A remotely operable device for detecting changes as they occur in the mass of a selected specimen is described. The device is characterized by a balance beam including at one end a support for receiving a specimen having a changing mass and suspension means, including a flexure, supporting the beam near its center of gravity for pivotal movement proportional to changes occurring in the mass of the specimen. Strain gages coupled with the flexure provide a read-out indicative of the pivotal movement imparted to the beam

Valinsky, J. P.

English

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https://ntrs.nasa.gov/search.jsp?R=19740018832 2020-03-17T15:00:28+00:00Z
United States Patent
Fletcher et al.
[in 3,812,924
[45] May 28, 1974
[54] DEVICE FOR MONITORING A CHANGE IN
MASS IN VARYING GRAVIMETRIC
ENVIRONMENTS
[76] Inventors: James C. Fletcher, Administrator of
the National Aeronautics and Space
Administration with respect to an
invention of; Joseph P. Valinsky,
Huntington Beach, Calif.
[22] Filed: Mar. 13, 1973
[21] Appl. No.: 340,791
[52] U.S. Cl 177/200, 177/211, 177/246,
73/141 A
[51] Int. Cl...... GOlg 19/00, GOlg 3/14, GOlg 1/18
[58] Field of Search 177/200,210,211,246,
177/D1G. 9; 73/141 A
[56] References Cited
UNITED STATES PATENTS
2,467,752 4/1949 Howe 177/211 UX
2,955,811 10/1960
3,029,883 4/1962
3,322,222 5/1967
Jonas et al 177/211 X
Kriznic 177/246
Baun 177/210
Primary Examiner—George H. Miller, Jr.
Attorney, Agent, or Firm—L. D. Wofford, Jr.; W. H.
Riggins; J. R. Manning
[57] ABSTRACT
A remotely operable device for detecting changes as
they occur in the mass of a selected specimen. The de-
vice is characterized by a balance beam including at
one end thereof a support for receiving a specimen
having a changing mass and suspension means, includ-
ing a flexure, supporting the beam near its center of
gravity for pivotal movement imparted thereto propor-
tionally to changes occurring in the mass of the speci-
men, and strain gages coupled with the flexure for
providing a read-out indicative of the pivotal move-
ment imparted to the beam.
3 Claims, 4 Drawing Figures
Onclas
00/14 40.476
PATENTEOW28I974 3.812.924
fTG.3.
" . 3,812,924 . . - . . . - . .
- - " ' • 1 • ' • : . ' . . . . . . - 2
DEVICE FOR MONITORING A CHANGE IN MASS . nFSrRlPnnN OF-THP nRAw.Mrs
IN VARYING GRAVIMETRIC ENVIRONMENTS BRIEF DESCRIPTION OF THE DRAWINGS
FIG !
 *
 a
 P"*8"? sectioned side elevation of a de-ORlfilN OF INVFNTIONORIGIN Oh IN VfcN I ION
 yice whjch embodies ^e principies of the instant inven-
The invention described herein was made in the per- 5 tion.
formance of work under a NASA contract and is sub- FIG. 2 is a schematic view of the device shown in
ject to the provisions of Section 305 of the National FIG. 1.
Aeronautics and Space Act of 1958, Public Law FIG. 3 is a fragmentary view, on somewhat of an en-
85-568 (72 Stat. 435; 42 U.S.C. 2457). larged scale, of the device shown in FIG. 1.
RA™<~Dr»iiNr»npTHC iwvcwnr»w 10 FIG 4 is a fragmented, perspective view of theBACKGROUND OF THE INVENTION mounting of a flexure and associated strain gages, as
The invention relates to weighing devices and more provided for the device shown in FIG. 1.
particularly to a device for detecting changes as they nPSPRlPTlON OF THF PRFFFRRFH
occur in the mass of a selected specimen. cxxur^^cJ?
The prior art is, of course, replete with weighing de- 15 EMBODIMENT
vices including those which utilize flexures and strain Referring now to the drawings wherein like reference
gages for indicating weight. Such devices are typified characters designate like or corresponding parts
by the patent to Cooke U.S. Pat. No. 3,667,560. throughout the several views, there is shown in FIG. 1
However, in the field of space exploration, it has be- a device 10 which embodies the principles of the in-
come increasingly desirable and even necessary to de- 20 slant invention.
tect changes as they occur in the mass of remotely ori- The device 10 preferably includes a base 12 upon
ented specimens. The need for remotely detecting which is mounted a pair of vertically oriented stan-
changes in mass in given specimens is particularly acute chions 14. Between the stanchions there is extended a
in peforming material testing operations as well as in transverse beam 16. From the beam 16 there is sus-
conducting probes. Furthermore, devices presently 25 pended a flexure 18 which is welded or otherwise se-
available generally are inadequate for remotely detect- curely affixed to the beam 16.
ing relatively small changes, in the order of three milli- Preferably, the flexure 18 is fabricated from a suit-
gram, as they occur in relatively large masses in the able stainless steel material of a strip-like configuration
order of 500 grams, with high resolution. ' having two thicknesses, as best illustrated in FIG. 3. As
ThegeneraT^r^o^oTtl^irTsEnl"in^eliti6rris,lhere- 30 a practical matter, the flexure 18 includes a central
fore, to provide a device particularly suited for re- portion 20 having a thickness of approximately one-
motely and continuously monitoring changes as they third that of its opposite end portions, designated 21.
occur in the mass of selected specimens.
