The electrostatic rotary microactuator (ESRM) is considered as one of the most promising candidates for the dual-stage servomechanisms as shown in Figure 3.1  because of simplicity of design and lower fabrication cost. A rotary microactuator consists of two parts, namely, a rotor and a stator as illustrated in Figure 3.2, which generate the actuating force. In brief, the capacitive PPs integrated to the rotor and stator elements generate the actuation force to drive the rotor.
The beam springs impose the restoring force opposing to the actuating force, thereby limiting the displacement of the rotor. The direction of the motion is perpendicular to the longitudinal direction of the PP.
The ESRM is best suited for dual-stage servomechanisms (Figure 3.1) requiring wider operational bandwidth and high-tracking accuracy better than 25,000 track-per-inch (TPI). Several versions of microactuators for the dual-stage servomechanism  were recommended, but the ES design configuration of the microactuator was
preferred because of trouble-free and cost-effective fabrication procedures. In addition, several configurations of electrodes were evaluated to enhance the force-generating capability and tracking accuracy over wide bandwidths. Two electrode configurations, namely, PP and interdigitated configurations are available for implementation in the design and development ofESRMs. The principal difference between these two types ofelectrodes lies in the direction ofmotion ofthe moving electrode known as the rotor electrode. Critical physical parameters of a conventional ESRM and the clearance variation are shown in Figure 3.2 .
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