M. Tomizuka

Publications (3)4.63 Total impact

• Article: Adaptive Output Regulation for the Rejection of a Periodic Disturbance With an Unknown Frequency

  Wonhee Kim, Hyungjong Kim, Chung Choo Chung, M. Tomizuka
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  ABSTRACT: This brief presents an adaptive output regulator, an add-on type output regulator with a frequency adaptation algorithm. The frequency adaptation algorithm, based on an internal model principle, is used to identify the frequency of a sinusoidal disturbance. By adding the modified adaptive algorithm to the add-on output regulator, the adaptive output regulator can reject a biased sinusoidal disturbance with unknown bias, magnitude, phase, and frequency, while preserving the merits of the output regulator and the performance of the pre-existing controller. It is shown that the proposed method is stable for frequencies within a connected compact set. The stability of the closed-loop system is analyzed by the singular perturbation method and averaging theorem. The proposed controller is applied to an optical disk drive for verifying the performance of the controller. The performance of the proposed method is validated by both simulation and experimental results.
  IEEE Transactions on Control Systems Technology 10/2011; · 1.77 Impact Factor
• Article: Design of the Tracking Controller for Holographic Digital Data Storage

  Choong Woo Lee, Bong Sik Kwak, Chung Choo Chung, M. Tomizuka
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  ABSTRACT: In this paper, we present a new tracking control method for holographic digital data storage systems. Holographic data storage systems that use disk media need a different tracking method from those that use optical and hard disk drives. Here, we present the design and implementation of the controller. Due to the intermittent characteristics of the tracking error signal (TES), the tracking controller is designed to regulate the tracking error only while valid TES is generated. Since the valid TES appears intermittently, we use a feedforward controller while the TES is not valid. Furthermore, the feedback control and the feedforward control are mode-switched depending on the RF sum signal level. We also show the stability of the closed-loop system employing the mode-switching controller. Experimental results show the effectiveness of the proposed tracking control algorithm. For a ??100 ??m repeatable run out at 1 Hz, we were able to reduce the TES to 3.13 ??m (1??) with mode-switching control.
  IEEE/ASME Transactions on Mechatronics 05/2010; · 2.87 Impact Factor
• Conference Proceeding: Anti-shock controller design for optical disk drive systems with a nonlinear controller

  Jong-Shik Baek, Chung Choo Chung, M. Tomizuka
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  ABSTRACT: This paper presents a modified nonlinear controller design for optical disk drive systems to improve antishock performance. It was proposed in previous work that a nonlinear anti-shock controller is added parallel to the original linear servo control loop to improve its tracking performance in the presence of external shock. In the previous work, a dead-zone type nonlinear element is used for the nonlinear controller and a PID control method is used for the linear controller. Although this parallel structure improves anti-shock performance, it has a relatively low stability bound. In this paper, a dead-zone with saturation is proposed for the nonlinear controller. Since this nonlinear element improves the stability margin, we can use a higher gain for the dead-zone than the previous one. In addition, we found that the overall controller with a lead-lag type linear controller has an improved stability margin over that with the PID type linear control in this application. Numerical simulation results and experimental results confirm that the proposed method provides better performance against external shock than the previous method
  American Control Conference, 2006; 07/2006