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-Castelló 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

IntroductionIntroduction

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

Motion MeasurementMotion Measurement

Kaufman’s devices

Pedaling DevicesPedaling Devices

Hodgins, Georgia Tech

Sarcos Uniport

TreadmillTreadmill

Sarcos TreadportATR ATLAS ATR GSS (ground

surface simulator)

Shaping the ground : ALFShaping the ground : ALF

2D Treadmill2D Treadmill

Omni-Directional Treadmill Torus Treadmill

Programmable Foot Programmable Foot PlatformsPlatforms

Iwata’s GaitMasterSarcos Biport

Programmable Foot Programmable Foot PlatformsPlatforms

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

Mathematical FormulationMathematical Formulation

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)

Inertial Force FeedbackInertial Force Feedback

f = m a

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 ?

ColgateColgate

1/(m s+b) 1/szoh

Zo(s)

H(z)

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

Collocation ProblemCollocation Problem

,v f

,

v L

L f

v f

,

,

v h L

f k L