Servo controller method and apparatus for high tracks per inch hard disk drives using a delay accomodating state estimator

A servo controller for a hard disk drive, comprising:

• means for obtaining said measured read-write head position Ycur;
• and
• means for calculating said control variable U based upon said measured read-write head position Ycur performing the steps:
• calculating an estimated state vector Xhat based upon a predicted state vector Xbar and based upon the difference between said measured read-write head position Ycur and a predicted read-write head position Ybar;
• calculating said control variable U based upon a regulator gain matrix K multiplied by said estimated state vector Xhat;
• replacing said predicted state vector Xbar based upon said estimated state vector Xhat and based upon said control variable U;
• and
• replacing said predicted read-write head position Ybar based upon said predicted state vector Xbar and based upon said control variable U;
• wherein each member of a state vector collection includes a read-write head position version, a read-write head velocity version and an unknown bias force version;
• wherein said state vector collection includes said estimated state vector Xhat and said predicted state vector Xbar;
• wherein said hard disk drive includes a disk surface accessed by a read-write head at said measured read-write head position Ycur;
• wherein said disk surface contains multiple physical tracks at a Track Per Inch (TPI);
• and
• wherein said TPI is at least 80,000 tracks per inch.