Disk drive with improved spin-up control

Abstract

A disk drive is disclosed comprising a head actuated over a disk, and a spindle motor operable to rotate the disk. The spindle motor operates according to a plurality of electrical cycles over a single revolution of the spindle motor, where each electrical cycle spans a cycle period. A plurality of the cycle periods are measured, at least two of the cycle periods are combined, and a rotation speed of the spindle motor is measured based on the combined cycle periods.

What is claimed is: 
     
         1 . A disk drive comprising:
 a head actuated over a disk;   a spindle motor operable to rotate the disk, wherein:
 the spindle motor operates according to a plurality of electrical cycles over a single revolution of the spindle motor; and 
 each electrical cycle spans a cycle period; and 
   control circuitry operable to:
 measure a plurality of the cycle periods; 
 combine at least two of the cycle periods; and 
 measure a rotation speed of the spindle motor based on the combined cycle periods. 
   
     
     
         2 . The disk drive as recited in  claim 1 , wherein the spindle motor operates according to N electrical cycles over a single revolution, and the control circuitry is further operable to generate the combined cycle periods by summing N consecutive cycle periods. 
     
     
         3 . The disk drive as recited in  claim 1 , wherein the control circuitry is further operable to:
 update the combined cycle periods by summing a running N consecutive cycle periods as each new cycle period is measured; and   update the measured rotation speed based on the updated combined cycle periods.   
     
     
         4 . A disk drive comprising:
 a head actuated over a disk;   a spindle motor operable to rotate the disk; and   control circuitry operable to:
 measure a rotation speed of the spindle motor; 
 generate a gain as a function of the measured rotation speed, wherein the function comprises a polynomial having a degree greater than one; and 
 spin-up the spindle motor based on the gain. 
   
     
     
         5 . The disk drive as recited in  claim 4 , wherein the gain comprises a feedback gain operable to amplify a feedback error signal. 
     
     
         6 . The disk drive as recited in  claim 5 , wherein the feedback error signal represents a difference between the measured rotation speed and a target rotation speed. 
     
     
         7 . A disk drive comprising:
 a head actuated over a disk;   a spindle motor operable to rotate the disk; and   control circuitry operable to:
 measure a rotation speed of the spindle motor; 
 generate a feed-forward control based on the measured rotation speed; and 
 spin-up the spindle motor based on the feed-forward control. 
   
     
     
         8 . The disk drive as recited in  claim 7 , wherein the control circuitry is operable to generate the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive. 
     
     
         9 . The disk drive as recited in  claim 7 , wherein the control circuitry is operable to generate the feed-forward control proportional to the measured rotation speed. 
     
     
         10 . The disk drive as recited in  claim 9 , wherein the feed-forward control compensates for a back electromotive force of the spindle motor. 
     
     
         11 . The disk drive as recited in  claim 7 , wherein the feed-forward control compensates for a drag torque of the spindle motor. 
     
     
         12 . The disk drive as recited in  claim 11 , wherein the control circuitry is operable to generate the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive. 
     
     
         13 . A disk drive comprising:
 a head actuated over a disk;   a spindle motor operable to rotate the disk; and   control circuitry operable to:
 measure a rotation speed of the spindle motor; 
 generate a control signal based on the measured rotation speed and a speed command profile; and 
 spin-up the spindle motor based on the control signal, wherein the speed command profile ensures a minimum spin-up time and a limited power consumption under a worst case environmental condition. 
   
     
     
         14 . The disk drive as recited in  claim 13 , wherein the environmental condition comprises an ambient temperature of the disk drive. 
     
     
         15 . The disk drive as recited in  claim 13 , wherein the speed command profile accounts for a maximum current draw of the spindle motor. 
     
     
         16 . A disk drive comprising:
 a head actuated over a disk;   a spindle motor operable to rotate the disk; and   control circuitry operable to:
 measure a rotation speed of the spindle motor; 
 generate a control signal based on a difference between the measured rotation speed and a target rotation speed; and 
 spin-up the spindle motor based on the control signal generated over a second fraction of a spin-up time; 
 wherein: 
 the target rotation speed is generated based on a speed command profile and the second fraction of the spin-up time; and 
 the control circuitry is operable to determine the second fraction of the spin-up time based on an initial measured rotation speed of the spindle motor prior to generating the control signal. 
   
     
     
         17 . The disk drive as recited in  claim 16 , wherein the control circuitry is operable to initialize the second fraction of the spin-up time so that an initial target rotation speed is greater than the initial measured rotation speed. 
     
     
         18 . The disk drive as recited in  claim 17 , wherein the initial target rotation speed ensures the spindle motor continues accelerating from the initial measured rotation speed when the control signal is generated. 
     
     
         19 . The disk drive as recited in  claim 18 , wherein the control circuitry is further operable to:
 initially control the spindle motor independent of the control signal for a first fraction of the spin-up time; and   after the first fraction of the spin-up time, control the spindle motor based on the control signal for the second fraction of the spin-up time.   
     
