Weighing device

Combination hydraulic-pneumatic weighting scale which has a base in which is located multiple load cell units to effect displacement of a quantity of hydraulic fluid. A flexible conduit interconnects the load cells with the gauge. The gauge indicator is moved by an air actuated Bourdon tube and can be calibrated accurately for any specific weight up to 300 pounds. There is sufficient displacement of hydraulic fluid to compress a substantial column of air in the Bourdon tube and cause deflection of the needle. The amount of air compression within the scale gauge causes a sufficiently large deflection in the Bourdon tube to effect a large needle deflection and thus to obtain weight indications over the full range of the scale with great accuracy.

BACKGROUND OF THE INVENTION 
This invention relates to weighing scales and more particularly to a 
combination hydraulic-pneumatic weighing scale intended primarily for 
medical office and home bathroom use. As those skilled in the art are 
aware many types of bathroom platform scales are available over a wide 
range of prices. There are several types available including the 
mechanical fulcrum and lever types, spring type units and either air 
actuated or hydraulic types. Most of the scales, however, and particularly 
those that are of the low priced spring and lever type, involve a 
considerable amount of error. They contain too many parts, have too much 
built-in friction and they cannot be calibrated accurately except at zero 
weight. Purely hydraulic units have tried to do the job with one small 
type of load cell which requires a high pressure gauge. Thus the problem 
with purely hydrauic units is the high operating pressure. Additionally, 
they require evacuation of all air in the system to prevent bottoming of 
the load cell before full travel of the indicator can be effected. Where a 
weighting scale system involves high pressure it is susceptible to 
developing leaks and hence further inaccuracies. Also, single load cell 
weighing scales have small fluid displacement so that calibrating the 
indicator needle accurately to the scale is difficult if not impossible. 
In short, a small amount of liquid moved means high pressure and a small 
amount of deflection in the platform and load cell for difficult gauge 
calibration. Another problem is that most present bathroom scales do not 
distribute the load equally. Accuracy may depend upon proportional 
centering of the load on the platform and such equalizing of the load is 
not always achieved. 
Patents which are of interest but not particularly pertinent to the instant 
invention are U.S. Pat. Nos. 2,516,545; 3,433,316; 3,637,034 and 
3,765,497. 
SUMMARY OF THE INVENTION 
The invention is a combination hydraulic-pneumatic bathroom platform 
weighing device or scale which has a platform base including four load 
cells. The load cells are specially designed, compressible units for 
displacing hydraulic fluid with flexible metallic bellows. The load cells 
are interconnected to a line which leads to a read-out scale measuring 
pounds of weight by a needle indicator which is actuated by displacement 
of a Bourdon tube. The Bourdon tube is in turn actuated by a compressible 
air column against which the hydraulic liquid from the load cells and the 
line is forced when a load is on the scales. A pair of alignment 
assemblies are provided between the base and the platform for holding the 
platform on the scale base and at the same time maintaining the platform 
in an aligned position. 
Accordingly, it is among the objects, features and advantages of the 
instant invention to provide a combination hydraulic-pneumatic weighing 
device utilizing a multiplicity of load cells which are designed to 
displace as much hydraulic liquid as is necessary to compress the air 
column for full indicator travel. Because of the amount of hydraulic 
liquid displaced by the load cells, a relatively large column of air in 
the Bourdon tube for actuating the scale indicator can be used. The design 
results in low pressures in the lines of the weighing device. The scale is 
less susceptible to developing leaks, is inexpensive, rugged and reliable. 
The scales are accurate and once calibrated are not easily disturbed. The 
quantity of hydraulic fluid displaced is relatively large compared to 
other prior art devices. The air column also provides the unit with a 
frictionless return spring without the need for load compensation when 
calibrating the assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The scale device has the base and platform unit, generally referred to by 
the number 20, and the scale or gauge portion generally designated by the 
number 22. The scale comprises base 24 and platform 26. A hose or conduit 
28 extends from the base to the scale 22. 
By reference to the remainder of the drawings it will be seen that the base 
member 24 has bottom wall 25 and upstanding side walls, 30, 32, 34 and 36 
defining an upwardly open housing somewhat rectangular in shape as shown. 
It will be recognized that the exterior shape could assume many 
configurations, including round or oval. Within housing 24 and supported 
on bottom 25 are four load cell units generally designated by the number 
40. For the purposes of this description and because the load cells 40 are 
standard and uniform in construction, the single unit as shown in FIG. 7 
will be described. 
Load cell 40 consists of a manifold housing 42 having line connection 
openings 44 and 46 in the base portion thereof. Manifold 42 has fluid 
cavity 48 and upper end 50. Chamber 48 is connected to line openings 44 
and 46 and has interior wall surface 52. An upper movable member generally 
designated by the number 60 is in this embodiment generally shaped in the 
form of an inverted cup. It contains upper or closed end wall 62, side 
wall 64 and has lower edge 66 with interior wall surface 68 defining 
piston cavity 70. The outside of wall 64 has a radially outwardly offset 
or annular stop surface 72 which acts as a limit to the distance which 
movable member 60 may depress into the manifold cavity 48. It will be 
noted that the outside diameter of the wall 64 clears the inside wall 52 
of the housing sufficiently to permit liquid to pass between the outside 
of the movable member and the upper end of the housing. Secured to both 
the manifold and the movable member is a flexible metallic bellows 74 with 
an unspecified number of convolutions. It is secured generally at the 
upper end of the movable member and to the upper end of the manifold by 
furnace brazing or fusion welding. Each end of bellows 74 has a ring 76 
and 78 fastened to it by roll seam welding and is used to prevent 
ballooning of the bellows axially when load is applied. An annular cavity 
80 is defined between the inside of the bellows and member 60. On the 
closed end of the piston is an opening 82 having a plug 84. It will be 
understood that when the load cell 40 is filled with hydraulic liquid the 
cavities 48,70 and 80 are completely filled, and that to provide for 
proper functioning all air bubbles or pockets will have been removed 
through the opening 82 before installing plug 84. 
