locomotion haptic devices : concepts and problems. ramon costa-castelló
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Locomotion Haptic Locomotion Haptic Devices : Concepts and Devices : Concepts and
Problems.Problems.
Ramon Costa-CastellóRamon Costa-Castelló
IndexIndex
IntroductionIntroduction
Known Locomotion Known Locomotion Haptic DevicesHaptic Devices
Control Problems in Control Problems in Locomotion DevicesLocomotion Devices
IntroductionIntroduction
Haptic : relating to the sense of touch.
Haptic feedback is a way of conveying information between a human and a computer.
The haptic display generates force feedback cues which may represent the resistance of a virtual wall, the roughness of a virtual texture, or the weight of a virtual mass.
IntroductionIntroduction
Locomotion haptic devices are mechanical are mechanical devices which allow the human operator to devices which allow the human operator to indicate movements inside a virtual environment. indicate movements inside a virtual environment. Walk, RunWalk, Run Special devices : bike, carSpecial devices : bike, car
In some cases this devices are also used to In some cases this devices are also used to feedback information about the environment and feedback information about the environment and the trajectory to the human operators.the trajectory to the human operators. Ground shape : flat floor, curved floor, slopes,…Ground shape : flat floor, curved floor, slopes,… Ground Properties : snow, grass, stone, …Ground Properties : snow, grass, stone, … Dynamic Environments : surf, ….Dynamic Environments : surf, ….
IndexIndex
IntroductionIntroduction
Known Locomotion Known Locomotion Haptic DevicesHaptic Devices
Control Problems Control Problems in Locomotion in Locomotion DevicesDevices
Programmable Foot PlatformsProgrammable Foot Platforms(tightly coupled)(tightly coupled)
Haptic Walker The Rodent Stepper
Capabilities OverviewCapabilities OverviewMotion Motion
specificationspecification PedalinPedalingg
TreadmiTreadmillll
2D 2D TreadmillTreadmill
PlatforPlatformm
forwardforward Ext.Ext. Ext.Ext. Ext.*Ext.*
turnturn OKOK Ext.Ext. Ext.Ext. Ext.*Ext.*
upup NONO Ext.Ext. Ext.Ext. Ext.*Ext.*
Motion Motion allowedallowed PedalinPedalin
ggTreadmiTreadmi
llll2D 2D
TreadmillTreadmillPlatforPlatfor
mm
forwardforward OKOK OKOK OKOK
turnturn OKOK Not Not naturalnatural
OKOK OKOK
upup NONO OKOK OKOK OKOK
Capabilities OverviewCapabilities OverviewGround Ground ShapeShape PedalinPedalin
ggTreadmiTreadmi
llll2D 2D
TreadmillTreadmillPlatforPlatfor
mm
planarplanar OkOk OkOk OkOk
slopeslope -- OkOk NoNo OKOK
arbitrararbitraryy
-- NoNo NoNo OKOKHapticHaptic PedalinPedalin
ggTreadmiTreadmi
llll2D 2D
TreadmillTreadmillPlatforPlatfor
mmGround Ground stiffnessstiffness
NONO NONO OKOK
Contact Contact shapeshape
NONO NONO NO*NO* NONO* ALF and GSS* ALF and GSS
Programmable Foot Platforms can be used in some specific rehabilitation.
IndexIndex
IntroductionIntroduction Known Locomotion Known Locomotion
Haptic DevicesHaptic Devices Control Problems in Control Problems in
Locomotion DevicesLocomotion Devices
Control GoalsControl Goals Generally speaking, a locomotion interface Generally speaking, a locomotion interface
should cancel a user’s self motion in a should cancel a user’s self motion in a location to allow the user to go to anywhere location to allow the user to go to anywhere in a large virtual space on foot. (in a large virtual space on foot. (Centering Problem))
Additionally, some of them can be designed Additionally, some of them can be designed to present textures of walking surface, i.e., to present textures of walking surface, i.e., slopes, roughness, hardness, and so on. slopes, roughness, hardness, and so on. ((Haptic Problem))
Security Issues : Machine/Human Stability Security Issues : Machine/Human Stability
The Complete PictureThe Complete Picture
InertialFrame
Virtual WorldFrame
Human ReferenceFrame
Robot 1Frame Robot 2
Frame
VirtualGround
I
V
H
F1
R1
Centering ProblemCentering Problem Goals :Goals :
Keep Robot end effector within manipulator Keep Robot end effector within manipulator workspaceworkspace
Minimize inertial forces introduced over humanMinimize inertial forces introduced over human Contradictory goalsContradictory goals
Further Analysis:Further Analysis: Determine allowed Inertial forces Determine allowed Inertial forces
((psychophysics, human stability affairs)) Manipulator WorkspaceManipulator Workspace Define Control laws (trade-off)Define Control laws (trade-off)
Haptic ProblemHaptic Problem
Human Human OperatorOperator
Haptic Haptic DisplayDisplay
ControlControl SystemSystem
VirtualVirtualEnvironmentEnvironment
Haptic Haptic InterfaceInterface
Haptic SimulationHaptic Simulation
hv
hfev
ef
Haptic InterfaceHaptic Interface
The consensus in the literature seems to be that the “ideal” interface device is one that has low friction, inertia, and backlash, is highly backdriveable, has a large force range and bandwidth, and has a suitable working volume. These can be conflicting goals.
Causality StructuresCausality Structures
Impedance Control : Measured Impedance Control : Measured position/velocity generated forceposition/velocity generated force
Admittance Control : Measured force Admittance Control : Measured force generated velocity/positiongenerated velocity/position
Control ApproachesControl Approaches
A key point in haptic design is stability.A key point in haptic design is stability.
To assure stability it is necessary to know To assure stability it is necessary to know all components (human operator is all components (human operator is unknown). unknown). human is assumed a passive system. Modularity design.
One approach which allows to design each one in a separate way is passivity.
Discretization-Discrete Time Discretization-Discrete Time Implementation (Implementation (“energy
leaks”)) Most Designs and made in continuous Most Designs and made in continuous
time. Implementation issues may time. Implementation issues may unstabilize the system :unstabilize the system : Integration (explicit integrators are non Integration (explicit integrators are non
passive)passive) Zero order holdZero order hold QuantificationQuantification
What happens with Performance ?What happens with Performance ?
Virtual Coupling Virtual Coupling (Brown & Colgate, (Brown & Colgate,
1997)1997)
1/(m s+b) 1/szoh
Zo(s)
Virtual Environment
T
-Virtual Coupling
Passitivity ObserverPassitivity Observer
Virtual Environment
PassivityController
Haptic Interface
Passivity Observer
ev
ef
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