Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2001-05-04
2003-05-20
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S568160, C318S453000, C318S459000, C360S075000, C360S290000
Reexamination Certificate
active
06566832
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to parking a read/write head of a head and disk assembly (HDA) to a landing zone and more particularly to reducing the time associated with parking the head/write head when power is removed from the HDA.
BACKGROUND OF THE INVENTION
Magnetic disk drive systems have become widely accepted in the computer industry as a cost effective form of data storage. In a magnetic disk drive system, a magnetic disk rotates at high speed while a magnetic read/write head flies slightly over the surface of the rotating disk. The magnetic disk is a carried by a spindle motor. The read/write head is suspended over the disk on a support arm. As the disk rotates at high speed, the aerodymanic properties of the read/write head provide a lifting force which floats the head over the disk surface on a cushion of air.
Two of the most critical periods in determining the read/write head life span occur during take off and landing. Prior to operation, the read/write head rests on an inner track or landing zone where the head is parked. As the disk begins to rotate from an initial, stopped position, the read/write head is dragged along the surface of the disk. Once the disk reaches sufficient speed, the aerodynamic lift floats the read/write head assembly away from the disk surface.
During shutdown of the disk drive system, the read/write head must land upon the surface of the magnetic disk. This landing typically occurs in the landing zone along the inner radius of the magnetic disk surface. After power to the magnetic disk drive spindle motor is shut-off, momentum continues to carry the magnetic disk through its rotation. Various friction sources slowly reduce the speed of rotation of the magnetic disk. As the disk rotation slows, the aerodynamic lifting force is reduced and the read/write head assembly contacts the disk surface in the landing zone area. Once the magnetic head contacts the disk surface, the head is dragged across the surface as momentum continues the magnetic disk rotation.
Magnetic read/write heads used in modern day disk drive systems are typically extremely small and delicate made of magneto-resistive heads and giant magneto-resistive heads. The dragging associated with take offs and particularly with landings is a primary source of wear for the read/write heads. Prior art have attempted to limit the length of the dragging by braking the rotation of the spindle motor. The solutions include circuitry for electrically shorting out the windings in a magnetic disk drive spindle motor following a predetermined time delay after power loss and retraction of the magnetic read/write head onto the landing zone area of the disk surface. Electrically shorting the coils causes the spindle motor to rapidly stop rotating.
Other prior art approaches to disk drive braking have used mechanical devices such as normally closed electric relays held in the open position by the power supply in the magnetic storage system. Upon loss of power, these relays return to their closed positions and electrically short out the spindle motor windings to brake the spindle motor. Mechanical relays have a number of drawbacks including additional constant power draw, large size, high cost and other inherent reliability limitations problematic of electromechanical components.
Another prior art approach includes the use of an aerodynamic actuator latch as disclosed in commonly assigned U.S. Pat. No. 5,319,511 titled “Aerodynamic Actuator Latch with Magnetic Return Spring for Hard Disk Drive”. The disclosure of the referenced patent is incorporated herein by this reference. The aerodynamic actuator latch system (or airlock) locks a rotary actuator assembly of a disk drive to restrain a data transducer at the landing zone during non-rotation of the disks and for releasing the latch in response to airflow generated by disk rotation. However, during power down, until the actuator latch system locks and the spindle motor stops rotating or reaches very low RPM, the data transducer may still be subjected to damage.
A recent trend has been to use hard disk drives as portable storage elements. Hard disk drive enclosures have been developed with removable slide mounts which enable the hard disk drives to be easily removed from a computer system. Moreover, some removable slide mounts feature hot swappable characteristics that allow the hard drives to be removed while the hard disk and the computer system are still operating. Hard disk drives used in such removable systems are often subjected to movement before the read/write heads have had a chance to be placed over the landing zone.
Therefore, it is desirable to provide an apparatus and methods of operating the same which parks a read/write head during power interruptions that overcomes the drawbacks of prior art solutions.
SUMMARY OF THE INVENTION
The present invention provides an apparatus for parking a read/write head during power interruptions and methods for operating the same which improves the time to park a read/write head. The novel improved apparatus is based on supplying power to retract circuitry while braking the spindle motor at the same time. Thus, according to one aspect of the invention, the apparatus for reducing the time to steady state an operating disk having an actuator arm coupled to a voice coil for latching the actuator arm when power is interrupted:, comprises a Y-winding spindle motor having a first winding, a second winding, and a third winding, and a spindle motor controller coupled to the Y-winding spindle motor configured to short the first winding and the second winding to produce a retarding force against the Y-winding spindle motor and to direct power produced by the third winding in series with the parallel combination of the first and second windings, to the voice coil for moving the actuator arm to a latched position using BEMF dynamically modulating vectors.
According to another aspect of the invention, the spindle motor controller shorts the first winding and the second winding in parallel to produce the retarding force. The spindle motor controller serially couples the third winding to the parallel combination of the first and second windings, and to the voice coil. Supplying power to the voice coil retracts the actuator arm which includes at least one read/write head to a landing zone area. Said combination of the windings provides more power for a longer duration.
According to another aspect of the invention, the first winding includes a first switch, the second winding includes a second switch, and the third winding includes a third switch and the spindle motor controller couples the first switch of the first winding with the second switch of the second winding and couples the third switch of the third winding to the voice coil. The first switch can include a first spindle MOSFET driver, the second switch can include a second spindle MOSFET driver, and the third switch can include a third spindle MOSFET driver.
According to another aspect of the invention, the latched position includes a parked position for the actuator arm. With the actuator arm in the latched position, the read/write heads remain secured to facilitate transport of the drive apparatus without damaging the read/write heads due to shorter stop time and less wear and tear.
According to yet another aspect of the invention, a power isolation switch is coupled to a power supply and wherein the spindle motor controller opens the power isolation switch when the power is interrupted. Isolating the power supply from generated back EMF via the windings of the spindle motor prevents leakage of power through the interrupted power supply.
An apparatus and method for parking a read/write head for a disk drive are provided by supplying back EMF to a retract circuitry and generating back EMF to brake the spindle motor. The time needed to park a read/write head and steady state the disk drive is reduced when power is removed. Disk drives can be moved sooner without the risk of damaging the read/write heads or the spindle motor bearings. Th
Duda Rina I.
Nappi Robert E.
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