high-precision adaptive control of large reflector surface
TRANSCRIPT
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High-Precision Adaptive Control of Large
Reflector Surface
Houfei Fang, Ubaldo Quijano and Eastwood Im
Jet Propulsion Laboratory
California Institute of Technology
Jim Moore and Jim Pearson
ManTech SRS Technologies
Kon-Well Wang and Jeff Hill
Department of Mechanical and Nuclear Engineering
The Penn State University
Changgeng Lui and Frank Djuth
Geospace Research, Inc.
Earth Science Technology Conference 2008
June 24, 2008
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Outline
• Introduction
• Inflatable Membrane Reflector Development
• Theoretical analysis of the reflector shape
control system
• Development of PVDF based actuators
• Demonstration of membrane reflector
• Conclusion
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Introduction
Architecture of the High-Precision Surface
Control System
• It consists of a large deployablereflector, a set of flexibleactuators (mounted on the back ofthe reflector), a wavefrontsensing metrology subsystem,and an active (feedback)controller.
• Guided by shape control laws, thecontroller periodically updatesvoltage signals to control theactuator strain at various antennapositions, thus maintainingdesired shape contour
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Outline
• Introduction
• Inflatable Membrane Reflector Development
• Theoretical analysis of the reflector shape
control system
• Development of PVDF based actuators
• Demonstration of membrane reflector
• Conclusion
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Inflatable Membrane Reflector Development
• Consist of two thin films, a reflector and acanopy, that are joined around the edges
• The films are joined using a leak tightbonding technique
• The reflector film is typically metalizedwith a vapor deposited coating (silver oraluminum)
• The reflector is integrated with an inflatabletorus
• Compliant features are used to minimizeloading changes
• The boundary tension is adjusted to achievethe best shape
10- and 5-meter inflatable reflector
Reflector Design
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Inflatable Membrane Reflector
• Maximum packaging efficiency
• Simple reliable deploymentmethod
• Offers a solution to aperture sizes>25 m where other antennatechnologies begin to be limited bylaunch vehicle volume and massrestrictions
• Low or zero CTE membranematerials are being develop tominimize in space thermaldistortion
4mx6m Off-Axis Inflatable Antenna
Advantages
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• The film was secured to the coatingdrum and put into the vacuum chamber.
• The chamber was evacuated to removeresidual solvent and then the film wasremoved for inspection prior to coating.
• The film was coated and removed.
• ~1200Å of aluminum was depositedonto the ~2-mil CP-1 thin film
• Since the film’s diameter was larger
than the coating drum length, the film
was rotated 90° and coated a 2nd time in
order to coat the “wings”
VDA Coating
Inflatable Membrane Reflector Development
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Inflatable Membrane Reflector Development
Precisely Shaped Casting Mandrel
• To cast the thin polymer films
• Removal of the coating aroundthe reflector / canopy bond band(i.e. 96” aperture line)
• Marking of the catenarylocations
• Attachment of thephotogrammetry targets
• Attachment of the actuators
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Recent Developments of Inflatable Antenna Technology
• On-axis, off-set, andCassegrain antennas havebeen designed and fabricated
• RF characterizations of off-set and on-axis antennashave been performed atfrequencies from X-band toKa-band
8.4 GHz Data for 4-m x 6-m Test Article
Inflatable Membrane Reflector Development
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Outline
• Introduction
• Inflatable Membrane Reflector Development
• Theoretical analysis of the reflector shape
control system
• Development of PVDF based actuators
• Demonstration of membrane reflector
• Conclusion
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Theoretical Analysis of the Reflector Shape
Control System
Reflector Modeling
• Shallow spherical shellapproximation
• Pre-tensioned membrane shellwith bending stiffness (internalinflation pressure)
• Simply supported boundaryconditions at the rim
• Modeled using Ritz method anda Fourier-Bessel expansion
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YSensors
Integrated
Reflector/Actuator
System
Least-Squares
Shape Control
ZFd
V
Vcntrl
Saturation
weffVmax
Control Algorithm
Sensor Measurement Locations
Sensor
Measurements
Theoretical Analysis of the Reflector Shape
Control System
• A Least-Squares shape control
• LS controller input is the displacement from all metrology sensor
measurements
• Using the equation obtained from the reflector model the desire
actuation voltage can be calculated.
