An object of the invention is to provide variable damping for resonant vibrations which may occur at different rotational speeds in the range of rpms in which a rotating machine is operated. A variable force damper in accordance with the invention includes a rotating mass carried on a shaft which is supported by a bearing in a resilient cage. The cage is attached to a support plate whose rim extends into an annular groove in a housing. Variable damping is effected by tabs of electrically conducting nonmagnetic material which extend radially from the cage. The tabs at an index position lie between the pole face of respective C shaped magnets. The magnets are attached by cantilever spring members to the housing

Cunningham, R. E.

English

NASA Technical Reports Server

United States Patent [191 
Cunningham 
~~ __ 
[54] VARIBLE FORCE, EDDY-CURRENT OR 
MAGNETIC DAMPER 
[75] Inventor: Robert E. Cunningham, Cleveland, 
[73] Assignee: The United States of America as 
Ohio 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 463,456 
[22] Filed: Feb. 3, 1983 
[51] Int. Cl.3 ................................................ G05B 5/01 
U.S. C1. ...................................... 318/611; 310/77; 
310/93; 335/100 
Field of Search ................................ 318/611-614, 
33 5/ 100 
[52] 
[58] 
318/460; 310/77, 93, 105-110; 324/125; 
t561 References Cited 
US. PATENT DOCUMENTS 
2,353,618 7/1944 Lamb .................................. 324/125 
3,099,094 7/1963 Ehrich et al. ................... 318/611 X 
3,277,357 10/1966 Willis ................................ 310/77 X 
3,699,369 10/1972 Hlipala ................................ 310/106 
4,142,610 3/1979 Alexander ........................ 310/77 X 
4,390,260 6/1983 Prinz ............................... 318/614 X 
4,398,111 8/1983 Zuch ..................................... 310/93 
Primary Examiner-B. Dobeck 
Attorney, Agent, or Firm-Norman T. Musial; John R. 
Manning; James A. Mackin 
24 
[11] Patent Number: 4,517,505 
[45] Date of Patent: May 14, 1985 
P I  ABSTRACT 
An object of the invention is to provide variable damp- 
ing for resonant vibrations which may occur at different 
rotational speeds in the range of rpms in which a rotat- 
ing machine is operated. 
A variable force damper in accordance with the inven- 
tion includes a rotating mass (12) carried on a shaft (11) 
which is supported by a bearing (13) in a resilient cage 
(14). Cage (14) is attached to a support plate (15) whose 
rim extends into an annular groove in a housing (17). 
Variable damping is effected by tabs (18) of electrically 
conducting, non-magnetic material which extend radi- 
ally from the cage (14). The tabs (18) at an index posi- 
tion lie between the pole faces of respective C-shaped 
magnets (19). The magnets (19) are attached by cantile- 
ver spring members (20) to the housing (17). 
By rotating the support plate (15) about the axis of shaft 
(l l) ,  the tabs (18) may be rotated through an angle 0 of 
about 40" away from the index or  0" position. At the 40" 
position minimum damping is obtained. 
To position support plate (15) to achieve a desired 
amount of damping, means for generating an electrical 
signal indicative of the vibrating displacement of shaft 
(11) such as displacement detector (29) and correction 
module (28) to control a servo (27). The servo (27) can 
drive the support plate (15) through various means such 
as gears, drive wheels or the like. 
12 Claims, 2 Drawing Figures 
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https://ntrs.nasa.gov/search.jsp?R=19850022021 2020-03-22T19:34:46+00:00Z
U.S. Patent May 14,1985 
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4,5 17,505 
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FIG. 1 
0 
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FIG. 2 
4,5 17,505 
1 2 
contacting surfaces may have little, if any, slip resulting 
in high stiffness values and little, if any, damping. 
U.S. Pat. No. 3,316,661 to Simpson et  a1 discloses an 
eddy current brake in which a movable shield or  shunt 
5 is interposed between a magnet and a rotating conduc- 
the magnet and the rotating conductor to shield vari- 
able portions of the conductor from the magnetic field 
to alter the area and shape of the magnetic field pene- 
U S .  Pat. No. 3,601,641 to Baermann discloses an 
eddy current and/or induction break or  clutch com- 
prised of a breaking inductor and a ferromagnetic eddy 
current conductor arranged for relative rotation with 
respect to one another. The magnetic field produced by 
the permanent magnet 38 can be increased or decreased 
by the electromagnetic field produced by a field wind- 
ing. Breaking torque can be adjusted by changing the 
energizing field of the A C  generator which feeds the 
u.s, Pat. No, 4,198,863 to Bartek discloses an electro- 
magnetic torsion stiffness arrangement having a con- 
ductor located on a disc rotating in an air gap between 
VARIBLE FORCE, EDDY-CURRENT OR 
MAGNETIC DAMPER 
ORIGIN OF THE INVENTION 
ployee of the United States Government and may be 
manufactured or  used by or for the Government for 
governmental purposes without the payment of any 
royalties thereon or  therefor. 
