Toshihiro Arisaka

Head-positioning control using resonant modes in hard disk drives

The best way to enhance the input/output (I/O) performance of a hard disk drive is by increasing the spindle speed. Therefore, the effect of windage vibrations caused by the airflow increases as the spindle speed increases. The servo bandwidth is limited by the primary resonant frequency of the mechanical system. However, the frequencies of the windage vibrations are higher than the primary resonant frequency. Accordingly, these frequencies are also above the servo bandwidth and are too high to be controlled by a conventional control system. In response to this problem, we have developed two methods for designing a servo control system that can suppress the windage vibrations. One method uses a stable mechanical resonant mode, and the other uses a stable resonant mode created by a digital filter. By using these methods, the head-positioning system can control the vibrations above the frequency of the primary resonant mode and the servo bandwidth. Application of these methods to actual hard disk drives showed that they can greatly decrease the windage vibrations, in which the peak frequency is about six times the open-loop gain 0-dB crossover frequency.

Flow-induced vibration reduction in HDD by using a spoiler

To reduce the flow-induced vibration (FIV) of the head stack assembly (HSA) in the hard disk drive (HDD), we experimentally studied the spoiler, which is put between disks. This study was carried out using a laser doppler vibrometer (LDV) to measure the amplitude of the head slider vibration. We also measured the power consumption of the spindle motor. As parameters of the spoiler shape, the thickness and the length were selected. From the experimental result, these parameters effect significantly both the heads vibration and the power consumption. This result suggests that the flow rate reduction with the spoiler causes a reduction of the HSAs FIV, and the energy loss with the spoiler causes an increase of the power consumption. We defined the spoilers FIV-reducing efficiency as a ratio of the amplitude reduction to the power consumption increase. The length change makes the peak value. This is caused by the fact that the FIV reduction becomes almost constant when the spoiler is longer than the carriage arm length inside disk region, although the spoiler length makes power consumption monotonically large.

Integrated Design of a Controller and a Structure for Head-positioning in Hard Disk Drives

In head-positioning systems of hard disk drives, the negative effects of a primary resonant mode are serious problems for positioning accuracy. In order to improve positioning accuracy, the primary resonant frequency should be increased because the effects of the primary resonant mode limit the servo bandwidth. An integrated design of a controller and structure for the head positioning system was developed to solve this problem. We showed that the servo bandwidth is limited not only by the peak frequency of the primary resonance but are also its residue. The proposed method decreases the negative impact of the primary resonant mode through a newly designed modal shape, and increases the servo bandwidth without the addition of any sensors or actuators. The effectiveness of this method was verified by designing an actual servo control system and experimentally measuring its bandwidth, demonstrating that the method increases the servo bandwidth without increasing the production cost.

Vibration Control of Hard Disk Drive with Smart Structure Technology for Improving Servo Performance

In hard disk drives, vibration suppression is very important to boost the servo performance for achieving the enhanced density of the disk and following precision of the system. It has been expected that technology of smart structure will contribute to the development of small and light-weight mechatronics devices with the required performance. This study proposes a new vibration control mechanism with smart structures technology in order to achieve significant vibration suppression in hard disk drive systems. First, modeling of the system is conducted with finite element and modal analyses. Next, the control system design and closed-loop simulation are performed with the proposed vibration control mechanism composed of piezoelectric sensors and actuators. Finally, a multidisciplinary design optimization on actuator location and control system is examined to enhance the closed-loop performance of the system.

Development on in-phase actuator mechanism in hard disk drives papers

This research shows the new design concept of an actuator in hard disk drives. The actuator which has several higher-order mechanical resonance determine the stability and mechanical noise suppression ability of the servo control system. We presented the new design concept that higher resonance are made in-phase to the first major resonance. In this concept, all the resonance with high gain are in-phase but the out-phase resonances gain are reduced. It is shown that the prototype actuator based on this concept can be compensated only by the compensator which is designed for the first major resonance.

Simultaneous design of mechanism and control system for smart structures (optimization of piezoelectric placement and application to magnetic disk drive)

The placement of the piezoelectric actuator and H/sub 2/ control system in a smart structure are simultaneously optimized by the genetic algorithm to achieve an enhanced vibration control performance. Efficient optimization algorithm based on a two-step procedure is employed in the simultaneous optimization. in which the optimal piezoelectric placement and state feedback controller are obtained by the genetic algorithm at the 1st-step and then the dynamic compensator for the output feedback is reconstructed at the 2nd-step of the optimization. It is verified by sonic applications with a plate structure and a magnetic disk drive that an enhanced performance for the vibration suppression can be achieved by the optimal design presented.

Antiflow-Induced Vibration Structure in Hard Disk Drive

To meet market demand for the high data density on the disk of a hard disk drive (HDD), reduction of disturbance causing track misregistration is needed. The main disturbance in HDDs in a server or a desktop PC is flow-induced vibrations caused by airflow due to the disk rotation. Generally, there are two kind of flow-induced vibration (FIV) of the structures inside a HDD. One is in-plane or out of plane vibration of the read/write component, i.e., the carriage. Another is out of plane vibration of the disk. In these experiments, we tried to reduce out of plane vibration of the disk and the carriage by making a simple structural change. The investigation is carried out to clear up a cause of FIV of the carriage. The result showed that the outflow from the disk region is strong and can be the cause of the out of plane vibration of both the disk and carriage. To counteract this fluid force, the plates were put against the disks to prevent wind disturbance. As a result, the flow-induced vibrations of the carriage and the disks were significantly reduced. Based on our results, we designed an anti-FIV structure.Copyright