Locomotion Haptic Devices : Concepts and Problems. Ramon Costa-Castelló

Index Introduction Introduction Known Locomotion Haptic Devices Known Locomotion Haptic Devices Control Problems in Locomotion Devices Control Problems in Locomotion Devices

Introduction 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.

Introduction

Introduction

Introduction are mechanical devices which allow the human operator to indicate movements inside a virtual environment. Locomotion haptic devices are mechanical devices which allow the human operator to indicate movements inside a virtual environment. Walk, Run Walk, Run Special devices : bike, car Special devices : bike, car In some cases this devices are also used to feedback information about the environment and the trajectory to the human operators. In some cases this devices are also used to feedback information about the environment and 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, ….

Index  Introduction Known Locomotion Haptic Devices Known Locomotion Haptic Devices Control Problems in Locomotion Devices Control Problems in Locomotion Devices

Motion Measurement Kaufman’s devices

Pedaling Devices Hodgins, Georgia Tech Sarcos Uniport

Treadmill Sarcos Treadport ATR ATLAS ATR GSS (ground surface simulator)

Shaping the ground : ALF

2D Treadmill Omni-Directional Treadmill Torus Treadmill

Programmable Foot Platforms Iwata’s GaitMasterSarcos Biport

Programmable Foot Platforms

Programmable Foot Platforms (tightly coupled) Haptic Walker The Rodent Stepper

Capabilities Overview Motion specification PedalingTreadmill 2D Treadmill Platform forwardExt.Ext.Ext.* turnOKExt.Ext.Ext.* upNOExt.Ext.Ext.* Motion allowed PedalingTreadmill 2D Treadmill PlatformforwardOKOKOK turnOK Not natural OKOK upNOOKOKOK

Capabilities Overview Ground Shape PedalingTreadmill 2D Treadmill Platform planarOkOkOk slope-OkNoOK arbitrary-NoNoOK HapticPedalingTreadmill Platform Ground stiffness NONOOK Contact shape NONONO*NO * ALF and GSS Programmable Foot Platforms can be used in some specific rehabilitation.

Index  Introduction Ö Known Locomotion Haptic Devices Control Problems in Locomotion Devices Control Problems in Locomotion Devices

Control Goals Generally speaking, a locomotion interface should cancel a user’s self motion in a location to allow the user to go to anywhere in a large virtual space on foot. () Generally speaking, a locomotion interface should cancel a user’s self motion in a location to allow the user to go to anywhere in a large virtual space on foot. (Centering Problem) Additionally, some of them can be designed to present textures of walking surface, i.e., slopes, roughness, hardness, and so on. ( ) Additionally, some of them can be designed to present textures of walking surface, i.e., slopes, roughness, hardness, and so on. (Haptic Problem) Security Issues : Machine/Human Stability Security Issues : Machine/Human Stability

The Complete Picture Inertial Frame Virtual World Frame Human Reference Frame Robot 1 Frame Robot 2 Frame Virtual Ground I V H F1 R1

Mathematical Formulation

Centering Problem Goals : Goals : Keep Robot end effector within manipulator workspace Keep Robot end effector within manipulator workspace Minimize inertial forces introduced over human Minimize inertial forces introduced over human  Contradictory goals  Further Analysis:  Determine allowed Inertial forces ()  Determine allowed Inertial forces ( psychophysics, human stability affairs )  Manipulator Workspace  Define Control laws (trade-off)

Inertial Force Feedback f = m a

Haptic Problem HumanOperator HapticDisplay ControlSystem VirtualEnvironment Haptic Interface Haptic Simulation

Haptic 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 Structures Impedance Control : Measured position/velocity generated force Impedance Control : Measured position/velocity generated force Admittance Control : Measured force generated velocity/position Admittance Control : Measured force generated velocity/position

Control 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 all components (human operator is unknown). To assure stability it is necessary to know all components (human operator is 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 Implementation () Discretization-Discrete Time Implementation (“energy leaks”) Most Designs and made in continuous time. Implementation issues may unstabilize the system : Most Designs and made in continuous time. Implementation issues may unstabilize the system : Integration (explicit integrators are non passive) Integration (explicit integrators are non passive) Zero order hold Zero order hold Quantification Quantification What happens with Performance ? What happens with Performance ?

Colgate 1/(m s+b)1/s zoh Zo(s) H(z)

Virtual Coupling (Brown & Colgate, 1997) 1/(m s+b) 1/s zoh Zo(s) Virtual Environment T - Virtual Coupling

Passitivity Observer Virtual Environment Passivity Controller Haptic Interface Passivity Observer

Collocation Problem