Control Strategy of Hardware-in-the-Loop Simulator EPOS 2.0 for Autonomous Docking Verification

Melak Zebenay > EPOS- A Robotics-Based Hardware in-the-Loop Simulator for Simulating Satellite RvD Operations >Aug 30, 2010

Slide 1

Control Strategy of Hardware-in-the-Loop Simulator EPOS 2.0 for Autonomous Docking Verification

M. Zebenay, T. Boge , R. Lampariello , R. Krenn German Aerospace Center (DLR)

Melak Zebenay >EPOS-A Robotics- Based Hardware in-the-Loop Simulator for Simulating Satellite RvD Operations >Aug 30,2010

Slide 2Melak Zebenay >EPOS-A Robotics- Based Hardware in-the-Loop Simulator for Simulating Satellite RvD Operations >Aug 30,2010

Slide Melak Zebenay >EPOS-A Robotics- Based Hardware in-the-Loop Simulator for Simulating Satellite RvD Operations >Aug 30,2010

Slide

Content

EPOS- European Proximity Operation Simulator facility

Docking simulation Concept

Control Strategy

1-DOF Docking Modeling

Target Impedance parameter Identification

Results

Conclusion and future work




Slide

EPOS 2.0 -European Proximity Operation Simulator

What is EPOS ?

Laboratory simulation of spacecraft proximity operationsReal-time, real size and real motion simulationHardware-in-the-loop simulator

Why EPOS?Calibrated test bed for proximity operations on RVD missions

quantitative performance tests on equipment level Verification and validation on

equipment levelverification and validation on

system level




Slide

EPOS 2.0 -European Proximity Operation Simulator

EPOS 2.0 Performance data:

Motion Ranges:

Range: 25 m

Roll/Pitch/Yaw: 360 deg

Commanding frequency: 250 Hz

Natural frequency : 8-10Hz

Max, Payload: up to 200 kgPosition accuracy (3D/3) : 1.56mm

Orientation accuracy (3D/3) : 0.20deg

Coming new feature of EPOS 2.0 :Online measurement system which measures relative position

Commands corrections to the robots




Slide


The goal of docking simulation capability:

Satellite simulator shall accept the measured force/torque and simulate the corresponding dynamic response of the two satellites

EPOS 2.0 facility maneuver the docking hardware to follow the output motion data of the satellite simulator

EPOS 2.0 facility shall have the same impedance (or passivity) as the simulated satellites

Advanced robotics control is suggested to fulfill above requirements




Slide


Schematic of EPOS facility control architecture :




Slide

Control Strategies (1/2)

Control challenges and solution strategies:

System time delay problem

What: Robot does not physically respond to a command immediately

Why: Intrinsic for the industrial robots (not a problem for their industrial applications)

Consequence: Unstable simulation process

Solution: Energy-based simulation process control




Slide

Control Strategies (2/2)

Control challenges and solution strategies:

Impedance mismatching problem

What: Contact impedance of EPOS does not match that of satellite

Why: docking hardware is constrained to the ground via the robot -

the active robot will interacts with the docking process

Consequence: Simulated docking behavior is inaccurate

Solution: Impedance/admittance robot control strategy




Slide

1-DOF Docking Modeling (1/3)

Ideal Satellite 1-DOF docking (contact) modeling

1-DOF Modeling of Satellite Docking using Spring-dashpot contact dynamics model of the contact force

)sin()cos()(

))((

))(11

(

)(

21

21

21

2112

22

11

1

tectectx

xkxbmm

mmx

xkxbmm

xxx

xkxbxm

xkxbxm

xkxbF

tt


Slide 10


Docking conditions using EPOS 2.0

kc

Compliant F/T

sensor Model

m2

k2

b2

x2

Robot 2 Impedance

model

m1

k1

b1

x1

Robot 1 Impedance

model


Slide 11


m1 m2

k1

b1

kc k2

b2

TargetM2

ServicerM1

k

b

Satellite docking Model

EPOS 2.0 docking Model

Requirements:

The approximated docking simulation shall have the same dynamic behavior like the real satellite docking model. Therefore it is required to have the same :

Final position and velocity after impact

Impact force/torque

Contact duration


Slide 12

Target Impedance parameter Identification (1/2)

Dynamic equation of the target Impedance model:

21

2211

mm

xmxmv

u

x

x

x

x

mm

tk

mm

b

m

b

mckk

tkbmmm

m

mck

mbtmkmmmm

ck

mm

tk

mm

b

m

b

mckk

x

x

x

x

0

0

0

0

2

2

1

1

)21

2

21

2

2

2(2

)2(

)22

()21

(2

1

2

1000

)2221

()21

(1

1

1)21

1

21

1

1

1(1

)1(

0010

2

2

1

1


Slide 13

Target Impedance parameter Identification (2/2)

Determining the unknowns k1, b1, k2 ,b2 assuming m1=M1 and m2=M2:

Computing states t=t1 and t=t2 where t1 and t2 is less than the contact duration.

))()(())()(()(

))()(())()(()(

)()(

)()(

21222122211

11121112111

1

2121

1111

1

1

ztxtxktxtxbtxm

ztxtxktxtxbtxm

txtx

txtx

b

k

cc

cc

))()(())()(()(

))()(())()(()(

)()(

)()(

21222122222

11121112122

1

2222

1212

2

2

ztxtxktxtxbtxm

ztxtxktxtxbtxm

txztxd

txztxd

b

k

cc

cc


Slide 14

Results

Given M1=750kg, M2=1050Kg, k=500000, b=30 v1(0)=0.3, v2(0)=0 kc=30000, bc=0

Assumed:M1=m1, M2=m1

Unknowns: k1, b1 , k2 and b2

Results: k1=8.0571e+005 b1=51.4286 k2=1.1280e+006; b2=72.0

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-500

-400

-300

-200

-100

0

100

200

300

400

500

Time (s)

For

ce

(N)

Comparing Forces

Sat Force

Target Imp model Force

Servicer Imp model Force

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-500

0

500Impact Forces Profile for Sat and Impedance model

Time (s)

For

ce

(N)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-500

0

500

Time (s)

Tar

Rob

mod

elF

(N

)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-500

0

500

Time (s)

Ser

Rob

Mod

el F

(N

)


Slide 15

Results

Position and velocity comparison between the ideal satellite and chaser satellite impedance model after contact

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

-16

-14

-12

-10

-8

-6

-4

-2

0

x 10-4

Time (s)

Comparing Displacement of Servicer

Dis

plac

emen

t (m

)

Ser Sat Disp

Imp model Disp

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

-0.035

-0.03

-0.025

-0.02

-0.015

-0.01

-0.005

0

Time (s)

Comparing Velocity of Servicer

Vel

ocity

(m

/s)

Ser Sat velocity

Imp model Velocity


Slide 16

Results

Position and velocity comparison between the ideal satellite and target satellite impedance model after contact

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

0.9984

0.9986

0.9988

0.999

0.9992

0.9994

0.9996

0.9998

1

Time (s)

Comparing Displacement of Target

Dis

plac

emen

t (m

)

Tar Sat Disp

Imp model Disp

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

-0.03

-0.025

-0.02

-0.015

-0.01

-0.005

Time (s)

Comparing Velocity of Target

Vel

ocity

(m

/s)

Target Sat velocity

Imp model Velocity


Slide 17

Conclusion and future work

Experiment using EPOS 2.0 to investigate the contact duration and contact force using different stiffness material.

Testing the target impedance using EPOS 2.0 is in progress

Extend the target impedance identification method for 3-DOF

Implement the control algorithm using the computed target impedance




Slide

Thank You!

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Control Strategy of Hardware-in-the-Loop Simulator EPOS 2.0 for Autonomous Docking Verification