle of the top surface of the load element with respect to horizontal is within ± 3 ° within ± 2 ° within ± 1.5 ° within ± 1 ° within ± 0.8 ° within ± 0.5 ° within ± 0.3 ° within ± 0.25 ° within ± 0.20 ° within ± 0.15 ° within ± 0.12 ° within ± 0.10 ° within ± 0.08 ° within ± 0.06 ° within ± 0.05 ° within ± 0.04 ° within ± 0.035 ° within ± 0.030 ° within ± 0.025 ° within ± 0.020 °.

Fig. 3A is a schematic top view of a planar load cell body according to an embodiment of the invention. FIG. 4 is an exemplary displacement graph illustrating the flexure arrangement and load cell arrangement of FIG. 3A in response to the deflection of a moment (Mz) along the transverse (Z) axis. Flexing reveals a mechanical hinge disposed in a generally transverse direction.

Fig. 5A to 5E are schematic top views of various planar load cell bodies according to embodiments of the present invention.

In some embodiments, two inventive load cell arrangements may form a double-ended planar load cell assembly having two planar load cell assemblies substantially similar or identical to that described above, but sharing a common unitary load cell body, and generally disposed at opposite ends thereof, optionally symmetrically disposed about a central transverse axis (Z-Z) of the load cell body.

In one typical configuration, the present planar load cell assembly includes a plurality of planar load cell assemblies sharing a single unitary load cell body, each having a lateral flexure arrangement mechanically bridging or connecting between a load element and a measurement beam. Typically, the load cell assembly may employ only these four planar load cells. Such an arrangement may exhibit significantly reduced cross-talk between load cells relative to 4 individual load cell bodies, or relative to 2 double-ended planar load cell assemblies.

FIG. 6 is a block diagram of a weigh scale or load cell assembly. An object to be weighed is placed on the top plate of the weighing scale of the present invention. During operation, vertical forces applied to the top deck are transferred to one or more of the load cell assemblies of the present invention (e.g., load cell assembly 100) configured to measure vertical forces. An electrical signal containing or associated with the weight information is communicated to the processor. The processor processes the signal or a modified form thereof to generate weight information, and this weight information may then be transmitted to, for example, a display device. The processor port may also be used for maintenance, calibration, or firmware updates.

FIG. 7 is an exploded view of an exemplary weight scale or load cell assembly 700 in accordance with one embodiment of the present invention. The weight scale 700 is typically a thin or (ultra-thin) flat scale, substantially as shown. The load scale 700 may include at least one load cell assembly, such as load cell assembly 705 (e.g., 4 load cell assemblies 105 as provided and described above, but only schematically illustrated here), or at least one double-ended planar load cell assembly (as described above), e.g., 2 such double-ended planar load cell assemblies.

The weigh scale 700 may have a solid top plate 720, the top plate 720 disposed above the load cell assembly 705, which may be attached to the load cell assembly 705 by mounting holes or elements 742 with a spacer or adapter plate 730 disposed therebetween. In the embodiment shown in fig. 7, each load cell assembly 705 is supported by a base, such as a weigh scale leg 750. In this implementation, the leg 750 may be attached to or associated with the load cell assembly 705 by a load contact region 740. Generally, an upper portion of the leg 750, or an element associated therewith (not shown), may protrude upwardly through the load contact area 740.

FIG. 8 is an exploded perspective view of a planar weigh scale or load cell assembly having a base plate according to an embodiment of the present invention. Each schematically illustrated load cell assembly 805 may be attached to a (typically single) base plate or base element 890. Such a base plate 890 may support a top plate or weighing surface 820 via at least one load cell assembly 805. In some embodiments, the top plate or weighing surface 820 may integrally include or be attached to a protruding element 822, the protruding element 822 adapted to pass through a load contact region 840 of the load cell assembly 805 in order to transfer a load to the load element 837.