     
         20 . A disk drive comprising:
 a head actuated over a disk;   a spindle motor operable to rotate the disk; and   control circuitry operable to:
 spin up the spindle motor to a target rotation speed using a spin-up controller; 
 after spinning up the spindle motor, initialize an integrator based on a state of the spin-up controller; and 
 control the spindle motor using a constant-speed controller comprising the integrator. 
   
     
     
         21 . The disk drive as recited in  claim 20 , wherein the state of the spin-up controller comprises an acceleration control signal applied to the spindle motor. 
     
     
         22 . The disk drive as recited in  claim 21 , wherein the control circuitry is operable to initialize the integrator according to:
   Accel− Kp ·Speed Err  
   where:   Accel represents the acceleration control signal;   Kp represents a gain of the constant-speed controller; and   SpeedErr represents a difference between a measured rotation speed of the spindle motor and a target rotation speed.   
     
     
         23 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, wherein the spindle motor operates according to a plurality of electrical cycles over a single revolution of the spindle motor, and each electrical cycle spans a cycle period, the method comprising:
 measuring a plurality of the cycle periods;   combining at least two of the cycle periods; and   measuring a rotation speed of the spindle motor based on the combined cycle periods.   
     
     
         24 . The method as recited in  claim 23 , wherein the spindle motor operates according to N electrical cycles over a single revolution, and the method further comprising generating the combined cycle periods by summing N consecutive cycle periods. 
     
     
         25 . The method as recited in  claim 23 , wherein the method further comprises:
 updating the combined cycle periods by summing a running N consecutive cycle periods as each new cycle period is measured; and   updating the measured rotation speed based on the updated combined cycle periods.   
     
     
         26 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:
 measuring a rotation speed of the spindle motor;   generating a gain as a function of the measured rotation speed, wherein the function comprises a polynomial having a degree greater than one; and   spinning up the spindle motor based on the gain.   
     
     
         27 . The method as recited in  claim 26 , wherein the gain comprises a feedback gain operable to amplify a feedback error signal. 
     
     
         28 . The method as recited in  claim 27 , wherein the feedback error signal represents a difference between the measured rotation speed and a target rotation speed. 
     
     
         29 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:
 measuring a rotation speed of the spindle motor;   generating a feed-forward control based on the measured rotation speed; and   spinning up the spindle motor based on the feed-forward control.   
     
     
         30 . The method as recited in  claim 29 , further comprising generating the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive. 
     
     
         31 . The method as recited in  claim 29 , further comprising generating the feed-forward control proportional to the measured rotation speed. 
     
     
         32 . The method as recited in  claim 31 , wherein the feed-forward control compensates for a back electromotive force of the spindle motor. 
     
     
         33 . The method as recited in  claim 29 , wherein the feed-forward control compensates for a drag torque of the spindle motor. 
     
     
         34 . The method as recited in  claim 33 , further comprising generating the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive. 
     
     
         35 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:
 measuring a rotation speed of the spindle motor;   generating a control signal based on the measured rotation speed and a speed command profile; and   spinning up the spindle motor based on the control signal, wherein the speed command profile ensures a minimum spin-up time and a limited power consumption under a worst case environmental condition.   
     
     
         36 . The method as recited in  claim 35 , wherein the environmental condition comprises an ambient temperature of the disk drive. 
     
     
         38 . The method as recited in  claim 35 , wherein the speed command profile accounts for a maximum current draw of the spindle motor. 
     
     
         39 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:
 measuring a rotation speed of the spindle motor;   generating a control signal based on a difference between the measured rotation speed and a target rotation speed; and   spinning up the spindle motor based on the control signal generated over a second fraction of a spin-up time;   wherein:   the target rotation speed is generated based on a speed command profile and the second fraction of the spin-up time; and   the method further comprises determining the second fraction of the spin-up time based on an initial measured rotation speed of the spindle motor prior to generating the control signal.   
     
     
         40 . The method as recited in  claim 39 , further comprising initializing the second fraction of the spin-up time so that an initial target rotation speed is greater than the initial measured rotation speed. 
     
     
         41 . The method as recited in  claim 40 , wherein the initial target rotation speed ensures the spindle motor continues accelerating from the initial measured rotation speed when the control signal is generated. 
     
     
         42 . The method as recited in  claim 41 , further comprising:
 initially controlling the spindle motor independent of the control signal for a first fraction of the spin-up time; and   after the first fraction of the spin-up time, controlling the spindle motor based on the control signal for the second fraction of the spin-up time.   
     
     
         43 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:
 spinning up the spindle motor to a target rotation speed using a spin-up controller;   after spinning up the spindle motor, initializing an integrator based on a state of the spin-up controller; and   controlling the spindle motor using a constant-speed controller comprising the integrator.   
     
     
         44 . The method as recited in  claim 43 , wherein the state of the spin-up controller comprises an acceleration control signal applied to the spindle motor. 
     
     
         45 . The method as recited in  claim 44 , further comprising initializing the integrator according to:
   Accel− Kp ·Speed Err  
   where:   Accel represents the acceleration control signal;   Kp represents a gain of the constant-speed controller; and   SpeedErr represents a difference between a measured rotation speed of the spindle motor and a target rotation speed.