An overview of glide testing

Abstract

Low flying air-bearings, "sliders," with contact sensors are used to "glide" test magnetic recording disks to be free of asperities above a predetermined height. A technical overview of the considerations necessary for accurate glide testing is illustrated by the example of an experimental flat plate PZT sensor, with electrodes divided into quadrants, to detect asperity contact. The flat plate PZT sensor detects the slider dynamic pitch, roll, and vertical vibrations of the air bearing by contact with asperities of sufficient mechanical stiffness. The sensor also detects contact by the extremely sensitive response of the resonant vibrations of the pZT/slider structure. Different linear combinations of the signal from the quadrants show mode selection based on mode symmetry. The signal response for increasing asperity interference is characterized for specific modes and a mode can be chosen by the appropriate linear combination of the signals from the quadrants. Calibration of the glide slider trailing edge flying height and roll using contact with artificial bumps of different heights is necessary for accurate glide testing. One can map the entire disk surface using the contact signal from both the air-bearing response and the bending mode response simultaneously to identify mechanically "stiff" asperities. Visualization of the mode shapes and characterization the PZT/slider structure using a laser heterodyne interferometer aid in the consistent fabrication of this class of PZT contact sensors. The considerations of sensor response, characterization of the contact signal, techniques to allow consistent PZT/slider fabrication, and calibration methods that allow the signal to be related to the test tolerances represent a technical overview of the requirements for any glide sensor technology.