1. Field of the Invention
The present invention relates to magnetic recording devices. More specifically, the invention relates to a partial or pseudo contact slider head with a magnetic transducer used for writing data to and reading data from a recording medium such as a magnetic disc.
2. Description of the Related Art
Magnetic recording systems transfer data through transducers that are supported by an air bearing film or layer as they move relative to the surface of a magnetic recording disc. Such transducers need to either "fly" (flying-type heads) at just a few micro-inches above a rotating disc surface or contact the rotating disc slightly (pseudo contact-type heads) within a safe range.
The air bearing film is produced by pressurization of the air as it flows between the rotating disc surface and the slider body. For pseudo contact heads, the air bearing functions to provide, without hard physical contact, a very thin clearance between the slider body and rotating disc. This minimizes surface wear and damage to the partial or pseudo contact head and magnetic disc during operation while maintaining a close separation to ensure a high density magnetic recording structure.
As the nominal flying height (distance between the slider body and the rotating disc surface) of the pseudo contact slider decreases, the magnetic transducer achieves higher resolution between individual data bit locations on the disc. Therefore, to achieve a higher recording density the flying height must be reduced as much as possible without causing reliability problems. Problems can occur when excessive and unwanted variations in the flying height result in hard contact between the pseudo contact slider and the rapidly rotating recording medium. Such hard contact leads to wear of the slider and the recording surface, and in certain conditions, can be catastrophic to the operation of the disc drive.
Accordingly, developments efforts continue to strive for lower and lower flying heights while trying to provide uniform or optimum flying height conditions across a range of flying conditions, such as tangential velocity variations from the inside to the outside tracks, high speed track seeking movement, and varying skew angles.
Disc circumferential speed increases linearly from the inner diameter (ID) to the outer diameter (OD) of the rotating disc. Because a slider typically flies higher as the velocity of the disc recording medium increases, there is a tendency for the slider's outer rail to fly higher than the inner rail. Therefore, the pseudo contact slider has a structure that ensures that a roll angle can be generated in an attempt to counteract the tendency of the outer rail to fly higher than the inner rail. The roll angle is defined as the tilt angle between the principal plane of the slider in the radial direction of the disc and the principal plane of the disc surface.
The ability to control or generate changes in the roll angle are important to counteract other forces generated during disc drive manufacture or operations. Some of these forces or factors that must be compensated for include: manufacturing errors in the gimbals which attach the slider to the suspension arm; dynamic forces applied to the air bearing slider by the track accessing arm during tracking accessing; and varying skew angles tangential to the disc rotation as measured from the slider center line.
For example, regardless of the particular skew angle with respect to the direction of air flow, unequal pressure distribution develops between the outer and inner side rails. This causes the slider to fly with the inner rail much closer to the disc surface than the outer rail. As a result, the probability of physical contact with the disc surface at this slider's minimum flying height increases. Therefore, there is a continuing effort to develop air bearing sliders that carry a transducer as close to the disc surface as possible with a constant flying height and roll angle regardless of the varying flying conditions such as disc velocity and skew angle variation.
To achieve stable flying characteristics, the slider should also fly at a pitch angle that falls within a safe predetermined range. The pitch angle is defined as the tilt angle between the principal plane of the slider body in the tangential direction of the rotating disc and the principal plane of the disc surface. The pitch angle is positive in the normal case in which the flying height of the rear portion of the slider is lower than that of the front portion of the slider. A transducer is generally situated at the lowest position of the rear portion of the slider. If the designed positive pitch angle is too small, the possibility exists that the slider will dip down or inadvertently transition to a negative pitch angle orientation, caused by internal or external interference for example, whereby the leading edge of the slider may hit the rotating disc. On the other hand, if the designed pitch angle is too large, the air stiffness needed for stable flying can be disadvantageously reduced, which may again result in a collision with the disc. Therefore, to maintain stability while avoiding the negative pitch angle situation, the slider should be configured such that the pitch angle can be controlled to fall within an optimum range.
