A hydraulic actuator designed for a thrust vector control system used as a shaker for a vehicle to determine the bending mode frequencies is described. The actuator is used as the prime mover and the frequency sensor for the flexible vehicle in a test tower. Advantages in using the actuator piston position with respect to a commanded position to obtain the bending mode frequencies are shown

Davis, P.

Thompson, Z.

English

NASA Technical Reports Server

NASA TECHNICAL
MEMORANDUM
NASA TM X-64689
ACTUATOR PARTICIPATION IN A BENDING
MODE IDENTIFICATION SYSTEM
By Zack Thompson and Perry Davis
Astrionics Laboratory
September i972
NASA
George C.
Marshall
.Marshall Space Flight
Space Flight Center,
Center
Alabama
(NASA-TM-X-6 4 689 ) ACTUATOR PARTICIPATIO N7-
IN A BENDING ODE IDENTIFICATION SYSTE ZN72-3338
Thompson, et al (NASA) Sep. 1972 19 p
G3/14 434 8 4
MSFC - Form 3190 (Rev June 1971)
https://ntrs.nasa.gov/search.jsp?R=19720025730 2020-03-23T09:56:46+00:00Z
TcrINICAL REPORT STANDARD TITLE PAGE'
1. REPORT NO. 2. GOVERNMENT ACCESSION NO. RECIPIENT'S CATALOG NO.
TM X-64689
4. TITLE AND SUBTITLE 5. REPORT DATE
September 1972
Actuator Participation in a Bending Mode Identification System 6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S) 8.PERFORMING ORGANIZATION REPORT #
Zack Thompson and Perry Davis
9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO.
George C. Marshall Space Flight Center 1 CONTRACT OR GRANT NO.
Marshall Space Flight Center, Alabama 35812
13. TYPE OF REPORT & PERIOD COVERED
12. SPONSORING AGENCY NAME AND ADDRESS
Technical Memorandum
National Aeronautics and Space Administration
Washington, D. C. 20546
15. SUPPLEMENTARY NOTES
Prepared by Astrionics Laboratory, Science and Engineering
16. :ABSTRACT
A hydraulic actuator designed for a thrust vector control system used as a shaker
for a vehicle to determine the bending mode frequencies is described. The actuator is used
as the prime mover and the frequency sensor for the flexible vehicle in a test tower. Advantages
in using the actuator piston position with respect to a commanded position to obtain the bending
mode frequencies are shown.
17. KEY WORDS 18. DISTRIBUTION STATEMENT
resonant frequency -. iclassified - unlimited .-
dynamic filter
bending mode identification
traveling notch filter -_;
shake test
19. SECURITY CLASSIF.(dthib rePt) 20. SECURITY CL Iflua._) 21. NO. OF PAGES 22. PRICE
Unclassified Unclassified 8 $ 3. 00
fl-PC *-1om 5292 (32 i19)
I
I
J.
BIBLIOGRAPHY
Davis, P. W.: Equations Describing the Engine Position Control System
for the Saturn S-I Stage of the SA-5 Vehicle. M-ASTR-IN-63-7, Marshall
Space Flight Center, Alabama, March 19, 1963.
Hosenthien, Hans H. and Borelli, M, T.: An Adaptive Tracking-Notch
Filter for Suppression of Structural Bending Signals of Large Space Vehicles.
NASA TMX-53000, October 1, 1963.
Kalange, M. A. and Neiland, V. R.: Saturn Engine Gimbal and Thrust
Vector Control System. SAE National Conference on Industrial Hydraulics,
October 17-18, 1963.
Thompson, Zack and Alcott, R. J.: Apollo Booster Flight Control System
Integration. Presented at the SAE-A-18 Committee Meeting, Houston,
Texas, December 11-13, 1963.
Weaver, C. H.: Study of Engine Position Control Systems. M-ASTR-62-2,
Marshall Space Flight Center, Alabama, January 19, 1962.
(' ,
APPROVAL NASA TM X-64689
ACTUATOR PARTICIPATION IN A BENDING MODE
IDENTIFICATION SYSTEM
By Zack Thompson and Perry Davis
The information in this report has been reviewed for security classifi-
cation. Review of any information concerning Department of Defense or
Atomic Energy Commission programs has been made by the MSFC Security
Classification Officer. This report, in its entirety, has been determined to
be unclassified.
This document has also been reviewed and approved for technical
accuracy.
MEVIN BROOKS/
