U.S. patent application number 09/146890 was filed with the patent office on 2002-01-03 for load cell with bossed sensor plate for an electrical weighing scale.
Invention is credited to GERMANTON, DAMON, GROSS, CHRIS.
Application Number | 20020000338 09/146890 |
Document ID | / |
Family ID | 22519441 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020000338 |
Kind Code |
A1 |
GROSS, CHRIS ; et
al. |
January 3, 2002 |
LOAD CELL WITH BOSSED SENSOR PLATE FOR AN ELECTRICAL WEIGHING
SCALE
Abstract
A sensor plate for use in a load cell for use in an electronic
scale comprising a planar first surface; a planar second surface
opposite the first surface having a depression formed therein
defining a flexure area; a load cavity formed in the second surface
having a conical receptacle end for receiving a strut; and sensors
disposed over the flexure area for generating a signal in response
to a load applied to the loading cavity wherein the strut has a
first conical projection end coupled to the conical receptacle end
of the loading cavity and a second end coupled to a footer member
such that the strut mechanically floats therebetween for providing
the applied load at a substantially central position at the load
cavity.
Inventors: |
GROSS, CHRIS; (YORKTOWN,
VA) ; GERMANTON, DAMON; (KENNALON, NJ) |
Correspondence
Address: |
ARTHUR L. PLEVY, ESQ.
DUANE, MORRIS & HECKSCHER, LLP
100 COLLEGE ROAD WEST, SUITE 100
PRINCETON
NJ
08540-6604
US
|
Family ID: |
22519441 |
Appl. No.: |
09/146890 |
Filed: |
September 3, 1998 |
Current U.S.
Class: |
177/211 |
Current CPC
Class: |
G01G 3/12 20130101 |
Class at
Publication: |
177/211 |
International
Class: |
G01G 003/14; G01G
003/08 |
Claims
What is claimed is:
1. A sensor plate for use in a load cell for an electronic scale
comprising: a planar first surface; a planar second surface
opposite said first surface having a depression formed therein
defining a flexure area; a load cavity formed in said second
surface having a conical end for receiving a floating strut; sensor
means disposed over said flexure area for generating a signal in
response to a load applied to said load cavity via said floating
strut, wherein said floating strut has a first projection coupled
to said conical end of said load cavity and a second projection end
coupled to a footer member such that said strut mechanically floats
therebetween for providing said applied load at a substantially
central position of said load cavity.
2. The sensor plate according to claim 1, wherein said flexure area
defines first and second flexure portions on which is disposed said
sensor means.
3. The sensor plate according to claim 2, wherein said load cavity
is positioned at substantially a center position of said sensor
plate.
4. The sensor plate according to claim 3, wherein said sensor means
is disposed on both of said flexure portions.
5. The sensor plate according to claim 4, wherein said sensor means
includes a pair of strain gauges disposed on each of said first and
second flexure portions, said strain gauges on first flexure
portion is cross coupled to said strain gauges on said second
flexure portion to equalize forces sent by said strain gauges in
response to an applied load.
6. The sensor plate according to claim 1, said strut having first
and second oppositely disposed conical projections engaging said
load cavity conical end and said footer member operative to
concentrate an applied load into said load cavity at a central
position.
7. The sensor plate according to claim 2, wherein said flexure
portions includes first and second strain gauges disposed thereon
and wherein deflections of said load cavity generate bending
moments in said flexure beams which places said first strain gauge
into tension and said second strain gauge into compression.
8. The sensor plate according to claim 1, wherein said flexure area
has a thickness of between 5 and 8 times less than a thickness
associated with said sensor plate.
9. A load cell for use in an electronic weighing scale comprising:
a sensor plate having a flexure area coupled between a loading
cavity having a conical end portion for receiving a strut, said
strut having a first conical projection engaging said loading
cavity and a second conical projection engaging an indentation
within a footer member for receiving an applied load, wherein said
strut is floatingly coupled between said sensor plate and said
footer member for transferring said applied load to said loading
cavity at a substantially central point; and sensor means disposed
on said flexure area for generating an electrical signal in
response to said transferred load applied to said loading cavity of
said sensor plate, wherein said electrical signal is indicative of
said applied load.
