A simple tool was developed to evaluate ramp/tab friction during dynamic ramp load/unloads on component level test stands for hard-disk drives. By extracting key attributes of each load/unload time-varying friction cycle, multiple valuable engineering studies were performed. A screening test of candidate ramp materials revealed a strong correlation between friction and wear, with acetal homopolymer and aliphatic polyketone being the most attractive choices. The rate of change of friction with temperature can significantly vary between materials. Data are also presented on friction versus load/unload cycles (showing the onset of wear), load velocity and tab roughness. With knowledge of extreme friction values on each section of the load ramp (slope, top, detent), their influence on actuator torque during load and unload can be calculated and included in tolerance analyses. It is shown that friction can play a significant role in multi-disk drives.
The technique of Suk et al.[1] is used to measure in-situ wear and debris generation versus suspension lift-tab roughness during ramp load/unload on a polyoxymethylene (POM) ramp. Image processing isolates depressed and raised portions on the ramp which are proportional to wear and debris, respectively. Both wear and debris grow logarithmically and are respectively proportional to average roughness ( ) and peak roughness ( ) as determined by Wyko measurements of the spherical lift-tab. As roughness tends toward zero, both are (not surprisingly) minimized. With a very smooth lift-tab wear is more accurately characterized as "deformation" and debris is almost absent. High roughness can increase initial coefficient of friction and require a substantial wearing-in period.
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