Dynamic magnetic information storage or retrieval – Fluid bearing head support – Disk record
Reexamination Certificate
2001-09-25
2003-05-06
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Fluid bearing head support
Disk record
C360S236100, C360S236200
Reexamination Certificate
active
06560071
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data storage systems and, more particularly, to a disc head slider for communicating with a recording medium.
BACKGROUND OF THE INVENTION
Disc drives of the “Winchester” and optical types are well known in the industry. Such drives use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers, which write information to and read information from the disc surfaces.
An actuator mechanism moves the sliders from track-to-track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each head gimbal assembly. The suspension includes a load beam and a gimbal. The load beam provides a load force which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam, or is integrated in the load beam, to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
The slider includes a bearing surface, which faces the disc surface. As the disc rotates, the disc drags air under the slider and along the bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the bearing surface, air compression along the air flow path causes the air pressure between the disc and the bearing surface to increase, which creates a hydrodynamic lifting force that counteracts the load force and causes the slider to lift and fly above or in close proximity to the disc surface.
One type of slider is a “self-loading” air bearing slider, which includes a leading taper (or stepped-taper), a pair of raised side rails, a cavity dam and a subambient pressure cavity. The leading taper is typically lapped or etched onto the end of the slider that is opposite to the recording head. The leading taper pressurizes the air as the air is dragged under the slider by the disc surface. An additional effect of the leading taper is that the pressure distribution under the slider has a first peak near the taper end or “leading edge” due to a high compression angle of the taper or step, and a second peak near the recording end or “trailing edge” due to a low bearing clearance for efficient magnetic recording. This dual-peak pressure distribution results in a bearing with a relatively high pitch stiffness.
The bearing clearance between the slider and the disc surface at the recording head is an important parameter to disc drive performance. As average flying heights continue to be reduced, it is important to control several metrics of flying height performance, such as flying height sensitivity to process variations, take-off performance and vibration damping capability.
Fly height loss due to manufacturing process variations has been observed to be an increasing source of intermittent head/media contact, as flying heights continue to be reduced, especially at sub half-microinch flying heights. Intermittent contact induces vibrations that are detrimental to reading and writing quality at such low flying heights. In addition, the ability of the air bearing to dampen vibrations and provide good take-off performance has been shown to be a critical factor in enabling sub half-microinch flying heights.
Slider air bearings possess three degrees of freedom, vertical motion, pitch rotation and roll rotation. These three degrees of freedom are associated with three applied forces, which include the preload force imposed by the load beam and the suction and lift forces developed by the air bearing. A steady-state flying attitude is achieved when these three forces balance each other.
At the steady-state flying attitude, the fluid bearing possesses intrinsic stiffnesses with respect to its three degrees of freedom. These stiffnesses are referred to as vertical, pitch and roll stiffness. In addition, contact stiffness is defined as a vectorial combination of the slider pitch stiffness and the slider vertical stiffness. Contact stiffness characterizes the vertical stiffness of the slider at the particular location of the pole tip. Contact stiffness, Kc, is defined as:
Kc
=
Kp
Kp
Kz
+
b
2
EQ
.
1
where “Kp” is the pitch stiffness, “Kz” is the vertical stiffness and “b” is the distance between the slider pivot point and the pole tip.
Manufacturing variations can cause variations in the pitch static angle (PSA) or the preload force, which impose variations in the slider flying attitude. However, increasing the pitch stiffness and vertical stiffness of the air bearing results in a larger resistance to variations in the slider's flying attitude. An increase in pitch and vertical stiffness can be achieved by generating more suction and lift force per unit area of the air bearing.
In general, contact stiffness (or “local pole tip stiffness”) is related to the amount of lift and suction force located at the vicinity of the pole tip, which is typically near the trailing edge of the slider. Therefore, moving the center of suction within the cavity closer to the pole tip can result in higher contact stiffness. The center of suction can be moved toward the trailing edge by reducing the depth of the cavity, increasing the depth of the “step” surfaces, or lowering the cavity/step depth ratio to produce a suction force that is more spread within the cavity. Increasing the cavity/step ratio has the tendency to create the center of suction closer to the cavity dam.
Also, at a given pitch angle, an increase in linear velocity will tend to spread the suction force within the cavity, thus moving the center of suction towards the trailing edge. This suggests interaction of two parameters on the location of the center of suction: (1) linear velocity; and (2) cavity/step depth ratio. Designing an air bearing for higher suction towards the pole tip can therefore include selecting the correct cavity/step depth ratio at a given linear velocity, which is dictated by the spindle speed and radius configuration of the disc drive. However, moving the center of suction towards the pole tip has been shown to compromise take-off performance, which degrades contact start-stop performance.
Another concept that has been proposed for increasing suction force near the pole tip is a “suction at trailing edge air bearing”, which can be achieved by moving the location of the cavity toward the trailing edge. However, this design does not fully utilize the large surface area on the slider located near the leading edge. This results in a loss of real estate that could have been utilized to increase suction and lift forces, which is known to increase air bearing stiffness and further decrease sensitivity to manufacturing process variations.
Improved slider bearings are therefore desired which minimize sensitivity of the slider to manufacturing variations by increasing contact stiffness while also enhancing take-off performance and improving damping capability of the slider.
SUMMARY OF THE INVENTION
One embodiment of the present invention is directed to a disc head slider which includes a slider body having a disc-opposing face with leading and trailing slider edges, a slider length measured between the leading and trailing slider edges, a bearing surface, a recessed area, an inlet and a convergent channel. The recessed area is recessed from the bearing surface. The inlet has a leading channel end, which is open to air flow from the leading slider edge, channel side walls and a trailing channel end. The convergent channel has a leading channel end, which is open to fluid flow from the inlet, channel side walls and a trailing channel end, which is closed to the fluid flow. The trailing channel end of the convergent channel is located along the slider length rearward of at least a porti
Boutaghou Zine-Eddine
Chapin Mark A.
Mundt Michael D.
Ryun Scott E.
Sannino Anthony P.
Cao Allen
Seagate Technology LLC
Westman Champlin & Kelly
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