10. The load cell according to claim 9, wherein said sensor plate
is substantially rectangular in shape.
11. The load cell according to claim 9, wherein said sensor means
includes a pair of strain gauges disposed on a portion of said
flexure area.
12. The load cell according to claim 11, wherein said strain gauges
on a first portion of said flexure area are cross coupled with said
strain gauges on a second portion of said flexure area to equalize
forces sensed by said strain gauges in response to an applied
load.
13. The load cell according to claim 12, wherein deflection of said
load cavity by said strut generates bending moments in said flexure
area which places said first strain gauge in contention and said
second strain gauge into compression.
14. The load cell according to claim 13, wherein said sensor plate
is sandwiched between a housing and said floating strut.
15. The load cell according to claim 14, wherein said footer member
is positioned within a spiral bias member.
16. An electronic scale for displaying the weight of a load applied
to said scale comprising: a platform; a plurality of load cells
attached to said platform for elevating said platform above a
supporting surface, each of said load cells supporting a portion of
a load and including a bossed diaphragm sensor plate having a
loading cavity, a flexure area and sensor means disposed on said
flexure area for generating an electrical signal is response to a
load applied to said loading cavity of said sensor plate, said
electrical signal being indicative of an applied load, wherein said
load applied to said loading cavity occurs via a strut having a
conical projection engaging a corresponding conical receptacle in
said loading cavity, said strut having a second conical projection
engaging a similarly shaped receptacle in a footer member such that
said strut is floatingly retained between said footer member and
said sensor plate; and display means for receiving said electrical
signals generated by said sensor plate in each of said load cells
and displaying the weight of the load.
17. The electronic scale according to claim 16, wherein said sensor
means include a pair of strain gauges disposed on first and second
portions of said flexure area, said strain gauges on said first
flexure area portion cross coupled with said strain gauges on said
second flexure area portion to equalize forces sensed by said
strain gauges in response to an applied load.
18. The electronic scale according to claim 15, wherein said sensor
means include a first and second strain gauges wherein deflection
of said loading cavity generates bending moments in said flexure
area, which places said first strain gauge into contention and said
second strain gauge into compression.
19. The electronic scale according to claim 18, wherein said sensor
plate comprises a first planar surface on which is disposed said
sensor means and a second surface opposite said first surface
having a depression formed therein defining said flexure area.
20. The electronic scale according to claim 19, wherein said first
planar surface includes a bonding pad and electrical
interconnections for electrically communicating with other said
load cells.
21. A load cell for use in an electronic weighing scale comprising:
a bossed diaphragm sensor plate having a conical strut engaging a
portion of said bossed diaphragm sensor plate for applying a force
thereto; and sensor means disposed on said bossed diaphragm sensor
plate for generating an electrical signal indicative of said
applied force.
22. The load cell according to claim 21, further comprising means
for fixedly positioning said conical strut at a first end; and a
movable backing plate engaging a perimeter portion of said bossed
diaphragm plate and operative to move laterally in consonance with
said bossed diaphragm sensor plate for maintaining engagement said
conical strut at a substantially center position within said bossed
diaphragm sensor plate, in response to an off-axis applied
force.
23. The load cell according to claim 21, wherein said sensor means
includes a pair of strain gauges disposed on a flexure area of said
sensor plate, said flexure area having a thickness tless than a
thickness T associated with a perimeter portion of sensor
plate.
24. The load cell according to claim 22, wherein said backing plate
is fixed in a vertical direction.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to electronic type platform
weighing systems, and more particularly to an improved load cell
and sensor plate for use in an electronic weighing scale.
