EP3990874A1

EP3990874A1 - Planar load cell assembly

Info

Publication number: EP3990874A1
Application number: EP20830831.2A
Authority: EP
Inventors: Michael Trakhimovich
Original assignee: SHEKEL SCALES (2008) Ltd
Current assignee: SHEKEL SCALES (2008) Ltd
Priority date: 2019-06-26
Filing date: 2020-06-19
Publication date: 2022-05-04
Also published as: GB201909216D0; IL289191A; EP3990874A4; AU2020307463A1; WO2020261075A1; CN114514415A

Abstract

An assembly including a load cell body having contiguous cutout windows, each formed by a pair of cutout lines and connected by a cutout base, the second window being transversely bounded by the first window,; measuring beams, disposed generally along edges of the body, each defined by a respective line of the first pair of cutout lines; first and second arrangements, each having a pair of flexure beams connected by first and second bases, respectively; a loading element, extending from the second base; and strain gages, attached to the beams, and a transverse flexural arrangement.

Description

PLANAR LOAD CELL ASSEMBLY

This invention claims priority from Great Britain Application Number 1909216.2, filed June 26, 2019, which application is incorporated by reference for all purposes as if fully set forth herein.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to weight measurement devices, and more particularly, to planar weighing devices employing load cell assemblies having integral flexures.

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 generally rectangular faces. Opposing surfaces of the load cell 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. When the weight on the platform is removed, the metallic load cell body is designed to return to an original, unstressed condition.

Planar load cells are known in the art, being disclosed, for example, in U.S. Patent No. 5,510,581, which patent is incorporated by reference for all purposes as if fully set forth herein. Planar-type load cells may have characteristically low amplitude signals. Parasitic noise may also be a major concern. For these and other reasons, high accuracy weight measurement may pose a considerable challenge.

The inventor has identified various deficiencies in planar load cell assemblies. These include deficiencies in weighing accuracy and sensitivity to off-center loading. SUMMARY

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 metal load cell body, the load cell body having a primary axis, a central longitudinal axis, and a transverse axis disposed transversely with respect to the primary and central longitudinal axes, a broad dimension of the load cell body being disposed perpendicular to the primary axis; each load cell arrangement including: (a) a first contiguous cutout window passing through the broad dimension and formed by a first pair of cutout lines disposed generally along or parallel to the central longitudinal axis, and connected by a first cutout 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 longitudinally defined by a respective cutout line of a first pair of cutout lines, each of the pair of cutout lines disposed generally along or parallel to the central longitudinal axis; (c) at least one strain gage, fixedly attached to a surface of a measuring beam of the measuring beams; (d) a loading element, longitudinally defined by an innermost pair of the cutout lines, and extending from an innermost flexure base, the transverse axis passing through the loading element, the loading element adapted to receive a vertical load; and at least one of the following structural limitations: (i) a hinge disposed in the metal load cell body, the hinge having a transverse orientation with respect to the primary and central longitudinal axes; (ii) at least one transverse flexure beam disposed in the metal load cell body, the hinge having a transverse orientation with respect to the primary and central longitudinal axes; and (iii) a transverse flexure arrangement disposed within the first contiguous cutout window.

According to further features in the described preferred embodiments, an angle of deviation from the transverse axis of the transverse orientation is within 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 transverse flexure arrangement is disposed so as to mechanically bridge or connect between the loading 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 metal load cell body, the load cell body having a primary axis, a central longitudinal axis, and a transverse axis disposed transversely with respect to the primary and central longitudinal axes, a broad dimension of the load cell body being disposed perpendicular to the primary axis; each load cell arrangement including: (a) at least a first pair of cutout lines, including an outermost pair of cutout lines, the outermost pair of cutout lines disposed generally along or generally parallel to the central longitudinal axis, and passing through the broad dimension, the outermost pair of cutout lines intercommunicating via a first transverse cutout base, to form a first contiguous cutout window passing through the broad dimension; (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 longitudinally defined by a respective cutout line of the outermost pair of the cutout lines; (c) at least one strain gage, fixedly attached to a surface of a measuring beam of the measuring beams; (d) a loading element, defined by [optionally an innermost] cutout arrangement, the transverse axis passing through the loading element, the loading element adapted to receive a vertical load; and (e) a transverse flexure arrangement.