The base plate 890 may be supported by one or more supports, such as legs 850, which may further be adapted to contact a floor or flat surface. Each load cell assembly 805 is anchored to a base plate or element 890, for example using fastening elements (not shown), such as bolts, as desired, and using spacers or adapter plates 830 through mounting holes or elements 842, or the like.

In the embodiment provided in FIG. 3, load cell assembly 100 may be adapted such that vertical impacts (e.g., objects that are struck with a large amount of force onto weighing platform 720) act primarily on flexures 127a-b and 117a-b while measurement beams 107a-b are largely or substantially entirely unaffected when secured within the weighing module (e.g., as depicted in FIG. 7 or FIG. 8). Thus, flexures 127a-b and 117a-b may act as vertical anti-vibration mechanisms for the measurement beams.

Examples

Reference is now made to the following examples, which together with the description provided above illustrate the invention in a non-limiting manner.

The vertical displacement of the various planar load sensors was evaluated experimentally. In these embodiments, the load cell body is made of aluminum 2024T3 with a sheet thickness of 2.0 mm. The capacity of each exemplary load cell is about 4 kg. Evaluation was performed by applying a transverse torque of 0.7kg cm and measuring the relative inclination angle in the transverse direction.

Comparative example 1

For a load cell having 2 intermediate longitudinal flexures disposed between the measurement beam and the load-receiving element, the relative tilt angle in the transverse direction is 0.59 °/(kg · cm), as shown in fig. 9A.

Comparative example 2

For a load cell with 3 intermediate longitudinal flexures disposed between the measurement beam and the load-receiving element, as shown in fig. 9B, the relative tilt angle in the transverse direction was 0.91 °/(kg-cm), an improvement of 0.32 °/(kg-cm) over the simpler design of fig. 9A. However, tooling costs are increased and, perhaps more importantly, there are physical tooling limitations with respect to the distance between the kerf lines, making this method of increasing the number of intermediate longitudinal flexures of limited value.

Example 3

The load cell of the present invention shown in figure 9C (the structure of this load cell can be seen more clearly in the schematic diagram provided in figure 9D) has only 1 intermediate longitudinal flexure disposed between the measurement beam and the load receiving element. However, the load cell also includes a lateral flexure mode adapted to increase lateral flexibility. The relative tilt angle of the load cell of the present invention in the lateral direction is 2.0 °/(kg · cm), an improvement of about 1.4 °/(kg · cm) over the simpler design of fig. 9A, and an improvement of more than 4 times is obtained using the design of fig. 9B.

It is noted that the vertical displacement achieved by the load cell of the present invention is about 1.5 times the vertical displacement achieved by the load cell of the comparative example. One consequence of this functionality is that overload protection may be significantly increased.

As used herein in the specification and in the claims section that follows, the terms "spring element" and "measurement beam" refer to a beam to which one or more strain gauges are attached or directly attached. Such strain gauges are not considered to be part of a "spring element" or "measuring beam".

As shown and described herein, the spring element or measurement beam is disposed along a longitudinal portion of the load cell body defined by a cutout window length of the spring element along a long dimension of the load cell body. At least one strain gauge associated with the spring element is positioned longitudinally within this longitudinal portion of the load cell body, typically between this cutout window and the closest longitudinal edge of the load cell body (i.e., generally parallel to the longitudinal axis).

As used herein in the specification and in the claims section that follows, the term "flexure beam" or the like refers to a spring element that is completely free of strain gauges.

As used herein in the specification and in the claims section that follows, the terms "flexure beam" and "spring element" are meant to have a length L_bWidth W_bAnd height H_bFor the beam L_b＞W_bAnd for the beam L_b＞H_b. More typically, L_b＞3·W_b、L_b＞ 5·W_bOr L_b＞7·W_bAnd/or L_b＞3·H_b、L_b＞5·H_b、L_b＞7·H_bOr L_b＞ l0·H_b。

As used herein in the specification and in the claims section that follows, the term "substantially" with respect to orientations and measurements such as "parallel," "along," and "central" is intended to limit deviation to

And (4) the following steps. More typically, this deviation isWithin a range of + -25%, + -20%, + -15%, + -10%, + -5%, + -3%, + -2%, + -1%, + -0.5%, + -0.2% or less.

