Theoretical and experimental study of lateral tape motion (LTM)

Lateral Tape Motion (LTM) is defined as the time-dependent displacement of magnetic tape perpendicular to the tape running direction (cross-track) and is measured using tape edge sensors. Using a servo system, the read/write head can follow the LTM up to a cutoff frequency imposed by the bandwidth of the head actuator. State of the art actuators have a bandwidth up to 500 Hz. High frequency LTM is referred to as the LTM which cannot be followed by the read/write head actuator, i.e., LTM with a frequency greater than 500 Hz.

High frequency lateral tape motion is a key problem in tape technology, since it limits the maximum achievable track density in a tape drive. To reduce high frequency LTM, it is important to identify and control all sources of lateral tape motion. The most important sources of high frequency LTM are edge contact between tape and tape drive components, non-repeatable roller axial run-out, air induced flutter and tape tension transients. Fig. 1 (a) shows a typical unfiltered LTM signal while Fig. 1 (b) shows the same signal, 500 Hz high pass filtered. We observe that the unfiltered signal shows a lateral displacement on the order of 60 µm while the high frequency components are on the order of 5 µm.

We are currently working on the following projects:

1. Investigating and characterizing the different sources of LTM.
2. Improving the tribological performace of tapes as they move over guides by introducing laser surface texturing.
3. Developing a dual-stage actuator tape head, that enables high-bandwidth track following capability.

Figure 2: Tape moving over a cylindrical guide surface	Figure 3: Pressure distribution over a dimple created by laser surface texturing