Abstract: According to one embodiment, a piezoelectric device drive method includes measuring gains including a first gain by applying voltages including a first voltage to a piezoelectric device at a first timing, calculating gain characteristics associated with the applied voltages from the measured gains, measuring a second gain by applying the first voltage to the piezoelectric device at a second timing, correcting the calculated gain characteristics based on the first gain and the second gain, and calculating a third gain based on the corrected gain characteristics and the second gain in a case where a second voltage other than the first voltage is applied.

Abstract: According to one embodiment, a disk storage apparatus includes a servo system. The servo system includes a state observer and performs a seek operation up to a target position with a current position of a head undetermined. The servo system performs the seek operation based on initial values including a temporary position, while allowing the state observer to operate based on the initial values, until the current position is determined. The servo system determines the current position based on the servo data read from the plurality of servo areas by the read module and a result of estimation by the state observer.

Abstract: According to one embodiment, a magnetic disk apparatus includes a magnetic disk having a plurality of tracks, each of the plurality of tracks having a plurality of servo areas and a plurality of data areas, the plurality of servo areas and the plurality of data areas being alternately arranged respectively, a magnetic head, and a processor. When a plurality of positioning errors related to one servo area are present in the first track, the processor updates the positioning error of the one servo area with a positioning error closest to a second track that is next to the first track. The processor writes data in the second track by a shingled write recording system by using the updated positioning error.

Abstract: According to one embodiment, a disk storage apparatus includes an interrupt controller and a servo controller. The interrupt controller determines whether or not to carry out servo interrupt processing and holds a number of negative results of the determination. The servo controller includes an internal model configured to calculate an estimated current position of the head. The servo controller corrects a state of the internal model based on the number of negative results of the determination and performs head positioning control based on a result of a calculation of the internal model, if the result of the determination by the interrupt controller is affirmative.

Abstract: According to one embodiment, a disk storage apparatus includes a read controller and a servo controller. The read controller contains a combined position generator including a state observer and a combined position calculator. The servo controller controls a seek operation of the head based on the combined position. The servo controller stores the servo information in a memory and determines an occurrence of a state offset as an error between an actual position of the head and the combined position. The servo controller corrects the predicted position by the state observer based on the servo information stored in the memory and the combined position when the occurrence of the state offset is detected.

Abstract: According to one embodiment, a disk storage apparatus includes a servo system. The servo system includes a state observer and performs a seek operation up to a target position with a current position of a head undetermined. The servo system performs the seek operation based on initial values including a temporary position, while allowing the state observer to operate based on the initial values, until the current position is determined. The servo system determines the current position based on the servo data read from the plurality of servo areas by the read module and a result of estimation by the state observer.

Abstract: According to one embodiment, a disk storage apparatus includes an interrupt controller and a servo controller. The interrupt controller determines whether or not to carry out servo interrupt processing and holds a number of negative results of the determination. The servo controller includes an internal model configured to calculate an estimated current position of the head. The servo controller corrects a state of the internal model based on the number of negative results of the determination and performs head positioning control based on a result of a calculation of the internal model, if the result of the determination by the interrupt controller is affirmative.

Abstract: According to one embodiment, a magnetic disk drive includes a storage unit, a head position detector and a head position estimator. The head position detector detects a position of a first head if the first head is switched to a second head. The head position estimator estimates a position of the second head based on the position of the first head, first and second voltages, polarities of first and second microactuators, gains of the first and second microactuators, and a first inter-head offset. The first and second voltages are applied to the first and second microactuators, respectively. The first inter-head offset is stored in the storage unit.

Abstract: According to one embodiment, a magnetic disk drive includes a storage unit, a head position detector and a head position estimator. The head position detector detects a position of a first head if the first head is switched to a second head. The head position estimator estimates a position of the second head based on the position of the first head, first and second voltages, polarities of first and second microactuators, gains of the first and second microactuators, and a first inter-head offset. The first and second voltages are applied to the first and second microactuators, respectively. The first inter-head offset is stored in the storage unit.

Abstract: According to one embodiment, a piezoelectric device drive method includes measuring gains including a first gain by applying voltages including a first voltage to a piezoelectric device at a first timing, calculating gain characteristics associated with the applied voltages from the measured gains, measuring a second gain by applying the first voltage to the piezoelectric device at a second timing, correcting the calculated gain characteristics based on the first gain and the second gain, and calculating a third gain based on the corrected gain characteristics and the second gain in a case where a second voltage other than the first voltage is applied.

Abstract: According to one embodiment, a servo controller of a magnetic disk drive includes a microactuator (MA) estimator, VCM actuator (VCMA) controller, a filter and an adder. The MA estimator estimates a first displacement of an MA from a control input to be provided to the MA. The VCMA controller controls a VCMA based on a positioning error between a target track and a first position of the VCMA. The first position is estimated from a position of a head and the first displacement. The filter estimates a second position of the VCMA corresponding to a delay in a displacement of the MA caused by hysteresis of the MA, from a state of the VCMA in a seek operation, and estimates a second displacement that is the delayed displacement of the MA, from the second position. The adder adds the second displacement to an input to the MA controller.

Abstract: According to one embodiment, a servo controller of a magnetic disk drive includes a microactuator (MA) estimator, VCM actuator (VCMA) controller, a filter and an adder. The MA estimator estimates a first displacement of an MA from a control input to be provided to the MA. The VCMA controller controls a VCMA based on a positioning error between a target track and a first position of the VCMA. The first position is estimated from a position of a head and the first displacement. The filter estimates a second position of the VCMA corresponding to a delay in a displacement of the MA caused by hysteresis of the MA, from a state of the VCMA in a seek operation, and estimates a second displacement that is the delayed displacement of the MA, from the second position. The adder adds the second displacement to an input to the MA controller.

Abstract: For a feedforward controller for controlling a position of a magnetic head in a magnetic disk drive, a vibration of the magnetic head is measured in a state in which a magnetic disk is rotated in the magnetic disk drive. From a spectrum of the measured vibration, a flutter frequency which is a frequency of a vibration caused by the magnetic disk fluttering is obtained. A filter is designed for each flutter frequency having a peak of a gain for a respective one of obtained flutter frequencies. The feedforward controller for controlling a position of the magnetic head is obtained by combining filters designed for the respective flutter frequencies.