A combination dual-spin gyroscopically stabilized device is described having a spinning rotor and a non-spinning platform. Two substantially lossless mechanical resonators, resonant at the spin frequency, are orthogonally positioned on the platform for compensation for the disturbing torque acting on the platform due to rotor misalignment

Donohue, J. H.

Zimmerman, B. G.

English

NASA Technical Reports Server

O »
REPLY TO
ATTN OF: . GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
JUL 8 1974
TO: KSI/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General
Counsel for Patent Matters
-•
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided;
U.S. Patent No. :
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent case No.
.V i_
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
YES /—7 NO
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words "...with respect to
an invention of ..."
Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19740019984 2020-03-17T15:03:40+00:00Z
United States Patent
D6nohue et al.
mi 3,818,767
[45] June 25, 1974
[541
[75]
PASSIVE DUAL-SPIN MISALIGNMENT
COMPENaA 1 UKa
Inventors: James H. Donohue, Ellicott City;
3,442 468
3 564931
5/1969
2/1971
lorillo
Humphrey
244/1 SA
74/5.5
Benjamin G. Zimmerman, Forest
Heights, both of Md.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: Sept. 29, 1972
[21] Appl. No.: 293,739
[52] U.S. Cl 74/5.5, 244/1 SA
[51 ] Int. Cl GOlc 19/02
[58] Field of Search 74/5.5, 5.42, 5.47, 5.41;
244/1 SA; 188/1 B
[56] References Cited
UNITED STATES PATENTS
3,393,555 7/1968 Flannelly 188/1 B
Primary Examiner—Manuel A. Antonakas
Attorney, Agent, or Firm—R. F. Kempf; John R.
Manning
[57] ABSTRACT
In combination with a "dual-spin" gyroscopically sta-
bilized device having a spinning rotor and a non-
spinning platform two substantially lossless mechani-
cal resonators, resonant at the spin frequency, are or-
thogonally disposed on the platform for compensation
for the disturbing torque acting on the platform due to
rotor misalignment.
5 Claims, 4 Drawing Figures
N74-28097^1
Onclas
_00/2J 42753
PATENTED JM251374 3,818,767
SHEET 1 OF 2
PATENTED « 51974 3,818,767
SHEET 8-OF 2
v, 41
i® C| I
--- 1
44
._ 1
d
-10
7G O—30
74 -8
-8
14
hit
14 3-10
.18
O--30
70-
46-
/
4fe
4G
—46
8
28
O—30
30
3,818,767
PASSIVE DUAL-SPIN MISALIGNMENT
COMPENSATORS
ORIGIN OF THE INVENTION
The.invention described herein was made by employ-
ees of the United States Government and may be man-
ufactured and used by or for The Government for gov-
ernmental purposes without the payment of any royal-
ties thereon or therefor.
BACKGROUND OF THE INVENTION
This invention relates to spin-stabilized devices of the
"two-body" or "dual-spin" configuration comprising a
spinning rotor and a stationary platform. In a space sat-
ellite, the rotor provides gyroscopic stabilization while
the platform is used for the mounting of those instru-
ments, for example, optical and electromagnetic trans-
mitters and receivers, whose operation or function may
be adversely affected by spinning. The platform, which
is commonly referred to as "mechanically despun",
must provide an extremely stable base for these instru-
ments.
As is well known in the art, the rotor's spin axis ide-
ally should both pass through its center of mass and
contain its principal axis of inertia. It is a characteristic
of gyroscopic stabilization that a disturbing torque, not
parallel to this spin axis, induces "nutation" or "preces-
sion" of this desired spin axis. An impulsive torque ap-
plied to a "dual-spin" system induces "free precession"
at a particular frequency determined only from the an-
gular momentum of the spinning body and the system's
Iran verse inertia. In order to dissipate the energy of this
precession, nutation dampers which are ideally tuned
to the nutation frequency are disposed on the station-
ary platform. These dampers are lossy mechanical reso-
nators which although maximally responding at the nu-
tation frequency, provide damping at a fairly broad
range of frequencies. Effectively, they dissipate the nu-
tational energy, so that the orientation of the spin axis,
and therefore the orientation of the platform, tends to
be inertially fixed.
The rotor is coupled to the platform by a motor bear-
ing assembly which determines the location of the spin
axis with respect to the "dual spin" device. Any mis-
alignment of the motor bearing assembly or unbalance
of the rotor forces the spin axis, to be either skewed
from the principal axis of inertia of the rotor or offset
from the center of mass of the rotor. This misalignment
or unbalance produces an additional disturbing torque
acting on the platform which causes a "nodding" mo-
tion of the spin axis in addition to the "free precession"
previously mentioned. This "nodding" occurs at the
spin frequency rather than at the nutation frequency.
The effect of the misalignment torque can be dimin-
ished by the nutation dampers but cannot be com-
pletely cancelled with the result that the state of the art
platform is not as stationary as may be required.
It is an object of the present invention to provide pas-
sive means, in addition to nutation dampers, for oppos-
ing the disturbing torque acting on the platform which