• Saturation block accounts for PVDF voltage saturation effects
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W – Error: Spherical shape notachieved on inflation
Heig
ht,
mRadial Location, m
* Not To Scale
-15 -10 -5 0 5 10 150
0.5
1
1.5
2
2.5
3
3.5
z0
zr
Initial Profile, w0(r)
Inflated Profile, winf(r)
Desired Profile, wr(r)
z
Sources of Shape Error
Thermal loading - Consider uniformand thermal gradient loading
-15 -10 -5 0 5 10 15
-15
-10
-5
0
5
10
15
178
183
188
193
198
m
T, (K)
m
T nom = 188K, T0 = 0, T=20K
-15 -10 -5 0 5 10 15
-15
-10
-5
0
5
10
15
178
183
188
193
198
m
T, (K)
m
-15 -10 -5 0 5 10 15
-15
-10
-5
0
5
10
15
178
183
188
193
198
m
T, (K)
m
T nom = 188K, T0 = 0, T=20K
-17.5 17.5 0
| wWerror
|max
0
wWerror
-17.5 17.5 0
| wWerror
|max
0
wWerror
-17.5 17.5 0 -17.5 17.5 0
| wWerror
|max
0
wWerror
Theoretical Analysis of the Reflector Shape
Control System
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Theoretical analysis of the reflector shape
control system
• Surface deformations due to combined uniform and gradient thermal load
• Limited actuator saturation
• RMS error reduction to 0.19mm (95.58 %)
Sample results — uniform + gradient thermal loading
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Theoretical analysis of the reflector shape
control system
• Surface deformations due to W-error (wmax = 2.8 mm)
• No actuator saturation occurs
• Patches near center are not utilized by the control law
• RMS error reduction to 0.0062mm (99.69 %)
Sample results – w-error
(mm) (mm)
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Outline
• Introduction
• Inflatable Membrane Reflector Development
• Theoretical analysis of the reflector shape
control system
• Development of PVDF based actuators
• Demonstration of membrane reflector
• Conclusion
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Development of PVDF Based Actuators
Overview of Fabrication Process
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• Over 170 actuators have
been fabricated for a 2.4-m
engineering model.
• Actuators have been tested
to 4KV, will be operated at
the maximum of 2 KV.
• A large number of epoxies
have been experimentally
studied and the most
suitable one has been
identified
• Actuator bonding process
has been developed.
Development of PVDF Based Actuators
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Outline
• Introduction
• Inflatable Membrane Reflector Development
• Theoretical analysis of the reflector shape
control system
• Development of PVDF based actuators
• Demonstration of membrane reflector
• Conclusion
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Demonstration of Membrane Reflector
0.2-m diameter engineering model
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Demonstration of Membrane Reflector
Demonstration video
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Outline
• Introduction
• Inflatable Membrane Reflector Development
• Theoretical analysis of the reflector shape
control system
• Development of PVDF based actuators
• Demonstration of membrane reflector
• Conclusion
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Conclusions
• Analytical model (integrated reflector, actuator, and controller)
has been developed and analyzed.
• Fabrication process for Electroactive Polymer (EAP) actuators
has been developed. EAP actuators have fabricated.
• 0.2-m diameter reflector engineering model has been fabricated
and demonstrated, showing that the EAP actuator technology is
promising for the surface control of large in-space deployable
reflectors.
• The feasibility of the EAP actuator technology as well as the high
precision surface figure control architecture has been
demonstrated.
• Future works include the development of 2.4-m diameter reflector
engineering model.
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End