According to still further features in the described preferred embodiments, there is disclosed a double-ended load cell assembly having two load cell arrangements disposed on a single metal load cell body, each of the load cell arrangements being in accordance with any of the above-described planar load cell assemblies, and/or in accordance with any of the planar load cell assemblies described hereinbelow.

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

According to still further features in the described preferred embodiments, the magnesium alloy is selected or adapted such that an elastic module (E) thereof is lower than that of load-cell grade aluminum alloy 2023.

According to still further features in the described preferred embodiments, the loading element, the second pair of flexure beams, the first pair of flexure beams, and the pair of measuring beams are mechanically disposed in series, such that a load disposed on the loading element acts upon the second pair of flexure beams prior to the first pair of flexure beams, and on the first pair of flexure beams prior to the pair of measuring beams. BRIEF DESCRIPTION OF THE DRAWINGS

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.

In the drawings:

Figure l is a block diagram of showing a series connection between the loaded loading beam and the measuring beam, via a flexure arrangement having at least two flexures, within a spring arrangement of a load cell assembly, according to embodiments of the present invention;

Figure 2 is a conventional schematic diagram of the strain gage electronics;

Figure 3 is a top, schematic view of a planar load cell arrangement, according to embodiments of the present invention;

Figure 3A is a top, schematic view of a planar load cell body, according to embodiments of the present invention;

Figure 4 is an exemplary displacement plot showing a deflection of the flexure arrangement and the load cell body of Figure 3 A, in response to a moment (Mz) along the transverse (Z) axis;

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

Figure 6 is a block diagram of a weighing scale or load cell assembly, according to embodiments of the present invention;

Figure 7 is an exploded perspective view of a planar weighing scale or load cell assembly, according to embodiments of the present invention;

Figure 8 is an exploded perspective view of a planar weighing scale or load cell assembly having a base plate, according to embodiments of the present invention;

Figures 9A and 9B are top views of (as yet unpublished) planar load cell assemblies of the inventor;

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

Figure 9D is a top, schematic view of the inventive planar load cell assembly of Figure 9C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles and operation of the low-profile 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.

Load cells with low profiles may have a characteristically low amplitude signal. Given limitations in the total weight to be measured, and the inherent sensitivity of load cells, the performance of such devices may be compromised by a high noise-to-signal ratio and by unacceptable settling times. Various embodiments of the present invention resolve, or at least appreciably reduce, parasitic noise issues associated with typical low profile load cells and enable high accuracy weight measurements.

Figure 1 is a block diagram schematically showing the operation of a spring arrangement, in loaded or operative mode, according to aspects of the present invention. Loading of the spring arrangement is effected by placing a load on, or below, the loading beam, depending on whether the loading beam is anchored to the weighing platform, or to the weighing base. As used herein and in the appended claims section, the loading beam may also be referred to as the“loading element” or as the“load-receiving element” or“load-supporting element” (depending on the configuration) of the load cell assembly. The spring arrangement may include - in addition to the measuring beam - a flexure arrangement (including at least one flexural element) operatively connected in series with the measuring beam. The flexure arrangement may be operatively connected, at a first end, to the loading beam, and at a second or opposite end, to the free or adaptive end of at least one measuring beam.

Substantially as shown, the flexure arrangement has n flexures ( n being an integer) operatively connected in series, the first of these flexures being operatively connected to the loading beam, and the ultimate flexure of the n flexures being operatively connected in series to a second flexure, which in turn, is operatively connected to the first flexure in an assembly of m flexures (m being an integer), operatively connected in series. The ultimate flexure of the m flexures is operatively connected, in series, to a measuring beam of the spring arrangement. Associated with the measuring beam is at least one strain gage, which produces weighing information with respect to the load.

