Vibration control of flexible bodies in steady accelerating environmen

Dixon, G. V.

Leatherwood, J. D.

Stephens, D. G.

English

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SUBJECT! Announcement of NASA-Owned U. 8. Patent8 i n  6TAR 
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and Code USI, the attached NASA-0wned.U. 8,’Patent ie being 
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/ Government or Corporate Employee 8 
8upplementary Corporate 
aioutce (if applicable) 8 
NASA Patent Cane No. ! *  
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NOTE - lg this  pakent cover8 an invention made by a corporate 
employee of a NASA Contractor, the following i 8  applicable8 
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*an in etition ’of 
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https://ntrs.nasa.gov/search.jsp?R=19710017693 2020-03-17T03:13:14+00:00Z
PATENTED HAR 2 1971 
d 
3,566,993 
INVENTORS 
JACK D. LEATHERWOOD 
DAVID G. STEPHENS 
BY GRAYSON V. DlXQN 
 ATTORNEYS 
United States Patent 3,566,993 
[ 721 Inventors Jack D. Leathemood 
Hampton; 
David G. Stephens, Yorktown; Gray V. 
Dixon, Hampton, Va. 
1211 Appl. No. 810,575 
[22] Filed Mar. 26,1969 
[45] Patented Mar. 2,1971 
I731 Assignee the United States of America, as 
represented by the Administrator of the 
National Aeronautics and Space 
Administration. 
[ 541 ACTIVE VIBRATION ISOLATOR FOR 
FLEXIBLE BODIES - 
2 Claims, 1 Drawing Fig. 
[52] U.S. Ci. ....................................................... 188/1, 
310151 
[ 5  11 Int. CI. ........................................................ F16f 15/02 
[50] Field of Search ............................................ 188/1B, 
103; 310/51; 248/(Inquired) 
14 -L-c 
J’ 10 
1 1 
, p20)p 
1561 References Cited 
UNITED STATES PATENTS 
2,361,071 10/1944 Vang ............................ 188/1(B) 
2,964,272 12/1960 Olson ........................... 188/1(B) 
3,483,951 12/1969 Boneshoetal. .............. 188/1(B) 
Primary Examiner- Duane A. Reger 
Attorneys-Howard J. Osborn and G. T. McCoy 
ABSTRACT: This disclosure is related to an active vibration 
control arrangement for isolating a flexible body from 
disturbances applied either externally or internally by inertial 
or other forces created by the body itself, and consists of an 
actuator having a movable element drivingly connected to the 
flexible body, controlled by a signal produced by excitatory 
reaction of the body together with means to produce a nullify- 
ing movement of the movable member in response to the 
signal. 
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3,566,993 
1 2 
subjected to steady acceleration components. 
In order to better understand the specific embodiment dis- 
closed as descriptive of the invention reference will now be 
made to the FIG. which is a schematic representation of a 
system according to the present invention. Referring to the 
FIG., 10 indicates generally the vibration control system. The 
supporting structure 12 is shown as a rocket booster, while the 
flexible payload 14 is shown illustratively as flexibly supported 
mass 20 by a schematic representation of a spring 16 and 
damper 18. The payload 14 is drivingly connected to an actua- 
tor 22 including a piston 24 which is actuated by a hydraulic 
cylinder 26, secured to the booster 12. 
The action of this actuator is controlled by a servo valve 28 
which generates a flow to the hydraulic cylinder to cause 
movement of the piston 24 proportional to the magnitude of 
electrical control signals to be herein described and in a 
direction corresponding to the polarity of these signals. 
A first signal X is produced by an accelerometer 30 propor- 
FiORal to the acceleration felt by the mass 20. This signal is 
compared to a command signal X,, which would be zero for 
Chis application, in turn producing an error signal X,. This 
error signal is then fed to an acceleration controller 32 com- 
prising a lead compensation network, which as is well known 
in the prior art, produces a high gain from high frequency 
signals and proportionally lower gain from lower frequency 
5ignals. Hence, the output 6 of the controller 32 is zero for DC 
or steady state acceleration loads 
The output S is amplified at 34 and then fed to the ser- 
dovalve 28, which in turn cmst;s the piston to muve I H ~  such a 
manner to oppose the acctleratisn prodc-mg, the sigwl, and 
proportionally EO its wrdgnrtua:, d i  pol: 7 [e4 out 8iBt~ve 
c i d w j i  c' fo limit ruarvernrqr 
ter 38 which measures the actuator piston position and 
produces an output signal Y proportional to the piston posi- 
with a preset command signal in the position 
roduce an output error signal Y, which is fed 
.. 
hi secondai y ~ontrdr! loop 
,.Ethe actchitor prrtun B'hrs I qx.!,de, A hear  pobcratiome- 
ACTIVE VIBRATION ISOLATOR FOR to the secondary control loop. This in turn restricts the piston 
FLEXIBLE BODIES to move about a fixed predetermined position. 
The invention described herein was made by employees of Since the Various COmpOnenk3 are in themselves Well known 
the United States Government and may be manufactured and 5 in the Prior arty such as the accelerometer, compensation lead 
used by or for the Government for governmental purposes network, servovalve, etc., it is not felt necessary to describe 
without the payment of any royalties thereon or therefor. and illustrate each of these in detail, but it will be clear to one 
