Multiple overload protection for electronic scales

An electronic scale is disclosed which has multiple overload protection features for protecting the load cell and a weight distribution plate from excessive strain due to vertical overload on the scale or from twisting resulting from an article being placed thereon which exceeds the load capacity of the scale, or from excessive forces due to mishandling of the scale. A first overload protection is in the form of a boss molded into the base of the scale on which the free end of the load cell abuts if an excessive load is placed on the platter of the scale. A second overload protection is in the form of a peripheral depending flange on the platter which abuts a peripheral portion of the a top cover to prevent excessive strain on the load cell and a weight distribution plate from excessive loading or mishandling of the scale. A third overload protection is in a plurality of ribs which are molded into the base and which extend upwardly adjacent the under surface of the four corners of the weight distribution plate so that the weight distribution plate abuts these ribs in the event that an excessive load is placed on the platter in an off center manner. The weight distribution plate is also provided with means for causing the weight of an article placed on the platter in an off center manner to be transferred to the point where the weight distribution plate is attached to the free end of the load cell so that an accurate weight is measured by the scale regardless of the placement of an article on the platter.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the field of electronic weighing 
scales, and more particularly to electronic scales designed particularly 
for use in weighing of mail pieces to determine the amount of postage 
required for mailing. 
Postal weighing scales, i.e., scales designed particularly for use in 
weighing mail, have long been well known, and many varieties of such 
scales have been developed, both for general use such as in industry mail 
rooms and offices, and by the US Postal Service in post offices and mail 
distribution centers. These scales typically range in capacity from one 
pound to as much as 200 pounds, depending on whether a particular scale is 
used primarily for letter mail or for heavier mail or packages. Earlier 
versions of these scales utilized various forms of mechanical balancing 
devices so that a load placed on the scale platter would cause a 
mechanically operated weight indicator to register the weight of the load 
on a visible scale, or cause a balance arm to seek a midpoint when a load 
equal to the weight of the load on the platter was applied to the arm. 
These scales were highly successful in operation, for the most part, and 
met with a considerable degree of commercial success. 
However, as in so many other forms of mechanical devices, the advantages of 
converting to electronic operating components became apparent. A principal 
factor involved in the conversion of postal scales from mechanical to 
electronic operating components was the fact that postal scales must have 
an extremely high degree of accuracy under virtually all operating 
conditions, and scales having electronic operating components were found 
to be consistently more accurate than those having mechanical operating 
component. The reason for the need for such high degree of accuracy is 
that postal scales are used for determining the amount of postage that 
must be applied to letter and small package mail, and to larger packages 
being mailed as parcel post, and even very slight inaccuracies in the 
weight given by a scale could potentially cause a serious loss of money, 
either for the mailer or for the USPS, depending on the manner in which 
the scale was inaccurate. This can be better appreciated when one 
considers the volume of the different types of mail handled by the Postal 
Service each year, which typically is in the billions of pieces. 
One problem that arose with scales having electronic operating components 
is that the load cell, which is the heart of an electronic scale, is a 
highly delicate instrument and is subject to damage in the event that it 
is subjected to a load in excess of the load for which it is designed. 
Basically, a load cell using strain gage technology can be a generally 
rectangular metallic body member which is adapted to have one end rigidly 
mounted on a frame so that the load cell is supported only at that end, 
with the rest of the body member being cantilevered from the mounting end. 
The other end of the body member is provided with some means for 
supporting a weight. Strain gages are mounted on the body member in 
appropriate locations that very slightly when the body member is deflected 
by the application of the weight. An electric voltage is applied across 
the strain gage which varies in accordance with the extent to which the 
strip is strained by the weight on the free end of the body member. 
Generally, there are several strain gages located at appropriate locations 
that allow them to be connected in the form of a Wheatstone Bridge, which 
is well known in the art. By suitable electronic devices also well known 
in the art, variations in the voltage across the bridge circuit metallic 
strip resulting from different weights applied to the free end of the body 
member can be read as different weights on various forms of digital 
readout devices. 
