Hardware Reference
In-Depth Information
Although the linear actuator seems to be a good design, it has one fatal flaw: The devices
are much too heavy. As drive performance has increased, the desire for lightweight actu-
ator mechanisms has become important.
Rotaryactuatorsalsousestationarymagnetsandamovablecoil,butthecoilisattachedto
the end of an actuator arm. As the coil moves relative to the stationary magnet, it swings
theheadarmsinandoutoverthesurfaceofthedisk.Theprimaryadvantageofthismech-
anism is its light weight, which means the heads can accelerate and decelerate quickly,
resultinginfastaverageseektimes.(Referto
Figure9.10
,
whichshowsarotaryvoicecoil
actuator.)
The disadvantage of a rotary system is that as the heads move from the outer to the inner
cylinders, they rotate slightly with respect to the tangent of the cylinders. This rotation
results in an azimuth error and is one reason the area of the platter in which the cylinders
are located is somewhat limited. By limiting the total motion of the actuator, the azimuth
error is contained to within reasonable specifications. Virtually all voice coil drives today
use rotary actuator systems.
