Hi everyone, my name is eric gonzalez and
today i'll be presenting our paper
REACH+: extending the reachability of
encountered-type haptics devices through
dynamic redirection in vr.
Encountered-type haptics is a feedback
paradigm designed to provide on-demand
physical representations of virtual
objects and environments.
Unlike wearable and handheld devices,
encountered-type haptic devices or EHDs
use an external system - such as a robotic
arm,
drone, or mobile robot - to position
touchable elements within the user's
workspace.
This approach presents a unique set of
challenges however, including predicting
where the user will touch,
device positioning inaccuracies, device
workspace limits which can make certain
areas
impossible to reach, and device speed
limits which can delay its arrival to
the point of contact.
In this work we focus on addressing the
latter two challenges
which have a significant impact on the
reachability of the EHD,
or its ability to properly position
itself at a target in time for contact.
Here on the left we see an example of an
EHD unable to reach a target above its
plane of movement.
On the right we see an example of an EHD
arriving late to the point of contact.
In this work we propose REACH+: a
framework to anticipate and correct for
these limitations using a perceptual
illusion technique known as reach
redirection.
For objects outside of the device's
workspace, the user's hand can be
redirected to a point within it as shown
in this clip.
For far off objects, we estimate the
arrival time of the user's hand
using a minimum jerk assumption and
redirect them to a point reachable by
the device given the time constraint.
Also known as haptic retargeting,
redirection is an interaction technique
to change the perceived location of a
haptic element by gradually offsetting
the virtual hand (shown here in blue)
from the real hand (shown here as an
outline). Users naturally correct for this
due to visual dominance,
and so their hand is redirected to the
desired location.
To illustrate our approach we'll use the
example of an omnidirectional mobile
robot positioning the physical proxy of
a virtual object on a table.
Here the EHD's workspace is a
rectangular plane the size of the table.
We first project the virtual object onto
the nearest point in the device's
workspace.
We then use data from the first 100
milliseconds of reach to estimate the
hand's arrival time at the point of
contact.
We do this using the minimum jerk
assumption which states that
point-to-point hand movements tend to
minimize the derivative of acceleration.
In practice, this means the hand's
velocity profile tends to follow a
bell-shaped curve.
We fit a polynomial of this form to the
first 100 milliseconds of data
and use the second zero to predict an
ETA for the reach.
Using this ETA we can then determine the
device's reachable space
and map the object to the nearest
reachable point.
Finally we apply redirection over the
remainder of the reach so the user's
physical hand is guided to the reachable
point.
In this way, we've now increased the
likelihood that the user will feel the
appropriate haptic feedback when they
touch the virtual object.
We focused our evaluation on
compensating for device speed limits
with REACH+, as previous work has
explored redirection for fixed offsets.
Participants were presented with a ring
of eight targets and told to reach to
the highlighted target.
In each trial a mobile robot EHD began
in the center of the ring and moved with
constant speed to the highlighted target
as the reach began.
We tested four device speeds between 20
and 35 centimeters per second
and three redirection conditions: none,
REACH+,
and Limited REACH+, in which the max
amount of redirection was limited to
three centimeters.
This last condition was intended to
capture redirection below perceivable
levels.
The general limit of three centimeters
was estimated using reported perceptual
thresholds by Zenner et al.
and based on our target layout. We first
looked at the impact of speed and
redirection on the device's on-time
arrival rate to the point of contact.
Overall we found a significant effect of
both redirection condition and speed on
arrival success.
For the slowest speed, both REACH+
and Limited REACH+ significantly
improved arrival success by 25%
and 14% respectively. After each reach,
participants rated whether the movements
of their real and virtual hands matched.
Overall REACH+ yielded more
noticeable redirection while Limited
REACH+ did not.
Participants also rated how well the
physical sensation met their
expectations of touching a real object.
At the slowest speed, REACH+ and
Limited REACH+ led to physical
interactions that better met users
expectations. In summary we presented
REACH+
an approach for improving interactions
with encountered-type haptics devices
using dynamic redirection.
Our findings suggests that REACH+ may
improve the performance of slow EHDs
by increasing on-time arrival rate and
improving users sense of physical
realism.
Additionally when limiting redirection
to below perceivable thresholds
similar performance improvements were
observed without redirection becoming
noticeable.
Thank you for your time.