Pathak P. M., Space Robots

7/28/2019 Pathak P. M., Space Robots

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Space Robots

Dr. Pushparaj Mani Pathak, Associate Professor

Mechanical & Industrial Engineering DepartmentIIT, Roorkee


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Introduction

Space robotsUsed for in-orbit construction, Satellite servicing.Maintenance of large space structures.

First in space 1981 Canadian Canadarm.Latest 2008- DextreA blend between vehicle and robot.Vehicle to arm ratio 10:1.A free-floating space robotic system

Spacecrafts position and attitude are not actively controlled.Does not dynamically interact with environment.

No external jets/thrusters used during manipulator activity.


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Linear and angular momenta conserved.Spacecraft moves freely - due to dynamical disturbancescaused by the manipulators motion.This disturbance of the base - deviation of the end-effector.Angular momentum conservation constraints non-integrable - non-holonomic system.

Space manipulator to perform (i) Motion control (ii)Force or torque control tasks.


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Motion control task - Difficult to achieve due tofree-floating base and dynamic coupling betweenthe manipulator and the base.The satellites attitude stabilization is necessary inmost cases to retain the communication link.Space robots are subjected to interaction forceswhenever they perform tasks involving motion,constrained by the environment.These interactions forces or moments must berestricted.


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Space Robots

ETS VII


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ETS VII


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The ETS-VII , or Engineering Test Satellite No. 7,was a satellite developed and launched bythe National Space Development Agency of Japan (NASDA).It was launched aboard an H-IIrocket from Tanegashima Space Center , on 28November 1997. [1]

The ETS-VII was equipped with a 2 metrelong robotic arm , which was used to carry out severalexperiments related to rendezvous docking and spacerobotics. [1]


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It was the worlds first satellite to beequipped with a robotic arm,and alsothe first unmanned spacecraft toconduct autonomous rendezvousdocking operations successfully.

Although it was originally intended tobe used for 1.5 years, the satellite wasfunctional for a period of almost five

years


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Dextre


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Dextre , also known as the Special PurposeDexterous Manipulator (SPDM ), is a two armedrobot, or telemanipulator , which is part of

the Mobile Servicing System on the InternationalSpace Station (ISS), and extends the function of this system to replace some activities otherwise

requiring spacewalks .It was launched March 11, 2008 on mission STS-123 .


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Dextre is part of Canada 's contribution to the ISSand is named to represent its dexterous nature. It issometimes also referred to as the Canada Hand ,

by analogy with the Canadarm and Canadarm2 .[1]

In the early morning of February 4, 2011, Dextrecompleted its first official assignment which

consisted in unpacking two pieces for Kounotori2 while the on-board crew was sleeping.


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Surface Robotic Systems: A range of rovers

Exploration of Mars done bymobile robot Sojourner in 1997.Spirit & Opportunity in 2004beamed images of Martianlandscape and data beamed by

them showed the presence of water there.


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Sojourner(1997) Spirit & Opportunity(2004)


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Stationary versus Mobile Base FormulationsInitial conditions for the link 0, velocity and acceleration for each arm willdepend on the vehicle state.The vehicle dynamics depend on

the arm interaction forces and moments,the external forces and moments acting on the vehicle.

AssumptionsSingle manipulator - revolute joints - open chain kinematic configuration.

Rigid links.Joint between link i and i+1 is numbered i+1.Link frames - named by number according to the link they are attached.Rotational inertias are defined about frames fixed at CM of body.

Mechanics and Modeling of Space Robots


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Difference between ground robot onflexible foundation and space robot


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Dynamic Model of A Space Robot


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NotationsA point or bodyB Observer

C Frame in which expressed

)( A

BC W

,


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Vehicle Dynamics

Linear dynamics of vehicle

V GV V V M F =

.

Angular Dynamics of theVehicle

)()()( V AV

V AV

V AV

V V hh N +=

,


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11 1 1 1( ) ( )i

i i i i i i i A i i i Ai Gi i i G A Gi i A in N R n P R F P R f

+

+ + + += + + +

Arm Dynamics

Angular velocitypropagation )()()(1

111

1+

++

+

++=

iii

i Aii

ii Ai

R

)]()([)()( 11 ++ += iii

i Ai A

ii A A

i A A P RV V Linear velocity propagation

)]()([)()(iG

iii

Ai Aii

A AiG

A A P RV V +=

1++= i A

iG A

i A f F f

Force and torquerelationship


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Free-Flying Robot Dynamics

Position of robot base onvehicleT z y xV r r r P ][0 =

.

)()( 000

V AV

V A R =

.

)]()([)()( 00 P RV V V V

V AV A

V V A A A A +=

...

Angular velocity

Linear velocity


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Vector bond graph of One

DOF Space Robot

)()()( 111

11

+

++

+

++= i

iii

Aiiii

Ai R

)]()([)()( 11 ++ += iii

i Ai A

ii A A

i A A P RV V

=

z

y

x

ccc s

sc

ct st

0

0

1

z y y z x x x I I I N )( +=

x z z x y y y I I I N )( +=

y x x y z z z I I I N )( +=


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Space Robot Setup at IITRoorkee


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Modelling of a Two DOFSpace Robot


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+++++

++++++=

)sin()sin(sin

)cos()cos(cos

21211

21211

l l r

l l r

Y

X Y

X

CM

CM

tip

tip

21 ++=tip

++++++++

+++++++=

)cos()()cos()(cos)sin()()sin()(sin

21212111

21212111

l l r l l r

Y X

Y X

CM

CM

tip

tip


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Modelling of a Three DOFSpace Robot

Free-floatingspacemanipulator


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A free-floating space manipulator consists of a serial robot

mounted on a satellite base.Generalised coordinatesJoint rotation ( i) of manipulator.Euler angle of the base ( , , ) in 3-2-1 convention.