BACKGROUND OF THE INVENTION
[0002] There are many different types of electronic weighing scales
in use today. One popular type of electronic weighing scale is
constructed with a platform for receiving the load to be weighed
and a set of levers, pivots, flexures, and torque tubes to
mechanically combine the forces applied to the platform by the
load, thereby enabling the measurement of these forces with a
single electronic load cell. The load cell is typically constructed
with a mechanically-deformable sensor plate which operates as a
force transducer. The sensor plate has bonded thereto one or more
sensor elements that serve to convert the mechanical bending forces
of the sensor plate into electrical signals. When a load is applied
to such a load cell, the sensor elements bonded to the sensor plate
produce electrical signals which are proportional to the load
applied to the load cell.
[0003] Another popular type of electronic weighing scale is
constructed with a platform which is supported by several
electronic load cells which each produce an output signal. The
output signals of the load cells are electrically averaged to
enable forces to be measured over a large area of the platform.
[0004] The sensor plates employed in the load cells described
above, are of many different designs. One such load plate design is
exemplified in U.S. Pat. No. 4,020,686 issued to Brendel.
[0005] The sensor plate disclosed therein is constructed with a
rigid force input section, a rigid force output section, and an
intermediate force moment carrying section coupled between the
force input and output sections. The sections are interconnected by
four horizontal flexural elements, four vertical flexural elements,
a pair of force measuring members, and a pair of connecting
structures. This design allows forces to be measured along a first
axis of the sensor plate and also moments about a second axis of
the sensor plate which is perpendicular to the first I . axis.
However, the rather tall profile of this sensor plate design
undesirably imposes minimum thickness requirements on the weighing
scales.
[0006] Another load plate design can be seen in U.S. Pat. No.
4,993,506 issued to Angel. The sensor plate disclosed therein is
fabricated from a single, flat metal stamping consisting of a flat
flexure beam where strain sensors are bonded, a flat U-shaped
loaded element attached to one end of the flexure beam, and a flat
mounting element attached to the other end of the flexure beam.
[0007] Still another load plate design is described in U.S. Pat.
No. 4,548,086 issued to Kastel. The sensor plate of Kastel is
fabricated from an areal spring material and is provided with a
force introducing section, a clamping section, and an intermediate
section connected to the force introducing section and the clamping
section by flexural webs which are equipped with sensor
elements.
[0008] The sensor plates described in U.S. Pat. Nos. 4,993,506 and
4,548,086 are relatively thin and thus, are used in low profile
scale designs which are presently very popular. Although these
sensor plate designs are relatively inexpensive to produce compared
with earlier designs, further reductions in machining costs and the
like are desirable.
[0009] Furthermore, prior art systems also utilize sensor plates
having surfaces which have corregated or slotted rather than flat
planar surfaces. This causes significant problems in attachment of
electronic wires and/or electronic devices to the plate. Still
further, numerous problems exist in the prior art regarding
off-axis application of a load to the sensor plate. Such
misalignment causes calibration and/or weight calculation errors,
thus minimizing the accuracy of the scale.
[0010] Accordingly, there remains a need for an improved sensor
plate and a load cell for use in electronic weighing scales which
is reliable, accurate, and substantially simple and economical to
manufacture.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a sensor
plate for use in a load cell for use in an electronic scale
comprising a planar first surface; a planar second surface opposite
the first surface having a depression formed therein defining a
flexure area; a load cavity formed in the second surface having a
conical receptacle end for receiving a strut; and sensor means
disposed over the flexure area for generating a signal is response
to a load applied to the loading cavity wherein the strut has a
first projection end coupled to the conical end of the loading
cavity and a second end coupled to a footer member such that the
strut mechanically floats therebetween for providing the applied
load at a substantially central position at the load cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a detailed understanding of the present invention,
reference should be made to the following drawings wherein:
[0013] FIG. 1A is a top plan view of an embodiment of the bossed
diaphragm sensor plate of the present invention.
[0014] FIG. 1B is a cross-sectional view of the sensor plate shown
in FIG. 1A.
