KianKeong Ooi

Multirate control of an HDD servo system with intersample ripple free

Discusses the intersample ripple problem in multirate control design of a hard disk drive (HDD) servo system. An intersample ripple-free multirate control scheme is presented. Based on the conventional multirate approach, a constraint on the controller parameters is introduced in the new scheme. The constraint is to force the multirate control inputs to converge to the same constant level so as to eliminate the intersample ripple in the system output.

Low Frequency Vibration Detection and Compensation in Hard Disk Drive

The paper proposes a control scheme for detecting and compensating the low-frequency vibrations in hard disk drive systems. A vibration detector is proposed, utilizing the down-sampled position error signal (PES). Due to the performance limitation in loop shaping, attenuating low-frequency vibration is usually penalized by high frequency disturbance amplification. This paper proposes an adaptive scheme to intelligently adjust a vibration reduction factor, such that when vibration level is low, the servo loop maintains its normal operation mode, and little or no compensation is carried out. Experiments on hard disk drives on a vibration shaker validated the effectiveness of the proposed compensation scheme.

Servo Systems Using Multi-rate Notch Filters To Attenuate Resonances Beyond Nyquist Rate

This paper presents a systematic computation method of discrete-time plant response based on the continuous-time bode measurement, also proposes a 2times multi-rate notch filter to attenuate the resonant mode higher than sampling rate

Modeling the Smpled-data System with a discontinuous Hold for Hard Disk Ramp Loading

This paper deals with modeling of the hard disk ramp loading with a discontinuous controller. The property of the sampled-data system with a discontinuous hold is studied. Further, explicit expression of the discrete-time transfer function of sampled-data systems with a discontinuous hold is provided for a class of continuous time plant. It is shown that with discontinuous hold, the hard disk plant sampled-time model is minimum-phase instead of non-minimum phase if with zero-order hold

Effective Low Frequency Disturbance Feed Forward Compensation Scheme for Mobile HDD Application

The advantage of low cost and large capacity gives strong driving force for hard disk to enter the consumer electronic market. One of the most challenging servo control issue faced in mobile application is to perform normal read/write operation when significant vibration is excited in HDD jogging/walking condition. This paper presents a simple yet effective method to improvement hard disk throughput with an add-on low frequency disturbance feed forward compensator. With the proposed approach, the track following performance is significantly improved in jogging/walking, and the hard disk is capable to meet the read/write throughput requirement with minimum servo controller re-design effort

IRFM control with application to HDD servo system

Summary form only given. In Moore et al (Automatica, vol. 29, no. 4, pp. 941-951, 1993), by changing the control input N times faster than the system output is sampled, it was shown that both the closed loop poles and zeros can be arbitrarily assigned. However, the multirate strategy produces a degradation in the intersample behavior, namely, intersample ripples appear. In Chen et al (Proc. IECON, pp. 1171-1176, 1999), a multirate control scheme was proposed to attack the intersample chattering. However, the method is only applicable to a control plant which has at least one integrator in its model. Here we present a new intersample ripple free multirate (IRFM) control scheme for general LTI systems. A constraint on the controller parameters is introduced in the scheme to force the multirate control inputs to converge to the same constant level in order to eliminate the intersample ripple.