Magnetic disk device and method

A magnetic disk device comprising:

• a magnetic disk including a track, the magnetic disk being provided with a radial servo region in which first servo data including a first burst pattern and a second burst pattern is recorded;
• a magnetic head configured to execute write and read on the magnetic disk;
• and
• a controller configured to
• move the magnetic head to a first radial position and a second radial position, the first radial position being a position that is radially offset from a track center of the track, the second radial position being a position that is radially offset from the track center and is different from the first radial position,
• execute a first operation when the magnetic head is at the first radial position and when the magnetic head is at the second radial position, the first operation including:
• acquiring a first burst demodulated signal and a second burst demodulated signal when the magnetic head passes over the servo region, the first burst demodulated signal being acquired by demodulating the first burst pattern included in the first servo data, the second burst demodulated signal being acquired by demodulating the second burst pattern included in the first servo data;
• calculating a first demodulation position of the magnetic head based on amplitude of the first burst demodulated signal and amplitude of the second burst demodulated signal;
• estimating an actual position of the magnetic head based on the first demodulation position and a sensitivity function of positioning control of the magnetic head;
• estimating amplitude of a third burst demodulated signal and amplitude of a fourth burst demodulated signal, each amplitude being obtained when the magnetic head is at the actual position and being estimated based on a Lissajous figure in which the amplitude of the third burst demodulated signal obtained by demodulating the first burst pattern included in the first second servo data and the amplitude of the fourth burst demodulated signal obtained by demodulating the second burst pattern included in the first servo data at various radial positions are indicated on a plane as values of coordinate axes different from each other;
• and
• recording a first difference and a second difference in association with a third radial position, the first difference being a difference between the amplitude of the third burst demodulated signal and the amplitude of the first burst demodulated signal, the second difference being a difference between the amplitude of the fourth burst demodulated signal and the amplitude of the second burst demodulated signal, the third radial position being one of the first radial position and the second radial position at which the magnetic head is positioned when the first operation is executed,
• execute a second operation when the magnetic head passes over the servo region after the first operation is completed for each of the first radial position and the second radial position, the second operation including:
• acquiring a fifth burst demodulated signal by demodulating the first burst pattern included in the first servo data;
• acquiring a sixth burst demodulated signal by demodulating the second burst pattern included in the first servo data;
• calculating a second demodulation position of the magnetic head based on amplitude of the fifth burst demodulated signal and amplitude of the sixth burst demodulated signal;
• acquiring, for the second demodulation position, a first interpolation difference by interpolating between the first difference associated with the first radial position and the first difference associated with the second radial position;
• acquiring, for the second demodulation position, a second interpolation difference by interpolating between the second difference associated with the first radial position and the second difference associated with the second radial position;
• correcting the amplitude of the fifth burst demodulated signal by using the first interpolation difference;
• correcting the amplitude of the sixth burst demodulated signal by using the second interpolation difference;
• and
• calculating a third demodulation position of the magnetic head based on the corrected amplitude of the fifth burst demodulated signal and the corrected amplitude of the sixth burst demodulated signal, and
• perform positioning control using the third demodulation position.

A method comprising:

• moving a magnetic head to a first radial position and a second radial position on a magnetic disk including a track, the magnetic disk being provided with a radial servo region in which first servo data including a first burst pattern and a second burst pattern is recorded, the first radial position being a position that is radially offset from a track center of the track, the second radial position being a position that is radially offset from the track center and is different from the first radial position;
• and
• executing a first operation when the magnetic head is at the first radial position and when the magnetic head is at the second radial position, the first operation including:
• acquiring a first burst demodulated signal and a second burst demodulated signal when the magnetic head passes over the servo region, the first burst demodulated signal being acquired by demodulating the first burst pattern included in the first servo data, the second burst demodulated signal being acquired by demodulating the second burst pattern included in the first servo data;
• calculating a first demodulation position of the magnetic head based on amplitude of the first burst demodulated signal and amplitude of the second burst demodulated signal;
• estimating an actual position of the magnetic head based on the first demodulation position and a sensitivity function of positioning control of the magnetic head;
• estimating amplitude of a third burst demodulated signal and amplitude of a fourth burst demodulated signal, each amplitude being obtained when the magnetic head is at the actual position and being estimated based on a Lissajous figure in which the amplitude of the third burst demodulated signal obtained by demodulating the first burst pattern included in the first servo data and the amplitude of the fourth burst demodulated signal obtained by demodulating the second burst pattern included in the first servo data at various radial positions are indicated on a plane as values of coordinate axes different from each other;
• and
• recording a first difference and a second difference in association with a third radial position, the first difference being a difference between the amplitude of the third burst demodulated signal and the amplitude of the first burst demodulated signal, the second difference being a difference between the amplitude of the fourth burst demodulated signal and the amplitude of the second burst demodulated signal, the third radial position being one of the first radial position and the second radial position at which the magnetic head is positioned when the first operation is executed.