This invention is concerned with vibration control and of ordinary skill in the art how to make and use the invention 
specifically to control of vibrations of flexible bodies, particu- from the schematic representation above described. For ex- 
larly in an environment producing steady acceleration corn- 10 ample, a Se~vOvalve and hydraulic actuator suitable for this 
ponents imposed on the flexible body. application is disclosed in U S .  Pat. No. 2,964,272. 
Prior art vibration isolator systems are generally ineffective From this description, the operation of the isolator should 
when attempts are made to apply them to systems wherein the be apparent. lf the paytoad l4 is subjected to an upward 
flexible body of interest is characterized by low frequency changing axxhat ion  from any Source as when subjected to 
resonances ( 1-10 Hz.), and is subject to steady and/or low 15 transient vibrations by the booster 12, an error signal X, is 
frequency acceleration components as well as higher frequen- produced, which is fed to the acceleration controller 32. Since 
cy vibrations. This situation exists in the launch vehicle- the acceleration is changing this yields an output 6 which is 
payload arrangement, wherein the payload may be flexible or then amplified, and if the position controller 40 does not over- 
may be more or less flexibly connected thereto and typically is rule the resulting signal K6, it is then applied to the servovalve 
subjected to launch vehicle vibrations during transport, ship- 20 28, to produce a downward movement of the piston 24, thus 
board operations, etc., steady accelerations during launching, nullifying the acceleration felt by the mass 20. Downward 
and transient low frequency disturbances during staging. disturbances cause a similar but oppositely directed move- 
Conventional passive isolators, usually comprised of springs merit. If a steady or very slowly changing acceleration is felt by 
and dampers, are not satisfactory in this environment since ex- the payload 14 as from launch g loads, the gain through the ac- 
cessive isolator deflections may occur under steady loads and 25 celeration controller is zero or nearly so, and no deflection of 
are not effective for isolating such low frequency flexible the isolation system results. 
bodies from very low frequency disturbances, white the active Hence, it can be Seen that a flexibly supported load can be 
isolator arrangements have been confined in the prior art to isolated from a wide range Of frequencies of disturbances ap- 
simple rigidly connected systems, and have not heretofore plied either internally or externally without undue changes in 
been successfully applied to this problem. 30 the equilibrium position of the isolator system due to steady 
Therefore, it is the object of this invention to provide a loadand/oracceleration levels. 
vibration isolation system for a flexible body which will effec- have been referred to for the 
tively control low and high frequency disturbances, and will at sake ofclarity, it is understood that the invention may be prac- 
the same time limit deflection of the m a s  member when it is ticed in many Ways, for example, the payloads to be isolated 
35 may be discrete or distributed systems: sensing elements could 
While Particular 
be position velocity, or acceleiation sensors i r  combinations 
of these; the actuating element could be hydraulic, pneumatic, 
electromechanical, etc.; and the control signals ,and networks 
could be fluidic rather than electrical in nature. 
1. An isolator system to isolate a flexible body from 
disturbances causing objectionable movement of said flexible 
body comprising: 
actuator means having a movable member connected to 
said flexibie body mass, control means causing said actua- 
tor movable member to move to oppose responsive move- 
ment of said flexible body to disturbances; 
said control means including means for applying a force to 
said movable member and including sensor means 
producing a signal corresponding to the movement of said 
mass member when said mass member responds to a 
disturbance and also including means for applying said 
force in response to said signal and in a manner indicated 
by said signal to oppose said movement; and 
compensation means eliminating the response of said mova- 
ble member to sensor signals corresponding to steady and 
very low frequency mass member response. 
2. An isolator system to isolate a flexible body from 
disturbances causing objectionable movement of said flexible 
actuator means having a movable member connected to 
said flexible body mass, control means causing said actua- 
tor movable member to move to oppose responsive move- 
ment of said flexible body to disturbances; 
said control mems inchdlng means for applying a force to 
sEid movable an-.mber sod including sensor means 
produmg a signal ~ o r ~ e s ~ ~ ~ ~ ~ ~ ~  to the movement of said 
HUMV, t~nemb.x w h ~ a  sa83 mass, member responds to a 
disturbm~t anci also nncludinng means for applying said 
force b response to said signal and irl a manner indicated 
by said signal to oppose said movement; and 
control loop means limiting the travel of said movable 
member to a ~ r ~ ~ ~ ~ e ~ ~ ~ ~ ~ 4 ~  e q 9 ~ t a t  maximum value. 
40 Weclaim: 
45 
50 
5 5  
60 body comprising: 
65 
70 
'i 5 


Active vibration isolator for flexible bodies Patent

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