SINGLE BLOCK LOAD CELL FOR PRECISION ELECTRONIC WEIGHING BALANCE
Technical Field
The present invention relates to a single block load cell for precision electronic weighing balance to measure the weight of an article. The present invention particularly relates to a single block load cell for precision electronic weighing balance having flexure joints of reduced width to filter the torsional or twisting moments of applied weight. Background of the invention
Single block load cell is generally a weight transmitting means used for transmitting the weight force acting on the weighing platter to a weight force-sensing medium i.e. a transducer assembly having a permanent magnet and a force coil.
In a known electronic weighing balance in which a Roberval mechanism and a set of levers are used for transmitting weight force. The said Roberval mechanism and the set of levers are integrated and machined in a single block of material integrating both the mechanism and the joining links. However the present weight transfer mechanism, machined in a single block of material, has provision to filter the undesired torsional moments. This provision is in the form of a thin neck made in the middle of the lever connecting the Roberval mechanism to the rest of the levers. The thin neck is achieved by machining from both the sides of the thickness of the single block. Though weighing balance of this nature has a provision to filter the torsional moment, it has an inherent risk of damaging the joining link which is located prior to the location of the thin neck compounded with difficulty in machining from both sides and maintaining thin neck at the centre of the thickness of the block. This weighing balance also requires an additional length of block to accommodate the thin neck in position.
Objects of the present invention
The primary object of the present invention is to provide a single block load cell for precision measurement of weight of an article by filtering the torsional moments of the applied weight by means of flexure joints of reduced width.
An object of the present invention is to provide a single block load cell, with flexure joints of reduced width that are less stiff in torsion and absorbs the torsional forces due to reduced polar moment of inertia at flexure joints.

Yet another object of the present invention is to provide a single block load cell, which eliminates the necessity of providing an additional length of the block in order to incorporate a means to remove torsional moments.
Still another object of the present invention is to provide a single block load cell, which is capable of preventing the application of execessive load to the weight transmitting elements by way of restricting excessive movement of moving parts. Summary of the present invention
The present invention provides a single block load cell for electronic weighing balance for measuring the precision weight of an article, said single block load cell comprising; a stationary vertical portion (9), a movable vertical weight receiving portion (8), a pivotal element (7) connecting stationary vertical portion (9) on one side and a vertical weight receiving portion (8) on the other side by means of a plurality of links (17,18,19, 21, 22 & 23) and weight transmitting elements (5,6 & 20), a movable upper horizontal portion (3) in functional connectivity with said vertical weight receiving portion (8) through the plurality of links (17,18,19, 21, 22 & 23) and weight transmitting elements (5,6 & 20), a movable lower horizontal portion (4) in functional connectivity with said vertical weight receiving portion (8) through the plurality of links (17, 18,19, 21, 22 & 23) and weight transmitting elements (5,6 & 20), a pair of flexure joints (10 & 13) of reduced width and a surface profile, disposed on said upper and lower horizontal portions (3&4) respectively, said flexure joints (10 & 13) are in proximity to the vertical weight receiving portion (8), and a pair of flexure joints (11 & 12) without a reduction in their widths disposed on said upper and lower horizontal portions (3&4) respectively, said flexure joints (11&12) are in proximity to the stationary vertical portion (9), said flexure joints (10,13,ll&12) are connected through the plurality of links (17, 18, 19, 21, 22 & 23) and weight transmitting elements (5,6 & 20). In case the weight is loaded on the platter is not directly perpendicular, but is partially perpendicular then additional torsional or twisting moments are developed. In order to eliminate these torsional or twisting moments, it is necessary to prevent these torsional or twisting moments from being transmitted to pivotal element through the vertical weight-receiving portion. This is achieved by using the flexure joints which are reduced in their width by removing the metal content from both sides of the width of the single block load cell. The reduced width of the flexure joints absorbs the

