Dynamic information storage or retrieval – Detail of optical slider per se
Reexamination Certificate
1997-02-21
2001-01-23
Klimowicz, William (Department: 2754)
Dynamic information storage or retrieval
Detail of optical slider per se
C360S294700
Reexamination Certificate
active
06178157
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to suspension systems for flying disk drive heads. More particularly, the invention relates to suspension systems for flying disk drive heads in which the head is caused to fly at a minimum glide height by adjusting the load force applied to the head in a direction normal to the disk surface while the disk drive is engaged in normal operation.
BACKGROUND OF THE INVENTION
High density disk drive systems based on magnetic, magneto-optic and optical storage principles generally use a transducer system which does not, under normal operating conditions, contact the surface of the recording medium. Such non-contact transducers are known in this art as flying heads because of the principles upon which they rely to maintain a correct position with respect to the surface of the recording medium.
A brief description of how a flying head flies is now given, with reference to FIG.
15
.
During operation of a disk drive, the recording medium, typically in the form of a specially coated disk of aluminum, glass or plastic, rotates at high speeds, e.g., 3600 RPM. The rotary motion of the disk
107
causes an air flow in the direction of rotation, near the surface
106
of the disk
107
. The head
101
is placed by a mechanical actuator or load arm
103
in proximity with the surface
106
of the disk so that the air flow passes between the surface of the disk and the lower features of the head, thereby forming a cushion of air
108
which generates an upwards force F
A
on the head
101
due to air pressure in the space between the disk surface and the lower features of the head
101
, with the lower features of the head defining an air bearing surface
110
. The cushion of air
108
that develops between the air bearing surface
110
and the surface
106
of the disk is referred to hereinafter as an air bearing.
The flying head
101
flies at a flying height
113
, defined herein as the separation distance between the air bearing surface
110
of the head
101
and the surface
106
of the disk, determined by the force balance between the air pressure F
A
of the air bearing
108
pushing the head
101
away from the surface
106
of the disk, and a downward force F
L
exerted through a spring
105
or suspension that mounts the head
101
to the load arm or actuator
103
.
The force F
L
has a magnitude determined by the physical dimensions of the spring, the spring constant of the spring material and the deformation of the spring which occurs in operation. The upward force F
A
applied by the air bearing depends on the finish of the disk surface, the linear velocity of the disk surface where it passes under the head, and the shape and size of the air bearing surface of the head. Whenever F
A
and F
L
are not equal, the head experiences a net force which causes it to move in a vertical direction corresponding to the direction of the net force. When F
L
=F
A
the head experiences no net force, and hence no vertical motion.
In conventional systems, as flying height
113
increases, the air bearing
108
grows, lowering F
A
, while spring
105
is compressed, raising F
L
. The relationship between each of the forces F
L
and F
A
and flying height
113
can be determined by application of aerodynamic principles to the system configuration, which can be done by making measurements on actual systems, or physical or computer-generated models of the system. The conventional system is designed so that F
L
=F
A
at the desired flying height when the disk
107
is spinning at its normal speed. When the disk spins down, i.e., slows to a stop, insufficient air flow occurs to maintain the air bearing between head and disk. Hence, insufficient air pressure and force are generated to counteract the downward force exerted by the spring or suspension, leading to contact between head and disk. Thus, when the disk
107
slows to a stop, the head
101
may come to rest on the disk surface
106
. Alternatively, the disk drive may include a mechanism that lifts the suspension
103
to prevent contact between the head and the disk when the disk spins down, but otherwise plays no role in normal disk drive operation.
Flying height
113
is one important parameter governing successful operation of a disk drive. At extremely large values for flying height
113
, excessive distance from the disk can cause unacceptable functional performance, for example, an inability to discriminate high frequency signals. Close proximity of the head to the disk improves functional performance. However, at extremely small values for flying height
113
, insufficient flying height or loss of separation between the head and the disk can result in aerodynamic instability, reliability problems and catastrophic product failure, e.g., a head crash which occurs when the head contacts the disk surface with sufficient force to cause damage to the head or the disk surface resulting in a loss of data. Avoiding potential damage often associated with contact between head and disk is the reason that some disk drives move their heads away from the disk surface to avoid contact when the disk spins down. The lowest height at which the head can fly without making contact with the disk surface is defined as the minimum glide height for the disk. Asperities, (i.e., microscopic bumps or roughness) in the disk surface are those features which are likely to be contacted first by the head.
One problem of disk drive manufacturing is that the physical parameters determinative of flying height. e.g., the spring characteristics (affecting load force), the design of the air bearing surface shape, manufacturing variations in the air bearing surface geometry and finish (affecting air bearing force), and the load arm position relative to the surface of the disk (affecting load force), exhibit some variation within a tolerance band which causes a corresponding variation in the load force or air bearing force and, in turn, flying height. Other sources of variation in flying height in a disk drive include variations in altitude (i.e., ambient air density), radial position of the head on the disk which varies the velocity of the air flow due to different track circumferential lengths at different track radii, and skew angle of the head relative to a line tangential to a track, all of which affect the air bearing force.
Conventionally, flying height is set by a mechanical adjustment made at the time of manufacture of a disk drive. The mechanical adjustment sets a static load force selected to provide a desired flying height under nominal conditions. For example, the static load force may be measured manually and adjusted by repositioning or bending the load arm
103
. Once set, the static load force remains substantially unaltered for the life of the disk drive, despite variations in operating conditions which may cause variation in other parameters determinative of flying height. Conventional systems are also known which employ closed loop feedback control systems to maintain a substantially constant flying height. Although such systems can compensate for variations in some parameters, there remain other uncompensated tolerance errors, such as variation in the actual minimum glide height from one disk to another.
Thus, flying height in conventional disk drives cannot be set to the minimum glide height. Rather, tolerance variations such as discussed above must be considered, adding a tolerance band to the nominal or design minimum glide height of a disk when setting the actual flying height. Therefore, in order to avoid any likelihood of unwanted contact between the head and the surface of the disk, conventional systems set a nominal flying height that is greater than the largest expected actual minimum glide height.
SUMMARY OF THE INVENTION
The present invention provides an improved method and apparatus for controlling the flying height of a flying disk drive head.
According to one aspect of the invention, there is provided a flying head mechanism having a controllable load force, for use wi
Berg John S.
Lee Neville K. S.
Digital Papyrus Corporation
Klimowicz William
Wolf Greenfield & Sacks P.C.
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