Active vibration isolator simultaneously isolates a flexible structure or payload from disturbances, attenuates the response of a flexible structure to transient disturbances, and maintains the equilibrium position of the payload within predetermined limits over a wide range of steady loads and accelerators

Dixon, G. V.

Leatherwood, J. D.

Stephens, D. G.

English

NASA Technical Reports Server

Xe
Payload	 I 
-.	 I Acceleration 
Controller 
April 1968	 .	 Brief 68-10123 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Improved Active Vibration Isolator 
Xc 
 Positon Servo	 i 
Controller Accelerometer 
Piston 
Actuator
Servo Valve 
Booster 
The active vibration isolator, shown in schematic 
form, is designed to perform the following functions 
simultaieoüsly: (1) isolate a flexible structure or 
payload from disturbances such as launch vehicle 
vibrations; (2) attenuate the response of a flexible 
structure to transient disturbances such as staging 
loads; and (3) maintain the equilibrium position of the 
payload within predetermined limits over a wide 
range of steady loads and accelerations. The isolator 
is an automatic controller that is especially suited for 
vibration protection of systems which experience 
changes in steady load and/or accelerations, such as 
on spacecraft. It may also be effectively used to pro-
vide vibration protection for systems during ground 
transportation, shipboard operation, and aircraft 
flight.
A passive vibration isolator, that is, a system which 
employs springs and dampers to isolate and attenuate 
dynamic disturbances, does not maintain a fixed 
equilibrium position and is not effective in isolating a 
payload from disturbances having frequencies that are 
less thanN/-2-- times the natural frequency of the 
isolator. Active isolator systems that have been 
studied previously are not effective in reducing the 
resonant response of a flexible body attached to a 
rigid mounting platform. 
The new active vibration isolator consists of the 
following components: sensing elements to measure 
the dynamic response of the flexible payload and 
position of an actuator; electrical control networks 
to compare the signals of the sensing elements with 
preset standards and to provide an output to the 
(continued overleaf) 
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actuator; and the actuator itself which applies a force 
to the payload so as to null the response of the pay-
load as well as to maintain a fixed equilibrium posi-
tion. 
The acceleration x of the flexible payload is meas-
ured by a servo accelerometer and the signal is com-
pared with a desired or command acceleration signal 
xc (which for this application is set equal to 0). The 
error signal Re is then sent to the acceleration 
control network for compensation. The output 6 of the 
acceleration control network is amplified, and the 
resulting signal Kb is used to drive the servo valve. 
The actuator responds to the servo valve command 
and moves the piston to null the response of the pay-
load. A linear potentiometer attached to the actuator 
piston measures the position of the piston. The dif-
ference between the measured position (Y) and the 
command position (Ye) is the error signal (Ye) which 
is fed to a secondary control loop. This loop restricts 
the isolator to move about a predetermined, fixed 
position.
Notes: 
I. Payloads to be isolated can be discrete or dis-
tributed systems. 
2. Sensing elements can be chosen to respond to 
position, velocity, or acceleration or to combina-
tions of these variables. 
3. The actuator can be hydraulic, pneumatic, or elec-
tromechanical. 
4. Inquiries concerning technical details may be di-
rected to:
Technology Utilization Officer 
Langley ResearchCenter 
Langley Station 
Hampton, Virginia 23365 
Reference: B68-10123 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: J. D. Leatherwood,
D. G. Stephens, and G. V. Dixon 
(LAR-10106) 
Brief 68-10123	 Category 05


Improved active vibration isolator

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