Experimental and numerical investigation of effect of stick-slip friction transition on lateral vibration of magnetic tapes
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Magnetic tape storage which is primarily used for long-term archival and backup of digital data, has historically been the most efficient, high-capacity and least expensive storage technology for huge quantities of data. Tape storage applications are in diverse fields such as corporate and government financial records, satellite imagery, credit card databases and patient medical records. Recently, the Linear Tape-Open (LTO) Ultrium format has emerged as the most dominant tape technology option in the mid-range tape drive market, with the LTO generation 5 (LTO-5) being capable of holding as much as 1.5 TB of uncompressed data on a single cartridge. Tape storage however has been traditionally challenged by competing technologies like hard disk drives (HDD), consumer optical storage devices which include CDs, DVDs and Blu-ray disk technologies, optical library systems and holographic storage systems. Thus, one of main goals of the tape industry is to design and manufacture advanced tape storage technologies that aim at reducing the price per unit data storage ($/GB).
In commercial tape drives, a flexible magnetic tape is transported between the supply and take-up packs at a fixed axial tension and transport speed and over edge and surface guides and read/write heads. The tape decks must assure accurate guiding and transport of the tape while it accelerates and decelerates by holding the axial tension constant. During transport, lateral in-plane vibration of tape's narrow edge causes misalignment between data tracks on the tape and position of read/write head and leads to reduced storage capacity. Lateral vibration (low and high frequency) is caused by excitation sources viz. pack run-out, flange impacts, pack tilts and tape edge weave. High frequency lateral vibration is more detrimental as it is difficult to move the read/write head to follow the tape's high frequency motion. To attenuate this vibration, surface guides (rollers or stationary guides) which control the lateral displacement of tape by applying friction on its wider surface, are used. Choice of an appropriate surface guide (or roller) is possible with an understanding of the physics involved in the surface friction between magnetic tape's wide surface and the roller.
This thesis is motivated by the need to conduct a detailed investigation into the frictional interaction between roller surface and magnetic tape and contribute towards the advancement of tape technology to meet the growing market needs. A parametric study is carried out with respect to the tape's axial tension and axial velocity in the following two aspects:
* An experimental setup is used to control these tape parameters and obtain lateral vibration measurements at two points equidistant from the tape-roller interface to understand the effect of stick-slip friction at the interface on tape's lateral vibration
* A numerical model is developed to study stick-slip friction between the roller surface and the tape that travels over it. The tape is modeled as an axially moving, tensioned, viscoelastic Euler-Bernoulli beam subjected to boundary disturbances arising from supply and take-up pack run-out and stick-slip friction between tape and roller surface.
These analyses are used to predict the possibility of sticking or slipping between the surfaces in contact, as a function of parameters viz. axial tension, axial velocity, surface roughness of roller and span length. A `dynamic phase diagram' is constructed to determine the regions in the stiffness-velocity phase-space where steady stick-slip motion occurs and its effects on lateral vibration of the magnetic tape.