Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
2000-07-10
2001-08-14
Raevis, Robert (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
Reexamination Certificate
active
06272909
ABSTRACT:
BACKGROUND
The present invention relates generally to magnetic recording media and, in particular, to apparatus and techniques for testing the glide height characteristics of magnetic recording media.
Disc drives are the primary devices used for mass storage of computer programs and data. Within a disc drive, a load beam supports a hydrodynamic air bearing slider close to a rotating magnetic disc. The load beam supplies a downward force that counteracts the hydrodynamic lifting force developed by the slider's air bearing. During operation, the magnetic head rides at a distance from the surface of the magnetic disc. That distance must be small enough to allow high density recording while preventing damage that would otherwise be caused by contact between the spinning disc and the magnetic head.
High areal densities currently are achieved by reducing the separation between the disc and the head to less than twenty nanometers (nm). However, some level of disc roughness is required to reduce adhesive forces when the head is at rest. The level of disc surface topography must, therefore, be kept within a tight range to fly the head safely at low altitudes while simultaneously preventing it from sticking to the disc surface when the head is at rest. Thus, the topography of the disc surface is critical to the proper operation of the disc drive.
As part of the process of manufacturing hard files, the quality of a magnetic disc is provided by determining the glide conditions which can be established between the disc and a glide head. In particular, the effect of outwardly projecting defects on the surface of the magnetic disc is studied during glide height testing. When such defects are large enough to close the gap between the magnetic disc and the glide head, the defects strike the glide head. The movement of the glide head can be sensed, for example, by a sensor such as a piezoelectric transducer, which generates an electrical signal indicating the adjacent passage of an outwardly projecting defect.
During testing, a gliding action is brought about as a layer of air, dragged along by the spinning disc surface, is compressed between the surface of the disc and the adjacent surface of the glide head. As a result of the gliding action, the glide head rides at a distance from the surface of the disc. That distance is referred to as the “fly” height of the glide head and is determined, in part, by the peripheral speed of the rotating disc and the air pressure surrounding the disc. Thus, the fly height of the glide disc can be varied by changing the speed at which the disc rotates. A glide avalanche breaking point (GABP), which is used by engineers to characterize the surface of the disc, can be obtained based on the interaction between the disc surface and the glide head at different fly heights.
Several difficulties arise, however, when the linear velocity of the disc is varied to obtain a measure of the glide avalanche breaking point. The impact energy which is detected by a sensor depends on the velocity and, in some cases, is approximately proportional to the square of the velocity. Thus, it can be difficult to interpret the signals received by such a sensor. Furthermore, changing the linear velocity can affect the pitch and roll of the glide head. That, in turn, can affect the level of interference detected by the sensor. Additionally, the relationship between fly height and linear velocity may not be linear at very low speeds, such as speeds less than 200 inches per second, making it difficult to correlate the velocity with fly height.
SUMMARY
In general, glide head apparatus and methods for testing surface characteristics of a disc, such as a magnetic disc, are disclosed. The techniques can be used, for example, to perform glide tests in which the fly height is varied while the linear velocity of the disc remains substantially constant.
According to one aspect, the glide head apparatus includes a gimbal, a slider and an actuator including a piezoelectric material disposed between the gimbal and the slider. A voltage applied across the piezoelectric material is controllable to cause the piezoelectric material to expand or contract depending on the applied voltage so as to vary a distance, such as the fly height, between the slider and a disc under test.
Various implementations include one or more of the following features. The voltage across the piezoelectric material can be controlled by a digital signal processor. The voltage applied across the piezoelectric material can be controlled to vary the fly height of the glide head apparatus without substantially varying the linear velocity of the disc under test. In some cases, the piezoelectric material is expandable over a range of at least about 0.010 inch.
The piezoelectric material can comprise a ferroelectric material, such as lead zirconium titanate. Other piezoelectric materials also can be used. In some implementations, multiple piezoelectric actuators are coupled in series. The voltages across the respective piezoelectric actuators can be controlled to provide a corresponding change in the fly height of the glide head apparatus.
In some embodiments, the glide head apparatus also includes an arm with a load arm, and an actuator for positioning the arm over the disc. The gimbal can be attached to the load arm. The apparatus also can include a transducer for sensing interactions between the slider and the disc under test.
According to another aspect, a method of testing surface characteristics of a disc includes causing the disc to rotate at a predetermined linear velocity with a glide head positioned at an initial fly height above a surface of the disc. The method further includes acquiring data indicative of interactions between the glide head and the disc while the disc is rotating at the predetermined linear velocity. The voltage across a piezoelectric actuator is changed to cause a corresponding change in the fly height between the glide head and the surface of the disc. The act of acquiring data can be repeated once the fly height has been changed.
One or more of the following features are present in some implementations. The act of changing the voltage across the piezoelectric actuator can cause a reduction in the fly height. Furthermore, the acts of changing the voltage and acquiring data indicative of interactions between the glide head and the disc can be repeated until sufficient information is acquired to determine a glide avalanche breaking point for the disc. Acquiring data at different fly heights can be performed while the disc rotates at a substantially constant linear velocity. The acquired data can be used to determine whether the disc passes the glide test.
Various embodiments include one or more of the following advantages. Using a substantially constant linear velocity as the fly height is varied during the glide test makes it easier to interpret the signals indicative of the interaction between the glide head and the disc. For example, the effect of unknown variables, such as the effect the velocity has on the impact energy between the disc and the glide head, can be removed or reduced. Additionally, using a substantially constant linear velocity can reduce the effects on the pitch and roll of the glide head that a changing velocity may cause.
Other features and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims.
REFERENCES:
patent: 4624564 (1986-11-01), Dahlgren
patent: 4862029 (1989-08-01), Kasai et al.
patent: 5021906 (1991-06-01), Chang et al.
patent: 5229951 (1993-07-01), Sugita et al.
patent: 5293094 (1994-03-01), Flynn et al.
patent: 5475488 (1995-12-01), Fukuzawa et al.
patent: 5488857 (1996-02-01), Homma et al.
patent: 5612841 (1997-03-01), Johnson
patent: 5638234 (1997-06-01), Hagen
patent: 5701218 (1997-12-01), Boutaghou
patent: 5703684 (1997-12-01), Lu et al.
patent: 5711063 (1998-01-01), Budde et al.
patent: 5757492 (1998-05-01), Tokutomi et al.
patent: 5774305 (1998-06-01), Boutaghou
patent: 5781378 (1998-07-01), Heitk
Sundaram Ramesh
Yao Wei H.
Fish & Richardson P.C.
Raevis Robert
Seagate Technology LLC
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