Disk drive with capacitance sensing of disk vibration and feedforward control for removal of read/write head track misregistration

A disk drive having a rotatable magnetic recording disk with a plurality of data tracks and a recording head movable across the disk surface for reading and/or writing data in the tracks, and wherein the tracks contain head position information detectable by the head, the disk drive comprising:

• an actuator for moving the head across the disk surface;
• a head position feedback controller responsive to position information detected by the head for generating a head position control signal;
• a capacitive sensor facing the disk surface;
• a capacitance sensing circuit coupled to the sensor for generating a signal representative of the distance between the sensor and the disk surface;
• and
• a feedforward controller responsive to the distance signal for generating a correction signal, the correction signal being combined with the head position control signal to generate an actuator control signal;
• wherein the distance between the sensor and the disk surface includes a component that is substantially repeatable for each angular location on the disk surface, and wherein the feedforward controller is responsive to the distance signal after removal of said component.

A magnetic recording disk drive comprising:

• a housing;
• a spindle motor attached to the housing;
• a magnetic recording disk having a plurality of generally concentric data tracks containing head position servo information, the disk being mounted to and rotatable by the spindle motor about an axis of rotation, the disk experiencing axial vibration during its rotation;
• a recording head for reading and writing data in the tracks, the head experiencing a track misregistration (TMR) frequency response as a result of axial vibration of the rotating disk;
• a voice coil motor (VCM) actuator for moving the head generally radially across the tracks and for maintaining the head on a desired track during reading and writing;
• servo electronics for converting servo information detected by the head to a digital position error signal (PES);
• a capacitive sensor attached to the housing and facing the disk surface;
• a capacitance sensing circuit coupled to the sensor for generating an analog signal representative of the distance between the sensor and the disk surface during axial vibration of the disk;
• an analog-to-digital converter for converting the analog distance signal to a digital distance value;
• a digital servo processor comprising a feedback controller for generating a head position control value from the PES and a feedforward controller having gain and phase characteristics to substantially match the TMR frequency response for generating a correction to the head position control value from the digital distance value, the processor outputting a corrected head position control value;
• and
• a digital-to-analog converter for converting the corrected head position control value to an analog actuator control signal to the VCM.