Another factor to consider regarding pitch angle is the general tendency for the pitch angle to increase when the skew angle increases as the slider is positioned nearer to the outer diameter of the disc. Thus the pitch angle should fall within a safe range regardless of the skew angle variations to ensure the desired dynamic performance reliability of the head/disc interface.
FIG. 1 is a schematic perspective view of a conventional tapered flat slider. In FIG. 1, two rails 11a are formed in parallel at a predetermined height on a surface of a slim hexahedron body 10a to thus form lengthwise extending ABS's. A tapered or sloped portion 12a is formed at each leading edge (toward the direction of disc rotation) portion of the ABS rails 11a and a central air bearing island 18 is formed at the trailing edge of the body. In such a structure, air within a very thin boundary layer rotates together with the rotation of the disc due to surface friction. The disc drags air under the slider and along the air bearing surfaces in a direction approximately parallel to the tangential velocity of the disc. When passing between the rotating disc and the slider, the air is compressed by the ramp 12a on the leading edge of the rails 11a. This pressure creates a hydrodynamic lifting force at the ramp section which is sustained along each of the rails 11a and central island 18 resulting in a lifting force, thus allowing the slider to fly and partially contact the disc surface. Actually, the side rails 11a and central island 18 function as a pneumatic bearing, and thus have a positive pressure region at a portion along an axis of an air flow generated by a rotation of the magnetic disc.
Although this conventional slider is easily and economically fabricated, it suffers drawbacks in that the flying height, pitch angle and roll angle vary considerably according to the skew angle of the rotary type actuator, i.e., according to the radial position of the slider over the disc surface. In effect, the lifting force is reduced because of the skew angle, which reduces the flying height. Also, the skew angle causes a rolling motion such that the flying height is not uniform under both of the side rails 11a. For flying heights of 3.0 millionths of an inch and greater, minor height and tilt fluctuations in the slider do not generally affect the read/write operations of the disc. However, current-day standards require flying heights below 2.0 millionths of an inch. At such small flying heights, even minor variations in flying height, pitch angle and roll angle can severely affect the reliability of the head read/write function of a hard disc drive.
In light of the above, and to better realize a constant flying height and constant pitch and roll angles and to obtain an improved contact start stop (CSS) performance, most current air bearing sliders have adopted a negative pressure air bearing (NPAB) type of configuration as shown in FIG. 2. Such a slider has the same conceptual structure of the slider shown in FIG. 1, together with a cross rail connecting the ABS rails. That is, as shown in FIG. 2, two ABS rails 11b, each having a slope 12b at a leading edge thereof, are formed in parallel on a surface of a body 10b. A cross rail 13b having the same height as the ABS rail 11b is formed near the leading edge between the rails 11b proximate the slopes 12b. The cross rail 13b creates a negative, or sub-ambient pressure cavity 15b in proximity to the central surface portion of the body 10b downstream of the cross rail 13b. Thus, since the pressure of the air passing over the cross rail 13b is diffused as it passes the negative pressure cavity 15b, a pulling or suction force is downwardly applied on the slider which reduces suspension gram load and provides the advantage of a fast take off from the disc surface. The counter action between the positive and negative forces reduces the sensitivity of the slider flying height relative to disc velocity and increases the slider stiffness characteristics.
Nevertheless, the NPAB slider of FIG. 2 does suffer some drawbacks. For example, the amount of negative pressure in the cavity 15b is dependent on the air flow direction, meaning that differing pressures will exist at differing skew angles. This results in a non-uniform operation along the full diameter of the disc. In particular, higher skew angles may cause more severe negative roll fluctuations compared to conventional tapered flat slider. Also, there is a tendency for debris to gather at the cross-rail 13b in the forward cavity 16b. Such debris can ultimately have an adverse effect on performance since the accumulated particles may cause head crashes and undue wear of the head and disc.