Herringbone grooved aerodynamic journal bearings have better stability characteristics than plane aerodynamic journal bearings. In addition, the use of flexibly supported bearings is one of the efficient way to improve the bearing stability. Therefore, the combination bearing systems have prospects of realization of ultra-high-speed operations. The purpose of this work is to evaluate the effect of external stiffness and damping elements on the bearing stability. The Voigt rheological model was used for the external elements, in which the stiffness and the damping were treated as the linear elements. It was clarified that the stability boundary of the herringbone grooved aerodynamic journal bearings supported by suitable stiffness and damping elements can be heightened more than three times compared with the rigidly supported bearings.
The purpose of this research is to produce microparts reinforced with unidirectional whiskers using laser stereolithography. Electrically conductive whiskers are added to a liquid photopolymer and an electric field is applied to the liquid photopolymer, which aligns the axes of the whiskers along the direction of the electric field. Then, the photopolymer is solidified with UV laser irradiation in a shape that is adjustable. When the electric field is applied, the whiskers are acted on by the moment that aligns them along the electric field in the liquid photopolymer. The liquid photopolymer does not begin to flow until the shear stress on the surface of the whisker reaches the value of the yield shear stress of the photopolymer. This characteristic is denoted as the Bingham property. Therefore, the whiskers do not rotate until the electric field is lower than the threshold value by means of the Bingham property. The Bingham property is measured and the values of the electric field required to rotate the whiskers are examined both theoretically and experimentally in this paper. Using the above results, solidified polymer structures containing unidirectional whiskers are fabricated.
We present an enhanced adaptive feed-forward cancellation (AFC) with variable gains to be used in the head positioning control system of a hard disk drive (HDD). The variable gains can help to improve the convergence characteristic of the enhanced AFC after the track seeking control. Therefore, the proposed enhanced AFC can improve the transient response of the head positioning after the track seeking control. The track seeking simulation results from HDDs showed that the proposed control method compensated for the disturbances caused by the repeatable run-out (RRO) and airflowinduced vibration immediately after the track seeking control.