Torquemeter for determining magnitude of torque generated by interaction of magnetic dipole between test specimen and ambient magnetic fiel

Boyle, J. C.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
REPLY TO 
ATTN OF G P  Apri l  5, 1971 
MEMORANDUM 
TO: h* ~ ~ I / S c i e n t i f i c  & Technical information Division +:,:: 
Attn: M i s s  Winnie M. Morgan 
FROM : ~P/Of f i ce  of Ass i s t an t  General 
Counsel f o r  Patent Matters 
SUBJECT: Announcement of NASA-Owned 
U.S. Patents  i n  STAR 
I n  accordance with t h e  procedures contained i n  t he  Code GP 
t o  Code US1 memorandum on t h i s  subject ,  dated June 8, 1970, 
t he  attached NASA-owned U.S. patent  i s  being forwarded for 
abs t rac t ing  and announcement i n  NASA STAR. 
The following information is provided : 
U.S. Patent No. 
Corporate Source Goddard Space F l igh t  Cente r  
Supplementary 
Corporate Source 
NASA Patent  Case No. : XGS-10013 
Gayle ' Parker 
Enclosure : 
Copy of Patent  
- . ., . . - - . . 
https://ntrs.nasa.gov/search.jsp?R=19710014249 2020-03-17T03:05:23+00:00Z
Aug. 12, 1969 J. C. BOYLE 3,468,361 
BALANCE TORQUEMETER 
Filed Aug. 30, 1967 2 Sheets-Sheet I 
Aug, 12, 11969 
Filed Aug. 30, 1967 
J. C. DOYLE 3,460,38 1 
BALANCE TORQUEMETER 
2 Sheets-Sheet z 
FIG. 2 .  INVENTOR Joseph C. BoyJe 
3,460,38 1 United States Patent Ofice ,, ,,, , ,,,, 
-- 
n 2 
of the magnetic moment or allow determination of the 
3,440,381 
BALANCE TORQUEMEmR magnitude and sense of control torques generated by a 
Joseph C. Boyle, fiekville, Md., assignor to the United system upon command' 
States of as represented by Accordingly, it is the object of the present invention 
of the National Aeronautic and Space Administration 5 to  provide simplified equipment to ~ e r f o r m  a simple, 
Filed Aug. 30, 1967, Ser. No. 465,209 direct measurement of torques upon a test specimen. 
Int. Cl. GO11 3/10 Another object of the invention is lo provide simplified 
U.S. CI. 73-133 6 Claims equipments for accurately measuring feeble torque pro- 
duced upon a heavy mass. 
10 Another object of the invention is to provide simpli- 
ABSTRPnCT OF THE IPISCEOSnE fied equipments for accurately and rapidly n~easuring 
A balance torquemeter for measurement of small 
torques, particularly those caused by a magnetic dipole 
moment acting upon a massive body, where the body is 
uncoupled from the torsional stiffness of conventional 
solid support systems by a hydrostatic support technique 
enabling measurements under frictionless conditions and 
where the opposing angular torque is provided by a fine 
torsion wire. 
torque produced upon a heavy mass. 
Another object of the invention is to provide a feeble 
torque measuring means with a short adjustable settling 
time. 
Another object of the invention is to provide a means 
of decoupling large masses from the torsional stiffness 
of a solid support system thereby enabling the measure- 
ment of feeble torques which act thereupon. 
Further objects as well as features and attendinn ad- 
vantages o fthe invention will become apparent from the 
following description when taken in conjunction with the 
The invention described herein may be manufactured accampanying drawings, in which: 
and used by and for the Government of the United States FIGURE 1 is a plan view, in partial section, of one 
of America for govenmental PurPoses without Payment 25 embodiment of the apparatus used in carrying out the 
of any royalties thereon or therefor. invention: 
DISCLOSURE F I G U ~  2 is a plan view, in partial section, of the preferred embodiment of the invention shown within a 
The present invention relates generally to torque meas- magnetic test facility. 
