  In this paper, static and dynamic behavior of an electro statically actuated
torsional micro actuator is studied. The micro actuator is composed of a micro
mirror and two torsional beams, which are excited with two electrodes. Unlike
the traditional micro actuators, the electrostatic force exerted to both side
of micro mirror, so the model is exposed to a DC voltage applied from the
ground electrodes. The static governing equation of the torsional micro
actuator is derived and the relation between rotation angle and the driving
voltage is determined. Local and global bifurcation analysis is performed,
considering torsional characteristics of the micro-beams. By solving static
deflection equation, the fixed points of the actuator are obtained. Critical
values of the applied voltage leading to qualitative changes in the micro
actuator behavior through a saddle node or pitchfork bifurcations for different
spatial condition are obtained. Furthermore the effects of different gap and
electrode sizes as well as beam lengths on the dynamic behavior are
investigated. It is shown that increasing the applied voltage leads the
structure to an unstable condition by undergoing to saddle node and pitchfork
bifurcations when the voltages ratio is zero and one, respectively.
