Page 346 - The Mechatronics Handbook

FIGURE 16.15 Electrostatic motor: 1-rotor, 2-stator electrodes.

plates separated by an insulation layer. The rotor rotates with a constant velocity between the two coplanar
concentric arrays of stator electrodes.

Selection Criteria
The selection of the proper actuator is more complicated than selection of the sensors, primarily due to
their effect on the dynamic behavior of the overall system. Furthermore, the selection of the actuator
dominates the power needs and the coupling mechanisms of the entire system. The coupling mechanism
can sometimes be completely avoided if the actuator provides the output that can be directly interfaced
to the physical system. For example, choosing a linear motor in place of a rotary motor can eliminate
the need of a coupling mechanism to convert rotary motion to linear motion.
In general, the following performance parameters must be addressed before choosing an actuator for
a specific need:

Continuous power output—The maximum force/torque attainable continuously without exceeding the
temperature limits
Range of motion—The range of linear/rotary motion
Resolution—The minimum increment of force/torque attainable
Accuracy—Linearity of the relationship between the input and output
Peak force/torque—The force/torque at which the actuator stalls
Heat dissipation—Maximum wattage of heat dissipation in continuous operation
Speed characteristics—Force/torque versus speed relationship
No load speed—Typical operating speed/velocity with no external load
Frequency response—The range of frequency over which the output follows the input faithfully, appli-
cable to linear actuators
Power requirement—Type of power (AC or DC), number of phases, voltage level, and current capacity

In addition to the above-referred criteria, many other factors become important depending upon the
type of power and the coupling mechanism required. For example, if a rack- and-pinion coupling mecha-
nism is chosen, the backlash and friction will affect the resolution of the actuating unit.

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