Passivity Control for Hybrid Simulations of Satellite Docking
Rainer Krenn, Klaus Landzettel, Toralf
Boge, Melak Zebenay
Institute of Robotics and Mechatronics
& German Space Operations Center German Aerospace Center (DLR), Oberpfaffenhofen, D-82234 Wessling
ICRA11 Space Robotics Workshop
May 13, 2011, Shanghai, China
2ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Contents of Workshop Contribution
Simulation activities in the context of On-Orbit ServicingFocus: Contact dynamics simulation
On-orbit servicing projects and contributionsCX-OLEV & Smart-OLEV
Modeling and simulation in softwareContact dynamics modelingDocking simulation results
Hybrid simulation using EPOS RvD
facilityIntroduction of hybrid simulation methodIntroduction of EPOS facilityContact dynamics simulation with EPOS
Numerical stability aspectsPassivity control
3ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
On-Orbit Servicing Projects –
OLEV Type Missions (Orbital Live Extension Vehicle)
Projects involved:CX-OLEV (ESA, Dutch Space & contractors)Smart-OLEV (Kayser-Threde, SSC, Senser
& contractors)Clients: Telecom satellites in GEOObjectives: Offer commercial services
Satellite operators (Eutelsat, Optus)Satellite live extensionFleet management
DLR contributionsRobotic docking tool (Capture Tool)Rendezvous and docking control algorithms (image processing) Docking simulations (S/W)
4ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
OLEV Servicing
Satellite
& Docking Payload
(Smart)
1
3
2
554
4
4
1) Capture Tool (CT)2) CT Deployment Mechanism (CDM)3) Target Illumination System (TIS) (2x)
4) Camera System (Far-, Mid-, Near-Range
Cameras with Electronics) (2x)5) Docking Payload Control Unit (2x)
5ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Capture Tool for Non-Cooperative Targets
6ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Docking Scenario
for Multi-Body System Simulation
ClientHot Bird series, with flexible solar wingsOrbit: GEOAOCS deactivated, momentum wheels loadedAerojet/Marquardt R4D nozzle, slightly tilted1194 mm launch adapter
Smart-OLEVOrbit: GEO + 2.178 m (R-bar)AOCS active75 mm
lateral misalignment,
2°
attitude error
in all axesFlexible Capture Tool deployment mechanism
|v| ≤
4 mm/s deployment/retraction velocityCapture Tool
Radial laser distance sensorContact switchesOperational Locking Crown
Contact sensitive bodies:Nozzle vs. Capture Tool + Locking CrownLaunch adapter vs. Client Support Brackets
Smart-OLEV
Support Brackets
Flexible BoomCapture Tool
Nozzle
Launch Adapter
Client Spacecraft
7ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
8ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Contact
Dynamics Model (3D, Multi-Point)
Surface meshingBounding volume tree generation Contact area detection algorithm
Elastic foundation model for contact force computation Friction model with stick-slip
9ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
0 50 100 150 200 250 300-200
-100
0
100
200
300
400
Simulation Time [s]
App
lied
Forc
e [N
]Lo
ckin
g C
row
nLo
ckin
g C
row
n R
F
W02
xyz
0 50 100 150 200 250 300-5
0
5
10
15
Simulation Time [s]
App
lied
Torq
ue [N
m]
Lock
ing
Cro
wn
Lock
ing
Cro
wn
RF
W02
xyz
0 50 100 150 200 250 300-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
Simulation Time [s]
Late
ral P
ositi
on E
rror [
m]
Clie
nt C
OM
- S
mar
t CO
MS
mar
t GR
F
W02
yz
0 50 100 150 200 250 300-0.01
0
0.01
Simulation Time [s]
Ela
stic
Def
orm
atio
n [-]
CD
M S
egm
ents
Ben
ding
W02
0 50 100 150 200 250 300-5
0
5x 10
-3
Simulation Time [s]
Ela
stic
Def
orm
atio
n [-]
CD
M S
egm
ents
Tors
ion
W02
0 50 100 150 200 250 300-5
0
5
10x 10
-3
Simulation Time [s]
Ela
stic
Def
orm
atio
n [m
]C
DM
Seg
men
tsA
xial
W02
0 50 100 150 200 250 300-100
-50
0
50
Simulation Time [s]
App
lied
Forc
e - C
SB
1 [N
] W02
0 50 100 150 200 250 300-100
-50
0
50
Simulation Time [s]
App
lied
Forc
e - C
SB
2 [N
] W02
0 50 100 150 200 250 300-100
-50
0
50
Simulation Time [s]
App
lied
Forc
e - C
SB
3 [N
] W02
10ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Hybrid Simulation Method
1.
Numerical simulation of satellite trajectory (S/W)Free floating dynamics of satellites, 6 DOFMicro-gravity / 0-gravity conditionsLarge flexible structures, solar panelsMomentum wheels, reaction wheels, thrusters
2.
Physical-mechanical display of computed trajectory
using industrial robotsAttachment of satellite mockupsPerform physical contact (capture tool, nozzle) Use of missions specific mechanisms,
actuators and sensors (capture tool, GNC-sensors)
3.
Sensor data feedback from facility specific sensorsRobot joint sensors actual trajectoryForce torque sensors contact dynamics purposes
11ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Hybrid Simulation Facility EPOS (European Proximity Operations Simulator)
1.
Development system for dynamics models: Matlab/SimulinkReal-time target for numerical simulation: VxWorks
2.
Robotic system for trajectory emulation: (Kuka, RSI, position controlled)3.
Force/torque sensor feedback: Schunk/DLR FTS (“Compliance”)
EPOS has a long history as open-loop satellite rendezvous simulator (ATV sensor verification).But: Is EPOS applicable for closed-loop contact dynamics simulations?
12ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Hybrid Simulation of Docked Configuration
Sat 1 Sat 2
FTS
Sat 1 Sat 2
System to be simulated“Ideal System”
Hybrid simulation setup
k
k
Numerical Simulation
Robotic System
Free floating rigid bodiesSpring at natural lengthv = 0
13ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Experimental Setup “Docked Configuration”
Simulating the elastically fixed configuration
(1 DOF) using single robot and
one-end supported aluminum sheet metal1.
Open hybrid simulation loop2.
Initial robot/satellite position with bent beam3.
Sensor calibration/reset (F = 0)4.
Close hybrid simulation loop again
Easy mechanical setupNearly linear stiffness and low dampingEasy stiffness adaptation by changing contact point distance from support point
(1500 N/m …
3000 N/m)Low risk of mechanical damage during experiment
14ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Observations
Expected: Stationary system at restObserved: Unstable system
Oscillating systemIncreasing amplitudes
0 50 100 150 200-30
-20
-10
0
10
20
30
Simulation Time [s]
App
lied
Con
tact
For
ce [N
]
0 50 100 150 200-0.04
-0.02
0
0.02
0.04
Simulation Time [s]
Pos
ition
[m]
RobotSimulation
0 50 100 150 200
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
Simulation Time [s]
Vel
ocity
[m/s
]
RobotSimulation
15ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Sources of Excitation? ---
Active Elements?
Simulation sampling rate not adequate for system dynamics?250 Hz >> eigen-frequency of contact dynamics problem
Force-Torque sensor errors and noise? Calibration error may cause change of static equilibrium positionMean of noise is zeroBut: May initiate system instability if active elements are in the loop
Passivity of robot system to be investigated
Numerical Simulation
Robotic System
Physical Contact
FT-Sensor
Simv Robv
FTSF FTSFOne-Port
NetworkOne-Port
NetworkTwo-Port
Network
16ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Observed Energy ErrorRobotic
System
Ctrlv Robv
FTSF FTSF
0
0
k
Error out i in ii
k
FTS i Rob i Ctrl ii
E dt P t P t
dt F t v t v t
0 50 100 150 200-20
0
20
40
60
80
100
120
Simulation Time [s]
Ene
rgy
Erro
r in
Sys
tem
[J]
0 50 100 150 200-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
Simulation Time [s]
Pow
er E
rror o
f Rob
ot [W
]
17ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Transfer Function of Robot System
123 123.05 123.1 123.15 123.2 123.25 123.3 123.35 123.40.0153
0.0153
0.0154
0.0154
0.0154
0.0154
0.0154
0.0154
0.0154
0.0154
0.0154
Simulation Time [s]
Pos
ition
[m]
RobotSimulation
70 ms
70 ms
76.6 76.62 76.64 76.66 76.68 76.7-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1x 10-5
Simulation Time [s]
Pos
ition
[m]
RobotSimulation
24 ms
Electro-mechanical systemAmplitude response of robot armPhase response of robot arm
Robot control system with preprocessing of external commands
LatencySmoothing of input signals
18ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Passivity ControlRobotic
System
Ctrlv Robv
FTSF FTSF
PC
SimF
Simv
11 12
11
1
11
1
; ; 0;
0; 0; 0
;;
Impedance causality:
Admittance causality:
Error iv Error i Error i
Sim iSim i FTS i i Sim i i
Error i
Error iF Error i
Ctrl i Sim i i FTS i i
E tk E t E t
dt v tF t F t t v t tE t
E tk E t
dtv t v t t F t t
121
1
; 0
0; 0; 0
Error iFTS i
Error i
E tF t
E t
PID type Energy ControlHybrid simulation of space robot applications
[Krenn, Schäfer, AIAA GNC 1999]
Time Domain Passivity ControlHaptic
devices[Hannaford, Ryu, ICRA 2001]
Dissipate energy errorMaintain system dynamics
19ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
0 100 200 300 400 500 600-2
-1
0
1
2x 10-3
Simulation Time [s]
Vel
ocity
[m/s
]
RobotSimulation
0 100 200 300 400 500 600-1.5
-1
-0.5
0
0.5
1
1.5
Simulation Time [s]
App
lied
Con
tact
For
ce [N
]
Experiment Results Using PID Type Energy Control
0 100 200 300 400 500 600-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
Simulation Time [s]
Con
trolle
r For
ce [F
]
0 100 200 300 400 500 600-5
0
5
10
15x 10-3
Simulation Time [s]
Ene
rgy
Erro
r in
Sys
tem
[J]
20ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
0 50 100 150 200 250-0.2
-0.1
0
0.1
0.2
Simulation Time [s]
Con
trolle
r For
ce [N
]
Experiment Results Using Time Domain Passivity Control
0 50 100 150 200 250-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
Simulation Time [s]
App
lied
Con
tact
For
ce [N
]
0 50 100 150 200 250-5
0
5
10
15x 10-5
Simulation Time [s]
Ene
rgy
Erro
r in
Sys
tem
[J]
0 50 100 150 200 250-1.5
-1
-0.5
0
0.5
1
1.5x 10-3
Simulation Time [s]
Vel
ocity
[m/s
]
RobotSimulation
21ICRA11 Space Robotics Workshop, Rainer Krenn, May 13, 2011
Conclusion & Future Work
Meaningful results for design phases A/B using software simulation.Hybrid simulation required for phases C/D/E
Real-time simulation requirementHardware-in-the-loop simulation requirements
Robotic systems are not passive Numerical instabilities of closed-loop simulationPassivity control solutions successfully implemented and tested at EPOS
PID energy control approachTime domain passivity control
Future work:Passivity tests at higher contact stiffnessTest of system transparency (accuracy of contact dynamics simulation)