At least two of such flexure arrangements, disposed in parallel, may be necessary for the loading element to be suitably disposed substantially in a horizontal position (i.e., perpendicular to the load). In some embodiments, and particularly when extremely high accuracy is not necessary, a single flexure disposed between the loading beam and the measuring beam may be sufficient. This single flexure load cell arrangement may also exhibit increased crosstalk with other load cell arrangements (weighing assemblies may typically have 4 of such load cell arrangements for a single weighing platform). For a given nominal capacity, the overload capacity may also be compromised with respect to load cell arrangements having a plurality of flexures disposed in series between the load receiving beam and the measuring beam. This reduced overload capacity may be manifested as poorer durability and/or shorter product lifetime, with respect to load cell arrangements having a plurality of flexures disposed in series. Nonetheless, the overall performance of the single-flexure arrangement may compare favorably with conventional weighing apparatus and load cell arrangements. In any event, for this case, m + n = -1.

When no intermediate longitudinal flexures are present (i.e., m + n = -2), the inventor has found that the arrangement is yet more compromised by crosstalk with other load cell arrangements, and the overload capacity may be yet further compromised.

Moreover, the inventor has found that when no intermediate longitudinal flexures are present, the planar load cell may exhibit poor or insufficient flexibility to transverse rotation.

The inventor has surprisingly found that by connecting the load-receiving element or tip to the measuring beams via a transverse (transversely disposed with respect to the longitudinal face of the load cell body) flexure arrangement, the overload protection is significantly increased.

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

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

The inventor has found that planar load cell sensitivity to various parasitical moments may be significantly reduced by increasing the load receiving element’s rotational flexibility in the transverse plane.

The inventor has discovered that by connecting the load-receiving element or tip to the weighing beams via at least one transverse flexure arrangement, the planar load cell may exhibit appreciably increased transverse flexibility, thereby reducing the parasitical moments. In addition, as described briefly hereinabove, this increased transverse flexibility may significantly contribute to the vertical displacement achieved by the load cell, thereby increasing the overload capacity of the load cell.

Typically, there are 4 strain gages per loading beam. Figure 2 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 strain gages may be configured in a Wheatstone bridge configuration, a configuration that is well known to those of skill in the art. 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.

With reference now to the Figures 3, Figure 3 is a top, schematic view of a planar load cell assembly 100, according to an embodiment of the present invention;

A load cell body 125 of planar load cell assembly 100 may be made from a block of load cell quality metal or alloy. Particularly advantageous embodiments employing particular magnesium alloys will be described hereinbelow.

Load cell body 125 may be fixed to a weighing assembly via one or more mounting holes or elements 142. A 1^st, typically contiguous cutout window 116 passes from a top face 110 through a bottom face 112, perpendicularly through the broad dimension (i.e., with respect to the other 2 dimensions of a three-dimensional Cartesian system) of load cell body 125. 1^st contiguous cutout window 116 may be generally C-shaped or U-shaped, and may have arms or a pair of cutout lines 118a, 118b running generally parallel to a central longitudinal axis 102 of load cell body 125, and connected or made contiguous by a cutout line or cutout base 118c. Both central longitudinal axis 102 and a transverse axis 104, disposed transversely thereto, run generally parallel to the broad dimension of load cell body 125. Both of these axes may be oriented in generally perpendicular fashion with respect to a primary axis 114. The thickness of load cell body 125 perpendicular to primary axis 114 is typically within a range of 1.5mm to 10mm, or 2mm to 10mm, and is designated WLCB.

Long sides 105a and 105b of load cell body 125 run generally along, or generally parallel to, central longitudinal axis 102.

As shown, measuring beams or spring elements 107a and 107b are each disposed between respective cutout lines 118a and 118b, and respective long sides 105a and 105b of load cell body 125, distal to cutout lines 118a and 118b with respect to transverse axis 104. When planar load cell assembly 100 is disposed in a vertically loaded position, the free end of each of beams 107a and 107b may be held in a fixed relationship, substantially perpendicular to the vertical load, by an end block 124 disposed at a free end 123 of load cell body 125.

