Method and apparatus for balancing a rotary actuator by modifying weight distribution characteristics of the rotary actuator for locating an installed head stack assembly portion center-of-gravity along a pivot axis

A method of individually balancing rotary actuators each for use in a respective rotatable head stack assembly (HSA) portion in a disk drive, each rotary actuator having a pivot axis, the rotatable HSA portion having an installed HSA portion center-of-gravity, the method comprising:

• a) for each rotary actuator individually determining a desired rotary actuator center-of-gravity location for locating the installed HSA portion center-of-gravity along the pivot axis for mitigating acceleration of the rotary actuator about the pivot axis due to external linear acceleration experienced by the disk drive during a track-follow operation;
• b) for each rotary actuator individually measuring weight distribution characteristics of the respective rotary actuator to determine an actual rotary actuator center-of-gravity;
• and
• c) for each rotary actuator individually selectively modifying weight distribution characteristics of the respective rotary actuator to locate the actual rotary actuator center-of-gravity at the desired rotary actuator center-of-gravity location.