Supplying power from a spindle motor in a disc drive system

Details Supplying power from a spindle motor in a disc drive system Supplying power from a spindle motor in a disc drive system

1999-10-28

2003-10-28

Hudspeth, David (Department: 2753)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

Reexamination Certificate

active

06639749

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the field of disc drive storage devices, and more particularly, but not by way of limitation, to supplying power from a spindle motor in a disc drive system.
BACKGROUND OF THE INVENTION
Modern hard disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a high speed. Information is read from and written to each disc in a plurality of concentric tracks by a transducer assembly mounted on an actuator arm. The outside circumference of each disc is referred to as the “outer diameter” (OD), and the center of each disc is referred to as the “inner diameter” (ID). A transducer assembly is said to “fly” over the disc surface as the disc rotates. When disc rotation velocity decreases, the layer of air supporting the transducer assembly above the disc surface diminishes and the assembly descends toward the disc surface. However, contact between the transducer assembly and the disc surface can damage the magnetizable medium and the transducer assembly. Furthermore, through a phenomenon called “stiction,” a transducer assembly can become temporarily “stuck” to the disc surface after contact with the disc surface. Stiction can damage the magnetizable medium, the transducer assembly, and/or the actuator arm when the disc drive system initiates disc rotation in an attempt to move the transducer assembly from the disc surface.
One approach to addressing this problem is to land the transducer assembly in a textured landing zone, preferably near the ID of the disc. Typically, data is not recorded in the landing zone, and the texturing of the landing zone surface minimizes stiction. The actuator arm is moved to an ID landing zone from the disc when the rotational velocity of the disc is decreased, thereby avoiding contact with the data area of the disc. The transducer assembly is moved back to the disc when the rotational velocity increases to allow it to fly above the disc surface.
An alternative approach for loading/unloading a transducer assembly is to move the actuator arm onto a ramp, preferably positioned outside the OD of the disc. The ramp supports the transducer assembly outside the diameter of the disc and prevents contact between the transducer assembly and the disc surface. An actuator arm typically sweeps a 25° arc from ID to OD to access tracks on a disc; however, the ramp feature can increase the total sweep (i.e., stroke) required of the actuator arm and a voice coil motor (VCM) to approximately 50°. Furthermore, the ramp presents additional resistance to the movement of the actuator arm, because the arm must ascend the sloped surface of the ramp, which also introduces an additional friction component.
A rotary VCM actuator, shown generally at
100
in
FIG. 1
, commonly provides the motive force to move the actuator arm
102
, and therefore the transducer assembly
104
, across the disc from ID to OD. The actuator arm
102
is cantilevered outward over the disc surface
106
from a common pivot structure
108
, while the coil
110
of the VCM
100
extends horizontally outward from the other side of the pivot structure. A permanent magnet and pole piece structure
112
is fixedly mounted to the housing
114
of the disc drive in such an arrangement that the coil
110
is movably supported in the middle of the magnetic field formed by the stationary magnet of the structure
112
.
Sophisticated control logic uses a servo algorithm to apply carefully calculated amounts and polarities of DC (direct current) power to the ends of the coil
110
for controllably moving the coil
110
within the magnetic field, thereby moving the actuator arm
102
across the disc surface
106
. As the coil
110
moves between the horizontal extremes of the stationary magnet in structure
112
, the actuator arm
102
moves across the disc surface
106
approximately between the ID and the OD. As such, the length of the stationary magnet structure
112
corresponds proportionally to the arcuate sweep of the actuator arm
102
.
In disc drive designs employing storage of the transducer assembly
104
outside of the OD, the length of the stationary magnet structure
112
is commonly increased to accommodate the increased sweep of the actuator arm. At the horizontal extremes of the stationary magnet structure
112
, the torque generated by the VCM is weaker than toward the horizontal interior of the VCM because the flux density is diminished. Applied torque is proportional to both flux density and current in the coil
110
. Accordingly, the torque applied to the actuator arm
102
by a particular DC current (i.e., as controlled by a particular servo algorithm) is diminished near the extremes of the actuator arm's sweep. In disc drive designs employing ramped storage of the actuator arm
102
outside of the OD, the diminished torque presents a difficulty moving the actuator arm
102
onto a ramp
116
. Even in the circumstance of a control power-down operation, the diminished torque outside the OD impacts the unloading of the transducer assembly to a ramp by requiring additional current from the power supply and/or changes in the servo algorithm.
The diminished torque may be addressed by increasing the length of the stationary magnets in structure
112
to extend the magnetic field at the outer extreme of the sweep. However, merely increasing the length of the magnets increases the cost and size of the components. Increasing the magnet length also decreases the flux density distributed between the poles. Therefore, to apply the same torque to the actuator arm
102
during normal operation, additional current must be supplied to the actuator coil
110
, unnecessarily increasing the normal power consumption of the disc drive system. The problem is how to provide adequate torque to the actuator arm
102
when it is needed to ascend the ramp
116
outside the OD of a disc surface
106
during a retract operation without unnecessarily increasing the cost, size, and, the overall power consumption of the disc drive system during normal operation.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide a method and system for unloading a transducer assembly to a ramp positioned outside an outer diameter of a disc in a disc drive system using supplementary power from back EMF generated by a spindle motor rotating from a velocity that exceeds the normal operating velocity.
In accordance with the preferred embodiment, a method for unloading a transducer assembly to a ramp positioned outside an outer diameter of a disc in a disc drive system including a spindle motor for rotating the disc and a positioning coil coupled to a power supply for moving the transducer assembly relative to the disc is provided. The disc is rotated at a first rotational velocity equaling a normal operational rotational velocity of the disc drive system. A retract signal is received. The rotation of the disc is accelerated to a second rotational velocity that exceeds the normal operational rotational velocity of the disc drive system, responsive to the retract signal. Power is decoupled from to the spindle motor. The positioning coil is energized with output from the power supply to retract the transducer assembly to the ramp, responsive to the retract signal. The positioning coil is also energized with back voltage generated from the spindle motor to retract the transducer assembly to the ramp.
In accordance with the present invention, a disc drive system for unloading a transducer assembly from a disc is provided. A spindle motor rotates the disc at a first rotational velocity being a normal operational velocity of the disc drive system. A spindle motor control module removes power provided to the spindle motor. A positioning coil coupled to a power supply moves the transducer assembly relative to the disc. A back voltage switching module diverts back voltage generated from the spindle motor to supplement the power provided to the positioning coil by the power supply, res

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