is due to rotor misalignment in order to achieve a high
degree of stability of the platform.
SUMMARY OF THE INVENTION
The misalignment torque acting on the platform is
directed perpendicular to the rotor's spin axis and ro-
tates at the spin rate. If this rotating torque vector is re-
solved into components along two specially orthogonal
axes on the platform, it will be recognized that each of
these components are sinusoidal functions of the spin
frequency. In addition, these sinusoidal components
5 are in phase quadrature. In accordance with the inven-
tion, two misalignment compensators, in the form of
substantially lossless torsional mechanical resonators,
resonant at the spin frequency, are disposed on the
platform directed along spacially orthogonal axes.
10 These resonators, starting from arbitrary initial condi-
tions, eventually oppose exactly the misalignment
torques, so that no net misalignment torque acts on the
platform.
Other objects and features of the invention will be
15 more fully apparent in the course of the following de-
scription and from an examination of the related draw-
ings wherein: ,
FIG. 1 schematically depicts a perspective of a dual-
spin device, such as a space satellite, showing the mis-
20 alignment compensators of the invention mounted
thereon.
FIG. 2 schematically shows the electrical circuit of an
electrical analogy, for analyzing the operation of the
misalignment compensators of the invention.
25 FIG. 3 shows a plan view of an assembly of two mis-
alignment compensators of an alternate embodiment,
said assembly also including nutation dampers.
FIG. 4 shows a plan view of still another embodiment
of the misalignment compensators in an assembly simi-
30 lar to FIG. 3.
DETAILED DESCRIPTION
In FIG. 1, the rotor 2 for gyroscopic stabilization is
rotably coupled to the stationary platform 4 by the
35
 motor bearing assembly 6. Two substantially lossless
mechanical resonators are disposed on the platform
directed along orthoronal axes 7 and 3 and each are
also directed perpendicular to the spin axis of the "dual
spin" system 5. It will be appreciated that these two or-
40
 thogonally directed resonators may be combined into
one sub-assembly. Each resonator is defined by a rata-
ble mass 8, a torsional wire-like spring 10, and axle 12,
axle supports 14, and a spring support 16. The ratable
mass and the axle form a rigid assembly which is rota-
45
 ble in the axle supports through the action of bearing
18. The mass-axle assembly has a predetermined mo-
ment of inertia and it may be broadly considered as ra-
table with respect to the platform since the axle sup-
ports 14, are attached to the platform. One end of the
torsional spring 10, is fixedly mounted to the axle 12,
while the other end of the torsional spring is fixedly
mounted to the platform 4 via the spring support 16.
Torque due to the resonator, which is directed parallel
to the axle, is coupled to the platform via the spring
support 16. The torsional spring 10 provides a means
for applying torque to the platform which is propor-
tional to the rotation angle of the mass 8 with respect
to the platform 4. The constant of proportionality is the
,- spring constant.
Each resonator is capable of applying a sinusoidal
torque to the platform. The combination of the two res-
onators' therefore has the capability of canceling the ro-
tating misalignment torque vector, since this vector
,, consists of two spacially orthogonal components which
are sinusoidal. Since the components of the misalign-
ment torque vector are sinusoidal at the spin fre-
quency, the resonators must be resonant at this fre-
50
3,818,767
3 . 4 . * • ._..
quency. Therefore the square root of the ratio of the discussion indicates there is cooperation between these
spring constant of the torsional spring 10 to the mo- parts:
ment of inertia of the ratable mass 8 must equal 2ir Each of the misalignment compensators produces
times the spin frequency. The bandwidth of the sub- two tyP6? of output, a "forced output" in response to
stantially lossless resonators, although generally nar- 5 *?misalignment torque excitation and a "free output-
row, should be selected to encompass the range of ex- wh^may be- th°U^ * £?, im!ial,condlt!°n- This
. . , . .. £,. . 6. , wil be recognized by those skilled in the mathematics
pected spin frequency variation. This can be done by
 of differentj£ equations. The "forced output" is the
selection of the Q of the resonators. Since, in practi- one which cancels the misalignment torque. The "free"
cal applications, some small amount of damping is un- outputs for these substantially lossless resonators are
avoidable, the "Q" may be selected by varying the 10 essentially undamped sinusoids. Since, the free outputs
product of the spring constant and inertia while main- cause "nodding" of the entire device they will be
taining the ratio of these parameters constant. damped out by the conventional damping mechanism
Nutation dampers 20, which are required in addition which are otherwise required for device stability, leav-
to the misalignment compensators for stabilizing the in8 only the forced output. Thus starting from arbitrary
platform, are shown mounted on the platform 4 di- l5 lnltial conditions (an arbitrary free output), the rnis-