One of the major advantages of the load cell as a measuring device for use 
in postal scales is that it is extremely accurate, permitting scale 
readings to within one part in 3000 to 5000 on a five pound scale. There 
is, however, a tradeoff in that the accuracy of the load cell is dependent 
upon a very sensitive construction that is easily damaged with overload. 
The problem is that with a typical load cell, the deflection of the free 
end of the cell is extremely small, in the order of ten thousandths of an 
inch, and if the load cell is deflected much beyond that amount, the bond 
of the strain gage to the base metal or the base material that stretches 
in response to deflection of the body member is permanently damaged, 
rendering the load cell useless. Thus, it is very important to provide a 
scale having a load cell control component with suitable means for 
preventing the load cell from being subjected to an excessive load, such 
as would occur if a user placed a load on the scale platter which exceeded 
the maximum weight for which the scale is rated, or possibly mishandled 
the scale in such a manner that a momentary impact on the scale platter 
caused the overload. 
In the prior electronic postal scales over which the scale of this 
invention represents an improvement, as represented by the scale shown in 
U.S. Pat. No. 5,072,799, issued on Dec. 17, 1991 to Freeman et al., and 
assigned to the assignee of this application, the load cell is mounted 
between a pair of identical cast metal body members, each of which has a 
central portion to which opposite ends of the load cell are connected. 
Each of the body members also has a plurality or legs extending radially 
outwardly, those from the lower body member supporting the assembly of the 
body members and the load cell in a suitable frame or housing, and those 
from the upper body member providing a suitable weight distribution plate 
for supporting the scale platter, thereby supporting the scale platter 
adjacent the four corners thereof. The load cell is protected against 
overload by an adjustable center downstop which includes a pair of 
downstop set screws which seat against a metal surface, such as the head 
of a bolt, and a controlled gap at the corners due to machining portions 
of the castings at each of the corners. 
Because of the particular use of the scale, i.e., to indicate the amount of 
postage required for mailing, the adjustability of the downstop had to be 
very critical, typically being in the range of 8 to 30 thousandths of an 
inch, with an adjustment tolerance of plus or minus one thousandth. As 
previously indicated, the actual deflection of the free end of a load cell 
is very small, and it was found, in the case of the cast metal body 
members of the previous scales, that the machining tolerances on the 
castings would not permit variations in the position of a load cell 
downstop to plus or minus one thousandths of an inch, particularly when 
there are two different components that are involved in the tolerance 
buildup. The height of the load cell, plus the tolerance of the machining 
of both surfaces of the downstop and the load cell mount on each of the 
two cast body members all contribute to rendering such a small variation 
in adjustability of the downstop virtually impossible without an 
adjustable downstop. Thus, the adjustable center downstop was required. 
Adjustable corner downstops were not required because the gap required 
between the ends of the legs of the case body members was much larger at 
the corners than was the deflection of the free end of the load cell, in 
the order of 100 to 125 thousandths of an inch, plus or minus 5 
thousandths. Therefore, these portions of the cast body members could be 
machined to produce the required tolerance variations. 
It should be understood that, while case metal body members with carefully 
machined parts and very accurate adjustable center downstops are well 
suited to the manufacture of a substantially large scale, such as would be 
used for weighing packages up to 200 pounds, this type of construction is 
too costly for smaller scales, such as five pound capacity scales that are 
used primarily to weigh letter mail, which renders them relatively 
noncompetitive. Thus, the need was recognized for an entirely different 
form of weight distribution plate and overload protection system for small 
capacity scales. The present invention accomplishes these objectives, as 
described in detail hereinafter, by eliminating the cast metal body 
members and also the adjustable center downstop, thereby greatly reducing 
the mechanical complexity of the scale, the cost of manufacturing, and the 
need for critical adjustment of movable parts. 
