Weighing scale with fluid pressure transmission means

A weighing scale of the type comprising a scale is disclosed wherein the weighing scale is table for bearing the thing to be measured; a first hydraulic cylinder disposed below the scale table; a feeler transmitting the pressure applied at the scale table to the first hydraulic cylinder; a second hydraulic cylinder connected to the first hydraulic cylinder by a pipe and disposed at a level below the first hydraulic cylinder to bear the pressure transmitted through the feeler; a probe forced to make a linear displacement corresponding to the amount of the pressure transmitted from the first hydraulic cylinder to said second hydraulic cylinder; and an electronic inductor to detect the range of the linear displacement and convert it into a corresponding digital data for display.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to weighing scales and relates more 
particularly to a weighing scale which utilizes fluid pressure 
transmission means to accurately transmit the pressure applied at the 
scale table thereof to an electronic inductor for converting into digital 
data for display. 
2. Description of the Prior Art 
Various types of weighing devices such as a pan scale, pole scale, spring 
balance scale, platform scale and other mechanical and electronic weighing 
instruments have been disclosed for testing the weight of things. In the 
known mechanical scales, friction force is inevitably produced during 
pressure transmission, which causes error in final test. Further, 
determination error commonly happens during testing the weight of a thing 
by a spring balance scale. The use of an electronic scale completely 
eliminates visual observation error, however, it still can not eliminate 
pressure transmission error. Because a mechanical pressure transmitting 
mechanism is still commonly used in the known structures of electronic 
scales, friction force happens between the parts of the mechanical 
pressure transmitting mechanism during pressure transmitting operation. 
Therefore, pressure transmitting error must be reduced as low as possible 
so as to obtain a high precision weighing scale. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished under the circumstances in 
view. It is therefore the main object of the present invention to provide 
a weighing scale for testing the weight of things, which utilizes 
hydraulic fluid for transmitting pressure to as to eliminate friction or 
error during pressure transmitting operation. 
According to Pascal's principle, the pressure everywhere in a fluid is the 
same, so that pressure applied at one point is transmitted equally to all 
parts of the container. Therefore, fluid pressure transmitting method can 
completely eliminate pressure transmitting error. This is the basic 
concept of the present invention. According to the present invention, 
there is disclosed a weighing scale comprising a scale table for bearing 
the thing to be measured; a first hydraulic cylinder disposed below said 
scale table; a feeler transmitting the pressure applied at said scale 
table to said first hydraulic cylinder; a second hydraulic cylinder 
connected to said first hydraulic cylinder by a pipe and disposed at a 
level below said first hydraulic cylinder to bear the pressure transmitted 
through said feeler; a probe forced to make a linear displacement 
corresponding to the amount of the pressure transmitted from said first 
hydraulic cylinder to said second hydraulic cylinder; and an electronic 
inductor to detect the range of said linear displacement and convert it 
into a corresponding digital data for display.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, therein illustrated is the preferred embodiment 
of the weighing scale of the present invention which is generally 
comprised of a scale table 1, a first hydraulic cylinder 2 and a second 
hydraulic cylinder 2', a pipe 3, a probe 4, a plurality of screws 5 and an 
electronic inductor 6. 
The scale table 1 is supported by a plurality of Z-bars 11, which absorb 
the pressure given to the scale table 1, having a feeler 12 extending 
downwards from the bottom edge thereof at the center and disposed in 
contact with the first hydraulic cylinder 2 below. 
The hydraulic cylinders 2 and 2' each is comprised of a cylindrical 
container 21, a cover plate 22 and a diaphragm plate 23. The hydraulic 
cylinder 2 has a plurality of bolt holes 211 around the topmost edge 
thereof and a bolt hole 212 through the side wall thereof at a suitable 
location with a pipe connector 31 fastened therein for connecting the pipe 
3. The cover plate 22 has a plurality of through-holes 222 corresponding 
to the bolt holes 211 on the cylindrical container 21, and a round hole 
222 at the center. The diaphragm plate 23 has a plurality of through-holes 
232 corresponding to the bolt holes 211 on the cylindrical container 21, 
and a circular recess 231 at the center. Screws 5 are respectively 
inserted through the through-holes 221 on the cover plate 22 and the 
through-holes 232 on the diaphragm plate 23 into the bolt holes 211 on the 
cylindrical container 21 to firmly secure the cover plate 22 to the 
cylindrical container 21 with the diaphragm plate 23 retained 
therebetween. The feeler 12 of the scale table 1 is inserted through the 
round hole 222 on the cover plate 22 of the first hydraulic cylinder and 
disposed in contact with the diaphragm plate 23 at the circular recess 231 
thereof. 
The second hydraulic cylinder 2' is disposed at a lower position and 
connected to the first hydraulic cylinder 2 by the pipe 3. Further, a feed 
hole (not shown) is made on the first hydraulic cylinder 2 for filling 
hydraulic fluid and, a drain valve (not shown) is made on the second 
hydraulic cylinder 2' for discharging hydraulic fluid. 
The probe 4 is fastened in the second hydraulic cylinder 2' with the bottom 
end thereof connected to the circular recess 231 at the center of the 
diaphragm plate 23 of the second hydraulic cylinder 2' and the top end 
thereof disposed in contact with the electronic inductor 6. When the probe 
4 is forced to press on the electronic inductor 6, the linear displacement 
thus measured is converted into corresponding digital data through the 
operation of a circuit board, for display through a liquid crystal 
display. 
According to Pascal's principle, the pressure everywhere in a fluid is the 
same, so that pressure applied at one point is transmitted equally to all 
parts of the container. Referring to FIG. 3, when the scale table 1 bears 
a pressure P, the pressure P will be partly absorbed by the Z-bars 11, and 
at the same time, the feeler 12 bears a pressure T which is applied at the 
diaphragm plate 23, and therefore, a force F is transmitted through 
hydraulic fluid to the probe 4 on the second hydraulic cylinder 2'. 
Therefore, 
EQU T.times.A2=F.times.A1 , 
in which: 
T=pressure at the feeler; 
A2=contact area between the probe 4 and the diaphragm plate 23; 
F=the force transmitted to the probe 4; 
A1=the contact area between the feeler 12 and the diaphragm plate 23. 
According to the aforesaid equation, in an enclosed hydraulic system in 
which the volumne is not changeable, if to confine the probe 4 to make a 
linear displacement within a certain range, i.e. within the induced area 
of the electronic inductor 6, it needs only to change the contact area 
between the feeler 12 and the diaphragm plate 23 and the contact area 
between the probe 4 and the diaphragm plate 23. By changing the contact 
area between the feeler 12 and the diaphragm plate 23 and the contact area 
between the probe 4 and the diaphragm plate 23, the present invention is 
suited for weighing light or heavy material. In making a mechanical 
weighing scale, the size, strength and hardness of the materials for the 
elements in the pressure transmitting structure have great concern with 
the precision. Therefore, in mechanical weighing scale, pressure 
transmission error is difficult to eliminate. The present invention is not 
just an application of Pascal's principle, it eliminates the friction 
problem between the hydraulic cylinder the the piston therein which is 
commonly seen in regular hydraulic press and jack.