Article

Variable structure parallel mechanisms, actuated with low-cost motors
with serially added elasticity (series elastic actuator--SEA), has considerable
potential in rehabilitation robotics. However, reflected masses of a SEA and
variable structure parallel mechanism linked with a compliant actuator result in
a potentially unstable coupled mechanical oscillator, which has not been
addressed in previous studies. METHODS: The aim of this paper was to investigate
through simulation, experimentation and theoretical analysis the necessary
conditions that guarantee stability and passivity of a haptic device (based on a
variable structure parallel mechanism driven by SEA actuators) when in contact
with a human. We have analyzed an equivalent mechanical system where a
dissipative element, a mechanical damper was placed in parallel to a spring in
SEA. RESULTS: The theoretical analysis yielded necessary conditions relating the
damping coefficient, spring stiffness, both reflected masses, controller's gain
and desired virtual impedance that needs to be fulfilled in order to obtain
stable and passive behavior of the device when in contact with a human. The
validity of the derived passivity conditions were confirmed in simulations and
experimentally. CONCLUSIONS: These results show that by properly designing
variable structure parallel mechanisms actuated with SEA, versatile and
affordable rehabilitation robotic devices can be conceived, which may facilitate
their wide spread use in clinical and home environments.

Langue : ANGLAIS