Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-02-28
2004-09-14
Hudspeth, David (Department: 2697)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S078090, C360S078070, C360S078060, C360S097020, C360S031000, C318S634000, C318S265000, C318S560000, C318S561000
Reexamination Certificate
active
06791785
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 coil that is inhibited from overheating and methods for providing the same.
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 adjacent 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 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 results in the permanent magnet applying a force onto the coil which is then transferred to the actuator arm in the form of a torque. 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 limits 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. According to the state of the art, the seek time required to reposition the transducer across a distance of 2-5 cm is typically in the range of 5-10 ms, thereby resulting in the transducer having a linear acceleration greater than 500 m/s2 or 50 g's. Consequently, to provide such large acceleration, a relatively large current is often required to flow through the coil.
Unfortunately, when large amounts of current are directed through the coil, the rate of heat gain caused by the finite resistance of the windings of the coil may exceed the rate of heat loss to the environment. Thus, if left unchecked for an extended period of time, a rapid succession of seek operations may excessively raise the temperature of the coil such that the drive will no longer be operable. For example, when subjected to an instantaneous or average current that is beyond the VCM's design limitations, the coil may generate excessive heat and deform the coil. Moreover, overmold material may delaminate from the actuator assembly, lose its rigidity and/or outgas particulates into the disk drive enclosure, with deleterious results. Such outgassing from the coil overmold, coil insulators and/or from other materials applied to the coil wires (such as wire lubricants, for example) may occur even at relatively low temperatures (85° C., for example). Thus, to prevent such damage, there is a need to inhibit VCM coil from overheating.
One possible solution to the problem of excessive coil temperature is to blindly limit the VCM control current, i.e. without sensing or estimating the coil temperature, so as to be absolutely sure that the temperature of the coil is less than a threshold value. For example, following a first seek operation, a subsequent seek could be delayed so as to be sure that heat added to the coil during the first seek operation is substantially dissipated to the environment before the subsequent seek occurs. Alternatively, the resistive heat gain in the coil could be reduced by reducing the commanded current through the coil. However, because of the difficulty in estimating how well the environment can remove heat from the coil, the foregoing methods of blindly limiting the coil current will likely require using overly conservative limitations. Thus, while possibly preventing the coil from overheating, the foregoing solution can result in unacceptably slow drive performance.
Another solution is proposed in U.S. Pat. No. 5,594,603 to Mori et al. and assigned to Fujitsu Limited, Japan. In this patent, the current applied to the coil is used to approximate the coil temperature. This method attempts to mathematically model the thermal behavior of the coil by inter-relating a group of factors that includes the VCM control current, the heat naturally radiated by the coil, the ambient temperature, and the thermal capacity of the coil. However, such modeling, although providing an indication of the present VCM temperature, requires considerable processing resources, thereby requiring the drive to include more expensive data processing components.
To reduce costs, the typical disk drive includes only a single processor. Usually, the single processor is required to perform many different functions, such as communicating with a host computer, keeping track of where data is stored on the disk, and controlling the movement of the transducer elements. Thus, the processor is “bandwidth limited” such that the processor is usually busy and, therefore, unable to perform the relatively aforementioned complicated calculations of the prior art.
Another proposed solution is proposed in U.S. Pat. No. 5,128,813 to Lee (hereafter the '813 patent) and assigned to Quantum Corporation. In this patent, a discrete temperature-sensing element is used to dynamically sense the VCM temperature during the operation of the drive. This patent discloses that the thermistor is mounted for thermal conduction directly to the head and disk assembly. While the temperature sensing element may, in fact, provide a direct measurement of the temperature of the VCM (in contrast to the Mori et al. patent above, for example), this method requires mounting a high precision thermistor to the drive and requires that appropriate signal conditioning means be provided to measure, quantize and interpret the resistance of the thermistor. In many aspects, however, disk drive designers and manufacturers operate in an environment that has acquired many of the characteristics of a commodity market. In such a market, the addition of even a single, inexpensive part can directly and adversely affect competitiveness. In this case, therefore, the addition of the thermistor and associated signal conditioning means discussed in the '813 patent may be of little practical value.
From the foregoing, it will be appreciated that there is a need for improved methods of inhibiting a voice coil motor from overheating that are inexpensive in their implantation and do not require substantially increased processing resources.
SUMMARY OF THE I
Messenger Carl R.
Nguyen David D.
Figueroa Natalia
Hudspeth David
Knobbe Martens Olson & Bear
Mobarhan, Esq. Ramin
Shara, Esq. Milad G.
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