One of the many difficulties arising in the designing of MEMS devices is the
limited range of motion and force that can be generated by
microactuators. Yeh et. al [8]
demonstrated linear electrostatic stepper motors with an
estimated force of 
at 35V and a travel of 
. The
layout of such a stepper motor is summarized in this section (Figure 1).
Figure 1: The layour of the stepper motor.
To meet the requirement of large motion, large force and low power
consumption, Yeh et. al. [8] developed
gap-closing electrostatic actuators. The gap-closing actuator can
generate high force with small gaps, but its range of motion is
limited to that gap (about 
). To increase the range of
motions, they employed the actuators in the stepper motor with an
attachment/detachment stepping cycle [7].
The stepper motor employs two actuator arrays and a shoe on each side
of a shuttle. The actuator arrays provide the shoes with
bi-directional motion with a travel equal to the actuator gap in each
direction. The shoes, located on each side of the shuttle, attach and
detach from the shuttle electrostatically.
The stepper motor cycle begins with the left shoe attached to the
shuttle. An actuator array connected to the left shoe closes its gap
and pulls the shoe and the attached shuttle by . Next the
right shoe attaches to the shuttle and its actuator array holds the
attached shuttle at its position. Then the
left shoe detaches from the shuttle and is returned to its initial
position by attached springs. The actuator of the right shoe then
closes its gap to advance the shuttle by another . Finally
the left shoe re-attaches itself to the shuttle and the cycle
repeats (Figure 2). In a stepping cycle, the
shuttle is advanced by two times of the actuator gap.
Figure 2: The stepper motor cycle.