Disk drive with method of constructing a continuous position signal and constrained method of linearizing such position signal while maintaining continuity

A method of determining an indicated position signal corresponding to a radial position of a read head over a rotating disk in a magnetic disk drive, the method implemented in a disk drive including a rotating disk and a read head for reading servo information from the rotating disk, the servo information including a servo pattern of four circumferentially successive, radially repeating servo bursts A,B,C,D that are arranged in quadrature to define an alternating plurality of AB and CD burst pair centerlines that are nominally spaced from one another by ½ servo track pitch units, the method comprising the steps of:

• reading four servo bursts A,B,C,D with the read head;
• determining whether the read head is closer to an AB burst pair centerline or to a CD burst pair centerline;
• and
• causing the fractional track PES value to equal ±¼ track pitch units at a commutation position midway between the AB and CD burst pair centerlines regardless of whether or not those centerlines are separated by ½ servo track pitch units by constructing a fractional PES value as P = - 1 4 ⁢ ⁢ ( C - D ) ( A - B )
• when the read head is closer to the CD burst pair centerline within a first fractional PES segment and as P = + 1 4 ⁢ ⁢ ( A - B ) ( C - D )
• when the read head is closer to the AB burst pair centerline within a second fractional PES segment, the first and second fractional PES segments continuously connected to one another at the commutation position to form an indicated position signal;
• and
• linearizing the fractional PES values within the fractional PES segments while keeping the fractional track PES values equal to one another at the commutation positions and keeping the indicated position signal continuous.

In a disk drive having a disk, a transducer, and an embedded servo control system including a servo sector having a primary burst pair joined at a primary burst pair centerline and a quadrature burst pair joined at a quadrature burst pair centerline, wherein the servo control system derives a primary position signal waveform from the primary burst pair and a quadrature position signal waveform from the quadrature burst pair, wherein the servo control system provides fractional PES segments that are subject to discontinuity when they are joined at a commutation position to form an indicated position signal, a method for producing a discontinuity-corrected position signal from the fractional PES segments, the method comprising the steps of:

• determining whether the transducer is closer to the primary burst pair centerline or the quadrature burst pair centerline;
• and
• if the transducer is closer to the primary burst pair centerline, constructing a fractional PES value from a first ratio of the primary and quadrature position signal waveforms;
• else
• if the transducer is closer to the quadrature burst pair centerline, constructing the position signal from a second ratio of primary and quadrature position waveforms;
• and
• applying a linearity correction to the fractional PES value which is applied independently of a width of the transducer and regardless of whether the transducer is nearer either burst pair centerline or the commutation position;
• whereby the indicated position signal is continuous at the commutation position and substantially linear between the commutation position and an adjacent commutation position.