Links are numbered - with zero from base to the last link.All joints are assumed to be revolute.The vehicle frame (V) (located at the CM of vehicle).An absolute frame A is considered.All linear velocities are referred to inertial reference frameAll angular velocities referred to link principal coordinateframe.


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Capsule for Vehicle Principal to EulerAngular Velocity Conversion

Euler angle velocity andvehicle velocity are relatedas

Input - principal angular velocity of the vehicle (3x1matrix as flow input,)

Output - Euler angular velocity (3x1 matrix as theflow output)

A transformer structure iscreated for matrix

multiplication. The output - product of the

3x3 matrix represented by thetransformer structure and theinput.

=

z

y

x

oscin s00

1

coscossincos

tancostansin


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Capsule for Angular Dynamics of a RigidLink in Space

The generalizedcapsule for the

principal angular velocity createdusing relation

1i

1i

1ii

i1ii1i

1iU R +

+

+

+

+

++=

^


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Capsule for Linear Dynamics of a RigidLink in Space

( )1iiii Aii A1i A P Rvv ++ +=

]][][[][][ ii

1ii A

ii A

1i A P Rvv += ++

=+

0

l

0

P i1ii [ ]

=+

00l

000

l 00

P

i

i

1ii

This capsule is created usingEq.

The linear velocities of thecenter of mass of the link are required for the link inertias in three directions.

[ ]T ig ig i 0l 0 P =


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]][][[][][ ii

1ii A

ii A

1i A P Rvv += ++


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Capsule For Euler Junction StructureUsed to represent therotational dynamics of a rigid body.Torque-angular momentum relation isused to construct thiscapsule.The 1 - junctionsrepresent the principalangular velocities of the rigid body

z y y z x x x I I I M )( +=

x z z x y y y I I I M )( +=

y x x y z z z I I I M )( +=


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Initialconfiguration

First joint torque= 10 Nm

2/2/

0

3

2

1

=

=

=


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Manipulator Base Position from spacecraft C.M. (m)R x = r z = 0.1, r y = 0.0 is assumed.

Motor inertiaFor joint 1 is assumed as 0.026 Kg-m 2.

For joint 2 and 3 is 0.001 Kg-m 2.For the simulation

Torque on first joint = 10 N-m

Torque on second and third joint = zero.Second and third joint initial rotation = 1.571 radians.

The Simulation is carried out for 2.8 seconds.

Simulation and Results


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Parameters Mass(Kg)

Ixp(Kg-m 2)

Iyp(Kg-m 2)

Izp(Kg-m 2)

Length(m)

Link 1 6.13 0.03 0.03 0.03 0.1

Link 2 15.69 0.22 0.01 0.22 0.4

Link 3 11.76 0.09 0.01 0.09 0.3

Space-craft 200.0 40.0 40.0 40.0


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Tip trajectory

Reference trajectory-

circular path of radius0.4m (i.e. the length of second link).

For ground robot it wouldhave traced the circular path.But for space robot failsto trace the circular pathdue to reaction of spacerobot on space vehicle.


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Center of mass tr ajectory of space vehicle

Plot shows a

continuous driftin the vehicle(C.M.) location.Due toconservation of angular momentum of a

free-floatingspace robotsystem


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Eul er angle var iation of space vehi cle

Figure indicatescontinuous changeof attitude of spacevehicle.


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Schematic diagram of dual-arm planar space robot

Multi Arm Space Robots

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Issues aretrajectorycontrol with

least basedisturbance


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Experimental set up


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f


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Rocker-Bogie Rover forSpace Exploration


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Many planetary exploration rovers have beendeveloped since 1960s for planetary exploration.Based on the features of the mobile mechanism in

robots, planetary exploration rovers have varioustypes such as wheeled, legged and tracked.Wheeled mobile mechanisms have excellent

features, such as high speed on a relatively flatterrain and easy control; so many researchers havedesigned their exploration rovers with wheeled

structure.


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Wheeled structure planetary rovers havefour-wheel, six-wheel and eight-wheel,etc.

Among these rovers, the six-wheeledmobile rover with rocker bogie mechanismhas superior adaptability and obstacle

climbing capability.These rovers have been used in Mars

Rovers.


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Planar Case


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A detailed kinematic and dynamicmodel of the rocker-bogie rover ispresented.

The motor and ground dynamics areadded to the system.

The performance of rover is analyzedfor obstacle climbing capability.


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Animations


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ReferencesP.M. Pathak , R. Prasanth Kumar, Amalendu Mukherjee, Anirvan Dasgupta,

A Scheme for Robust Trajectory Control of Space Robots, SimulationModelling Practice and Theory, Volume 16, Issue 9,( October 2008), Pages1337-1349.R . MERZOUKI , A. K . SAMANTARAY , P. M. PATHAK , B. OULD BOUAMAMA ,INTELLIGENT MECHATRONIC SYSTEMS : MODELING , CONTROL AND DIAGNOSIS ,SPRINGER LONDON , 2013.Pushpendra Kumar and Pushparaj Mani Pathak , Dynamic Modeling,Simulation and Velocity Control of Rocker-Bogie Rover for SpaceExploration, International Journal of Intelligent Mechatronics and Robotics

(IJIMR), 1(2), 2011, 27-41.Haresh Patolia, P. M. Pathak , S. C. Jain, Trajectory Control of a Dual ArmSpace Robot with Small Attitude Disturbance, SIMULATION, Transactionsof The Society for Modeling and Simulation International, 2010, pp. 188-204.Wikipedia


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Pathak P. M., Space Robots

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