Disk drive employing BEMF spindle speed control or wedge spindle speed control
AssigneeWestern Digital Technologies, Inc.
InventorsKuang-Yang Tu, Chuanwen Ji
Life of this patent
Estimating the term…
Abstract
A disk drive is disclosed employing either back electromotive force (BEMF) spindle speed control or wedge spindle speed control. The BEMF spindle speed control is used to calibrate a reference time period representing an accumulation of a predetermined number of wedge-to-wedge times. During wedge spindle speed control, a wedge time period representing an accumulation of a predetermined number of wedge-to-wedge times is measured, and a wedge speed error is computed as the difference between the reference time period and the wedge time period.
Claims30
A disk drive comprising:
- (a) a disk comprising a plurality of tracks, wherein each track comprises a plurality of data sectors and a plurality of servo wedges;
- (b) a head actuated over the disk;
- (c) a spindle motor for rotating the disk at an operating speed in response to a spindle control current, the spindle motor comprising a plurality of windings which generate a back electromotive force (BEMF) voltage;
- (d) a BEMF detector for generating a BEMF signal by comparing the BEMF voltage to a threshold;
- and
- (e) a disk controller for:
- measuring a BEMF speed error responsive to the BEMF signal during a BEMF spindle speed control mode;
- updating the spindle control current in response to the BEMF speed error to drive the disk at the operating speed;
- measuring a wedge-to-wedge time representing a time period between each servo wedge;
- calibrating a reference time period representing an accumulation of a predetermined number of wedge-to-wedge times while the BEMF speed error is substantially zero;
- switching to a wedge spindle speed control mode;
- measuring a wedge time period representing an accumulation of a predetermined number of wedge-to-wedge times;
- generating a wedge speed error representing a difference between the reference time period and the wedge time period;
- and
- maintaining the disk at the operating speed by updating the spindle control current in response to the wedge speed error.
A method of operating a disk drive, the disk drive comprising a disk having a plurality of tracks, wherein each track comprises a plurality of data sectors and a plurality of servo wedges, a head actuated over the disk, a spindle motor for rotating the disk at an operating speed in response to a spindle control current, the spindle motor comprising a plurality of windings which generate a back electromotive force (BEMF) voltage, and a BEMF detector for generating a BEMF signal by comparing the BEMF voltage to a threshold, the method comprising the steps of:
- (a) measuring a BEMF speed error responsive to the BEMF signal during a BEMF spindle speed control mode;
- (b) updating the spindle control current in response to the BEMF speed error to drive the disk at the operating speed;
- (c) measuring a wedge-to-wedge time representing a time period between each servo wedge;
- (d) calibrating a reference time period representing an accumulation of a predetermined number of wedge-to-wedge times while the BEMF speed error is substantially zero;
- (e) switching to a wedge spindle speed control mode;
- (f) measuring a wedge time period representing an accumulation of a predetermined number of wedge-to-wedge times;
- (g) generating a wedge speed error representing a difference between the reference time period and the wedge time period;
- and
- (h) maintaining the disk at the operating speed by updating the spindle control current in response to the wedge speed error.
Dependencies are inferred from the claim text.