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Figure 8.16 Magnetic Levitation Haptic Interface.
(Illustration: Carnegie Mellon University, with
permission)
replacement of one of the cables by an actuator helps to increase the force efficiency
and useful work space (Brau et al., 2005).
8.4.1.4 Fixed interfaces with magnetic levitation
Magnetic levitation interfaces are another special case of interfaces with a parallel
structure. Here, the branches are replaced by magnetic fields acting directly on the
mobile platform. Several interfaces of this type have been developed by the Depart-
ment of Electrical and Computer Engineering of the University of British Columbia in
Canada (UBC Maglev Wrist (Salcudean et al., 1995)). This architecture has been opti-
mised in the Robotics Institute of the Carnegie Mellon University in the United States
for the designing of the HapticMagnetic Levitation Device (Berkelman&Hollis, 1997;
Berkelman & Hollis, 2000) (Figure 8.16) marketed by the Butterfly Haptics company
(butterflyhaptics.com) under the name of Maglev 200. The robot gripper is fixed on
a flotor integrating coils having a flowing electric current in levitation in a magnetic
field created by magnets located at the stator. The complete absence of structure pro-
vides this solution with an exceptional performance for the efforts rendered (force and
peak torque of 40N and 3.6Nm, force resolution of 20mN, maximum stiffness of
50N/mm). However, the travel is very limited (24mm diameter sphere and more or
less 8 degrees), which considerably reduces the use of such devices for VR applications.
8.4.2 Internal reaction force feedback interfaces
The second category of force feedback interfaces consists of the interfaces in which
several segments of the interface are in contact with the user. These are referred to as
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