BRIEF SUMMARY OF THE INVENTION 
The present invention provides multiple overload protection features for 
certain critical components of the scale, specifically the load cell and 
the weight distribution plate, which at last minimizes if not altogether 
eliminates the possibility of serious damage to these parts. One aspect of 
the invention is directed toward protecting the load cell against 
excessive strain resulting from central vertical loading on the scale 
platter. Another aspect is directed toward protecting the load cell and 
the weight distribution plate against excessive strain resulting from 
off-center loading of the scale platter. A third aspect is directed toward 
protecting the load cell and the weight distribution plate from excessive 
strain resulting from shock to these parts caused by the scale being 
dropped during shipment or use, or from other mishandling. A significant 
feature of the invention is the design of a weight distribution plate that 
transfers the weight of an article being weighed at the point where the 
scale platter supporting the article is connected to the load cell so that 
off-center loading of the platter has no detrimental effect on the load 
cell. A further feature of the present invention is the provision of means 
for protecting the weight distribution plate against any undue twisting 
force while removing the platter from the scale in the event that an 
operator uses excessive force in disconnecting the platter from the means 
that normally secures it to the scale. 
In its broader aspects, the present invention is an electronic weighing 
scale having multiple overload protection features for protecting certain 
components of the scale against excessive strain. The electronic scale 
comprises a generally rectangular housing having a bottom wall and a 
plurality of upstanding side walls, an elongate load cell having one end 
thereof fixedly mounted on a portion of the bottom wall, a top cover 
having planar dimensions closely approximating those of the housing and 
fixedly secured thereto, a weight distribution plate having planar 
dimensions closely approximating those of the housing and fixedly mounted 
on the free end of the load cell, and a platter supported on the weight 
distribution plate. Finally, there is a plurality of abutment means for 
preventing excessive strain on the load cell and on the weight 
distribution plate, with the result that the load cell and said weight 
distribution member are protected against damage from excessive strain 
imposed on said load cell and said weight distribution plate from 
excessive central loading of said platter, from excessive off center 
loading of said platter and from shock due to mishandling. 
In some of its more limited aspects, there is a first abutment means 
disposed on the housing for preventing downward movement of the free end 
of the load cell beyond a predetermined limited established for the load 
cell which comprises a raised boss disposed on a portion of the bottom 
wall in underlying relation to the free end of the load cell and forms a 
limit beyond which the free end of the load cell cannot be depressed. 
There is a second abutment means for preventing downward movement of the 
platter beyond a predetermined limit set for the platter, which comprises 
a depending peripheral flange surrounding the platter in overlying 
relationship to a peripheral portion of the upper surface of the top 
cover, the lower edge of the flange being disposed in closely adjacent 
spaced relationship with the upper surface of the top cover and 
constituting a predetermined limit beyond which the platter cannot be 
depressed. 
And there is a third abutment means for preventing downward movement of the 
weight distribution plate beyond a predetermined limit set for the weight 
distribution plate which comprises a plurality of upstanding abutment 
members disposed adjacent the four corners of the housing, and having 
upper edges disposed in closely spaced underlying relationship with the 
four corners of the weight distribution plate and which constitute a 
predetermined limit beyond which the corners of the weight distribution 
plate cannot be depressed. 
Finally, there is an abutment means disposed on the underside of the top 
cover in overlying relationship to the four corners of the weight 
distribution plate against which the corners of the weight distribution 
plate bear while removing the platter from the scale in the event that the 
platter does not easily disengage from the weight distribution plate and 
tends to draw it upwardly. 
Further, a feature of the invention is the design of the weight 
distribution plate which includes means for changing the resistance to 
bending of one end thereof with respect to the other end thereof to 
compensate for the difference in resistance to bending of opposite ends of 
the weight distribution plate which result from the weight distribution 
plate being connected to the free end of the load cell in an off center 
manner. This comprises a plurality of slots formed in the weight 
distribution plate which extend from the end thereof adjacent the point of 
connection of the weight distribution plate to the free end of the load 
cell toward the center of the weight distribution plate for a distance 
sufficient to reduce the resistance to bending of that end of the weight 
distribution plate so that it is equal to the resistance to bending at the 
other end thereof. 
Having described the general nature of the present invention, it is a 
principle object thereof to provide a multiple overload protection system 
for an electronic scale having multiple overload protection features for 
protecting certain critical components of the scale from excessive strain. 
Another object of the present invention is to an electronic scale in which 
the weight distribution plate cannot be damaged due to excessive strain 
imposed on it during removal of the platter from the scale. 