rected along orthogonal axes. alignment compensators eventually provide a torque
That the misalignment compensators are effective in S^^^SSSSSSE 2S
eliminating the misalignment torques on the platform
 tially Ioss]ess ^ esonators and the nutation damping ,ossy
will be clear by considering the electrical analogy resonators produce torques to achieve a high degree of
shown in FIG. 2 which analogizes the operation of one stability of the platform. FIG. 4 shows another alternate
of misalignment compensators of the invention. In ac- embodiment wherein the pivots 24 of FIG. 3 are re-
cordance with the analogy, the spin frequency sinusoi- ' placed by a torsion wire suspension. There, tensioned
dal current generator I, represents the sinusoidal com- wires 46 connect the ratable mass 8 to the supports 26.
ponent of the misalignment torque which is directed , These wires act as torsional springs in a similar manner
parallel to the axle of one of the misalignment compen- ^ the P>vots 24 of FIG. 3.
sators. The capacitance C, represents the moment of . Although several embodiments of this invention have
inertia of the platform along this direction and the volt- b.eetn 1"u.sJ.ratf.d aPd described it will be appreciated
., . .u i i •. r.L i .<• that modification is possible without departing from its
age V, represents the angular velocity of the platform
 irk and for example, the misalignment com-
m this direction. The series resonator 42 represents a
 30 pensators instead of being torsional resonators may be
misalignment compensator and is resonant at the spin iinear resonators which are orientated parallel to the
frequency. The inductance U represents the inverse of
 spin axis 5 (FIG. 1), and which are displaced from the
the torsional spring constant while C2 represents the spin axis in orthogonal directions by a predetermined
moment of inertia of the ratable mass of the resonator. lever arm. In this embodiment as well as those previ-
The angular velocity of the ratable mass of the mis- 35 ously discussed, the resonators apply torque to the plat-
alignment compensator is represented by the voltage form along orthogonal axes which axes are also perpen-
Vz. The lossy resonator composed of L3, C3, and Rg is dicular to &e spin axis of the dual-spin configuration,
resonant at the nutation frequency and represents a nu- w 1 '
tation damper. As tan be seen from FIG. 2, since the
 L^combination with a "dual-spin" gyroscopically
series resonator 42 which represents a misalignment 40
 stabiHzed device having a rotor spinning about a spin
compensator is resonant at the frequency of the current
 axis at ^ essentially constant spin rate which is rotat-
generator, it absorbs all the generator's current. Thus,
 ably coupled to a non-spinning platform, said dual spin
by analogy, the angular velocity of the platform is zero device having nutation damping means, the improve-
while the angular velocity of the ratable mass, is such ment comprising:
that all the torque acts upon it. Stated another way, the 45 A first mechanical resonator, resonant at a predeter-
resonator produces a torque which completely opposes mined frequency equal to the spin rate, disposed on
the misalignment torque. the platform so as to apply torque to said platform
FIG. 3 shows another embodiment of the misalign- .in a direction perpendicular to the spin axis; and
ment compensators and indicates an assembly of the ^^^^^^^^^yfp^
two compensators into one unit. In this embodiment 50
 form ^ ^ ^ H J tQ J» ^ ^ P ^
the bearing 18 and torsional spring 10 are replaced by
 rection perpendicular both to the spin axis and to
a pivot 24 at each end of the ratable mass 8. The pivot
 the direction of torque application of the first reso-
24 has one end fixedly mounted in a bore in the ratable nator.
mass 8 and the other end fixedly mounted in a bore in 2. The improvement of claim 1 where each of the me-
the supports 26. This pivot is a commercially available chanical resonators are substantially lossless,
item which has the characteristic of a torsional spring 3. The improvement of claim 1 wherein each of the
whose longitudinal axis can resist shear and bending mechanical resonators are torsional'resonators corn-
forces. The supports 26 are attached to plate 28 which prising:
has holes 30 for mounting this assembly onto the plat- ^ A mass which is ratable with respect to the platform;
form. In this embodiment, the torques proportional to 60 fd sPnn8 means.for fPPlying torque to the p lat-
the rotation angle of the mass with'respect to the plate J^ SS^JfcSf °f — °f «*
are coupled to the platform via the pivots 24 and the
 4 Thfi improvement of claim 3 where ^ •
supports 26. The spring constant of the resonator is the
 means comprises a wire coupling the mass to the plat-
sum of the spring constants of the pivots at each end of
 65 forrrii
the ratable mass 8. Thus, the pivots are springs which 5. The improvement of claim 3 where the spring
are in series. Nutation dampers 20 may advantageously means comprises two springs which are in series,
be included in such an assembly since as the following * * * * *


Passive dual spin misalignment compensators

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server