DESCRIPTION 
The invention described herein was made by an em- tor. The shunt may be moved through the gap between 
10 trating the disc. 
1. Technical Field 
The invention relates to high speed rotating machin- 15 
ery and is directed more particularly to  damping appa- 
ratus for reducing resonant vibrations of the rotating 
parts. 
With any rotating machinery there is one or  more 
rotating speeds at which the rotating body will develop 20 windings. 
resonant vibrations. These vibrations cause stress on 
support bearings and the shaft supporting the rotating 
mass and will cause early destruction of these compo- 
fuel and oxidizer pumps used on the main engines of a 25 rotar,, motion. 
nents. Of high 'peed, turbomachinery are the magrletic systems, The disc also serves to dampen the 
NASA space These pumps are for liquid 
Oxygen and liquid hydrogen' Such machines have very 
high power to weight ratios and are required to 'perate 
U.S. Pat. No, 3,510,705 to O'Neill et a] discloses a 
magnetic hysteresis device having a magnetic hysteresis 
member and at least one magnetizing head supported 
to operating 'peed, it is colnmon to 30 dissipated within the member by magnetic hysteresis to 
encounter one or system frequencies. A produce a hysteresis drag force opposing the relative 
capability of varying the stiffness and damping Of shaft movement. The hysteresis drag force may be varied in 
bearing supports operating through such accordance with a predetermined function of the rela- 
for relative movement in such a way that energy is at rotor speeds of up to 36,000 rpm. 
In accelerating 
frequencies is an important goal. Having this capability 
can reduce the magnitude of the forces transmitted to  35 
the bearings and seals and can, therefore, Prolong their 
life or  possibly prevent sudden and catastrophic failure. 
tive displacement of the member and head. 
U.S. Pat. No. 3,637,169 to Tossman et discloses a 
pendulum having a vane member formed of electrically 
conductive, nonmagnetic material which swings be- 
tween pole faces of a magnetic structure and creates 
has 4o eddy current losses within the vane member to dissipate 
been attempted by a number of different devices. In one coulombic energy. 
such device, the shaft bearings are supported in resilient u.s, Pat. NO. 4,200,003 to  Miller discloses a rotary 
materials Or by springs having Predetermined spring disc damper using magnetic fluid as the damping me- 
rates. dium. The damper comprises a permanent magnet rotor 
In turbomachines such as turbojet engines, radial and 45 enclosed in a magnetically permeable housing. The  
axial compressors, and high speed gas liquefiers, fluid housing contains a magnetic fluid which is held in place 
film dampers are often used. These dampers employ a by the magnetic forces generated by the magnet rotor. 
viscous fluid film between moving parts. Vibrational The torque of the damper may be varied by changing 
energy induced in the rotor and transmitted to the bear- the viscosity of the magnetic fluid or  the level of the 
ing supports is dissipated as heat in shearing the viscous 50 magnetic flux in the magnetic circuit. 
fluid. 
The so-called squeeze film damper dissipates energy DISCLOSURE OF THE INVENTION 
by pumping a viscous fluid in and out o f a  narrow annu- According to the invention, one end of a shaft carry- 
lus. The amount of damping and stiffness is determined ing a rotating mass is supported by a suitable bearing 
by the original design and expected amplitudes ofvibra- 55 which, in turn, is supported resiliently in a cage mem- 
tion. The squeeze film type dampers normally must be ber. The cage member is attached to a plate which may 
located very close to a bearing where lubricating oils be rotated to position electrically conductive, non-mag- 
are available in large quantities, thus creating a design netic tabs which extend radially from the cage member. 
problem. At an index position of the support plate each tab lies 
Another type of damper commonly used is a friction 60 within the pole faces of a respective C-shaped magnet. 
o r  coulomb damper. In this type damper the energy Each magnet is supported by a cantilever spring from a 
dissipated is dependent on the coefficient of friction of housing in which the support plate is free to  rotate. 
two contacting surfaces under applied pressure. The Maximum damping of shaft vibrations is achieved 
problem here is to predict the amount of damping and when the tabs are positioned within the pole faces of 
stiffness available for any given vibrational situation. If 65 their respective magnets. By rotating the support plate, 
the contacting surfaces are under too little pressure, slip the cage member with the attached tabs can be rotated 
relative to one another may produce erratic amounts of through an angle of approximately 40" to  achieve mini- 
damping. Conversely, if the pressure is too great, the mum damping effect. 