urement, and more particularly to an apparatus for deter- 30 According to the present invention, in order to deter- 
mining the magnitude, acting upon a test specimen, of mine directly the torque acting upon a massive body, 
the torques which are generated by the interaction be- the body is mounted on a suitable frame which is pro- 
tween the magnetic dipole of a test specimen and am- vided hydrostatic support and which decouples the mass 
bient magnetic fields. from the torsional stiffness of a solid support system. A 
A permanent magnet or a bar of soft iron tends to 35 centrally mounted vertically oriented torsion member 
align itself with the earth's magnetic field. The strength affixed to the pedestal and to ground provides angular 
of this tendency is determined by a property of the ob- compliance to applied torques about the central axis. For 
ject called the "magnetic moment." Since the geomag- the torsion member, a fine wire having an appropriately 
netic field of the earth is not confined t o  the surface of soft torsional resistance may be used because the mass 
the earth, even those objects which are traveling in outer of the specimen is not being supported by the torsion 
space are subject to forces arising from interactions with member. To minimize settling-out time, adjustable veloc- 
our magnetic field. Accordingly, if a spacecraft in orbit ity type dampers are provided to impede and damp tor- 
has a significant magnetic moment, the geomagnetic sional oscillation of the specimen and to facilitate rapid 
fields will produce a torque upon the spacefract which, stable measurements of disturbing torques. 
if undesirable, can only be counteracted by the wasteful 45 Discussed in detail in the following description, is a 
expenditure of energy in an opposing manner. On the particular embodiment of the invention for determining 
other hand, attitude control systems can be designed to the magnetic torque upon a massive body, such as may be 
make use of such magnetically induced torques to sta- experienced by a satellite having a magnetic moment when 
bilize or control a spacecraft. acted upon by the geomagnetic fields of the earth. It is to 
It is important to  know, prior to lanuch, the magnetic 50 be understood however, that the underlying concepts are 
moment of a spacecraft because through magnetic bal- equally applicable to torque measurements alising from 
ancing techniques, this moment can be reduced to an in- control torque devices such as momentum wheels, gas, 
significant value, or its effects can be taken into consider- ion, or microthrust propulsion jets, electromagnetic pres- 
ation. sures due to transmission or reception of radio frequency 
There are several methods in the prior art for meas- 55 or optical energies, transmission of circularly polarized 
uring magnetic moment. The most common is to  meas- energy, electric dipole moments, or eddy current 
ure the magnetic field due to the test specimen. When interactions. 
making measureemnts on large specimens with small With reference to FIGURE 1, the torque meter assern- 
magnetic moments, this method gives poor results be- bly is comprised of an annular water tight basin or con- 
cause it becomes necessary to make measurements at  60 tainer 10 having an open upper end. The basin i s  filled 
distances great enough so that the assemblage resembles with a liquid, preferably water 11 in which thc contam- 
a simple magnetic dipole. However, when these dis- inates have been removed; however, other fluids have 
tances become large, the field intensity for small dipole been used, the only requirement being that the Ilrrid must 
moments is so low as to prohibit accurate measurements. exhibit newtonian viscosity characteristics, i.e., zero shear 
Another method entails the use of a test specimen as the 65 resistance at zero velocity. An annular enclosed pontoon 
rotor of a permanent magnet alternator using the elec- member 12 having a smaller width than the width of the 
trical output of the alternator as a measure of the dipole annular basin 10 is buoyantly floated upon the fluid within 
moment. This method requires complicated equipment the basin. Resting upon the pontoon 12 is the support 
and is obviously impractical for anything so massive as frame 13 and support frame web 14 which provide struc- 
an entire spacecraft. In the ideal situation it is desirable 70 tural rigidity for the centrally located specimen mounting 
to be able to test an entire spacecraft in an magnetically pad 15. The torsion wire 16 is located along the central 
isolated environment which wo~lld enable measurement axis indicated by 17 of the torque meter and i s  colinear 
3,460,381 
3 4 
with the central axis of the annular pontoon 12. The tor- Calibration of the torquemeter of FIGURE 2 has been 
sion wire is provided some small amount of tension to accomplished by a number of independent methods. First, 
restlain radial motion of the pontoon 12. The torsion the torquemeter can be considered an absolute instrument 
bracket I8 having a lower arm 19 and an upper arm 20, since its sensitivily can be calculated from direct measure- 
not shown, is afixedly attached at its upper arm to the ments of the dimensions of the device including the diam- 
bottom of the support frame 13. An upper portion of the eter of the torsion wire and knowledge of its modulus 
torsion wire 116 indicated at 21 is connected to the upper of rigidity. However, additional methods of calibration 
arm 20 at the exact point at which the center line passes for dete~mining the torquemeter sensitivity have also been 
through the uppei arm, and the lower section indicated employed, which in combination with an error analysis, 
by 22 of the torsion wire 16 is connected to the lower arm closely correlate with the calc~llated values and which 
19 along the center line. A tie block 23 which is centrally show that the sensitivity of this embodiment is linear with 
fastened by any appropriate means, i.e., clamping, weld- dependable repeatability and fine resolution, i.e., a small 
ing, etc. to torsion wire 16 is clamped to the upper and model had a sensitivity of 8.8 dyne-cm./arc second and a 
lower paraliel flat fiexure members 24 and 25, respectively. larger model had a sensitivity of 23.02 dyne-cm./arc sec- 
The flexure members are adapted to rigidly clamp and 15 ond with a repeatability of 5 3 0  dyne-cm. and a resolu- 
restrain the torsion wire 16 with respect to rotation, while tion O F  t 10 ciyne-cm. 
