1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive comprising a spindle motor employing anionic/cationic lubricant to reduce disk surface potential.
2. Description of the Prior Art
Disk drives employ a spindle motor for rotating a disk while a head writes data to and reads data from the disk. The spindle motor comprises a plurality of permanent magnets and a plurality of windings. When the windings are energized with current according to a commutation sequence the resulting magnetic flux interacts with the magnetic flux of the permanent magnets to rotate a rotating component about a stationary component. Because the disk is attached to the rotating component, any voltage that builds between the rotating component and the stationary component raises the potential at the surface of the disk which can damage the head, particularly magnetoresistive (MR) heads.
A low resistance material (e.g., steel) can be used for the bearings disposed between the rotating component and stationary component in order to reduce the potential at the disk surface. However, bearings made of a high resistance material (e.g., ceramic) provide several performance enhancing benefits. For example, ceramic bearings typically exhibit high axial and radial stiffness, a smooth surface, and are more spherical which reduces disk runout as well as acoustic noise. In addition, less lubricating grease is required due to the smooth surface of ceramic bearings which reduces friction thereby improving power efficiency.
Another known technique for reducing the potential at the disk surface is a ferro-fluidic seal which provides a low resistance electrical path between the rotating component and stationary component of the spindle motor. However, the complexity and component count of ferro-fluidic seals increase the cost of the spindle motor as well as the likelihood of failures due to defects.
There is, therefore, a need for a simple, less expensive technique for reducing the potential at the disk surface in a disk drive in order to protect the head.