[0015] FIG. 1C is a cross-sectional view of the sensor plate
showing tension and compression sections associated with the
flexure area.
[0016] FIG. 2A represents a partial cross-section associated with
one side of the bossed diaphragm load cell having a floating
conical strut according to an embodiment of the present
invention.
[0017] FIG. 2B represents a partial cross-section associated with
one side of the bossed diaphragm load cell having a fixed conical
strut according to an alternative embodiment of the present
invention.
[0018] FIG. 3 is a schematic circuit diagram which depicts how the
strain gauges of the sensor plate are coupled.
[0019] FIG. 4 is a view of the biasing element shown in FIG. 2.
[0020] FIG. 5 is a perspective view of a load cell comprising
sensor plate, reinforcement member and strut according to the
present invention.
[0021] FIG. 6 is a plan view of a second surface associated with
the sensor plate having an annular depression and conical cavity
formed therein according to the present invention.
[0022] FIG. 7 is a perspective view illustrating each of the major
elements used in assembling the load cell according to the present
invention for use in an electronic weighing scale.
[0023] FIG. 8 is a perspective view of an electrical weighing scale
employing load cells equipped with the bossed diaphragm sensor
plate according to the present invention.
[0024] FIG. 9A-B represent a partial cross sectional view and a top
view respectively of the bossed diaphragm sensor plate and backing
plate assembly according to the embodiment illustrated in FIG.
2B.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring collectively to FIGS. 1A and 1B, a load cell
sensor plate 10 according to an embodiment of the present invention
is shown. Generally, the sensor plate 10 is fabricated from sheet
metal in a substantially flat rectangular configuration, which
allows the sensor plate to be used in low profile load cell
designs. The unitary design of the sensor plate 10 provides
substantially reliable performance and enables the sensor plate to
be simply and economically manufactured.
[0026] FIG. 1A shows a first planar surface 20, a bossed sensor
plate 10 on which is disposed sensor means comprising strain gauges
1-4 interconnected in a circuit configuration as identified in FIG.
3. As one can ascertain, surface 20 is substantially planar and
includes bonding pads 30 and 40 disposed respectively between
strain gauges 1, 2, and 3, 4. The flat planar surface 20
facilitates electrical interconnection between the sensors formed
on the surface 20 and the remainder of the electronic circuitry
housed within the electrical weighing scale via circuit 35 and
electronic connector 36 as shown in FIGS. 5 and 8. The sensors are
disposed over a thinned surface area of the bossed sensor plate
defined as a flexure area in order to sense bending moments
resulting from an applied load or force.
[0027] Referring now to FIG. 1B, the sensor plate 10 comprises a
boss diaphragm structure having a flexure area which, in the
preferred embodiment, is substantially annular and is illustrated
in FIG. 1B by first and second flexure portions 24 and 30 defined
in the sensor plate. The flexure portions or beams are defined in
the sensor plate between apertures or slots 16, 18. Mounting
sections 12 and 14 enable the sensor plate 10 to either rest or be
anchored within the interior of a load cell as illustrated in FIG.
2 (reference numerals 12A, 14A). In a preferred embodiment the
flexure area 25 has a uniform thickness t less than the overall
thickness T of the sensor plate. Preferably flexure area is between
5 and 8 times less than the overall thickness T of the sensor plate
thus allowing for appropriate flexing and sensing of the force
applied to the load cell. Note further that the sensor pairs are
preferably placed directly opposite one another as illustrated in
FIG. 1A and FIG. 9B to provide an equalized sensing of the applied
force impacting the load cell.
[0028] As shown in FIG. 1B, sensor plate 10 further includes cavity
22 for receiving a conical shaped projection for concentrating an
applied load to the load cell. Cavity 22 comprises substantially
circular side walls 23 terminating in a conical shaped end portion
22A. Cavity 22 has a diameter d of sufficient size to receive a
strut 43 (see FIGS. 2A-B) having a conical shaped projection 44
which engages the cavity at substantially the point p at the center
of the cone along the designated Y-axis. The conical projection 44
from strut 43 inserted into cavity 22 functions to concentrate an
applied load to the boss diaphragm structure plate 10 which
generates a bending moment applied to the flexure portions 24 and
30.