permitting. flexing in the vertical direction to accommo- As an illustration of the practical application of the 
date some vertical motion of the pontoon 12. Both parallel method and apparatus described, assume that mametic 
flexure members are attached to a fixed support bracket moment measurements are to be made on a spacecraft. 
26, which bracket serves as the stable reference for  the 20 The equivalent permanent dipole moment of a spacecraft 
invention. A plurality of vertically adjustable damper is a veclor that can be resolved into components along the 
paddles 27 are movably attached to the support frame 13 body axes. Thebe components can be determined from the 
and are immersed in a fluid in the damper basin 28. A torque generated about the vertical axis, when the space- 
plurality of fluid filled containers disposed at 120° inter- craft is oriented with the body axis of interest in a hori- 
vats about the periphery of the support frame web com- 25 zontal plane and where the magnetic field vector is hori- 
prise the damper basin 28. The damper basins are filled zontal, preferably at right angles to the body axis. This 
with a damper fluid 29, the viscosity characteristics of requires two orientations of the spacecraft on the torque- 
which control the critical damping factor. Annular pon- meter. In general, both an equivalent permanent and an 
toon 12 rnay be filled with air at one atmosphere or may induced dipole moment will be present. Barring sat~ira- 
be filled with any fluid that is Jess dense than the fluid in 30 tion effects, these can be separated by the following two- 
thc annular basin 10. The amount of buoyancy desired measurement techniques. The first torque measurement 
dependr on the mass of the test specimen and 011 the pel- will result in a total magnetic torque, 
missible vertical motion of the toralon wire 16 and flexure L=MXN 
members 24 and 25. Reference mirror 30 is shown at- 
tached to the specimen mounting pad 15 preferably with 33 and, where M and H are orthogonal, 
its pIain reflective face perpendicular to the radius of the 
annular pontoon. $f ,-p-M,f M,  
FIGURE 2 illustrates the manner in which the torque 
meter is specifically adopted to perform magnetic moment Mzmagnetic field intensity 
measurements upon a spacecraft. All materials are se- *' L=torque 
lected for their nonmagnetic and nonconductive proper- M=total equivalent magnetic dipole moment 
ties insofar as is practical. For example, pontoon 12, Mi=induced equivalent magnetic dipole nlonlent 
made of poiystyrene foam, is hydrostatically supported M,=permanent equivalent magnetic dipole moment 
within the fiberglass annular basin 10 with a plywood 
frame 13 mounted &ereupon. The torsion wire 16, made 4 j  If the direction of the magnetic field vector IS  reversed, 
of Or nonlnagnetic beryllium copper having low the torque due to the induced dipole moment will not re- 
hvsteresis losses, is restrained in torsion by the pair of verse. 
flexure fiber glass members 24 and 25, respec- Af- - h? lively. In this embodiment, the annular fiber glass basin ,--- N -&ID + 111, 
10 is a%xedly attached on the other end of the parallel j g  
flexure members 24 and 25 and the basin 10 therefore which yields 
becomes the fixed station. In order to place the spacecraft 
specimen 31 at the center of the magnetic facility 31 and M nf? L1-I,, A{, = --L---- = ---- 
to isolate the spacecraft from disturbing aerodynamic 2 2H 
egects, a stable wooden pedestal 33 with an upper wooden j j 
airshield assembly 26 and plywood side panels 35 are Mt+M LlSLr ,w, =------- = - - - 
provided. In use, the temperature difference between the 2 2H 
inside and outside of the airshield assembly 26 is main- The invention provides therefore, an apparatus for de- 
tained at an appropriately small value to avoid torques termining the magnitude of very small torques acting upon 
induced by convection air currents. The newtonian fluid 11 60 a large mass by hydrostatically supporting said mass in a 
wilhin the annular basin 10 is preferably water because of nonshear resistive manner, and by providing a soft com- 
i t s  convenience in use. The damper basins 28, constructed pliant member for supplying the resistive torques in a 
as a plurality of protuberances along the periphery of the measurable manner, thus enabling direct measurement of 
annular basin 110, use water as the damping fluid 29. The the torque acting on the mass. While the specific embodi- 
fiber glass damper paddles 27 are adjustably immersible (ij ment has been described with particularity for the purpose 
within the damper basin 28 to provide for damping factor of explaining the invention, it is not so limited, and mod- 
variation. Reference mirror 30 which indicates motion ifications and variations thereof should be obvious to  
about the torquemeter center line 17 is mounted on the those skilled in the art. For example, while the apparatus 
bottom of a plastic or fiber extension or sting 36, the op- has been described as employing an enclosed pontoon float 
posed end of the sting 36 being affixedly attached to the 70 member, the invention may find utility where the pontoon 
torsion bnacket 18 at its lower arm 19. The autocollimator member may be internally pressurized and may be con- 
37 aligned through porthole 35 with the reference mirror structed with an open bottom. Likewise, transducers other 
30 provides an electrical error signal to recorder 39 than the mirror-autocollimator combination may be used. 