/~m icr-rc A MP. ci U/IK/I A D v r>c TUC iwvcwrinw Tne lowermost end portion 21 of the flexure 18, asOBJECTS AND SUMMARY OF THE INVENTION
 35 shown in FIG. 3, is weided or otherwise rigidly affixed
Accordingly, it is an object of the instant invention to to a balance beam 22 so that the beam is suspended for
provide a device for monitoring changes in the mass of limited pivotal motion about an axis passing through
selected specimens. the central portion 20 of the flexure 18. Hence, it can
It is another object to provide a device for remotely be appreciated that the flexure 18 is stressed in re-
monitoring changes occurring in the mass of selected 40 sponse to forces which act on the beam 22 in p_lanes_
specimens. normal to the longitudinal axes thereof.
It is another object to provide a device having strain The beam 22 preferably is of an open-truss configu-
gages for detecting and measuring changes in mass as ration and includes four rods 24, FIG. 4. These rods ex-
the change occurs in a selected specimen. tend in a first direction, designated forwardly, from the
It is another object to provide for use in continuous 45 center of gravity of the beam 22 while four rods 26 ex-
monitoring operations a remotely operable, highly sen- tend in an opposite direction, designated rearwardly,
• sitive device for detecting relatively small changes in from the center of gravity of the beam. The rods 24, as
large masses of selected, nonunifprm specimens.. well as the rods 26, are caused to converge and inter-
It is still another object to provide a remotely opera- sect at their distal ends. A plurality of interconnecting
ble, practical, efficient and accurate device for detect- transverse support rods 28 also are employed in lending
ing changes as they occur in the mass of a selected support to the rods 24 near their midpoints.
specimen having a balance beam suspended near its As best shown in FIG. 4, an anchor plate 30, nor-
center of gravity by a flexure having mounted thereon mally related to the longitudinal axis of symmetry of
a strain gage for detecting motion imparted to the beam the beam 22, is provided in a plane extended through
in response to changes in mass of a specimen thereby the beam near its center of gravity. This plate serves as
in spaced relation with the center of gravity. an anchor plate to which the lower portion 21 of the
These and other objects and advantages are achieved flexure 18 is affixed, by welding or the like.
through a use of an elongated balance beam suspended In order to assure that the center of gravity of the
from a flexure and including a specimen support pro-
 6Q beam 22 is located within the plane of the anchor plate,
vided at one end thereof in spaced relation with the in order to establish a balanced condition for the beam,
flexure for receiving selected specimens, a counterbal- there is provided a counterbalancing weight 32 affixed
ancing mass affixed to the beam near the flexure, and to the distal ends of the rods 26. As a practical matter,
strain gages mounted on the flexure for detecting stress the counterbalancing weight 32 includes a screw-
induced in the flexure in response to changes in the
 6J threaded shaft 34 coaxially aligned with the longitudi-
mass of the specimen, as will become more readily ap- nal axis of symmetry of the beam 22 and rigidly affixed
parent by reference to the following description and to the distal ends of the rods 26, by welding or the like.
claims in light of the accompanying drawings. Upon the shaft 34 there is seated a mass 36, preferably
3,812,924
provided as a metallic block having a concentric bore
including internal screw threads for receiving therein
the shaft 34. Therefore, it should be apparent that the
mass 36 is positionable in axial directions relative to the
anchor plate 30 by advancing the mass along the screw
threads of the shaft 34.
To the distal ends of the converging rods 24, there is
affixed a suitable bracket 38. The bracket 38 serves as
a coupling through which a specimen holder 40 is con-
nected with the beam 22. The specimen holder 40, as
shown in FIG. 1, preferably includes multiple trays 42
united through a plurality of rods 44 suspended in
spaced relation from a support plate 46. The support
plate 46, in turn, is coupled with the bracket 38
through a coupling 50 including a flexible cable 52 af-
fixed thereto at one end and having a hook-and-eye 54
provided at its lowermost end. Accordingly, it should
be apparent that selected specimens placed on the trays
42 are supported by the beam 22. .
It is, of course, to be understood that the greater the
ratio of the distances between the test specimen, as it
is supported by the specimen holder 40, and the flexure
18, and the counterbalancing weight 32 and the flexure
18, the greater is the realizable resolution of the device
10. A ratio of 6 to 1, depicted in FIG. 2, has proven
quite adequate for measuring three milligram weight
changes occuring in a 500 gram specimen.