A 2^nd, typically contiguous cutout window 126 also passes from top face 110 through bottom face 112, perpendicularly through the broad dimension of load cell body 125. 2^nd cutout window 126 may be generally C-shaped or U-shaped, and may have arms or a pair of cutout lines 128a, 128b running generally parallel to central longitudinal axis 102, and connected or made contiguous by a cutout line or cutout base 128c. 2^nd cutout window 126 may be enveloped on three sides by 1^st cutout window 116 (such that the 2^nd cutout window is transversely bounded by the 1^st contiguous cutout window). The orientation of 2^nd cutout window 126 may be 180° (i.e., generally opposite) with respect to 1^st cutout window 116.

Load cell body 125 has a first flexure arrangement having a first pair of flexure beams 117a, 117b disposed along opposite sides of central longitudinal axis 102, and distal and parallel thereto. First pair of flexure beams 117a, 117b may be longitudinally disposed between the first pair of cutout lines and the second pair of cutout lines, and mechanically connected or coupled by a first flexure base 119.

As shown, load cell body 125 has a second flexure arrangement 126 that may optionally be generally longitudinal. The second flexure arrangement may have a second pair of flexure beams 127a, 127b disposed along opposite sides of central longitudinal axis 102, and distal and optionally generally parallel thereto. Second pair of flexure beams 127a, 127b may be longitudinally disposed between the first pair of cutout lines and the second pair of cutout lines, and mechanically connected or coupled by a second flexure base 129.

A transverse flexure arrangement 136 may be disposed within 1^st (outermost) cutout window 116, and more typically, within 2^nd (or innermost) cutout window 126 as well. Typically, transverse flexure arrangement 136 may be disposed so as to mechanically bridge or connect between loading element 137 and the spring arrangement, e.g ., to or via second flexure base 129 and/or first flexure base 119.

Transverse flexure arrangement 136 may include at least one transverse flexure beam such as transverse flexure beams 138a, 138b and 138c. Such beams may be disposed on either side or both sides of a loading area or load-contact area 140, which is described in further detail hereinbelow.

As used herein in the specification and in the claims section that follows, the term“transverse flexure beam” is used as would be understood to those of skill in the art. For the avoidance of doubt, such a transverse flexure beam may be a flexure beam disposed at an angle with respect to the traverse axis, such that the beam has a transverse component (e.g., related to the cosine of the angle of deviation from the transverse axis). Typically, the angle of deviation from the transverse axis of such transverse flexure beams is within 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°.

Transverse flexure beams 138a, 138b and 138c may be formed by one or more cutout structures 179a, 179a having comb-like cutout lines including a cutout backbone line 180a, 180b, and one or more transverse cutout lines 181a, substantially as shown. Typically, the angle of deviation from the transverse axis of such transverse cutout lines is within 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°

Cutout structures 179a, 179a may be spaced and dimensioned such that transverse flexure arrangement 136 has a labyrinth or labyrinth-like transverse flexure beam structure.

More generally, the transverse flexure beams may be disposed and dimensioned to form a transverse hinge having a transverse character or component. Typically, the angle of deviation from the transverse axis of such a transverse hinge is within 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°

A dimensionless parameter (D_tb) characterizing transverse beam length (L_tb) may be defined as follows:

Dtb = Ltb / Wi b

where W _b is the width of the load cell body in the transverse direction. The inventor has found that the length of such beams in the transverse direction may be such that D_tb is 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_tb is within a 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 cutout lines described above may typically 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 0.5mm.

In some embodiments, the ratio of Wco to WLCB (WCO AVLCB) 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, the ratio of Wco to WLCB (WCO AVLCB) is within a 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. Loading element 137 may also include a loading area or load-contact area 140, which may be the threading of a hole ( e.g ., the threading being for receiving a load, e.g, for receiving or connecting to an upper, weighing platform, or for supporting a load, e.g. , connecting to a base, leg, or support (disposed below load cell body 125) of a weighing system (described with respect to Figure 11). Loading area or load-contact area 140 may be positioned at an intersection of central longitudinal axis 102 and transverse axis 104.

