1. Field of the Invention
The present invention relates to a disk drive and more particularly to a magnetic disk drive having a head stack assembly with a plastic inner sleeve.
2. Description of the Prior Art and Related Information
A typical hard disk drive includes a head disk assembly ("HDA") and a printed circuit board assembly ("PCBA"). The HDA includes at least one magnetic disk ("disk"), a spindle motor for rotating the disk, and a head stack assembly ("HSA") that includes a head with at least one transducer for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly ("HGA") that extends from the actuator assembly and biases the head towards the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
The industry presently prefers a "rotary" or "swing-type" actuator assembly which conventionally comprises a body portion that rotates on a pivot bearing cartridge between limited positions, a coil portion that extends from one side of the body portion to interact with one or more permanent magnets to form a voice coil motor, and an actuator arm that extends from an opposite side of the body portion to support the HGA.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a head attached to the gimbal. The load beam has a spring function which provides a "gram load" biasing force and a hinge function which permits the head to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator am and a gimbal end that connects to the gimbal which carries the head and transmits the gram load biasing force to the head to "load" the head against the disk. A rapidly spinning disk develops a laminar air flow above its surface that lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be "flying" over the disk when in this state.
Early head stack assemblies typically included an all metal "E-block" which included an all metal body portion and metal actuator arms that were formed from a single block of metal, e.g. aluminum. A metal pivot bearing cartridge was installed in the bore of the HSA via a side-pull screw. Such E-blocks provided consistent grounding of the actuator arms and unitary movement of the actuator arms such that relative radial movement between the arms, due to, for example temperature changes, was insignificant.
Later head stack assemblies, often called "hybrid" HSAs, were typically formed by overmolding a plastic body portion over several individual metal actuator arms. Hybrid HSAs were an improvement over the E-block HSAs from an assembly point of view because the plastic body portion allowed metal pivot bearing cartridges to be press-fit into the bore of the plastic body portion. Such press-fitting reduced the cost of assembling the components since screws and the associated threaded openings in the pivot bearing cartridge and the body portion were eliminated. Also, particulates due to inserting the screw into the associated threaded openings were not generated and press-fitting the pivot bearing cartridge into the bore was quicker which reduced assembly time of the components.
In hybrid HSAs, a vertical ground pin was needed to connect the individual actuator arms to one another within the plastic body portion to provide grounding to the actuator arms. Hybrid HSAs, however, were subject to inconsistent grounding because of inadequate contact between the ground pin and the actuator arms after the ground pin was inserted in respective holes in the arms. Moreover, thermal relaxation of the plastic body portion could cause the metal actuator arms to move out of radial alignment relative to one another such as during drive operation when significant temperature changes occurred within the disk drive.