It is to 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 subcombination.

While 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.

While 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. All publications, patents, and patent applications mentioned in this specification, including PCT publication number WO/2019/123440, are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

Claims

1. A planar load cell assembly, comprising:

at least one load cell arrangement disposed on a single metallic load cell body having a main axis, a central longitudinal axis, and a transverse axis disposed transverse to the main axis and the central longitudinal axis, a wide dimension of the load cell body being disposed perpendicular to the main axis;

each of the load cell arrangements comprises:

(a) a first continuous slit window passing through the wide dimension and formed by a first pair of slit lines disposed generally along or parallel to the central longitudinal axis and connected by a first slit base;

(b) a pair of measuring beams disposed along opposite edges of the load cell body and generally parallel to the central longitudinal axis, each of the measuring beams being longitudinally defined by a respective cut line of a first pair of cut lines, each of the pair of cut lines being disposed generally along or parallel to the central longitudinal axis;

(c) at least one strain gauge fixedly attached to a surface of a measurement beam of the measurement beams;

(d) a load element longitudinally defined by an innermost pair of said cut lines and extending from an innermost flexure base, said transverse axis passing through said load element, said load element adapted to receive a vertical load; and at least one of the following structural limitations:

(i) a hinge disposed in the metal load sensor body, the hinge having a transverse orientation relative to the primary axis and the central longitudinal axis;

(ii) at least one transverse flexure beam disposed in the metallic load cell body, the hinge having a transverse orientation relative to the primary axis and the central longitudinal axis; and

(iii) a lateral flexure arrangement disposed within the first continuous cutout window.

2. The planar load cell assembly of claim 1, wherein the angle of departure from said transverse axis of said transverse orientation is in the range of 0 ° to 70 °, 0 ° to 60 °, 0 ° to 45 °, 0 ° to 40 °, 0 ° to 35 °, 0 ° to 30 °, 0 ° to 25 °, or 0 ° to 20 °.

3. A planar load cell assembly as claimed in claim 1 or claim 2, wherein the lateral flexure arrangement is provided so as to mechanically bridge or connect between the load element and a spring arrangement of the load cell arrangement.

4. A planar load cell assembly, comprising:

each of the load cell arrangements comprises:

(a) at least a first pair of incision lines including an outermost pair of incision lines disposed generally along or generally parallel to the central longitudinal axis and passing through the wide dimension, the outermost pair of incision lines communicating with each other through a first cross-cut base to form a first continuous incision window passing through the wide dimension;

(b) a pair of gauging beams disposed along opposite edges of the load cell body and generally parallel to the central longitudinal axis, each of the gauging beams being longitudinally defined by a respective one of the outermost pair of the incision lines;

(d) a load element defined by a cutout arrangement, the transverse axis passing through the load element, the load element adapted to receive a vertical load; and

(e) a lateral flexure arrangement.

5. A double ended load cell assembly having two load cell arrangements provided on a single metallic load cell body, each of the load cell arrangements being in accordance with any one of claims 1 to 4.

6. The planar load cell assembly of any one of the preceding claims, wherein the metallic load cell body is made of a magnesium alloy, wherein the magnesium content of the magnesium alloy is in the range of 85% to 98%, 88% to 98%, 90% to 98%, or 92% to 98% by weight or by volume.

7. The planar load cell assembly of claim 6, wherein said magnesium alloy is selected or adapted such that its modulus of elasticity (E) is lower than the modulus of elasticity of load cell grade aluminum alloy 2023.

8. The planar load cell assembly of any of the preceding claims, wherein said load element, said second pair of flexure beams, said first pair of flexure beams and said pair of sense beams are mechanically arranged in series such that a load disposed on said load element acts on said second pair of flexure beams before acting on said first pair of flexure beams and acts on said first pair of flexure beams before acting on said pair of sense beams.