Generation of higher-order harmonic sine and cosine sequences by indexing a first-order sine/cosine table

A direct access storage device including an electro-mechanical apparatus, comprising:

• a rotatable assembly mounted for rotation about an axis;
• a moveable follower assembly;
• a position controller for said moveable follower assembly, said position controller controlling the position of said moveable follower to register a first feature of said moveable follower with a second feature of said rotatable assembly as said rotatable assembly rotates about said axis, said position controller correcting harmonic misregistration between said first and second features by calculating a correction value using a higher-order trigonometric sequence, said position controller generating said higher-order trigonometric sequence by:
• (a) constructing a table having a plurality of values arranged as a finite-length, first-order trigonometric sequence;
• (b) indexing the table to yield a different sequence of the values, based on an order number of a desired higher-order harmonic;
• and (c) catenating the values according to the different sequence to yield a higher-order trigonometric sequence whose order is the order number.

A direct access storage device comprising:

• an enclosure;
• at least one disk having at least one media-bearing surface, said media-bearing surface having at least one track;
• means for rotatably supporting said disk within said enclosure;
• a read/write head;
• an arm/suspension assembly supporting said read/write head;
• means for actuating said arm/suspension assembly to position said read/write head over said track of said disk;
• and
• means for controlling said actuating means, said controlling means including
• means for constructing a table having a plurality of values arranged as a finite-length, first-order trigonometric sequence,
• means for indexing the table to yield a different sequence of the values, based on an order number of a desired higher-order harmonic,
• means for catenating the values according to the different sequence to yield a higher-order trigonometric sequence whose order is the order number, and
• means for calculating a local PES-correction value for said track, using the higher-order trigonometric sequence.