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Free-hand haptic interfaces
This project dealt with two different approaches for haptic
feedback, the first one focusing on a free-hand, wide-area haptic
device based on the so-called SmartMesh, and the second one focusing
on a portable feedback device based on dielectric elastomer
actuators.
A concept for a wide area haptic feedback device has been developed
(the SmartMesh), which uses a deformable structure to imitate an
object, or a region of interest of it - similar to the notion of
"digital clay". Due to its actual physical presence, the object can be
naturally touched and explored with the whole hand. In order to verify
the concept, a prototype has been constructed, which shows the
deformation capabilities of the structure. The SmartMesh is a multi
degree of freedom, multi loop mechanism based on a mesh of nodes and
extendable links. It can be deformed and controlled by altering the
lengths of the links. The prototype has not been actuated due to the
lack of adequate state-of-the-art actuation technology. In view of the
actuation of such a structure with thousand of actuators a careful
study of the controlling system was required. A novel concept for a
control algorithm relying on a physically-based modeling technique has
been developed and implemented with a mass-spring system. The system
not only allows to approximate the desired shape, but simultaneously
also provides the parameters required to drive all the actuators.
The aim of this project is to develop a force feedback device,
which provides satisfying touch sensations to the operator's hand, and
is portable, powerful, lightweight, and non-obstructive. We mainly
studied dielectric elastomer (DE) actuators which exhibit high power
density, fast response and low cost. Moreover, we evaluated the
integration into the aforementioned hand-based device. Two main
threads were pursued: the conceptual device design and the development
of corresponding DE actuators. For a typical grasping geometry, a
total of 22 concepts were evaluated, out of which two solutions were
selected.
The first one has contractile stripe DE actuators integrated into a
glove on the dorsal side of the fingers. The actuator elongates when
following voluntary movements of a user. It contracts when an
interaction between the user and the virtual object occurs,
consequently providing blocking forces to the user. For this solution
a flat chain-like linear DE actuator was demonstrated. Elementary
actuators of the chain with flexible housings were manufactured and
characterized.
The second concept, with linear DE actuators between the thumb and
other fingers, provides the force feedback by pushing the fingers
against each other. For this second solution, a stable manufacturing
process for free-standing linear spring DE actuators, including the
required infrastructure, has been set up at EMPA Dubendorf. Currently
the actuator (L?W: 70?12 mm) shows 26% elongation when applying 4
kV. In order to evaluate the glove concept, a functional prototype is
currently under development.
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