Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2002-01-31
2004-08-24
Hudspeth, David (Department: 2653)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06781787
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computer data storage devices and, in particular, relates to a hard disk drive having an actuator controller that adjusts seek current profile on the fly so as to improve seek performance.
2. Description of the Related Art
Hard disk drive storage devices are an important component in virtually all computer systems. In particular, hard disk drives provide computer systems with the ability to store and retrieve data in a non-volatile manner such that the data is maintained even if power is removed from the device. The popularity of these devices is based on their ability to quickly store and retrieve large quantities of digital information at low cost. However, because the computer industry continually strives to provide computer systems with increased performance, there exists a need for improved disk drives having increased data access speeds.
The typical hard disk drive comprises one or more pivotally mounted disks having a magnetic recording layer disposed thereon and a plurality of magnetic transducer elements for affecting and sensing the magnetization states of the recording layer. The recording layer comprises a large number of relatively small domains disposed thereon that can be independently magnetized according to a localized applied magnetic field and that can be maintained in the magnetized state when the external field is removed. The domains are grouped into concentric circular tracks each having a unique radius on the disk and data is written to or read from each track by positioning the transducer over the disk at the corresponding radius while the disk is rotated at a fixed angular speed.
To position the transducer with respect to the disk, the typical hard disk drive further comprises a head stack assembly (HSA) that includes a transducer, a pivotally mounted actuator arm for supporting the transducer, a voice coil motor (VCM) for exerting a torque onto the actuator arm, and a servo-controller for controlling the VCM. The VCM comprises a coil of conducting wire wound into a plurality of loops and a permanent magnet disposed adjacent the coil. The servo-controller initiates movement of the actuator arm by directing a control current to flow through the coil which generates a torque that moves the actuator arm. Because the direction of the torque is dictated by the direction of control current flow, the servo-controller is able to reposition the transducer by first directing the control current through the coil so as to angularly accelerate the actuator arm in a first direction and then reversing the control current so as to angularly decelerate the actuator arm.
The time required to reposition the transducer in the foregoing manner is known as the “seek time” of the drive and is an important performance factor that affects the throughput of the drive. For example, a drive having a short seek time will be able to access a requested track of data more quickly than a drive having a longer seek time. Currently, in high performance mass-market drives, the seek time required to reposition the transducer for a given distance of 0.8-0.85 cm is typically in the range of 5-10 ms.
In a typical seek operation, the transducer accelerates, coasts, and decelerates according to the predetermined control of the current applied to the VCM. The transducer, through a feedback control, typically requires some settling time to settle on the proper target track. Once the transducer is on the proper track, a track following current is provided to the VCM in order to maintain tracking.
To perform a seek operation, the current supplied to the VCM typically follows a predetermined profile that includes acceleration and deceleration phases. The profiles are typically stored in the controller, for example in a lookup table. The profiles are generally configured such that maximum acceleration and deceleration values leave ample margins between the values and maximum current that is available for use. One reason for having such margins is that the maximum current available for use by the VCM varies with the operating conditions and drive parameters of the disk drive. Such operating conditions may include factors such as temperature and supply voltage. The drive parameters may include driver FET resistance and VCM winding resistance. As is known in the art, operating conditions and drive parameters both affect how much current can be delivered to the VCM. Consequently, to avoid having the profiles exceeding the maximum available current, the profiles are generally configured in a conservative manner with ample margins that can accommodate a wide range of operating conditions and drive parameters. One method is to determine the worst case scenario of operating conditions and drive parameters, and formulate the worst case operating parameters accordingly.
One reason for attempting to have the current profile always within the available range is that seek operations that demand current beyond what is available may cause a situation where deceleration phase is not able to stop the transducer at the target track. In such a situation, the transducer overshoots the intended target, and a substantial amount of extra time is required to bring the transducer back and settle at the target track. Because of such a negative consequence, the deceleration profiles are generally configured to have ample reserve of current.
One disadvantage of utilizing conservative current profiles is that some seek time is sacrificed. In particular, the deceleration of the VCM, considered to be more important than the acceleration, is configured in a conservative manner because the available current is not known. Thus to decelerate the transducer using profile with conservative deceleration magnitude, the time required for deceleration needs to be extended.
To overcome such degradation in seek time in disk drives where certain specified seek time needs to be achieved for substantially all reasonable operating conditions, one solution is to use a high torque generating magnet to obtain a higher torque for a given VCM current. Such a high torque generating magnet may be implemented by using a magnet formed from high performance magnet materials, or by increasing the physical size of the magnet. While such a solution does achieve a specified seek time using the traditional conservative current profiles, both implementations of the high torque generating magnets are significantly more costly.
From the foregoing, it will be appreciated that there is a need for improved system for performing seek operations. To this end, there is a need for a system that utilizes the full range of available current to the VCM to form a current profile so as to improve the seek performance of the hard disk drive.
SUMMARY OF THE INVENTION
The aforementioned needs are satisfied by one aspect of the invention that relates to a hard disk drive comprising a rotatable disk having a magnetic recording media. The rotatable disk defines a plurality of concentric servo tracks. The hard disk drive further comprises a pivotable actuator that is movable with respect to the rotatable disk. The hard disk drive further comprises a transducer disposed on the actuator so as to be movable with respect to the disk so as to be positionable on a selected servo track of the plurality of concentric servo tracks. The hard disk drive further comprises a voice coil motor that moves the pivotable actuator in response to an applied current so as to permit movement of the transducer from a first location to a second location. The movement comprises an acceleration phase and a deceleration phase. The hard disk drive further comprises a controller for controlling the applied current according to a current profile. The current profile has a first portion corresponding to the acceleration phase, and a second portion corresponding to the deceleration phase. The controller monitors a parameter indicative of the movement of the actuator during the application of the first portion of the current p
Codilian Raffi
Gibbons Kent W.
Hudspeth David
Knobbe Martens Olson & Bear
Shara, Esq. Milad G.
Slavitt Mitchell
Western Digital Technologies Inc.
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