This looks almost interesting enough that we might want to invite them to
the R&D committee meeting. Or maybe they need to tour the IBTC.
Haptics lab aims for good VR vibes
By R. Colin Johnson
EE Times
(10/02/00, 4:56 p.m. EST)
BALTIMORE _ While most virtual-reality engineering focuses on accurately
mimicking
the visual elements of experience, Allison Okamura's new Haptic Exploration
Lab at
Johns Hopkins University focuses instead on the sensation of touch.
"The sense of touch is a key mechanism used by humans to learn about their
world,"
said Okamura. "The same should be true in VR, but today designers are
concentrating
heavily on visual presentation. My lab will instead explore means for
displaying
both tactile perception through the skin and kinematic perception through
the position
and movement of the joints and muscles."
Perception, as opposed to sensation, holds the key to Okamura's refinement
of VR
accuracy, since sensations can conflict even in real life, whereas
perceptions reflect
a decision to "trust" an interpretation of sensations. For instance, a
pencil in
a glass of water appears to be broken because the visual sensation shifts
abruptly
where it emerges from the water.
Humans "perceive" the pencil as straight, however, because they can verify
by touching
the pencil that it remains unbroken where it emerges from the water, even
though
visual sensations suggest that it is broken. Primates, especially humans,
use touch
as their "perception verifier," but most lower animals follow their nose _
for instance,
a dog would verify that the pencil remains unbroken by smelling it.
Unfortunately, the ability to verify conflicting sensations and conjure an
accurate
internal perception is almost entirely missing in current VR environments.
Even sophisticated
electronic gloves only track the position of the hands for display in VR.
"We want to characterize materials in the real world, so that we may then
mimic the
necessary sensations in VR that will allow people to accurately perceive
materials,"
said Okamura.
She will present her preliminary results and future research directions in
November
at the American Society of Mechanical Engineers' Dynamic Systems and
Control Conference.
There she will describe a method of accurately mimicking the vibrational
characteristics
of wood, aluminum and rubber.
"Today, even if you bump into a wall in VR, it just tells you that an
obstacle exists.
But in real life, when you bump into something, you use the resulting
vibrational
sensation to perceive the wall as made of a certain type of material," said
Okamura.
Everyone admits that rapping on a wall is the best way to tell if its made
of wood
or just has an imitation wood grain veneer. However, no one has
characterized the
"output" vibrations of materials as a result of an "input" rap of the
knuckles. Therefore,
there are no existing models to reproduce those vibrations in VR.
"There are all kinds of physical models available to accurately represent
the 3-D
geometry of objects _ how things look from different angles _ but there are
no models
available to represent the vibrational signatures of materials," said Okamura.
Consequently, Okamura cut through the theoretical logjam by skipping the
model for
now, settling instead for recording the vibrations of real materials from
sensors
and then playing back the recording into a haptic display. Using real human
subjects
to experience the recorded vibration sensations, Okamura was able to
accurately induce
the perceptions of wood, aluminum and rubber.
"We allowed the test subjects to select the best parameters for our
vibrational recordings
by comparing them with vibrations from real materials," said Okamura.
Subjects used a tethered stylus (from San Jose-based Immersion Corp.) to
"tap" on
real wood, aluminum and rubber blocks for direct sequential comparisons
with nine
different parameter sets of the real recordings. The parameters of the
recordings
were variables such as a multiplier for amplitude of the vibration waveform
corresponding
to the impact velocity of the stylus. Other parameters besides the
amplitude-velocity
slope included the decay rate and frequency parameters of the recordings.
All test
subjects were able to exceed 80 percent accuracy in identifying virtual
materials
of wood, aluminum and rubber after about 15 minutes of parameter selection.
Tele-operated medical surgery is one area where the new virtual reality
system could
find an immediate application. "There are many tactile problems to be
solved for
tele-operated surgery. For instance, when you put a needle through the skin
it is
hard to avoid overshoot; you have to compress the skin to get the needle
through,
but once it's through you have to back off the pressure in just the right
manner
to end up with the needle at the right depth," said Okamura.
Solving the needle insertion problem, however, would involve characterizing
the soft
tissues of the human body _ a difficult task that illustrates how far
haptics research
needs to travel from characterizing the simple vibrational characteristics
of wood,
aluminum and rubber. Consequently, for the foreseeable future, Okamura's
lab will
perform basic research into what she calls "dexterous manipulation."
Ultimately, multiple robotic fingers will cooperate to grasp, manipulate
and explore
the world, for the same reason that humans verify conflicting visual
sensations.
"You have to work backward from the object to the actuators that will
manipulate
it when formulating a dextrous manipulation problem for a robot," said
Okamura. In
doing so, a system of equations can be built that describes the
robot-object system
in terms of shared characteristics, such as points of contact, finger-arm
locations
compatible with object geometry, and kinematic bounds such as how much
pressure can
be applied when picking up an egg.
The first step in dexterous manipulation is usually to calculate backward
from the
desired pressure on the object, to the fingertip forces to be employed by
the robot.
>From there things get complicated, since accuracy in anthropomorphic
robotic hands
involves rolling and sliding them against the object as it is manipulated.
Calculations
take as input the location, texture and relative velocities of object and
fingertip,
and output parameterized velocities to describe the motions of the contact
frames
over the fingertip and object surfaces.
While other labs have explored most of these dexterous manipulation
problems, Okamura
believes her effort will have unique aspects that pull together diverse
multidisciplinary
resources to solve the problem. Automated grasping and motion planning, for
3-D manipulation
of realistic virtual materials with rolling and sliding, will be the
ultimate goal
of the lab. Today such calculations must be done offline, but Okamura
believes that
better algorithms can soon solve the problem.
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Lloyd Rasmussen, Senior Staff Engineer
National Library Service f/t Blind and Physically Handicapped
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