Embodiments of the present invention relate generally to the field of adjusting the fly height of a sensor and, more particularly, to contact detection.
Magnetic storage disk drives includes one or more disks having a magnetic surface for storing data on concentric tracks. The disks are rotated about a central spindle at a spin rate that depends on the particular disk drive. Data is written to and read from the magnetic disk by a magnetic transducer positioned above the disk surface. The transducer typically includes a read head to read data from the disk and a write head for writing data to the disk.
To write data to or read data from the storage disk, the transducer is positioned above the storage disk while the storage disk is spinning. The transducer is positioned on a slider which is generally mounted on a gimbaled flexure portion. The gimbaled flexure portion is attached to one end of a suspension's load beam assembly. An opposite end of the suspension's load beam assembly is attached to the in-line rotary voice coil actuator, which provides pivotal motion to slider. A spring biases the load beam and slider with the read/write transducer towards the storage disk, while the air pressure beneath slider developed by storage disk rotation relative to slider pushes slider away from the storage disk. The gimbaled flexure enables slider to present a “flying” attitude toward the storage disk surface and follow its topology. An equilibrium distance defines an “air bearing” and determines the “flying height” of the transducer. Although the separation between the transducer and storage disk created by the air bearing reduces transducer efficiency, the avoidance of direct contact of the slider with the storage disk improves reliability and extends the useful life of the read/write transducer and storage disk.
For typical disk drives, nominal flying heights are on the order of 0.1 to 0.5 micro inches. For a given transducer, the magnetic storage density of the disk increases as the space between the transducer and the storage surface of the storage disk is reduced. Thus, a very low flying height is desirable and must be balanced with transducer reliability over a reasonable service life of the storage disk drive.
During operation, flight height adjustments occur through the use of a thermal control module. The thermal control module typically includes a heater circuit which, when heated, actuates the transducer. As a voltage is applied to the thermal control module and the heater circuit is heated, the transducer is moved downward toward the surface of the disk. With sufficient voltage or power applied, the transducer or the slider on which the transducer is mounted may make contact with the disk surface.
Conventional disk drives detect contact between the slider and the disk surface via detection of friction between the transducer and the disk surface. The friction is detected by way of a position error signal from the disk drive resulting from the contact. This manner of detecting contact requires sufficient contact to be made to cause the friction. Such hard contact can result in reduced reliability of the disk drive.