  We present HapTable; a multimodal interactive tabletop that allows users to
interact with digital images and objects through natural touch gestures, and
receive visual and haptic feedback accordingly. In our system, hand pose is
registered by an infrared camera and hand gestures are classified using a
Support Vector Machine (SVM) classifier. To display a rich set of haptic
effects for both static and dynamic gestures, we integrated electromechanical
and electrostatic actuation techniques effectively on tabletop surface of
HapTable, which is a surface capacitive touch screen. We attached four piezo
patches to the edges of tabletop to display vibrotactile feedback for static
gestures. For this purpose, the vibration response of the tabletop, in the form
of frequency response functions (FRFs), was obtained by a laser Doppler
vibrometer for 84 grid points on its surface. Using these FRFs, it is possible
to display localized vibrotactile feedback on the surface for static gestures.
For dynamic gestures, we utilize the electrostatic actuation technique to
modulate the frictional forces between finger skin and tabletop surface by
applying voltage to its conductive layer. Here, we present two examples of such
applications, one for static and one for dynamic gestures, along with detailed
user studies. In the first one, user detects the direction of a virtual flow,
such as that of wind or water, by putting their hand on the tabletop surface
and feeling a vibrotactile stimulus traveling underneath it. In the second
example, user rotates a virtual knob on the tabletop surface to select an item
from a menu while feeling the knob's detents and resistance to rotation in the
form of frictional haptic feedback.