torsional moments by becoming less stiffer in torsion because of reduced polar moment of
inertia.
Brief description of the drawings
The invention may best be understood by referring to the following description and
accompanying drawings that are used to illustrate embodiments of the invention. The
invention is illustrated by way of example in the embodiments and is not limited in the
figures of the accompanying drawings, in which like references indicate similar elements.
Fig 1 depicts the side view of the single block load cell of the present invention with the
weighing platter mounted on it.
Fig 2 is the isometric view of the single block loadcell.
Fig 2A and 2B illustrate exploded views of exemplary shape and surface profiles of the
reduced width portions of the load cell of the present invention.
Fig 3A depicts the cross section of the flexure joints of reduced width of the single block
load cell.
Fig 3B and 3C depict the obsorption of effect due to partially perpendicular weight by
reduced width of flexure
Fig 4 depicts the application of weight and the corresponding transmission of the weight.
when flexure (10 & 13) are reduced in width.
Fig 5 depicts the application of weight and the corresponding transmission of the weight.
when flexure (11 & 12) are reduced in width.
Figs 6 and 7 depict the working of the single block load cell when a partially perpendicular
load is acting on the weighing platter.
Fig 8 depicts various types of flexure joints.
Detailed description of the invention
The present invention provides a single block load cell for electronic weighing balance for
precision measurement of weight of an article. The single block load cell of the present
invention is now described by referring to the accompanied diagrams. Initially, by referring
to Figs 1 & 2, wherein a single block load cell (2) with a weighing platter (16) is shown.
The single block load cell (2) of the present invention is a metallic block, preferably of
rectangular shape. The weighing platter (16), is mounted on on one end of the single block
load cell (2) by means of a weighing platter support (1) for the placement of the selected

article that needs measurement of weight. The weighing platter support (1) is permanently fixed to single block loadcell by using fasteners. The weighing platter support (1) supports and also facilitates for the removal and placing the platter in postion. A set of four portions in a parllellogrammic shape is formed from an arrangement of a vertical weight receiving portion (8), a stationary vertical portion (9), an upper horizontal portion (3) and a lower horizontal portion (4). These four portions (8,9,3&4) are metal blocks disposed to form a parllellogrammic shape. The arrangement of said four portions of the single block load cell (2) forming parllellogrammic shape is now explained in detail.
The vertical weight receiving portion (8), which is connected to the weighing platter (16) on one side, said weight receiving portion (8) is disposed to receive a weight placed on the weighing platter (16). The stationary vertical portion (9), forming the other end of the single block load cell (2) is fixed to the weighing machine (not shown in this figure) by fastening screw members (14 & 15). By way of this construction, the two portions viz., the vertical weight receiving portion (8) and the stationary vertical portion (9) are disposed on either side of the single block load cell (2) to form two elements of the parallellogrammic shape of the single block load cell (2).
The upper horizontal portion (3) is arranged on the upper surface of the single block load cell (2) to extend from the weight receiving portion (8) on one side to the stationary vertical portion (9) on the other side. The upper horizontal portion (3) is perpendicular to the vertical weight receiving portion (8) and stationary vertical portion (9). The lower horizontal portion (4) is arranged at the bottom surface of the single block load cell (2) to extend from the weight receiving portion (8) on one side to the stationary vertical portion (9) on the other side. The lower and upper horizontal portions (3) and (4) are parallel to each other. These two lower and upper horizontal portions (3) and (4) form another set of elements of the parallellogrammic shape of the single block load cell (2). The upper and lower horizontal portions (3) and (4) are provided with horizontal gaps (24) and (25) respectively. These gaps (24) and (25) are provided to enable the displacement or movement of the vertical weight receiving block (8) in both vertical and lateral directions, on receiving weight from the weighing platter (16).
These four portions (8,9,3&4) are arranged in the single block load cell (2) of the present invention to a form a parallellogrammic shape since the opposite portions (3&4) and

