Transcript kinesthetic displays for remote & virtual environments

KINESTHETIC DISPLAYS FOR
REMOTE & VIRTUAL
ENVIRONMENTS
-Blake Hannaford and Steven Venema
Presented By
Subhashini Ganapathy
Sasanka V. Prabhala
Contents
•
•
•
•
•
•
•
•
Introduction
Characteristics of the Kinesthetic Channel
Simulation
Types of kinesthetic Displays
Kinesthetic Displays and Selection issues
Safety Issues
Application
Implementation and Design Approach
Introduction
• Different ways of perceiving the
environment
• Haptic Displays
– Kinesthetic Display
– Tactile Display
• Kinesthesis
– Sensations derived from muscles, tendons and joints and
stimulated by movement and tension
HISTORY
• In virtual reality the perceptions from a
simulated environments are conveyed to
the user
• Hence teleoperation and virtual reality
share the same user interface issues
• Thus much of the information presented is
drawn from the field of teleoperation
Characteristics of the
Kinesthetic channel
• Two different roles of kinesthetic
sensations
• Body position sense
• Contact between the body and the external
environment
Comparison between Kinesthetic
Information and other modalities
Kinesthetic Displays
Visual & Auditory
Displays
•Kinesthetic sensations
•The visual and the
involve bi-directional flow of auditory channels are oneenergy between the humans
way, information-only
and the environment
flows.
•Kinesthetic sensations
•The environment can
cannot be reproduced by the only be recorded &
information system alone
synthesized, replicated by
•To sense the environment is the information system
to modify the environment
•Environment cannot be
modified
Physics: Position/Force
Simultaneity
• The problem with the Virtual environment and the
teleoperations is how to produce the bi-directional
properties of mechanical energy flow
• One way is to use “FORCE FEEDBACK” technique in
which velocity is sensed and to apply the appropriate
force to the operator and vice versa
• The usual implementation constrain is to sense and leave
one variable and to control the other variable and the
physical restriction is to interface the energy system to the
information-only system
• The kind of information needed to conveyed to reproduce
the kinesthetic sensation or contact is difficult to deduce
as there may be many possible modes of contact between
objects and the existence of multiple contact points
Simulation
Simulation is studied using three levels of
realism
Second order linear system
Point contact ( Continuous)
Point contact ( Discontinuous)
Second order linear systems
• A second order linear system is permanently
attached to the users hand at the kinesthetic
display
• The kinesthetic display will appear to have
certain mass, damping, and spring like behavior
and the control system necessary to produce this
effect can be produced by “IMPEDENCE
CONTROL”.
• It is global model in that it applies to all values of
position
Point contact continuous and
discontinuous
• This form of realism applies to the local region of
space (soft and hard surfaces)
• The rapidity with which a display can calculate
and apply forces to the human hand determines
the level of realism
• Soft surfaces will cause force to increase
gradually as contact is made while those with
hard surfaces will cause discontinuous force
trajectories
Body Reference Frame/Object
Extent
• Visual sensations appear to exist in space which
is external to the observer where as the
kinesthetic sensations are always perceived with
respect to a body reference as opposed to the
world reference frame
• When viewing a complex scene the eye
movement generates a scan path during which
our retina image a sequence of detailed spots on
the scene where as kinesthetic contact sensations
are spatially localized to specific object
Types of kinesthetic Displays
•
•
•
•
Contact Modeling
Force-Feedback Displays
Displacement-Feedback Displays
Cross-Modal Displays
Contact Modeling
• Net work theory allows to model the interaction between
the operator and the simulated or remote environment
using the network theory which is applicable to both
mechanical and electrical energy transmission
• The equation shows that it is possible to control at most
one of the two mechanical system variables force and
velocity
CONTACT MODELLING
Human Operator
Kinesthetic Display
Vp
Z1 (v)
F1
Z2 (v)
Fp
One-port model of a kinesthetic display and human operator
F1 – Z1 (V p)-Z2 (Vp) = Fp
F2
Forced-Feedback Displays
• The most common approach to implement kinesthetic
interaction is to sense the operators velocity/position and
to apply force at the point where the velocity is sensed
assuming the contact point to be the operators hand
• This mode of kinesthetic display should have the
following characteristics:
– Must produce accurately the forces intended to be
applied
– Should have high bandwidth
– Capable of sufficiently large forces so that the contact
can be simulated
Displacement-Feedback
displays
• In this method of implementing the kinesthetic interaction
is to sense applied force and to impose a controlled
displacement on the display
• This displacement is calculated by a dynamic world
model from the response of the simulated object to the
measured operator contact force
• This mode of kinesthetic display should have the
following characteristics:
1. It should accurately reproduce the displacement intended to
be applied
