Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Utility Patent
1997-09-04
2001-01-02
Sniezek, Andrew L. (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S078040, C360S078140
Utility Patent
active
06169641
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to control systems. More particularly, the present invention relates to methods and devices for controlling a head position actuator of a disk drive.
BACKGROUND OF THE INVENTION
Disk drives are widely used for retrieving and/or storing a variety of information (i.e., audio, computer, and video data). A disk drive typically includes one or more circularly shaped disks mounted on a shaft or spindle. The disks are rotated by the shaft at a high rate of speed for recording and reproducing data.
Each of the disks is usually divided into a plurality of concentric tracks. The concentric tracks of the disks are arranged on the upper and lower surfaces of the disks with varying radii. The concentric tracks are identified through servo information located on each track or a dedicated servo disk.
The disk drive usually includes one or more transducers or heads associated with each surface of the disks. The heads are moved across the surfaces of the disks by an actuator. The actuator positions the heads over a selected track of the disks to access the information recorded on the selected track or to write data to the selected track.
The process of moving the heads of a disk drive from a present track to a selected track is known as a seek, while maintaining the heads over the center of the selected track during a read or write operation is referred to as track following. During a seek operation, the heads are usually moved as rapidly as possible from the present track to the selected track in order to minimize seek time.
One method of minimizing seek time is to apply a maximum control signal to the actuator to accelerate the heads as fast as possible to a halfway point. At this point, an opposite control signal is applied to the actuator to decelerate the heads to the desired track. This is referred to as a “bang—bang” technique. However, variations in the control signals, the supply voltage, the gain of the actuator, the environment surrounding the drive, and the mechanical characteristics of the disk drive can cause the heads to overshoot or undershoot the selected track. Consequently, it can be quite difficult to accurately move the heads from one track to another in a seek operation utilizing “bang—bang” techniques.
Known disk drives typically utilize a velocity profile when moving the heads of a disk drive from a present track to a selected track. As the heads are moving to the selected track, the velocity profile is followed as closely as possible during acceleration and deceleration of the heads. In particular, the velocity of the heads is estimated at various points and compared to the required velocity profile to generate an error signal. The error signal is provided to the actuator to correct the difference between the estimated velocity and the required velocity profile of the heads. When the required velocity profile is greater than the estimated velocity, the heads are accelerated. When the required velocity profile is less than estimated velocity, the heads are decelerated. The estimated velocity is compared to the velocity profile until the heads reach the selected track.
However, the use of a velocity profile may not assure that the desired track will be reached in a minimum amount of time. First, the velocity profile usually does not account for the discrete times at which command updates can be made to the actuator. Therefore, it can be difficult to force the required control actions to coincide with the command update times. As a consequence, the command signals are usually applied to the actuator for a longer or shorter period of time than required. This can result in an error of the final state (i.e., an overshoot, an undershoot or arrival at a different final state).
Second, the velocity profile usually does not assure zero velocity and position error at a desired track at a sampling time of the system. As a result, there will be residual errors that are usually eliminated by another operation (i.e. a track acquisition operation) before the seek can be completed. The time needed to reduce the residual errors to acceptable levels can typically require several sample times of the system. Thus, the time required to dampen out the residual errors increases the total time for a seek. Finally, unaccounted changes in the parameters of the system can force a velocity profiling system to overshoot or undershoot the desired target track.
SUMMARY OF THE INVENTION
The present invention relates to methods and devices for controlling a head position actuator of a disk drive. A controller is utilized to control the actuator to allow seek operations to be performed in the shortest time possible allowed by the dynamics of the actuator and the sampling and control update rates of the system. The controller can accurately and quickly cause a head of disk drive to move to a selected track of a disk with minimal overshoot or undershoot.
The head can meet specific states at particular quantizied time intervals. The head can be moved from an initial state to a final state (i.e., position, velocity, and acceleration) in a minimal number of sampling or control update time intervals (i.e., servo bursts). A set of control/command signals is generated to cause the head or actuator to change from an initial state to an intermediate state or a reachable set of states. From the intermediate state, control/command signals are generated to ensure that the head arrives at the desired position or track with approximately zero velocity and acceleration error in a minimum amount of discrete sampling or control update time intervals.
The head can reach the final state with near zero state error at a specific sampling or control update time, despite uncertainty in the gain and other parameters of the actuator. The final state may be selected to coincide with a sample time of the system or a control update time.
One device in accordance with the present invention comprising an actuator to move a head of a data storage apparatus. A servo controller is coupled to the actuator and provides control command signals to the actuator to move the head from an initial position to a final position at a discrete time interval.
One method in accordance with the present invention comprising the steps of moving the head from an initial track to a final track without utilizing a separate track acquisition operation to position the head over the final track.
The invention, together with attendant advantages, will best be understood by reference to the following detailed description of the presently preferred embodiment of the invention, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4805050 (1989-02-01), Aoyagi et al.
patent: 4920462 (1990-04-01), Couse et al.
patent: 5245595 (1993-09-01), Yasukawa
patent: 5285330 (1994-02-01), Masaki
patent: 5402287 (1995-03-01), Shimizu et al.
patent: 5831787 (1998-11-01), Yoshida et al.
patent: 5844744 (1998-12-01), Suzuki et al.
Patent Abstract of Japan vol. 15. No. 71, Kaneko, Magnetic Head Positioning Control Method, Feb. 19, 1991.
Motorola Inc.
Sniezek Andrew L.
LandOfFree
Methods and devices for controlling a head position actuator... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods and devices for controlling a head position actuator..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods and devices for controlling a head position actuator... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2535476