The Ohio State University

Effect of magnetic Tape Thickness on Durability and Lateral tape motion Measurement and modeling in a Linear Tape Drive

Thomas George Hayes IV
B.S. M.S. Thesis,
Department of Mechanical Engineering, August 2006

ABSTRACT

Development of advanced magnetic tapes is needed to accomodate the ever-increasing requirements to store large amounts of data. The advancements that are being made concern the construction and data format on the tape in order to increase the total amount of data that can be stored per unit volume. Changes in construction include moving to thinner substrates and coatings so a greater length of tape may be wound on a cartridge. These changes include moving away from magnetic particle (MP) tapes to sputtered and metal evaporated magnetic layers and coating both to minimize the thickness of the layers as well as to increase the areal density of the media. As the media and drives become able to write narrower and narrower tracks, lateral tape motion (LTM) becomes increasingly problematic.

Tests were conducted to evaluate the durability of MP tapes both magnetically and tribologically, and the influence of tape thickness on LTM was studied. The parameters studied were debris accumulation, edge damage, LTM amplitude, LTM frequency spectrum, and coefficient of friction. Magnetically, signal level and dropouts were monitored. A new method of measuring LTM was developed which used a video camera to monitor a tape with a longitudinal reference mark. This method was compared to the traditional optical edge probe method which is unsatisfactory because is convolves repeatable tape motion and edge defects into the LTM measurement. In order to better understand the mechanics of LTM, a vibration model was developed which accounted for the axial motion of the tape and was compared to dynamic and static experimental results.

Results of the experiments show that the thinner substrate tape exhibits lower LTM but higher coefficient of friction and debris generation. Videographic measurement of LTM proved to be successful and succeeded in rejecting some repeatable motion and edge defect contributions and correlated very well with the optical edge probe with a measurement resolution on the order of 1 µm. Limitations in this iteration proved to be a limited frame rate of the video equipment and no reliable method to mark the tape in-situ to approximate a magnetic signal written by the head. The vibration model was verified with both static and dynamic tests. The model also shows that the natural frequencies are lowered with increased axial velocity due to the gyroscopic nature of the system. These gyroscopic forces also result in deformed mode shapes and can render the system unstable.