(8&9) are equal in length and to achieve a parallel movement of the weight irrespective of the position of the weight on the weighing platter (16) without disturbing the orientation of the weighing platter (16).
The transmission of weight from the weighing platter (16) to the other portions of the single block load cell (2) is achieved by the combination of kinematic links and flexure joints as described hereinafter.
Normally, kinematic links are used to successively magnify the displacements or reduce the forces so that even a very small weight placed on the weighing platter (16) causing a small movement of the weighing platter (16) can be sensed. Flexures are used as substitutes for mechanical pin joints. These are used to eliminate error developed due to the presence of clearances in pin joints. By way of using the flexures the movement is transmitted through the bending of flexure joints.
The arrangement of the combination of kinematic links and the flexure joints comprises a plurality of weight transmitting units (5, 6 & 20) forming a kinematic link, a pivotal element (7) and a plurality of the flexure joints (17, 18, 19, 21, 22 & 23). The weight transmiitng units (5,6 & 20) are blocks of metal to effect the transmission of the applied weight. The plurality of flexure joints are realised by introducing local flexibility against bending or torsion by reducing the area of cross section locally. Therefore, the resultant motion of the applied weigth is transmitted through bending at flexure joints. It is to be note here that the total number of flexure joints that are desired in the single block load cell (2) also depends on the number of levers used in a kinematic link mechanism to achieve the desired magnification of displacement or reduction of forces. The lower end of the vertical weight-receiving portion (8) is connected to a flexure joint (17). The flexure joint (17) is cooperatively linked to the vertical weight-receiving portion (8) on one side and lower end of the weight-transmitting unit (5) on the other side. The cooperative linkage between the flexure joint (17) and the vertical weight receiving portion (8) is to convert the downward motion of the platter (16) as the downward motion of the joint (17) at which veritcal weight receiving portion (8) is connected to the vertical link (5). The vertical weight-transmitting unit (5) is arranged parallel to the vertical weight-receiving portion (8) on one side and to the stationary vertical portion (9) on the other side. A pair of slits or air gaps (26 & 27) positioned in between the vertical weight receiving

portion (8), stationary vertical portion (9) and the vertical weight-transmitting unit (5) is to provide movements to the vertical weight-transmitting unit (5) and vertical weight receiving portion (8). The vertical weight-transmitting unit (5) is substantially a rectangular block formed between the air gaps (26 & 27). A flexure joint (17) is disposed in proximity to the one end of the lower horizontal portion (4) connecting the vertical weight receiving portion (8) to the vertical weight-transmitting unit (5). A flexure joint (18) is connected to the other side of the vertical weight transmitting unit (5). As a result, the upper end of the vertical weight-transmitting unit (5) is also movably linked to the flexure joint (18). According to this constuction, the flexure joints (17 & 18) are disposed to transmit the weight from the vertical weight receiving portion (8) to the lateral weight-transmitting unit (6) of the single block load cell (2).
A flexure joint (19) connected to the flexure joint (18) to further transmit the weight motion in an axis parallel to the upper horizontal portion (3) and the lower horizontal portion (4) towards the stationary vertical portion (9). A lateral weight transmitting unit (6) is positioned between the flexure joint (18) and the flexure joint (19) to move laterally on application of the weight. In accordance with this construction, the flexure joint (19) functions as fulcrum for the lateral weight-transmitting unit (6) in respect to the stationary vertical block (9).
Therefore, the vertical weight force from the vertical weight-transmitting unit (5) is converted into horizontal weight force in the lateral weight transmitting unit (6) with the help of the flexure joints (18 and 19). The flexure joint (19) acts as a fulcrum for the lateral weight transmitting unit (6), such that the vertical weight force from the weight-transmitting unit (5) is converted into downward movement of the lateral weight transmitting unit (6) with the flexure joint (19) acting as a fulcrum.
A pivotal element (7), which is also a metal block formed at the end of kinematic link on which the force coil (not shown in the figures) is mounted using levers and fasteners. Shape of the pivotal element can be varied so as to facilitate to mount the levers holding the force coil. The arrows as shown in Fig 2 represent the movement of pivotal element (7) due to the weight placed on the weighing platter (16).
The pivotal element (7) is connected to the weight-transmitting unit (6) is further connected to a pivotal element (7) by means of a connecting lever (20). The connecting