It is another object of the present invention to provide an electronic 
scale in which the weight of an article is transferred at the point where 
the weight distribution plate supporting the platter is connected to the 
load cell so that off-center loading of the platter has no detrimental 
effect on the load cell. 
It is a still further object of the present invention to provide an 
electronic scale in which the expensive cast metal body members and also 
the adjustable center downstops are eliminated, thereby greatly reducing 
the mechanical complexity of the scale, the cost of manufacturing, and the 
need for critical adjustment of movable parts. 
These and other objects and advantages of the present invention will be 
more apparent from an understanding of the following detailed description 
of a presently preferred embodiment of the present invention when 
considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, and more particularly to FIG. 1 thereof, the 
major components of the scale of the present invention are shown in an 
exploded manner, and are seen to comprise a housing, indicated generally 
by the reference numeral 10, a load cell, indicated generally by the 
reference numeral 12, a weight distribution plate, indicated generally by 
the reference numeral 14, a top cover, indicated generally by the 
reference numeral 16, and finally a platter, indicated generally by the 
reference numeral 18, on which the mail piece to be weighed is placed. 
With reference, now, to all of the figures, it will be seen that the 
housing 10 is generally rectangular and has oppositely disposed upstanding 
side walls 20, an upstanding rear wall 22, a very short, upstanding front 
wall 24, and a bottom wall 26 to which the side, rear and front walls are 
connected. A plurality of feet 28 are suitably connected to the underside 
of the bottom wall 26 in recesses defined by wall portions 30 (see FIGS. 1 
and 3) for supporting the scale. The housing 10, as well as the top cover 
16 and the platter 18, in this instance are formed of injection molded 
polycarbonate blend plastic, although other types of plastic blends with 
similar characteristics are available. An upstanding wall 32 extends 
across the housing 10 between the side walls 20 to divide the space within 
the housing 10 into forward and rearward compartments 34 and 36, the 
former for the electronic components which are actuated by a plurality of 
push buttons that extend through suitable openings 38 formed in the top 
cover 16, the latter for the load cell 12 and other electronic components 
that will not fit in the forward compartment 34. 
As best seen in FIGS. 1 and 2, the bottom wall 26 is provided with a recess 
40 located adjacent to one of the side walls 20, and which is bounded by 
an elongate upstanding boss 42 on the laterally inward side of the recess 
and an overlapping laterally extending flange 44 on another elongate 
upstanding boss 46 formed on the opposite side of the recess 40. A metal 
support plate 48 is disposed in the recess 40 and is held in place by the 
overlapping flange 44. A fixed end 50 of the load cell 12 is positioned on 
the support plate 48 and is connected to the base and housing member 10 by 
suitable screws 52 which pass through openings in the bottom wall 26 and 
the support plate 48 and threadedly engage the fixed end 50 of the load 
cell 12. The opposite or free end 54 of the load cell 12 is connected to 
the weight distribution plate 14 by means of similar screws 56 which pass 
through openings in the plate 14 and are threadedly engaged with the free 
end 54 of the load cell 12. It should be noted that the connection of the 
weight distribution plate 14 to the free end 54 of the load cell 12 is the 
only means by which the weight distribution plate 14 is mounted within the 
base and housing member 10. Further details of the weight distribution 
plate will be fully explained below. 
The top cover 16 is dimensioned to overlie the housing 10, and includes a 
push button access portion 60 which includes the aforementioned button 
access openings 38 and overlies the forward compartment 34 in the base and 
housing member 10. The remainder of the top cover 16 is a generally 
rectangular portion 62 which overlies the rearward compartment 36 in the 
housing 10. The rectangular portion 60 includes a pair of downwardly 
extending protrusions 64 (only one of which is seen in FIG. 3 due to the 
change in direction of the section line 3--3 in FIG. 2), each of which has 
a mounting annulus 66 which rests on top of a boss 68 located on the end 
of an upwardly extending cylindrical post 70 formed integrally with the 
bottom wall 26. A screw 72 passes through each annulus 66 and is 
threadably engaged with the upper end of each post 70 to secure the top 
plate 16 to the housing 10. As best seen in FIGS. 1 and 3, the top cover 
16 has a peripheral, downwardly extending flange 74 that engages with a 
peripheral upwardly extending flange 76 formed on the upper edges of the 
side walls 20 and rear wall 22 to ensure that the top cover 16 is firmly 
seated on the housing 10. 