~ h c r e b y  any angular niotion of the mirror 30 from the For example, a differential capacitor in an A.C. bridge 
pi ecatablrshed alignment is continuously transcribed. 75  circuit, a differential transformer in an A.C. bridge circuit, 
3,460,381 
5 6 
a strain gage system or piezoelectric transducer or an opti- a paddle, said paddle being adjustably connected lo said 
cal lever or interferometer are among other possible alter- frame on one end, and immersed rn said second fluid 
natives. In addition the invention may be utilized for the adjacent said second end. 
study of perturbation torques arising from any source. 5. Apparatus as defined in claim 4, wherein: 
What is patented as new and desired to be secured by said first container comprises inside and outside con- 
Letters Patent of the United States is: centric cylindrical walls having a space therebetweell 
1. Apparatus comprising: and a bottom wall between said two concentric cylin- 
a first container having an open top, said first container drical walls, said inside concentric cylindrical wall 
immovably connected to a fixed station; defining a central passageway through said first con- 
a hydraulic fluid confined within said first container; 10 tainer; 
a pontoon floated upon said first fluid and being adapted a bracket, said bracket being a rigid U-shaped rnen~ber 
for rotation; having two arms and being affixedly connected by 
damper means interposed between said pontoon and one arm to said frame and being positioned within 
said fixed station for absorbing the energy of relative said central passageway through said first container; 
motion therebetween; 16 said torsion member having a first and second end ancl 
a torsion resistive member, connected to both the pon- a center point therebetween, said first end being affix- 
toon and said fixed station; and edly attached to one arm of said bracket and said 
a reference marker, said reference marker being affixed second end being affixedly attached to the other arm 
to said pontoon so that the angular displacement be- of said bracket; 
tween said pontoon and said first container can be 20 a single axis flexure member, said flexure member be- 
measured. ing attached between said center point of said tor- 
2. Apparatus comprising: sion member and said fixed station. 
a first container having an open top, said first container 6. Apparatus as defined in claim 2, wherein: 
being mounted upon a fixed station; said reference marker comprises a member having a 
a first fluid confined within said first container having 25 reflective characteristic; 
a known specific gravity; a collimator, said collimator directed along a radial ref- 
a pontoon floated upon said first fluid, said pontoon erence line which intersects said centrai axis and 
having a central axis and a specific gravity less than which is perpendicular to a surface of said reflective 
said first fluid and being adapted to rotate about said member whereby small angular deviations of said 
central axis; 30 reflective member are measurable. 
a frame, said frame being substantially completely sup- 
ported by said floated pontoon; References Cited 
a torsion member having a first end, said first end being 
affixedly connected to said frame at a first point along UNITED STATES PATENTS 
said central axis and said torsion member being affix- 35 83 1,794 911906 Lohle ---------------- 308-9 
edly attached to said fixed station at  a second point 2,498,995 211950 Manning ----------- 73-117.4 
along said central axis; and 2,574,795 11119.51 Miller ----------- 73-133 XR. 
a reference marker, said marker being connected to said 2,614,184 1011952 ~ o b i n s o n  --------- 308-9 XR 
frame. 2,634,120 4/1953 Ouaida 177-207 
3. Apparatus as defined in claim 2, wherein: *' 2,643,543 611953 Herzog --------------_. 73-59 
a velocity type damper is afiedly connected between 3,200,633 811965 McCoy 73-9 
said frame and said fixed station. 
4. Apparatus as defined in claim 3, wherein said veloc- CHARLES A. RUEHL* Primary Exalniner 
ity type damper comprises: 
a second fluid container having an open end; 45 U.S. Cl. X.R. 
a second fluid confined within said second container; 73-1 17; 308-9; 324-34 


Balance torquemeter Patent

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