Platform member 26 has generally flat wall or surface 90 with depending 
edge or skirt 92 which, as can be seen in FIG. 6, extends downwardly on 
the outside below the upper edge 37 of the base. An appropriate decorative 
pad 94 is applied to the top of the platform wall 90. 
As can best be seen in FIGS. 4, 5 and 6, appropriate alignment assemblies 
generally designated by the number 100 are provided to keep the platform 
aligned on the base and to restrict the amount of upward movement of the 
platform. The alignment assemblies comprise guide socket 102 which extends 
upwardly into the base a predetermined distance to accommodate the head 
104 of bolt 106. An opening is provided in the sockets 102 so that the 
shank 106 of the bolt may pass through. The upper end of the sockets, of 
course, act as an abutment surface for the head. On the under side of 
platform member 90 are spacer blocks 108 with openings 110 therein. On the 
underside of block 108 and shaped to threadably receive bolts 106 are 
elastic plate nuts 112. Downward motion of the platform 26 is limited by 
the load cells while upward movement and maintenance of alignment is 
determined by the alignment assemblies 100. 
The scale or indicator unit 22 has a needle 120 mounted on a shaft 122. 
Needle 120 and shaft 122 are actuated by a Bourdon gauge or tube having 
hollow tube 124 connected to fitting 126. Inside and as part of the 
Bourdon tube is the mechanism for translating motion of the tip 125 of the 
tube into rotary motion of the needle. The mechanism consists of link 128 
connected to gear segment 130 which engages the pinion 132 on needle shaft 
122. It is to be noted that this invention does not include the elements 
of the Bourdon tube per se except insofar as it is a preferred form of 
device for utilizing a compressible column of air. Fluid from the load 
cells 40 is cumulatively displaced through interconnecting load cell lines 
41 into outside line 28 leading to the gauge 22. Hydraulic fluid is part 
of the system in the line 28 up to fitting 126 as at the end 129 of line 
28. The Bourdon tube 124 is filled with air. As a load is received on the 
platform the pistons of the four load cells are depressed into their 
housings moving fluid into line 28 and into the Bourdon tube and thus 
compressing the air column in tube 124. The use of four load cells gives a 
predetermined hydraulic liquid displacement for sufficient compression of 
the air column to result in deflection of the tube. The tube deflection 
results in full indicator needle deflection for maximum design weight 
indication. It will be appreciated, reference being had to FIG. 7, that 
the depressable portion of the load cell can only be forced into the 
manifold to the point where stop surface 64 engages the upper edge 50 of 
the manifold. While a series arrangement of load cells has been shown, a 
parallel arrangement as shown in dotted lines 43 in FIG. 2 may also be 
employed. The primary and important factor is the large volume liquid 
displacement to obtain sufficient compression of the air in Bourdon tube 
124 to give full needle deflections and therefore maximum weight readings 
on the scale 121. The system can be filled with the required amount of 
hydraulic liquid through valve 134 and line 136 as illustrated in FIG. 3. 
The embodiment as shown in FIGS. 8-10 represents another manner of 
construction of the invention. Those parts of the scale device, generally 
designated by the number 150, which are not changed will bear the same 
numbers as the first embodiment. Parts which are changed will be 
designated with different numbers. 
A manifold number, designated genrally as number 152, is a generally 
rectangular metallic or plastic plate member having wide edges 154, 156, 
158 and 160, and top surface 162. To reduce weight the center section is 
removed as at 164. Load cells 170 are disposed as shown generally at the 
four corners of the manifold. The manifold includes upwardly open load 
cell cavities 166 for each of the load cell structures which will be 
described in greater detail hereinafter. Passages 168 interconnect the 
cavities 166. Since the design of the manifold is such that the passages 
168 are drilled or reamed, entrance openings 174 from the wide edges of 
the manifold are provided and sealed with threaded plugs 176. 
Load cells 170 are constructed as shown in FIG. 10. A downwardly 
depressable top member 178 forms the upper end of the load cells. Located 
on the upper surface 162 of the manifold around the edge of cavity 166 is 
a corrosion resistant steel flange member having upstanding annular wall 
182 and the horizontal anchoring portion 180 by which the flange is 
secured to the manifold as with rivets 184 or other means. Gasket 186 is 
disposed between anchoring portion 180 and the manifold to seal against 
leaks. Metallic bellows 188 interconnects annular wall 18 and top member 
178. The bellows may be attached to the top member and flange by brazing 
or fusion weld. The platform assembly 26 bears on head 190 of bolt 192 
which extends through a central opening in top member 178. While it is not 
shown, the shank of the bolt may be threaded and the lower end of the bolt 
is spaced a predetermined distance above the bottom of cavity 168 in order 
to stop the downward travel when it reaches its maximum desired movement. 
The bolt obviously allows for adjustment and calibration of the individual 
load cell and the amount of hydraulic fluid that will be displaced when a 
load is applied. It will be noted also that manifold 152 includes sockets 
153 for the heads 104 of alignment bolts 106.