lever (20) has two flexure joints, namely a flexure joint (22) cooperating with the transmitting unit (6) and a flexure joint (21) cooperating with the pivotal element (7), at both ends. These flexure joints (21 & 22) transmit the force in tandem between the transmitting unit (6) and the pivotal element (7). Another flexure joint (23) is provided which interconnects the pivotal element (7) to the stationary vertical portion (9) of the single block load cell of the present invention. Here, the flexure joint (23) functions as a fulcrum for the pivotal element (7) with respect to the stationary vertical portion (9). The pivotal element (7) of the single block load cell of the present invention is provided with a pair of hollow passages (A & B). The force coil, which is part of electromagnetic transducer assembly (not shown) comprising a force coil and a permanent magnet is connected to the pivotal element (7) by means of levers (not shown) and fasteners (not shown), utilizing the hollow passages (A & B) within the pivotal element (7). In the present invention, the plurality of flexure joints that can be used in the single block load cell (2) are now explained by referring to Fig 8 of the accompanied diagrams. Suitable flexure joints having different profiles can be used in flexure joints without affecting its desired functional output. As an exemplary embodiment some of the profiles of the flexure joints are depicted in Fig 8 of the accompanied diagrams.
In addtion to four portions (8,9,3 &4) arranged in the single block load cell (2) to a form a parallellogrammic shape to achieve a parallel movement of the weight irrespective of the position of the weight on the weighing platter (16) without disturbing the orientation of the weighing platter (16), in the present invention, now by referring to Fig 2A&2B, in order to achieve an accurate measurement of the weight, flexure joints of reduced width (10 & 13) are formed on the upper horizontal portion (3) and the lower horizontal portion (4). Now by specifically referring to Fig 2A, the flexure joints (10) & (13) as used in the present invention are described. A pair of flexure joints (10)&(13), which are having a profile surface and rectangular shaped in cross-section along the plane of weight acting, are formed at one end of the upper horizontal portion (3) and the lower horizontal portion (4). The width of the flexure joint (10), at one end of the upper horizontal portion (3) and in proximity to the vertical weight receiving portion (8), is reduced by removing material from both sides of the width of the single block loadcell (2), to make it less stiff in torsion.

Similarly, the flexure joint (13) is provided at one end of the lower horizontal portion (4), in proximity to the vertical weight receiving portion (8), said flexure joint (13) disposed to be in same axis as that of the flexure joint (10).
These flexure joints (10 & 13) of reduced width are provided to absorb the torsional or twisting moments which are developed due to partially perpendicular weight acting on the weighing platter (16) and to absorb the torsional or twisting moments before it is transmitted further for the measurement of the weight of an article with a desired accuracy. In the present invention flexure joints with reduced witdth (10&13) are shown, wherein these flexure joints (10&13) are in close proximity to the vertical weight receiving portion (8). However, it is also within the scope of the present invention, to provide a single block load cell (2) by making any one or more flexure joints (10,13,ll&12) of reduced width thereby resulting less stiff, the torque generated as result of the application of weight is absorbed, before transmitted further. One such exemplary embodiment is shown in Fig 2B. Flexure joints (10) & (13) are linked to the weighing platter (16) through the vertical weight transmitting block (8) of the single block loadcell (2).
The kinematic links which are linked to the four portions (8,9,3&4) forming the parallellogrammic shape of the single block load cell (2) are used to magnify the displacements or reduce the forces so that even a very small weight placed on the weighing platter (16) causing a small movement is sensed. Flexures or flexure joints are used in the single block load cell (2) as substitutes for elements like mechanical pin joints, to enable the transmission of motion through the bending of the flexure joints. The flexures joints of reduced width (10 &13) are further explained by referring to Fig 3 A, 3B and 3C of the accompanied diagrams. Fig 3A, depicts the cross section of the flexure joints of reduced width of the single block load cell of the present invention. The flexure joints (10 & 13) are reduced in their width by removing the metal content from both sides of the width of the single block load cell by process of machining. The flexure joints (10 & 13) of reduced width absorbs the torsional forces developed due to partially perpendicular weight force on the weighing platter (16), by becoming less stiffer in torsion because of redued polar moment of inertia. Whenever the partially perpendicular load is acting on one edge of the flexure joint (10) as shown in Fig 3B or on the opposite edge as shown in Fig 3C, the torsional moment developed due to partially perpendicular weight