In the exemplary embodiment provided in Figure 3, first and second flexure arrangements may form a generally longitudinal flexure arrangement 180, mechanically disposed between loading element 137 and measuring beams or spring elements 107a and 107b.

At least one strain gage, such as strain (or“strain-sensing”) gages 120, may be fixedly attached to a surface (typically a top or bottom surface) of each of measuring beams 107a and 107b. Strain gages 120 may be adapted and positioned to measure the strains caused by a force applied to the top of the“free” or“adaptive” side 123 of load cell body 125. When a vertical load acts on free end (i.e., an end unsupported by the base) 123 of load cell body 125, load cell body 125 undergoes a slight deflection or distortion, with the bending beams assuming a double-bending configuration having an at least partial, and typically primarily or substantially, double-bending behavior. The distortion is measurably sensed by strain gages 120.

It may thus be seen that planar load cell assembly 100 is a particular case of a load cell assembly having the load beam and spring arrangement of Figure 1. In this case, the number of intermediate flexures is 2, such that m and n both equal zero. In addition, the intermediate flexures are intermediate flexure beam pairs connected by a flexure base. Similarly, the measuring beams are connected at a first end by the fixed end of load cell body 125, and at the opposite end by adaptive end 124 of load cell body 125.

A load cell body 125 may be made from a block of load cell quality metal or alloy. For example, load cell quality aluminum is one conventional and suitable material. In some embodiments, the alloy may advantageously be a magnesium alloy, typically containing 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 an elastic module (E) that is lower, and preferably, significantly lower, than that of aluminum.

The flexure arrangements and measuring beams of the planar load cell assembly should be dimensioned and structured such that under loading in an operative mode, the broad face of loading element 137 is close to 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°, with respect to the vertical or the direction of the load, at“full capacity” or“nominal capacity” of the load cell. The closer such a configuration is to 90°, the greater the weighing accuracy.

As used herein in the specification and in the claims section that follows, the term“nominal capacity”, and the like, as known in the art, is the load that effects 1 microstrain (0.1% of the strain) in the length of the measuring beam.

Alternatively, with the low-profile load cell assembly disposed in an operative or weighing mode, and with a load disposed on the loading element so as to achieve the nominal load capacity, an angle of a top surface of the loading 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°, or within ±0.020°.

Figure 3A is a top, schematic view of a planar load cell body, according to embodiments of the present invention. Figure 4 is an exemplary displacement plot showing a deflection of the flexure arrangement and the load cell arrangement of Figure 3A, in response to a moment (Mz) along the transverse (Z) axis. The deflection reveals a mechanical hinge disposed in a generally transverse direction.

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

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

In one typical configuration, the inventive planar load cell assembly includes a plurality of planar load cells sharing a single, integral load cell body, each planar load cell assembly having a transverse flexure arrangement mechanically bridging or connecting between the loading element and the measuring beam. Typically, a load cell assembly may employ solely these four planar load cells. Such an arrangement may exhibit appreciably reduced crosstalk between load cells, with respect to 4 individual load cell bodies, or with respect to 2 double-ended planar load cell assemblies.

Figure 6 is a block diagram of a weighing scale or load cell assembly. An object to be weighed is placed on the top plate of a weighing scale of the present invention. During operation, vertical forces applied to the top plate are transferred to one or more of the inventive load cell assemblies ( e.g ., load cell assembly 100) configured to measure vertical forces. Electrical signals containing, or correlated with, weight information, are communicated with a processor. The processor processes the signals, or adaptations thereof, to produce weight information, and may then transmit this weight information, for example, to a display device. A processor port may also be available for maintenance, calibration or firmware updates.

