V. Kartik

Track-Following High Frequency Lateral Motion of Flexible Magnetic Media With Sub-100 nm Positioning Error

Lateral motion of the magnetic tape in data storage applications misaligns the flexible medium relative to the recording head and reduces the potential for decreasing data track width and spacing, and thereby the achievable data storage density. In order to reduce the effect of misalignment between the tape and the recording head, the head is mounted on a track-following actuator that can compensate for the position error up to a frequency that is governed partly by its mechanical resonances; this bandwidth is typically 1 kHz or less for conventional voice coil-based actuators. This paper introduces the design and implementation of a track-following actuator that is piezo-electrically actuated in order to potentially achieve a significant increase of bandwidth and positioning precision. A proof-of-concept is prototyped and experimental results are presented. An H∞ controller is designed and implemented to compensate for typical disturbances such as periodic runout of packs and rollers, or non-periodic flange impacts. Preliminary closed loop experimental results with an experimental low lateral motion tape path, and conventional servo format and media demonstrate a reduction in positioning error standard deviation to 74.5 nm, with simulations indicating a potential for further improvement to 20.6 nm with the use of improved media and servo format.

High Speed Nanopositioner with Magneto Resistance-Based Position Sensing

Abstract High bandwidth, high resolution nanopositioning is a key enabling technology for nanoscale metrology and manipulation. A scanner design with good dynamical behavior is essential for high speed nanopositioning. Through a combination of high stiffness/rigidity of the flexures, a low carried mass, and direct mechanical connections, an X-Y scanner is designed which has excellent dynamical behavior with the first resonant frequencies beyond 4 kHz in both scan axes. For closed loop operation of such fast scanners, there is a need for high bandwidth, low noise sensing schemes. A sensing concept based on the property of magneto-resistance (MR) shows great potential towards enabling low-noise position sensing over a very wide bandwidth. This paper details experimental studies in achieving high bandwidth nanopositioning through a combination of scanner design with superior dynamical behavior, novel low noise, high-bandwidth MR-based position sensing, and modern control techniques.

Scanning Probe Microscopy using Higher-Mode Electrostatically-Actuated Microcantilevers

Abstract High-throughput scanning probe microscopy can be achieved by employing a large array of microcantilevers in parallel operation. Intermittent-contact operation of the microcantilevers is essential to reduce sample-damage and tip-wear. The first flexural bending mode of the microcantilevers is typically used in various intermittent-contact methods. The throughput of such methods is low due to the low resonant frequency and the high quality factor of the microcantilevers. The intermittent-contact methods often rely on demodulation electronics which renders them unsuitable for parallel scanning probe microscopy applications. In this paper, an intermittent-contact method is presented that uses the higher flexural bending modes of the microcantilevers for high-speed operation. The microcantilevers are electrostatically actuated at a higher normal flexural bending mode such that the tip comes out of contact from the sample-surface during each oscillation cycle. The scanning probe microscopy images are obtained by direct sampling of the micro cantilever deflection signal. This method is suitable for parallel scanning probe microscopy applications. Corroborating modeling and experimental results are presented.

Friction-Induced Dynamics of Axially-Moving Media in Contact With an Actively-Positioned Surface

The dynamics of an axially-moving flexible medium are examined in the context of an application where the medium is partially supported by a frictional surface, that actively-orients itself relative to the direction of transport. The stability and motion of the medium are of interest in a magnetic tape data storage application where the orientation of a sensing surface is continuously altered in order to ‘follow’ the medium’s motion. Moving media that are in contact with such guiding surfaces experience friction excitations induced by the relative motion in addition to what is observed with a stationary guiding surface. Friction-induced bending moments, as well as tension fluctuation beyond the permissible limits for the flexible material can erode the potential benefits of such active positioning. This paper describes some of these dynamic phenomena using the simplified example of a planar guiding surface whose orientation is dynamically altered relative to the moving medium. A physical model for the friction-induced excitation of the moving medium is developed, and the dynamics are analyzed for their effect on critical design parameters such as the achievable bandwidth of the active control algorithm, as well as with respect to constraints on the geometry and positioning of the guiding surface.Copyright