[0029] Referring to FIG. 1B, the first flexure portion 24 includes
a compression section 26 and a tension section 28. The line of
demarcation between the compression and tension section 26, 28 is
shown by dotted line L1. Similarly, second flexure beam 30 includes
compression section 32 and tension section 34, which are shown
separated by dotted line L2. The first flexure portion 24 includes
the strain gauge 1 bonded to the surface of its compression section
26 and the strain gauge 2 bonded to the surface of the tension
section 28. Similarly, second flexure portion 30 includes strain
gauge 3 bonded to the surface of its compression section 32 and
strain gauge 4 bonded to the surface of its tension section 34. The
strain gauges preferably consist of piezo-resistor sensing
elements. FIG. 1C illustrates the operation of the tension and
compression sections of flexure 30 in response to a load.
[0030] FIG. 3 shows the electrical interconnection of the strain
gauges 1-4 for equalizing the forces sensed by the strain gauges.
Cross coupling is accomplished by electrically coupling the strain
gauges of the first flexure beam in series with those of the second
flexure beam to form the bridge structure 36 depicted in FIG. 3.
This circuit structure will supply an output signal which will very
accurately characterize the total load applied to cavity 22 of the
sensor plate 10. It should be understood that the sensor plate of
the present invention is not limited to the strain gauge
arrangement described above. Accordingly, other well known sensor
arrangements may be employed in the bossed diaphragm sensor plate
of the present invention if desired.
[0031] FIG. 2A depicts a cross-sectional view of a boss diaphragm
sensor plate 10 of the present invention as it is used in the low
profile load cell designated by numeral 50. A load cell 50
comprises a housing 51 which contains the boss diaphragm sensor
plate 10, and a spiral positioner biasing element 72. As shown in
FIG. 2A, a strut member 43 having a substantially circular cross
section and oppositely disposed conical shaped ends 44 and 45
operates to apply a load to the bossed sensor plate 10. Conical
projection 45 of strut 43 engages reinforcement member 86 having a
substantially flanged portion 87 which rests upon element 72.
Conical grooved portion 92 of reinforcement member 86 is adapted to
receive conical end 45 in such a manner as to allow strut 43 to
mechanically "float" between member 86 and sensor plate 10. That
is, for any twist or rotation resulting from a force applied
resulting from an off axis force applied to the load cell, floating
strut 43 operates to direct the load to center point p along the
y-axis so that the load cell is self correcting, and thus operates
to evenly distribute the applied force. Absent such a floating
structure, off-center loading would result in off-axis forces
detected by the sensor arrangement and factored into the weighing
calculation resulting in erroneous or inaccurate weight readings.
Thus, the load cell arrangement comprising the boss diaphragm
sensor plate 10, strut 43, and reinforcement member 86 combine to
self-correct for any off-center loading that may occur as a result
of twisting, rotation, or uneven surfaces associated with the
angular position of the foot rest for each load cell. Moreover, the
boss diaphragm design allows for low cost manufacture of the load
cell by requiring only a milling operation to be performed in order
to generate a load cavity and associated flexure area. Finally, the
planar design facilitates electrical interconnection on the top
surface of the load cell to achieve a low cost and highly accurate
product. As one can ascertain from FIG. 2A, strain gauges 1 and 2
are disposed over flexure portion 24 of the overall flexure area 25
while sensors 3 and 4 are disposed flexure portion 30 for sensing
and/or compression resulting from the applied load.
[0032] In an alternative embodiment shown in FIG. 2B the load cell
50 includes strut 43 fixedly position within member 86 at one end
and conically engaging lower cavity 22 via projection 44. Note that
when referring to the drawings, and in particular to FIGS. 2A and
2B, like parts are indicated by like reference numerals. The
embodiment shown in FIG. 2B further includes flexible backing plate
55 having arm portions 57 which support and engage bossed diaphragm
sensor plate 10 that mounting sections 12 and 14 (and at 12A and
14A).