Figure 7 is an exploded view of an exemplary weighing scale or load cell assembly 700, according to one embodiment of the present invention. Weighing scale 700 is typically a low-profile or (ultra-low profile) planar weighing scale, substantially as shown. Weighing scale 700 may include at least one load cell assembly such as load cell assembly 705 (e.g., 4 of load cell assemblies 105, as provided and described hereinabove, but shown only schematically here), or at least one double-ended planar load cell assembly (as described hereinabove), by way of example, 2 of such double-ended planar load cell assemblies.

Weighing scale 700 may have a solid top plate 720 disposed above load cell assemblies 705, which may attach to load cell assembly 705 via mounting holes or elements 742, with shims or adapter plates 730 disposed therebetween. In the embodiment shown in Figure 7, each load cell assembly 705 is supported by a base such as weighing scale leg 750. In this embodiment, leg 750 may be attached to, or associated with, load cell assembly 705 via a load contacting area 740. Typically, an upper portion of leg 750, or an element associated therewith (not shown), may protrude up through load contacting area 740.

Figure 8 is an exploded perspective view of a planar weighing scale or load cell assembly having a base plate, according to embodiments of the present invention. Each schematically-shown load cell assembly 805 may be attached to a (typically single) base plate or base element 890. Such a base plate 890 may support top plate or weighing surface 820 via at least one load cell assembly 805. In some embodiments, top plate or weighing surface 820 may integrally include, or be attached to, a protruding element 822, adapted to pass through a load contacting area 840 of load cell assembly 805, so as to deliver a load to loading element 837.

Base plate 890 may be supported by one or more supports such as leg 850, which may be further adapted to make contact with a flooring or flat surface. Each load cell assembly 805 is anchored to base plate or base element 890 via mounting holes or elements 842, e.g ., using fastening elements such as bolts (not shown), and using shims or adapter plates 830, or the like, as necessary.

In the embodiment provided in Figure 3, load cell assembly 100 may be adapted, when secured within a weighing module (e.g, as described in Figure 7 or in Figure 8), such that a vertical impact (e.g, an object that is slammed down with great force onto weighing platform 720) acts mainly upon flexures 127a-b and 117a-b, while measuring beams 107a-b remain largely or substantially completely unaffected. Thus, flexures 127a-b and 117a-b may serve as a vertical shock-protection mechanism for the measuring beams.

EXAMPLES

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

The vertical displacement of various planar load cells was evaluated experimentally. In these examples, the load cell bodies were fabricated from aluminum 2024 T3 having a sheet thickness of 2.0 mm. The capacity of each exemplary load cell was approximately 4 kg. Evaluation was performed by applying a transverse torque of 0.7 kg*cm, and measuring the relative angle of inclination in the transverse direction.

COMPARATIVE EXAMPLE 1

For a load cell having 2 intermediate longitudinal flexures disposed between the measuring beam and the load receiving element, shown in Figure 9A, the relative angle of inclination in the transverse direction was 0 597(kg*cm)

COMPARATIVE EXAMPLE 2

For a load cell having 3 intermediate longitudinal flexures disposed between the measuring beam and the load receiving element, shown in Figure 9B, the relative angle of inclination in the transverse direction was 0 917(kg*cm), an improvement of 0 327(kg*cm) with respect to the more simple design of Figure 9A. However, the machining cost is increased, and perhaps more significantly, there are physical machining limitations with respect to the distance between cutout lines, such that this approach of increasing the number of intermediate longitudinal flexures is of limited value.

EXAMPLE 3

The inventive load cell shown in Figure 9C (the structure of this load cell may be more clearly viewed in the schematic drawing provided in Figure 9D) has only 1 intermediate longitudinal flexure disposed between the measuring beam and the load receiving element. However, the load cell further includes a transverse flexure pattern adapted to increase transverse flexibility. The relative angle of inclination in the transverse direction for this inventive load cell was 2 07(kg*cm), an improvement of about 1.4 (kg*cm) with respect to the more simple design of Figure 9A, over 4 times the improvement attained utilizing the design of Figure 9B.