The scale platter 18 is basically a generally rectangular body member 80 
which has approximately the same dimensions as the rectangular portion 62 
of the top oover, and is provided with four identical legs, one of which 
is indicated generally by the reference numeral 82 in FIG. 1. Each leg 82 
has a plurality of webs 84 radiating outwardly from a central point of 
intersection 86 (see FIG. 3), which extend downwardly from the underside 
of the body member 80. In the embodiment disclosed, each leg 82 has four 
webs 84, although this number can vary. The webs 84 terminate downwardly 
in spaced relationship to the underside of the body member 80 to define a 
plurality of supporting surfaces 86 which rest on the upper surface 88 of 
a grommet, indicated generally by the reference numeral 90 in FIG. 1. As 
seen in FIGS. 1 and 3, there are four such grommets, each having a 
peripheral slot 92 which engage with the inner circular edges of apertures 
94 formed in the weight distribution plate 14. The grommets 90 are 
positioned in the apertures 94 by being inserted into the open throats 96 
of the apertures 94, the grommets 90 having sufficient resilience to 
distort inwardly while being inserted through the throats 96 and then 
expending to seat firmly in the apertures 94. As best seen in FIG. 3, the 
webs 84 of the legs 82 have a reduced diameter portion 98 which projects 
through an aperture 100 in each of the grommets, the lateral projection of 
the webs 98 and the inner diameter of the apertures 100 being selected 
such that the webs 98 are gripped by the inner edges of the apertures 100 
with sufficient strength to firmly retain the platter 18 on the weight 
distribution plate 14, but not so tightly that it cannot be readily 
removed by a user simply by lifting the platter upwardly. It should be 
noted that the top cover 16 is provided with openings 102 which are 
sufficiently large to enable the webs 84 to pass therethrough without the 
webs 84 touching the inner edges of the apertures 102 so that the platter 
18 is supported solely by the weight distribution plate 14. 
As previously mentioned, the present invention provides multiple overload 
protection features for the scale which are intended to at least minimize 
if not entirely eliminate the possibility of damage either to the load 
cell 12 or to the weight distribution plate 14, either from overloading 
the scale in the course of normal use or from various forms of mishandling 
during shipment or at the location of use. The overload protection 
features of the present invention comprise a series of abutment means 
built into the scale, a first of which prevents downward movement of the 
free end 54 of the load cell 12 beyond a predetermined limit established 
for the load cell 12. A second abutment means prevents downward movement 
of the corners of the platter 18 beyond a predetermined limit set for the 
corners of the platter 18. And a third abutment means prevents downward 
movement of the corners of the weight distribution plate 14 beyond a 
predetermined limit set for the corners of the weight distribution plate 
14. 
Thus, as seen in FIGS. 1 and 3, the first of the abutment means comprises 
an upstanding boss 104 that is molded into the bottom wall 26 beneath the 
load cell 12 and adjacent the free end 54 thereof, the purpose of the boss 
104 being to prevent further downward deflection of the free end 54 of the 
load cell 12 after the maximum load for which the scale is designed has 
been reached. Since the boss 104 is fixed relative to the scale, it 
represents a predetermined limit beyond which the free end 54 of the load 
cell 12 cannot be depressed, thereby prevent damage to the load cell 12 
from excessive strain being applied to the delicate strain gages bonded to 
the load cell 12. As previously mentioned, the deflection of the load cell 
12 is very slight, being in the order of 0.015 thousandths of an inch, 
plus or minus one thousandths, for a five pound scale. In actual practice, 
the capacity of the load cell for a particular scale can be selected at 
about twice the weighing capacity of the scale in order to more easily 
accommodate off-center loading of the platter 18, and to allow for more 
freedom in the design of the center and corner overload protection 
features. 