[0033] In a fixed strut embodiment, as the foot 84 may tend to
angle off-axis, the subassembly comprised of the boss diaphragm
sensor plate 10 and the backing plate 55 operate to move laterally,
thereby maintaining the point 44 of strut 43 in the center of the
conical depression 22A in plate 10. This feature provides a more
secure assembly with less risk of displacing any parts and provides
for increased stability without loss of accuracy. FIGS. 9A and B
illustrate more detailed cross-sectional and top views respectively
of the embodiment shown in FIG. 2B including the bossed diaphragm
sensor plate 10 and backing plate 55. As clearly illustrated in
FIGS. 9A and B, hole 58 is provided in backing plate 55 to allow
for electronic wires or interconnections between the sensors of the
load cell for communication with other load cells and with the
remainder of the weighing scale. The backing plate is disposed in a
circular configuration over the mounting sections 12 and 14
(element 59) so as not to impact on the flexure area 25. The
backing plate is preferably made of a lightweight material such as
a plastic having a circular top configuration 59 and having
square-like arms 57 which enable the backing plate to fit snugly
around the metal bossed diaphragm. As shown in FIGS. 2B and 9A, the
backing plate disposed on the bossed diaphragm within housing 51 is
fixed in the Y-axis for direction but maintains degrees of freedom
within the X and Z (out of the page) planes to permit lateral
movement in order to maintain the strut in substantially the center
of the bossed diaphragm.
[0034] In the embodiments of FIGS. 2AB, reinforcement member 86
comprises a hardened steel insert. The hardened steel reinforcement
member 86 is disposed within an aperture 100 of foot cell 84
extends out from the top of foot 84. Gripping surfaces 94 engage
the inner walls of load cell 84 to prevent inadvertent removal of
member 86. Biasing element 72 as shown in FIGS. 2 and 4, has a
rectangular shaped outer frame 74 having width and length
dimensions substantially similar to sensor plate 10 width and
length dimensions, includes an annular member 78 which is coupled
to the frame 74 by a plurality of resilient, spiral-shaped arm
members 80. Biasing element 72 also ensures that conically grooved
surface 92 (FIG. 2A) of reinforcement member 86 is engaged with
projection 45 on strut 43. The flanged portion 87 of member 86 fits
within annular member 78 of spiral bias element 72, resting on lip
73 (see FIG. 4) such that a top surface of member 86 is planar with
annular surface 78A. Pad 110 fits within the cavity 85 of foot
member 84 in order to provide a solid and stable base.
[0035] As one can ascertain, operation of the load cell is as
follows. A load is applied to the load cell 50 via the foot 84
which engages reinforcement member 86 causing projection 44 on
strut 43 to be applied to portion 22A of cavity 22 resulting in
deflection which causes the flexure beams 24, 30 of the sensor
plate to bend. The bending forces are sensed by the strain gauges
1, 2, 3, and 4 which generate an electrical signal that is
indicative of the load applied to cavity 22 of the boss diaphragm
sensor plate 10. The boss diaphragm plate 10 of the present
invention allows the load cell 50 to be constructed with a very low
profile, since the present invention sensor plate provides both
load support and load measurement in a single planar member which
enables the load cell 50 to be employed in many different
applications involving the measurement of weight. Note that the
load cell may also be provided with a conventional power switch
means (not shown) of well-known types capable of powering up or
powering down an electronic weighing scale.