2. Background Art 
In the Prior art damping of rotating 
4,5 17,505 
3 
Electronic circuitry may be provided to measure the 
displacement or speed of the rotating shaft. A signal 
representative of these parameters may be modified and 
amplified to drive a servo which rotates the support 
plate to a position which will achieve the desired damp- 
ing for a particular frequency or speed of rotation. 
BRIEF DESCRIPTION OF T H E  DRAWINGS 
FIG. 1 is a transverse cross-sectional view of a vari- 
able force, eddy current or magnetic damper embody- 
ing the invention. 
FIG. 2 is a cross-sectional view taken along the lines 
2-2 of FIG.  1. 
DESCRIPTION O F  A PREFERRED 
EMBODIMENT 
Referring now to FIG.  1, there is shown a variable 
force, eddycurrent damper 10 constructed in accor- 
dance with the invention. A shaft 11 carries a mass 12 
such as a turbine which rotates with the shaft 11. 
One end of the shaft 11 is journaled in a bearing 13 
which is disposed in one end of a bearing support such 
as a squirrel cage spring 14. The other end of the squir- 
rel cage spring 14 is attached to the center of a bearing 
support carrier plate 15 which has a circular rim. 
The shaft 11 extends through an aperture 16 in the 
spring cahier 15 and coaxially through the squirrel cage 
spring 14. Spring carrier plate 15 is rotatably supported 
by an annular groove in a housing 17 in which the eddy 
current damper 10 is disposed. 
To the end that resonant vibrations of the shaft 11 and 
rotating mass 12 will be adequately damped, tabs 18 of 
highly electrically conductive, nonmagnetic material 
are attached to and extend radially from the squirrel 
cage spring 14 adjacent the bearing 13. When the spring 
carrier 15 is at 0" index position, as will be described 
presently with regarding to FIG. 2, each tab 18 is posi- 
tioned between the poles of a respective C-shaped mag- 
net 19. 
Each C-shaped magnet 19 is supported by a cantile- 
ver spring 20 from the housing 17. The C-shaped mag- 
nets 19 are provided with rare earth magnetic pole faces 
21 to increase the magnetic strength applied to the tabs 
18. 
Referring now to FIG. 2, there is shown a transverse 
sectional view taken along the line 2-2 of FIG. 1. The 
tab 18 on the left as viewed in FIG. 2 is aligned with line 
22 at a 0" index position when it is in maximum surface- 
to-surface confrontation between the pole faces of its 
respective C-shaped magnet 19. 
Similarly, at the 0" position of spring carrier 15, all of 
the remaining tabs will be positioned between the pole 
faces of their respective C-shaped magnets 19. At the 0" 
position of the spring carrier 15, maximum damping 
effect is obtained. By rotating the spring carrier 15 
through an angle (p of 40" to a position, as indicated by 
line 23, substantially zero damping is effected. 
In order to rotate the spring carrier 15 to a desired 
position or angle (p whereby the tabs 18 are positioned 
as desired, a tab positioner 24 is provided as illustrated 
in FIG. 1. Tab positioner 24 includes a wheel or gear 25 
5 
10 
15 
20 
25 
30 
35 
40 
45 
4 
is supplied with a correction signal from a correction 
module 28 in response to radial movement of the rotat- 
ing mass 12 as measured by a displacement detector 29. 
Displacement detector 29 may be any one of well 
known types operating on capacitive, inductive or light 
beam principles. The signal generated by the displace- 
ment detector 29 is related to the radial displacement of 
the rotating mass 12 and after being amplified and/or 
modified by the correction module 28, drives the servo 
27. 
Rotation of the carrier plate 15 can also be accom- 
plished by directing to the servo 27 a signal related to 
the rotating speed (rpm) of the mass 12 so that at certain 
rpms plate 15 rotates to place the tabs 18 at predeter- 
mined positions. These positions may be determined 
empirically by rotating mass 12 at various speeds and 
determining the rpm's at which unacceptable resonant 
vibrations occur. Plate 15 is then rotated to provide 
maximum damping for each particular rpm at which the 
resonant vibrations occur. When these factors are 
known, an rpm counter for the mass 12 can signal servo 
27 to adjust the plate 15 for maximum damping. 