2. It must have high bandwidth
3. It must be rigid enough to completely block the operators
hand when contact is meant to be conveyed with a rigid
object
Cross-Modal Displays
• This type of display keeps the user feedback in the
information domain and thereby avoids the difficulties of
reproducing or simulating bilateral energy flow
• This can be achieved if one of the variable from the
simulated or remote contact is controlled by the operator,
and the other is displayed to the operator at a different
point or through a different sensory modality
• The power at each port is zero but information about the
simulated or remote interaction is conveyed
Kinesthetic Display Design &
Selection Issues
•
•
•
•
•
•
Kinematics
Degrees of Freedom
Workspace
Singularity Analysis
Human Interface
Dynamics
Requirements : Kinematics
• Kinesthetic display must be capable of
exchanging energy with an operator using
the mechanical system variables “force”
and “velocity”
• A common “ground” or reference must
exist between the operator and the display
Kinematics
• The requirements are met by using
kinematically articulated mechanism with
joints and articulated links configured with
one end connected to the “ground” and the
other connected to the operator’s hand
• A display’s kinematic parameters are
describe the interrelation between the
display’s DOF or joints
Degrees of Freedom
• DOF(Degrees of freedom) allows motion along
or around a single axis
• The number of positions and orientations that a
mechanism with a single prismatic DOF can only
achieve motion along a single line in space
• Though the increase in DOF gives complete
freedom of motion there are a lot of restrictions
like the increase in DOF increases the complexity
and cost of the display
Workspace
• When all DOFs are considered
simultaneousely the ranges of motion
describe the “ workspace” of the display
• The work space of higher-DOF display is
difficult to describe mathematically due to
higher dimensionality
• The size of the workspace depends on the
type of task that is to be done
Singularity Analysis
• A display mechanism is said to be
“singular” when one or more joints is at a
motion limit or when two or more joint
axes become parallel
• The display mechanism should be designed
such that no singularities are encountered
within the workspace that the operator is
expected to use
Human Interface
• The kinesthetic display must be suitable for
human use and comfort
• The display performance is constrained by
the human arm that is grasping the
mechanism
• The region of operation is very essential to
determine the manipulation activities
Dynamics
• The fidelity of a force-feedback display system is
inherently limited by the display mechanism
itself
• The force available to the operator is reduced by
terms accounting for the friction and inertia of
the display mechanism
• The effects of mass, friction and stiffness on the
transfer of force from display to operator and the
transmission of velocity from the operator to the
display
Dynamics
Force Display
Command
x, v
k
F
M
Operator
a
Fa
= The accurate force
k
= The mechanism stiffness
Ff (x, v) = The friction of the
transmission system
F0
= The force at the
mechanism/operator interface
x
= the position of the
mechanism/operator interface
v
= The velocity of the
mechanism/operator interface
Dynamic model of one-dimensional
kinesthetic display
Ff (x, v)
Kinesthetic Display Examples
• Salisbury/JPL force-feedback display
– An important design feature of it is the location of the
singular point of its wrist mechanism.
– Force-Feedback displays
• Utah Displacement Display
– Displacement-Feedback display
– The system senses force applied by the human operator
to the joints of the display mechanism, and control the
device to achieve a displacement based on that of a
kinematically identical slave arm.
Safety Issues for Kinesthetic
Interfaces
• Kinesthetic displays have a great display
and are finding application in a wide
variety of rehabilitation related
applications
• Examples:
» Force-reflecting joysticks for wheel-chair control
» Six DOF head-input devices for improved assistive
robot dexterity
Safety Issues
• If the force-feedback is uncontrolled or
improperly limited, the applied forces and
moments may represent a potential hazard
to the operator or people nearby
Application
• Field of Biochemistry
• Field of microteleoperation
Implementation Issues and
Design Approach
• The “hard-contact” problem
• Real-time dynamic modeling
• Mechanism design
Conclusion
While much research remains to
be done in this area, the current state of the
art allows at least rudimentary forms of
these displays to be added to existing
virtual environment implementations
References
•Safety Issues for Kinesthetic Interface in Assistive Robotics,
RESNA’96 Proceedings
•www.ijvr.com/ijvr/glossary/glossary.htm
•gypsy.rose.utoronto.ca/#research
Ergonomics Teleoperation & Control
Laboratory
•Clark, F.J. and Horch, K. W. (1986) Kinesthesia, in Handbook
of Perception and Human Performance, Boff et al.(Eds), New
York: Wiley-Interscience
•Hannaford,B.(1989) A design framework for teleoperators with
kinesthetic feedback, IEEE Trans. Robot. Autom., 5, 426-34
•B.Hannaford, ‘Kinesthetic Feedback Techniques in
Teleoperated Systems,’ In “Advances in Control and Dynamic
Systems”, pp. 1-32, C.Leondes, Ed., Academic Press, San
Diego, 1991