Significantly, the vertical displacement achieved by this inventive load cell was approximately 1.5 times larger than the vertical displacement achieved by the load cells of the comparative examples. One ramification of this feature 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“measuring beam” refer to a beam having one or more strain gages attached or directly attached therewith. Such strain gages are not considered to be part of the“spring element” or“measuring beam”.

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

As used herein in the specification and in the claims section that follows, the term“flexure beam”, and the like, refers to a spring element that is devoid of strain gages.

As used herein in the specification and in the claims section that follows, the terms“flexure beam” and“spring element” refer to beams having a length L_b, a width W_b, and a height ¾, for which L_b > W_b, and for which L_b > ¾. More typically, L_b > 3*W_b, L_b > 5*W_b, or L_b > 7*W_b, and/or L_b > 3·¾, L_b > 5·¾, L_b > 7·¾, or L_b > 10*H_b.

As used herein in the specification and in the claims section that follows, the term“generally”, with respect to orientations and measurements such as“parallel”, “along”, and“central”, is meant to limit the deviation to within ±30%. More typically, this deviation is within ±25%, ±20%, ±15%, ±10%, ±5%, ±3%, ±2%, ±1%, ±0.5%, ±0.2%, or less.

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.

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.

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. 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

WHAT IS CLAIMED IS:

1. A planar load cell assembly comprising:

at least one load cell arrangement disposed on a single metal load cell body, said load cell body having a primary axis, a central longitudinal axis, and a transverse axis disposed transversely with respect to said primary and central longitudinal axes, a broad dimension of said load cell body being disposed perpendicular to said primary axis;

each said load cell arrangement including:

(a) a first contiguous cutout window passing through said broad dimension and formed by a first pair of cutout lines disposed generally along or parallel to said central longitudinal axis, and connected by a first cutout base;

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

(c) at least one strain gage, fixedly attached to a surface of a measuring beam of said measuring beams;

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

(i) a hinge disposed in said metal load cell body, said hinge having a transverse orientation with respect to said primary and central longitudinal axes;

(ii) at least one transverse flexure beam disposed in said metal load cell body, said hinge having a transverse orientation with respect to said primary and central longitudinal axes; and

(iii) a transverse flexure arrangement disposed within said first contiguous cutout window.

2. The planar load cell assembly of claim 1, wherein an angle of deviation from the transverse axis of said transverse orientation is within 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°

3. The planar load cell assembly of claim 1 or claim 2, wherein said transverse flexure arrangement is disposed so as to mechanically bridge or connect between said loading element and a spring arrangement of said load cell arrangement.

4. A planar load cell assembly comprising:

each said load cell arrangement including:

(a) at least a first pair of cutout lines, including an outermost pair of cutout lines, said outermost pair of cutout lines disposed generally along or generally parallel to said central longitudinal axis, and passing through said broad dimension, said outermost pair of cutout lines intercommunicating via a first transverse cutout base, to form a first contiguous cutout window passing through said broad dimension;

(b) a pair of measuring beams, disposed along opposite edges of said load cell body, and generally parallel to said central longitudinal axis, each of said measuring beams longitudinally defined by a respective cutout line of said outermost pair of said cutout lines;

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

(e) a transverse flexure arrangement.

5. A double-ended load cell assembly having two load cell arrangements disposed on a single metal load cell body, each of said 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 said metal load cell body is made of a magnesium alloy, wherein a magnesium content of said magnesium alloy, by weight or by volume, is within a range of 85% to 98%, 88% to 98%, 90% to 98%, or 92% to 98%.

7. The planar load cell assembly of claim 6, wherein said magnesium alloy is selected or adapted such that an elastic module (E) thereof is lower than that of load-cell grade aluminum alloy 2023.

8. The planar load cell assembly of any one of the preceding claims, wherein said loading element, said second pair of flexure beams, said first pair of flexure beams, and said pair of measuring beams are mechanically disposed in series, such that a load disposed on said loading element acts upon said second pair of flexure beams prior to said first pair of flexure beams, and on said first pair of flexure beams prior to said pair of measuring beams.