Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-07-13
2004-06-08
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S077080, C360S078140, C360S077020
Reexamination Certificate
active
06747836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to electromechanical servo and other positioning systems and methods for use with magnetic hard disk drives (HDDs), and more particularly, to a position control system and method for disk drive servo positioning in an HDD system that utilizes two mechanically connected but separately positionable actuator assemblies in a dual stage configuration to position a read-write head relative to a magnetic disk.
2. Relevant Background
Millions of HDD systems are produced every year and competition for the revenue from the sale of these HDD systems has resulted in a demand for cost effective and highly accurate read-write operations. To read or write data on a spinning magnetic disk requires accurate dynamic, ongoing positioning of a read-write head in a HDD system relative to a desired track on the magnetic disk. Because measuring the actual position of the head is difficult and expensive to achieve, HDD system manufacturers have dispensed with position sensing. Instead, HDD systems presently use position control systems that position the head using relative track position information obtained or read directly from data contained on the disk itself.
For many conventional HDD systems (such as the HDD system
10
shown in FIG.
1
), the absence of this measurement is of minor importance because the actual track position varies in space due to runout. As shown, a conventional HDD system
10
may include an actuator assembly
12
with a pivoting actuator
14
that positions a read/write head
16
by positioning or moving an actuator arm
18
relative to tracks on the magnetic disk
20
. Often, the actuator
14
is a current driven voice coil motor (VCM). Runout is the deviation from perfect concentric circles of the positions of the tracks on the magnetic disk
20
and includes deterministic or repeatable runout and random or nonrepeatable runout. Due to the existence of runout, the relative position of the head
16
with respect to a track on the magnetic disk
20
is more important and useful for controlling the position of the head
16
by operating the VCM actuator
14
for reading and writing of data.
The track position data read or obtained via the head
16
is contained in specific areas of the magnetic disk
20
surface called servo wedges
22
. There are typically fifty to one hundred equally spaced servo wedges
22
on the surface of each magnetic disk
20
. The position data includes track number (and/or cylinder number for multiple disk systems
10
) and burst information that quantifies the position offset of the head
16
from a center line of the track currently being read by the head
16
.
A conventional position control system
30
is shown in the block diagram of FIG.
2
. The position control system
30
utilizes a feedback position control approach to position the head
16
relative to a particular track on the magnetic disk
20
. As shown, an input command signal or input variable
32
is provided to a VCM controller
34
which processes the signal
32
and passes a useful control signal
36
to the mechanical system
38
(such as actuator assembly
12
). The mechanical system
38
further processes the control signal
36
to address such variables as nonlinear friction
40
, torque bias and viscous friction
42
and then acts to position the actuator arm
18
and read/write head
16
along the track center line as commanded by the input set point command
32
. The position control system
30
(e.g., the HDD electronic system) processes the track number and center line offset in signal
44
read by the head
16
. The effect of runout is modeled by adding a disturbance in the form of a signal
46
to the (unmeasured) absolute position in the feedback section to form a composite position error signal (PES)
48
. The PES
48
is fed to the VCM controller
34
as feedback that is used to update and/or correct the position of the read/write head
16
. The actual angular position, y
pa
50
, is not measured by the control system
30
.
To provide a competitive edge, HDD systems are being designed and configured with much higher track density to allow storage of more data on similarly-sized magnetic disks. While providing more data storage, these higher track densities have created problems in controlling the position of the read/write heads rapidly with acceptable accuracy. High track density HDD systems place high demands on the control system for resolution and the control system needs to have sufficient bandwidth or capacity to provide useful rejection of disturbances, such as mechanical vibration.
In HDD systems, such as the system
10
shown in
FIG. 1
, the resonant structural modes of the actuator arm
18
are excited by rapid acceleration during slewing (i.e., a rapid change of position when the system
10
moves at full speed from one track position to another) and rapid decelerations while braking to a stop. Excitation of resonant structural modes causes mechanical vibration resulting in unwanted movement of the head
16
that makes accurate tracking of the position of the head
16
very difficult, especially in the presence of runout. Due to the stiffness and length of the actuator arm
18
, conventional VCM-based actuator assemblies
12
such as that shown in
FIG. 1
can have very high resonant frequencies, e.g., in the kilohertz range, that require bandwidths in control systems to be large, such as 500 to 800 Hertz. Even with these larger bandwidths, existing control systems are often incapable of quickly and accurately controlling head position. Hence, HDD system designers and manufacturers continue to demand new actuator assemblies to overcome vibration problems. However, changes to the actuator assemblies create new and often unexpected challenges in providing a system and method for controlling the position of the head relative to the magnetic disk.
Hence, there remains a need for an improved method and system for identifying and controlling the positioning of a read/write head relative to tracks on a magnetic disk. Preferably, such a system would enable high performance track following of magnetic track position in the presence of runout and at least in some embodiments, provide high accuracy of positioning of a head without the use of external motion and/or position sensing devices.
SUMMARY OF THE INVENTION
The present invention addresses the above discussed and additional problems by providing a position control system and associated method for providing accurate and efficient control over an actuator assembly in a disk drive system. The actuator assembly includes a primary actuator, such as a VCM actuator, with a large stroke for positioning or pivoting a primary actuator arm to obtain rapid and larger movements to rapidly position a head near a desired track on a disk. The actuator assembly also includes a secondary actuator with a small stroke mounted pivotally on the primary actuator arm for positioning a secondary actuator arm that supports the read/write head over the centerline of a desired track. The position control system includes a primary actuator controller, a secondary controller and a feedback system that in combination are uniquely adapted for independently controlling each of the actuators to overcome prior difficulties with mechanical vibration, saturation and locking of the secondary actuator.
More particularly, a position control system is provided for use in a disk drive system for positioning a head relative to a storage disk in response to an input command signal. The disk drive system includes a primary actuator for positioning a primary actuator arm and a secondary actuator linked to the primary actuator arm for positioning a secondary actuator arm on which the head is mounted. The position control system includes a feedback system or circuit for receiving the input command signal, for splitting the input command signal into a primary and a secondary input command signal and for modifying the primary and secondary input command signal
DeLellis Joseph R.
Stevens Arthur L.
Kubida William J.
Sniezek Andrew L.
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