force on the weighing platter is not transmitted to the kinematic links (5, 6 & 20), pivotal element (7), different flexure joints (17,18, 21 & 22) and to the fulcrums (19 & 23). This torsional force is absorbed by making any one or more of the flexures less stiff in torsion. So, flexure joints (10 & 13) are made less stiff so as to ensure that the torsional forces are absorbed even before reaching the links (3 & 4) and thereby to the pivotal element (7). Therefore, the present invention provides a single block load cell for electronic weighing balance for measuring weight of an article, said single block load cell comprising; a stationary vertical portion (9), a movable vertical weight receiving portion (8), a pivotal element (7) connecting stationary vertical portion (9) on one side and a vertical weight receiving portion (8) on the other side by means of a plurality of links (17,18,19, 21, 22 & 23) and weight transmitting elements (5,6 & 20), a movable upper horizontal portion (3) in functional connectivity with said vertical weight receiving portion (8) through the plurality of links (17,18,19, 21, 22 & 23) and weight transmitting elements (5,6 & 20), a movable lower horizontal portion (4) in functional connectivity with said vertical weight receiving portion (8) through the plurality of links (17,18,19, 21, 22 & 23) and weight transmitting elements (5,6&20), and a pair of flexure joints (10&13) of reduced width and a surface profile, disposed on said upper and lower horizontal portions (3&4) respectively, said flexure joints (10&13) are in proximity to the vertical weight receiving portion (8), a pair of flexure joints (11&12) without a reduction in their widths disposed on said upper and lower horizontal portions (3&4) respectively, said flexure joints (11&12) are in proximity to the stationary vertical portion(9),said flexure joints (10,13,ll&12)are connected through the plurality of links (17,18,19,21,22&23) and weight transmitting elements (5,6 &20). In one aspect of the present invention, the load cell wherein the flexure joints (11&12) are of reduced width and the flexure joints (10 & 13) are without a reduction in their width. In another aspect of the present invention, the load cell wherein the reduced width of flexure joints is at the end of the upper and lower horizontal portions (3 &4). In further aspect of the present invention, the load cell wherein surface profile of flexure joints of reduced width is in rectangular shape at the cross section along plane of weight. The functional aspects of the single block load cell (2) of the present invention are now explained by referring to Figs 4-5 of the accompanied diagrams. When a weight is placed on the weighing platter (16) it causes a downward motion of the weighing platter (16). The

downward motion of the platter (16) manifests itself as the downward motion of the point at which vertical weight receiving portion (8) is connected to the weight transmitting element (5) through a flexure (17) at one end. The same motion appears at the point of the weight transmitting element (6) where it is connected to the another end of the weight transmitting element (5) through another flexure (18). This results in an enlarged upward motion at the point of the weight transmitting element (6) where it is connected to another weight transmitting element (20) through a flexure (22). The same enlarged motion appears at the point of the pivotal element (7) where it is connected to the weight transmitting element (20) through a flexure (21). This causes an even more enlarged upward motion of the pivotal element (7) at its left extreme resulting in a similar motion of the magnetic coil mounted on it. This motion is opposed and neutralized by the magnetic restoring force. The path of transmittal of the weight from the weighing platter (16) through kinematic links of the flexure joints (17,18,22&21), weight transmitting element (5,6&20) and fulcrum (19&23) of the single block load cell (2) is depicted with arrows as shown in Figs 4 & 5.
Figs 6 & 7 depict the working of the single block load cell(2) when a partially perpendicular load is acting on the weighing platter (16). When a weight (W) is placed partially out of perpendicular on the weighing platter (16), the weight causes a downward motion of the weighing platter (16) and also a torsional moment "Q" or "R" as shown respectively in Figs 6&7. As shown in Fig(6), flexures (10)&(13) absorb the torsional moment developed due to the partially out of perpendicular weight on the platter (16) by being flexible to the extent of "Q" and in the direction as indicated. Accordingly, undesired torsional moments are absorbed, as explained in the previous paragraphs, by the flexures (10 &13 or 11&12) whose widths are reduced. The downward motion of the weighing platter (16) causes the displacement of the load cell by an amount and it is displaced from its original position as shown by perforated lines. The downward motion of the weighing platter (16) further causes the downward motion of the point at which the vertical weight-receving portion (8) is connected to the weight-transmitting unit (5) through a flexure joint (17). The same motion appears at the point of the lever (6) where it is connected to the top of the weight-transmitting unit (5) through another flexure joint (18). This results in an enlarged upward motion at the end point of the weight-transmitting