The second of the overload protection abutment means comprises a depending 
flange 106 which surrounds the platter 18 on the four sides thereof, and a 
peripheral portion 108 of the upper surface of the top cover 16 which lies 
outside of an upstanding rib 110 which surrounds the top cover on three 
sides thereof. As best seen in FIG. 3, when the platter 18 is properly 
positioned on the scale, there is a gap of approximately 0.130 inches 
between the under surface of the flange 106 and the upper surface of the 
peripheral portion 108 of the top cover 16. It will be apparent that, 
since the upper surface of the peripheral portion 108 of the top cover is 
also fixed relative to the scale, it represents a predetermined limit 
beyond which the lower surface of the corners of the flange 106 cannot be 
depressed, thereby preventing torsional damage to the load cell in the 
same manner as that set forth above with regard to the raised boss 104 
preventing a vertical overload, and also preventing damage to the weight 
distribution plate 14 by preventing excessive strain on the weight 
distribution plate 14. 
The third of the overload protection abutment means comprises a plurality 
of upstanding ribs 112 which are located approximately in the four corners 
of the housing 10, as seen in FIG. 3. The upper edges of the ribs 112 are 
normally disposed in spaced relationship with the underside of the weight 
distribution plate 14 adjacent the portions thereof that define the 
throats 96 at the four corners of the weight distribution plate 14. 
Again, it will be apparent that, since the ribs 112 are also fixed relative 
to the scale, they represent a predetermined limit beyond which the 
corners of the weight distribution plate 14 cannot be depressed, thereby 
preventing damage thereto from excessive twisting strain on the weight 
distribution plate 14 and excessive torque on the load cell. 
Referring to FIGS. 2 and 3, a means of protection is provided to prevent 
excessive strain from being imposed on the weight distribution plate 14 
and the load cell 12 while the platter 18 is being removed from the scale. 
As previously described, the platter 18 is attached to the scale by the 
reduced diameter portion 98 of the legs 82 passing through the apertures 
100 in the grommets 90, with the bottom surfaces 86 of the webs 84 resting 
on the upper surfaces 88 of the grommets 90. With this arrangement, if one 
of the grommets 90 grips a leg 82 of the platter 18 too tightly and the 
platter 18 is removed from the scale, the corner of the weight 
distribution plate 14 where that grommet is located will be twisted 
upwardly, thereby imposing an excessive twisting strain on the weight 
distribution plate 14. To prevent this from occurring a pair of downwardly 
extending ribs 114 are disposed on the underside of the top cover 16 
adjacent the side edges thereof, the bottom edges 116 being disposed in 
closely spaced relationship with the upper surface of the corners of the 
weight distribution plate 14. It will again be seen that since the ribs 
116 are affixed to the top cover 116 and are therefore fixed relative to 
the scale, they constitute a predetermined limit beyond which the corners 
of the weight distribution plate 14 cannot be moved upwardly, thereby 
preventing damage to the weight distribution plate 14 and the load cell 12 
from excessive twisting strain on the weight distribution plate during 
removal of the platter 18 from the scale. 
A feature of the present invention resides in the design of the weight 
distribution plate 14, which transfers the full weight of an article on 
the platter to the point at which the weight distribution plate 14 is 
fixedly mounted on the free end 54 of the load cell 12, regardless of 
where the article is placed on the platter. The weight distribution plate 
14 includes a means for changing the resistance to bending of one end 
thereof with respect to the other end thereof to compensate for the 
difference in resistance to bending of opposite ends of the weight 
distribution plate which result from the weight distribution plate being 
connected to the free end 54 of the load cell 12 in an off center manner, 
as clearly seen in FIGS. 1 and 3. The result is that the peripheral flange 
106 on the platter 18 will abut the peripheral portion 108 of the upper 
surface of the top cover 16 when the maximum load for which the scale is 
rated is placed anywhere around the periphery of the platter 18, as 
described above for the second overload protection feature. 
Thus, as best seen in FIG. 2, the weight distribution plate 14 is provided 
with a pair of slots designated generally by the reference numeral 118 
adjacent the corners of the plate that are proximate the free end 54 of 
the load cell 12 to which the weight distribution plate 14 is connected. 
