Researchers have designed numerous
haptic controllers to render objects in
virtual reality. However, many objects and
interactions involve the coordinated use
of both hands and feedback between the
hands is typically absent. We present
Haptic Links electromechanical
connections which attach to standard VR
controllers to enable inter controller
force feedback through variable
stiffness actuation. In this clip the
user freely switches between dual
pistols and a rifle held in both hands
attached to their VR controllers is a
haptic link. The haptic link allows for
full six degree of freedom motion while
shooting the pistols.
However when using the rifle the haptic
link joining the controllers becomes
rigidly locked
allowing the user to handle and aim the
gun like a real two-handed weapon. We can
also render variable stiffness along a
continuous range. Here as we pull back
the drawstring on a virtual bow the
hinge between these controllers becomes
increasingly stiff with distance then
relaxes upon firing. To appropriately
position controllers to render a new
object we introduce an input method that
we call summoning. That is the user
performs a gesture which moves their
controllers into the proper position
enabling our system to haptically render
the object through stiffening. Here the
user can summon either a car or a
motorcycle by holding their hands in the
shape of a steering wheel or handlebars.
We designed three haptic links capable
of rendering different types of inter
controller feedback. Each haptic link
attaches to an existing unmodified VR
controller. The first link is a highly
articulated ball-and-socket chain with a
cable threaded along its length. Linear
actuators mounted to the controllers
pull this cable tight pressing each ball
into the neighboring socket and globally
stiffening the chain in its current
configuration.
Our second haptic link uses a hinge
composed of several interleaved layers.
By compressing these layers we increase
the friction between them and create a
braking force. While the hinge controls
the distance between the controllers a
ball joint beneath each controller
enables rotation which is locked using
an actuated set screw. Our third haptic
link uses the same ball joints but has a
directionally selective break on its
hinge. Small servos disengage the pawls
of two opposing ratchets allowing for
inward motion, outward motion, both, or
none. This design enables us to render
walls and surfaces such as in this
interaction where inward motion is
halted as the user grasps a virtual
object with both hands.
These last two designs allow us to
constrain particular degrees of freedom
while leaving others free such as in
this example where the controllers can
move together and apart in a locked
orientation to render a trombone
interaction. We envision a number of
extensions for these devices such as
manually ground
one controller on the body or on another
surface to enable grounded force
feedback interactions on the other
controller. Our paper describes the
design and implementation of our haptic
links as well as interaction techniques
and scenarios leveraging their
capabilities. Our user evaluation shows
that users can perceive many two-handed
objects or interactions as more
realistic with haptic links than with
typical unlinked VR controllers.