Cpief, Guidance and Control Systems Division
J. L. MACK
Chief, Systems Division
F. B. MOORE
Director, Astrionics Laboratory
(C O
MSFC-RSA, Ala
TABLE OF CONTENTS
Page
INTRODUCTION .. .................................... i
BENDING MODE IDENTIFICATION .......... .............. 4
BIBLIOGRAPHY ................. ................. 11
iii
LIST OF FIGURES
Figure Title Page
i. Vehicle and actuator test schematic ................ 5
2. Actuator and load block diagram .................. 5
3. Amplitude curves for transfer functions ............. 6
4. Change in amplitude curves for load changes .......... 7
5. Overall amplitude curves for load changes ........... 8
6. Lumped parameter model ....................... 9
7. Actuator and load dynamics ..................... 9
8. Piston position with respect to piston command
with multiple resonant load ............ 0........ 1
iv
DEFINITION OF SYMBOLS
Units
mA/deg
deg/mA.
deg/deg
deg/deg
deg/deg
mA.
deg
deg
Definition
amplifier transfer function
servovalve and actuator transfer
function
notch and shaping network
load transfer function
open loop transfer function
differential valve current
error signal
piston ideal position and piston
position unloaded, respectively
actuator piston position
engine position
input command
feedback signal
Laplace operator
frequency
pressure feedback gain
feedback gain
deg
deg
deg
deg
1/s
Hz
(M 5 /S) /N
v
Symbol
KG
a 1
KG
v 2
G3
G4
F
o
Al
E -
P, p
p
Pe
Of
S
f
K
H1
DEFINITION OF SYMBOLS (Concluded)
Symbol Definition Units
K1 K1 K0 N/M
K1 + Ko
A piston area M2
vi
TECHNICAL MEMORANDUM X-64689
ACTUATOR PARTICIPATION IN A BENDING
MODE IDENTIFICATION SYSTEM
INTRODUCTION
To design filters for the body bending frequencies of a flexible body
vehicle, it is first necessary to determine the bending frequencies and their
influence on vehicle stability. An analytical derivation is made to get the
first approximation of the frequencies, then elaborate testing is conducted
to verify the derived information. The vehicle or stage is suspended in the
test tower by long cables arranged to permit free vibration (Fig. 1). To
obtain frequency response information, the vehicle is then vibrated by connect-
ing a large shaker to the aft part of the vehicle and sensing the motion of
the vehicle at various points.
A thrust vector control system is capable of generating the forces
necessary for shaking the vehicle. The bending mode frequencies can be
determined from the actuator piston position.
To control the angular position of the engine, a servosystem that will
attenuate the commands to the dynamic load in the vicinity of the load
resonant frequency must be used. The desired servo would filter out the load
resonant frequency and give the proper attenuation in the neighborhood of
that frequency. A block diagram of a system of this nature is shown in
Figure 2.
The transfer functions are as follows:
K G = 909
a 1 S2 2( 0.7)S 
(300)2 + 300 2 
K G = 2.49
v 2 So )
I
S2 2t 
+ S +
_n n
s2 2( O. 416) S 
(7 270.37)2 + (7057) +
1
G4
+ 2- S +
\n n/
An amplitude ratio frequency response of the system with the notch
filter is shown in Figure 3. This system contains the dynamics of the load,
the driving amplifier, the actuator, the servovalve, and the necessary
dynamics to give the proper response.
In a multiengine control system, it is desirable from a hardware
viewpoint to design one servoloop that can be interchangeable from engine to
engine. Because of the tolerance used in manufacturing the stage structure,
the engine, and the actuators, it is difficult to predict exactly what the
resonant frequency of the load will be. It is desirable to have a system that
would track the resonant frequency of the load and adjust the servosystem
notch so that it would always be set at the proper frequency.
The closed-loop transfer function of the actuation system contains a