As discussed previously, one particular application of 
the above-described invention is in pumps operating in 
cryogenic environments such as liquid hydrogen. Ad- 
vantageously, cryogenic temperatures increase the con- 
ductivity of the tabs 18 and, consequently, increase the 
damping effectiveness of the eddy current shaft damper 
described above. Tests have shown that the damping 
provided when tabs 18 are aluminum and the apparatus 
is immersed in liquid nitrogen is seven times greater 
than when the tabs 18 are at room temperature. 
Theoretically, if tabs 18 are copper the damping ef- 
fect should be 11 times greater in liquid nitrogen than at 
room temperature. With a low purity copper material, 
however, the damping in liquid nitrogen was only 29 
times as great as at room temperature. With all condi- 
tions being the same, copper, because of its high con- 
ductivity, has greater damping effect than aluminum. 
While the variable force damper shown in FIG. 2 
utilizes permanent magnet 20, it will be understood that 
electromagnets can also be used. Also, while four tabs 
18 are shown, three tabs with associated magnets may 
be used as well as five or more tabs with associated 
magnets. Of course, less damping is effected with three 
tabs while more than four tabs add to the weight and 
complexity of the damping apparatus without propor- 
tionately increasing the damping effect. 
It will be understood that changes and modifications 
50 may be made to the above-described invention without 
departing from its spirit and scope as set forth in the 
claims appended hereto. 
I claim: 
1. A variable damper for substantially eliminating 
5 5  resonant vibrations in a rotating mass carried on a shaft 
in a housing and wherein the shaft is provided with at 
least one bearing, said damper comprising: 
a resilient support for said bearing, said support being 
rotatable about the axis of rotation of said shaft; 
a carrier plate for said bearing support comprising a 
rotatable plate, said bearing support being attached 
60 
carried on a shaft 26. The wheel 25 engages the-rim of 
the spring carrier plate 15 so that by rotating the shaft 
26 some predetermined number of turns, plate 15 will be 
rotated, thereby positioning the tabs 18 as desired. 
In order that the spring carrier may be automatically 
rotated to a prescribed damping position, shaft 26 of the 
tab positioner 24 may be rotated by a servo 27. Servo 27 
to said carrier plate for rotation therewith; 
a plurality of tabs extending radially from said bear- 
ing support, said tabs being of electrically conduc- 
tive, nonmagnetic material; 
a plurality of magnets equal in number to said plurai- 
ity of tabs, each magnet having at least one pole 
face in non-contacting, maximum surface-to-sur- 
65 
4.517,505 7 -  
5 
face confrontation with a respective tab when said 
plate is in a 0" index position; and 
means for rotating said carrier plate whereby said 
tabs may be positioned from the 0" index position 
to one in which there is minimum surface-to-sur- 
face confrontation between the tabs and respective 
magnets. 
2. The damper of claim 1 wherein a cryogenic liquid 
is applied to said tabs and magnets. 
3. The damper of claim 1 wherein said bearing sup- 
port is a squirrel cage spring. 
4. The damper of claim 1 wherein said magnets are 
C-shaped with each tab lying between the poles of a 
respective magnet when said carrier is in said 0" index 
position. 
5. The damper of claim 4 wherein each pole of the 
C-shaped magnets is provided with a rare earth metal 
pole face. 
6. The damper of claim 1 wherein each magnet is 
resiliently supported on said housing. 
7. The damper of claim 1 and including an adjusting 
shaft carrying a drive wheel engaging said carrier plate 
to rotate the same, when said shaft is turned. 
8. The damper of claim 7 and including: 
means for generating a first electrical signal indica- 
tive of radial displacement of said rotating mass; 
6 
servo means drivingly connected to said adjusting 
shaft; and 
means for adjusting said first electrical signal and 
directing it to said servo whereby said carrier plate 
is rotated to a prescribed position in accordance 
with the resonant vibrations of said rotating mass. 
9. The damper of claim 1 wherein said tabs are of a 
material selected from the group of metals comprising 
copper and aluminum. 
10. The damper of claim 1 wherein said magnets are 
electromagnets with a predetermined, constant field 
strength. 
5 
10 
11. The damper of claim 1 and including: 
first means for generating an electrical signal related 
to the rotational speed of said rotating mass; 
second means for rotating said carrier plate between 
a 0" index position which provides maximum 
damping and a position which provides minimum 
damping, and; 
third means for transmitting said signal from said first 
means to said second means whereby said carrier 
plate is automatically positioned to  provide prede- 
termined damping at a plurality of specific rota- 
tional speeds of said rotating mass. 
12. The damper of claim 11 wherein said second 
means comprises a servo driving a wheel which engages 
a rim portion of said carrier plate. 
15 
20 
25 
* * * * *  
30 
35 
40 
45 
50 
55 
60 
65 


Variable force, eddy-current or magnetic damper

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