Reducing the Magnetic Tape/guide Friction Coefficient by Laser Surface Texturing: Experimental Analysis

The friction coefficient is an important parameter in designing magnetic tape transports. We have introduced laser surface texturing to reduce the friction coefficient between guides and magnetic tape. The surface features enhance the formation of an air bearing and hence, reduce the friction coefficient. INTRODUCTION Lateral tape motion (LTM) is defined as the time-dependent motion of the tape, perpendicular to the tape transport direction. It is a friction related phenomenon that can cause track misregistration [1]. Although friction between tape and tape drive components was observed to attenuate lateral tape motion [2], it is well known that tape drives with pressurized air bearing guides instead of rotating guides exhibit significantly lower LTM than tape drives with rotating guides [3]. Eliminating rotating tape drive components suppresses lateral tape motion due to run-out of those components. However, pressurized air bearing guides require an external compressor which is an obstacle for commercialization of this type of tape drive. This paper explores the possibility of creating an efficient low speed air bearing between a magnetic tape and a cylindrical guide, thereby expanding the speed range of low friction. LASER SURFACE TEXTURING Laser surface texturing (LST) is a well established technique [4] to create semi-spherical dimples on the surface of tribological components, by means of a material ablation process with a pulsed laser [5]. These dimples act as microhydrodynamic bearings, thereby creating a local pressure increase between the sliding surfaces. This, in turn, increases the load carrying capacity for such bearings and reduces the friction coefficient for a constant load. We have investigated laser surface texturing of magnetic tape guide surfaces in order to reduce tape/guide friction. EXPERIMENTAL SET-UP The experimental set up, shown in Fig. 1, consists of a guide mounted on an adjustable speed DC-motor. A tape sample is positioned over the guide surface and is connected to a load cell that measures the tension 1 T at one end, while at the other end it is subjected to a known tension 2 T by a dead weight (see Fig. 1 a)). The load cell is mounted on a sled that can slide in a circular groove to allow a variable wrap angle. Fig. 1 b) indicates the forces 1 T and 2 T and the wrap angle θ . The wrap angle was taken 90° for all experiments with MP tape and 45° for all experiments with ME tape. The measured force 1 T combined with the known “slack side” tension 2 T and the wrap angle θ enable calculation of the average friction coefficient f from the ratio 1 2 / T T and the classical belt/pulley equation, given e.g. in [6]