numerator term that is exactly equal to the denominator in the transfer
function of the load. The numerator term exist3 because the hydraulic fluid
is compressible and the degree of compression is a function of the load
acceleration, or force on the piston. The overall transfer function is a
product of the servoloop and the load transfer functions. The development
of this follows.
Since
p FS = o
C 1+ F
c o
where
2
+ S +22.64 +2 S + 1
n n
F
F~SS2 2(0.7)s3S 7 + 1) 3 2 + (0 S 2 2+ (0.416) S + 1(300)7+ 300 (70.57) 2 (70.57)
G4 =
+ S + 1
n n 
~~~~~~p = ~22.64 + 2 S +
Pc "(S (3772 + [I 7)- +300] 2(0.416) +22.64 2 +
377 + 300l + 5 +i0 j(70-57) 70.57 J 2.
The parameters of the load can be changed at random to produce any
natural frequency, and the notch filter will always be at the proper frequency.
P oPc i + F ') 
22.64(. S2 2 ) [| 
0) [ S2 2(0.7) S ] [s+ 2(0.416) si S +64 (S2. +2 +) °° ' [-" s+ (7 + 0 ] + 22. 64 +S 
A representation of the traveling notch is shown in Figures 4 and 5.
The natural frequency of the dynamic load was the only parameter varied.
To obtain tracking and the proper amount of attenuation for a dynamic
load, it is necessary for the actuator piston position (3 ) to be a function
of engine acceleration. This is how the transfer function PB // i is obtained.
The traveling notch and associated shaping networks are mechanical compo-
nents and are installed within the actuator body.
3
BENDING MODE IDENTIFICATION
It has been established that the actuator will produce a notch at the
resonant frequency of the load and that the notch will follow changes to the
resonant frequency. To evaluate the actuation system to see if it would also
produce a notch for loads that have more than one resonant frequency, the
lumped parameter model in Figure 6 was used. The following equations
must be solved simultaneously to obtain a load to the actuator.
F = K (f - t p)
0 = - Koh + (K l + K0 ) t p - Kl pi
0 = -K ip + (K2 + K1 + M1 S2 )21 - K2/20 p 3
2
o 2 -K + (K + K + M S) )2 - K 13
O = -K 3 pB2 + (K3 + M3 S 2 ) 3
A block diagram of these equations and the actuator dynamics is shown
in Figure 7.
A frequency response of this system A p/1 C is shown in Figure 8.
These frequencies and the lumped parameters were not intended to
simulate any particular vehicle bending frequencies. This simulation does
illustrate how an actuator can be used to shake a test vehicle and use the
actuator piston position to determine the bending frequencies. The piston
position potentiometer voltage can be of any magnitude necessary to achieve
desired resolution and sensitivity.
The same conventional sensors presently used on this type of test
may be used.
4
CABLE
GROUND
SHAKER
Figure 1. Vehicle and actuator test schematic.
5
Figure 2. Actuator and load block diagram.
CABLE
o
 
t. 
o
 
e 
t 
0
C
'0
 
-r-
i 
0
|~~~~~~~~~~
0
_
 
a=
/~~~~~~
o
s 
~
 
u
- 
A
- 
-
o
 
C
0
L
~
~
~
~
~
~
~
l 
-
=
~
 
4
N
a
(9p OLY 
I l I 
Id 
W
V
=
~
 
=
 
e 
I 
1 
| 
-
"
 
(gP O
IL
U
R
 galU
. Ild
N
 
lW
. 
_
 
_
 
N
 
N
 
x
 
~
~
~
~
~
~
~
~
~
w
 
·r
 
a
(SP) 
011tM
 
3aolndw
6
//I
.
-
-\\11/ C
t 
_
_
,
_
 
~
~
~
~\ 
U
Ln 
C3 
in 
en 
_
 
-\ 
_
_!
_
-
 
S 
( 
i 
_
_
 
_\__1
.
_
 
_
P- 
-
-
-
O
 
N
 
L
N
 g 
"
 
u7.Lidv
oO
 
rUagbf
Cd
o
 
o40 laU'
z 
0
Lu
,
 
-
b 
a
LU 
Q.UCd.9U.za)7
_
Ic
Fo
 
sn 
o
 
an 
o
 
Ln 
o
 
O
 
o
 
an
 
a
 
a
 o
-
-
-4
- 
I 
.
.
.
.
.
.
.
(gP) 
o
u
.vI 
3an1 n
 dW
Y
8
C
Cko
Uz 
)
O
;a
I 
cd
-4
-
_4
/2.
F= A PA A
K1
Figure 6. Lumped parameter model.
P- -
Figure 7. Actuator and load dynamics.
9
-
-
+
 
+
 
+
Cd
_
_
_
' 
0Cd
-
=
 
=
 
=
 
-
E 
-
-
.
,
 
-
o00
z 
.J
uJ
0
Upb 
0 
'fl 
0 
en 
C 
an 
an 
o
 
LI 
o
(up) OiiVH 3anllldW
Y
10


Actuator participation in a bending mode identification system

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server