unit (6) where it is connected to another connecting lever (20) through a flexure joint (22). The same enlarged motion appears at the point of the lever i.e. pivotal element (7), where it is connected to the connecting lever (20) through a flexure joint (21). This causes even more enlarged motion of the pivotal element (7) at its extreme left position resulting in a similar motion of the force coil (not shown) mounted on it. This upward motion of force coil is caused by the partially perpendicular weight acting on the weighing platter (16) which resulted after absorbing the torsional moment by reduced width of flexure (10 &13). The measurement and display of the weight by using the load cell (2) of the present invention is performed in a known way by a transducer assembly (not shown in Figures) which comprises a permanent magnet and the force coil. Transducer assembly operates with reference to an initial value of zero position. The upward motion of the force coil, caused by the weight on the weighing (16) platter, disturbs the initial zero position, thus causing a change in the value of the current running through the force coil. Suitable electronic arrrangements can be used for converting the change in the value of the current into a numerical value and to display the same as an indication of the measured weight. Advantages
1. The single block load cell of the present invention is easy to be machined and also
saves on material wastage.
2. The torsional moments developed due to partially perpendicular weight forces on
weight platter are absorbed resulting accurate measurement of the weight. The removal
of torsional moments also results in preventing the flexure from the risk of being
damaged due to these forces.
Many different embodiments of the present invention may be constructed without departing from the spirit and scope of the invention. It should be understood that the present invention is not limited to the specific embodiments as described in the specification. The present invention is intended to cover various modifications and equivalent arrangements included within the scope and spirit of the claims.

We Claim:
1. A single block load cell for electronic weighing balance for measuring weight of an
article, said single block load cell comprising; a stationary vertical portion (9), a
movable vertical weight receiving portion (8), a pivotal element (7) connecting
stationary vertical portion (9) on one side and a vertical weight receiving portion (8) on
the other side by means of a plurality of links (17, 18, 19, 21, 22 and 23) and weight
transmitting elements (5,6 and 20), a movable upper horizontal portion (3) in
functional connectivity with said vertical weight receiving portion (8) through the
plurality of links (17, 18, 19, 21, 22 and 23) and weight transmitting elements (5,6 and
20), a movable lower horizontal portion (4) in functional connectivity with said vertical
weight receiving portion (8) through the plurality of links (17, 18, 19, 21, 22 and 23)
and weight transmitting elements (5,6 and 20), and a pair of flexure joints (10 and 13)
of reduced width and a surface profile, disposed on said upper and lower horizontal
portions (3 and 4) respectively, said flexure joints (10 and 13) are in proximity to the
vertical weight receiving portion (8), a pair of flexure joints (11 and 12) without a
reduction in their widths disposed on said upper and lower horizontal portions (3 and
4) respectively, said flexure joints (11 and 12) are in proximity to the stationary vertical
portion (9), said flexure joints (10,13,11 and 12) are connected through the plurality of
links (17,18,19, 21, 22 and 23) and weight transmitting elements (5,6 and 20).
2. The load cell of claim 1, wherein the flexure joints (11 and 12) are of reduced width
and the flexure joints (10 and 13) are without a reduction in their width.
3. The load cell of claim 1, wherein the reduced width of flexure joints is at the end of the
upper and lower horizontal portions (3 and 4).
4. The load cell of claim 1, wherein the surface profile of the flexure joints of reduced
width is in rectangular shape at the cross section along the plane of weight.