It is important to understand, however, that the
greater the ratio of the distances between a test speci-
men and the flexure 18, and the counterbalancing
weight 32 and the flexure, the greater is the tendency
to impart undesired oscillation to the beam. Therefore,
a dash pot 56 is provided and coupled with the beam
22 through a suitable rod 58. The dash pot 56, prefera-
bly, is filled with oil of a suitable viscosity and includes
a pressure plate 60 disposed therein and affixed to the
coupling 58. Since the design and construction of dash
pots are well known, a detailed description of the dash
pot 56 is omitted in the interest of brevity.
Oscillatory motion imparted to the beam 22 is de-
tected by a plurality of strain gages 62 affixed to the
flexure 18 at the central portion 20 thereof. Preferably,
the strain gages 62 are provided in pairs at opposite
sides of the flexure and serve to measure bending stress
in the flexure as a force is applied vertically to the beam
22. Since the design and construction of strain gages
also are well known and the operation of such devices
is fully understood, it suffices to understand that the
strain gages 62 are coupled with a suitable source of
electrical energy and provide an electrical read-out sig-
nal indicative of the stress induced in the flexure 18. As
currently employed, the strain gages are of the type
available under the designation PREMMCO EA-0-
6-250BGi-120, Option W. The strain gages 62 are, of
course, coupled with a suitable read-out and recording
device 64. As a practical matter, the device 64 also in-
cludes suitable telemetry circuitry for telemetering
data acquired as changes occur in the mass of speci-
mens supported by the holder 40.
OPERATION
It is believed that in view of the foregoing descrip-
tion, the operation of the device 10 will be readily un-
derstood and it will be briefly reviewed at this point.
With the device 10 assembled in the manner herein-
before described, it is readied to be employed in an en-
vironment such as is found in celestial space and which
may be substantially duplicated in test chambers and
the like. It is, however, quite important to appreciate
that the device is not limited to use in such environ-
ments.
5 Selected test specimens, the mass of which is to be
observed, are deposited on the specimen holder 40 and
the counterbalancing weight 32 is so positioned so that
no bending stress is imparted to the flexure 18. It is im-
portant to understand, also, that the weight 32 is of a
10 suitable mass, and is positioned along the shaft 34 at a
selected distance from the flexure 18. Once balanced
in an operative environment, a continuous re-balancing
of the beam 22 is not required. Changes in the mass of
• specimens supported by the specimen holder 40 now
15 serve to increase the bending stress imparted to the
flexure 18. This stress is proportional to changes in the
mass of the specimens supported by the holder 40 and
results from changes in forces applied to the balance
. beam 22 as a consequence of changes in the mass of the
20 specimens. The stress, in turn, is detected by the strain
gages 62 and an electrical signal indicative of the stress
now is applied to the read-out circuit 64. From here the
signal is transmitted for utilization in a manner consis-
tent with the intended utility of the device 10.
25 in view of the foregoing, it should readily be apparent
that the device embodying the instant invention is re-
motely operable and is capable of being employed in
hostile environments for detecting relatively small
changes in relatively large masses of specimens.
30
 Although.the invention has been herein shown and
described in what is conceived to be the most practical
and preferred embodiment, it is recognized that depar-
tures may be made therefrom within the scope of the
invention, which is not to be limited to the illustrative
35
 details disclosed.
We claim:
1. A device for monitoring changes as they occur in
the mass of a selected specimen comprising:
an elongated balance beam including means for sup-
porting at one end thereof a specimen having a
constantly changing mass, and means for support-
ing a fixed mass at the opposite end thereof;
said balance beam defining an open truss structure
comprising a plurality of rods and an anchor plate,
said rods being spaced from each other at said an-
chor plate and converging in one direction toward
said specimen supporting means and in the other
direction toward said fixed mass supporting means;
the distance between said anchor plate and said spec-
imen supporting means being substantially greater
than the distance between said anchor plate and
said mass supporting means;
,, suspension means including a flexure depending from
an elevated support supporting the balance beam
for pivotal motion imparted thereto in response to
the changing mass of said specimen, said flexure
being rigidly affixed at its opposite ends to said ele-
60 vated support and to said anchor plate whereby the
flexure is stressed proportionately with respect to
pivotal motion imparted to said beam;
said flexure comprising a central portion of reduced
thickness between said anchor plate and said ele-
6, vated support;
means for measuring the stress of said flexure com-
prising a plurality of strain gages affixed to said
central portion of said flexure;
40
45
3,812,924
said fixed mass supporting means comprising a
screw-threaded shaft coaxially aligned with the lon-
gitudinal axis of symmetry of said beam and thread-
edly engaging said mass.
2. The invention as defined in claim 1 including a
fluid-containing 'dash pot supported beneath said bal-
ance beam, a pressure plate disposed in said dash pot
and coupled to said beam.
3. The invention as defined in claim 1 wherein said
specimen supporting means is spaced substantially six
times further from said anchor plate than is said mass.
* * * * *
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Device for monitoring a change in mass in varying gravimetric environments

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