Non-linearity compensation for hard disk drives

The method of claim 3 wherein said second table is created by the steps of:

• selecting a sample of possible operating ranges from said normalized torque constant profile;
• calculating the ratio of the torque constant for two spaced apart head positions for each operating range in said sample;
• determining the offset of said sample operating range from said nominal operating range;
• matching said offset with said ratio to form an entry in a torque constant ratio vs head position offset table;
• repeating steps 1 through 4 of this claim 7 for a plurality of samples.

In a hard disk drive that includes an electric motor used to move an actuator arm which carries a magnetic read/write head in an arc any distance across a rotating disk within a mechanically defined operating range and wherein the torque constant of said electric motor varies across the operating range on a given drive as a function of head location and the operating range varies from drive to drive due to variations in the manufacturing process for said drive, and wherein the location of said head with respect to magnetic tracks written onto said disk is determined by reading servo information from said tracks, and wherein said variation in torque constant may be compensated for with a torque constant multiplier, an improved method of determining the torque constant multiplier for any location of said head within its operating range for any disk comprising the steps of:

• creating a first table that relates the torque constant multiplier of said motor with the location of said head over said disk for substantially all head locations over the disk possible with said manufacturing process;
• defining a nominal operating range of head location in said first table;
• creating a second table that relates the ratio of said torque constants at two spaced apart head locations in said first table to a head location offset from said nominal operating range;
• measuring said parameter proportional to said torque constant at first and second spaced apart locations on the disk drive under consideration;
• calculating the ratio of said first and second parameters
• determining the offset of the operating range of the disk drive under consideration from said nominal operating range from said second table;
• modifying the head location as determined by reading said servo information with said offset to form an offset head location;
• obtaining the value of said torque constant multiplier associated with said offset head location in said first table.

In a hard disk drive that includes an electric motor used to move an actuator arm which carries a magnetic read/write head in an arc any distance across a rotating disk within a mechanically defined operating range and wherein the torque constant of said electric motor varies across the operating range on a given drive as a function of head location and the operating range varies from drive to drive due to variations in the manufacturing process for said drive, and wherein the location of said head with respect to magnetic tracks written onto said disk may be determined by reading servo information from said tracks, and wherein said variation in torque constant may be compensated for with a torque constant multiplier for each track, an improved method of determining the torque constant multiplier for any location of said head within its operating range for any disk drive fabricated with said manufacturing process, comprising the steps of:

• creating a torque constant multiplier table at all locations possible with said manufacturing process by:
• a determining the value of the torque constant of said electric motor substantially at all locations possible with said manufacturing process;
• b determining a normalized torque constant profile by dividing all torque constant values by the value of the torque constant at mid stroke;
• and
• c inverting the values of the normalized torque constant profile;
• determining a nominal operating range within said torque constant multiplier table;
• creating a torque constant ratio vs head position offset table by:
• a selecting a first operating range from all possible operating ranges from said normalized torque constant profile;
• b determining the ratio of torque constant at two spaced apart locations in said first operating range;
• c determining the head offset in said torque constant multiplier table that said first operating range is from said nominal operating range;
• d matching said offset with said torque constant ratio to form a first entry in said torque constant ratio vs head position offset table;
• and
• e repeating steps a through d for a plurality of different operating ranges;
• calibrating a particular drive by
• a measuring the torque constant at the two spaced apart head locations used to create said torque constant ratio vs head position offset table;
• b calculating the ratio of said torque constants for said particular drive;
• c determine the offset for said particular drive by finding the offset in said torque constant ratio vs head position offset table associated with said torque constants for said particular drive;
• modifying the head location as determined by reading said servo information with said offset for said particular drive to form an offset head location;
• obtaining the value of said torque constant multiplier associated with said offset head location.