Actuator

The actuator is a mechanical device on which the arms are mounted. It positions the arms to the tracks on the surface of the platters. This positioning movement must be extremely precise and quick because the speed of the drive depends on it. There are two types of actuators, a stepper motor and voice coils.

The stepper motor actuator is the older of the two and uses a motor which only stops at predefined “steps” as it turns around. These stopping locations correspond with the tracks on the platter disk. The motor shaft has two thin strips of metal wrapped around it, which connect to the arms.

Actuator Assembly

The voice coil actuator is the more modern of the two and got its name because its technology is similar to that used to drive audio speakers. Voice coil is much faster, more insensitive to thermal issues and generally more reliable than stepper motors. It uses a voice coil to position the arms on the platter. The coil uses electromagnetic attraction and repulsion and is wrapped around a metal protrusion on the end of each arm. The whole assembly also contains a strong permanent magnet, so when current is fed to the coil, the electromagnetic field generated causes the heads to move. The direction of movement is based on either attraction or repulsion. Because we can easily control the current, the arms can be positioned much more precisely than using a stepper motor.