The slots 118 have first straight portions 120 which merge into curved 
portions 122, which then extend one quarter the distance around the 
grommets 90, and then merge into second straight portions 124 which extend 
for approximately the same length as the first straight portions 120. The 
specific configuration of the slots 118 causes the weight distribution 
plate 14 to yield more readily to the bending force of a weight on the 
periphery of the platter 18 adjacent the point of connection of the weight 
distribution plate 14 to the load cell 12 than it would to the weight so 
placed adjacent the opposite end of the weight distribution plate. The 
reason for this is that the point of connection of the weight distribution 
plate 14 to the load cell 12 is off center with respect to the weight 
distribution plate, with the result that a weight on the platter 18 
adjacent that end of the weight distribution plate 14 will exert a smaller 
bending force on the weight distribution plate 14 at the point of 
connection to the load cell 12 due to the shorter bending arm. On the 
other hand, a weight on the platter 118 adjacent the other end of the 
weight distribution plate 14 will exert a larger bending force on the 
weight distribution plate 14 at the connection point due to the much 
longer bending arm. The slots 118 compensate for the differences in the 
bending arms in the weight distribution plate 14 regardless of where the 
weight is placed on the platter 18 by, in effect, "softening" the weight 
distribution plate 14 on the side near the point of connection to the load 
cell 12 so that it exerts less resistance to bending. 
While it is not necessary to go through a theoretical analysis of the 
formulas for determining the specific shape of the slots shown in the 
embodiment of the invention illustrated and described herein in order to 
fully understand the invention, it nevertheless should be understood that 
the shape of the slots is calculated to offset variations in the degree of 
deflection of the platter at the four corners thereof resulting from 
sources of deflection other than the weight distribution plate 14. For 
example, it has been found that the housing 10 permits a certain amount of 
deflection of the platter 18 at the four corners thereof due to the 
inherent deflection of the load cell 12 where it is connected to the 
housing 10. The load cell 12 also permits a certain amount of deflection 
of the platter 18 at the four corners thereof due to the inherent 
deflection of the load cell 12 along its length between the point where it 
is connected to the housing 10 and the point where the weight distribution 
plate 14 is connected to the load cell 12 itself has an inherent degree of 
deflection. In order for the second overload protection feature to be 
effective, the bottom of the flange 106 should bottom out on the upper 
surface 108 of the top cover when the maximum load for which the scale is 
rated (e.g., 5#) is placed anywhere around the periphery of the platter 
18. Since the known degrees of deflection at the corners of the platter 
resulting from the housing 10 and the load cell 12 are known from careful 
measurement, and are different at opposite ends of the weight distribution 
plate, by appropriate formulae the shape of the slots 118 can be 
calculated so make the total deflection of the platter 18 at the four 
corners thereof equal. 
As an example of the foregoing, in the case of the 5# scale disclosed 
herein, the normal gap between the underside of the flange 106 and the 
adjacent upper surface 108 of the top cover 16 is about 0.125". The 
housing deflection at the two corners of the platter 18 adjacent the point 
of connection of the weight distribution plate 14 to the load cell 12 has 
been found to be 0.020 inches at each corner, and the load cell deflection 
at the same corners has been found to be 0.014". Thus, the deflection of 
the weight distribution plate 14 at these corners must be 0.091" in order 
to provide a total deflection of the platter 18 at these corners of 
0.125". At the opposite corners, however, the housing deflection has been 
found to be 0.005" and the load cell deflection 0.010". Thus, the 
deflection of the weight distribution plate at these corners must be 
0.110" in order to provide the same total deflection to the platter 18. 
Thus, it should now be clear that the specific shape of the slots 118 
provide the necessary degree of "softening" of the weight distribution 
plate 14 so that it provides a lesser degree of deflection at the corners 
adjacent to the point of connection of the weight distribution plate 14 to 
the load cell than it does at the opposite corners. 
It is to be understood that the present invention is not to be considered 
as limited to the specific embodiment described above and shown in the 
accompanying drawings, which is merely illustrative of the best mode 
presently contemplated for carrying out the invention and which is 
susceptible to such changes as may be obvious to one skilled in the art, 
but rather that the invention is intended to cover all such variations, 
modifications and equivalents thereof as may be deemed to be within the 
scope of the claims appended hereto.