[0036] Referring now to FIG. 5, there is shown a perspective view
of a load cell 50 comprising the boss diaphragm sensor plate 10,
strut 43, and reinforcement member 86. As shown in FIG. 5, sensor
plate 10 is substantially square with a substantially planar first
surface 20 and second surface 12 opposite first surface 20 on which
is formed an annular depression 18 which defines a flexure area on
which are disposed sensor means comprising strain gauges 1, 2, and
3, 4 such that the flexure beams 24 and 30 are formed as
illustrated in FIG. 1B. Circular cavity 22 is formed in
substantially the center of the plate such that a substantially
cylindrical projection 21 having cavity 22 disposed therein, is
formed. The projection is coplanar with the remaining flat portion
of surface 12 as illustrated in FIG. 5. Cavity 22 as previously
mentioned, included conical shaped end 22A (FIGS. 1B, 2A-B) for
receiving similarly shaped strut 43 floatingly disposed therein.
The other end of strut 43 floatingly engages conical shaped cavity
92 of reinforcement member 86 which is retained in foot cell member
84 and which engages spiral bias member 72 (not shown).
Alternatively, as previously stated, the other end of strut 43 may
fixedly engage foot 84 via reinforcement member 86 such that the
strut remains in a fixed location at one end. Still further, a
backplate (not shown) is adapted to snuggly fit around the outer
surface and mounting portions of sensor plate 10 and operative to
move laterally in consonance with the bossed diaphragm sensor plate
for maintaining engagement of the conical strut at a substantially
center position within the plate in response to off-axis forces.
The first surface 20 of plate member 10 is protected by housing 51
which serves also to secure the device within the scale. FIG. 7 is
a perspective view of each of the major elements for assembling the
load cell of the present invention for use in a transparent
weighing scale 115 having a glass platform 118.
[0037] In FIG. 8 there is shown an electronic weighing scale 115
which employs the load cell 50 of the present invention. Generally,
the scale 100 comprises a platform 102 supported in each corner by
a load cell 50 constructed as described earlier. The scale 100 also
includes a display assembly 104 which is electrically coupled to
the sensing arrangement of each sensor plate contained in the load
cells 50 via wiring 106. The load cells may or may not include the
power switch means discussed previously.
[0038] When a load is placed on the platform 102, the load is
distributed among the four load cells 50, such that each strain
sensing arrangement of each load cell's sensor plate 10 generates
an electrical signal which is proportional to the load on the load
cell 50. The four signals generated by the load cells 50 are
transmitted by the wiring 106 to the display assembly 104 which has
electrical circuitry that combines the four signals into a single
analog signal which is proportional to the sum of the loads on the
four individual lead cells 50. The display assembly 104 also
includes an amplifier (not shown) that amplifies the combined
analog signal, and an analog-to-digital converter (not shown) which
translates the analog signal to a digital signal. Additional well
known circuitry in the display assembly 104 transforms the digital
signal into a reading in pounds or the like which is digitally
displayed on the display screen 108 of the display assembly 104.
The electrical circuitry contained in the display assembly 104 is
well known in the art and an example of such circuitry can be found
in the copending U.S. patent application Ser. No. 08/385,349,
incorporated herein by reference.
[0039] It should be understood that the embodiment described herein
is merely exemplary and that a person skilled in the art may make
many variations and modifications to the embodiment utilizing
functionally equivalent elements to those described herein. For
instance, while there has been shown a substantially rectangular or
square shaped plate member 10, a plate member having a circular or
even triangular perimeter or any other geometric configuration may
also be provided. Similarly, while an annular depression has been
illustrated over which the flexure members and sensors are
disposed, other geometric configurations are also contemplated,
including substantially rectangular channel-like sections, as well
as any other geometric shape which allows for the flexure of
particular portions of the sensor plate. In addition use of the
backing plate 55 illustrated in FIG. 2B may also be contemplated as
part of the dual-coned floating strut depicted in the embodiment of
FIG. 2A. Moreover, while in the preferred embodiment the thickness
t of a flexure member is between 5 and 8 times less than the
overall thickness T of the plate, other relative dimensions may
also be utilized according to particular applications and
requirements. Any and all such variations or modifications, as well
as others which may become apparent to those skilled in the art,
are intended to be included within the scope of the invention as
defined by the appended claims.
* * * * *