ChoonKiat Lim

Frequency-domain transfer function of digital multirate controller with current estimator

A multirate controller with a current estimator is a recent but useful control technology. This scheme has less phase loss due to a zeroth-order-hold (ZOH) and controller discretization in comparison to the continuous form as compared to the single-rate scheme. This brief presents the modeling of the frequency-domain transfer function of a multirate controller with a current estimator. Based on this model, the control engineer can evaluate the open-loop response in terms of phase margin, gain margin, open-loop gain crossover, and so on. This brief applies the model to a hard disk drive (HDD) servo control. The experimental data accurately match the model responses.

Hinge pivot for disk drive

This paper discusses the findings of a hinge pivot for use in hard disk drives (HDD). The actuator assembly in a HDD is supported by a pivot cartridge and controlled by a servo system to perform seek and track following operations for data recording. The cartridge is composed of a pair of pre-loaded ball bearings. Due to the demand for thin hard disk drives and hence, the need to reduce the height of the actuator assembly, a hinge pivot is proposed to replace the set of bearings. The shaft of the pivot is connected to the sleeve with thin hinges made of ultra-high heat-resistant polyamide film, such as Upilex. Measurement showed that the hinge pivot did not exhibit the nonlinear effects during low frequency actuation, such was inherent for ball bearing pivots. Experiment also showed that at least a million life cycles can be achieved without any performance degradation.