Sang-Eun Baek

Design of a dual-stage actuator control system with discrete-time sliding mode for hard disk drives

This paper considers discrete-time design of a dual-stage actuator control system with sliding mode for hard disk drives. A state estimator based sliding mode controller is designed in the discrete time domain. A design methodology is also addressed to complete the design of the control system. The performance of the proposed sliding mode control algorithm is tested through simulations. Very fast seek in microactuator range is attained while not exciting the microactuator resonance. Through the results of simulations it is demonstrated that the proposed discrete-time sliding mode control system is a very prospective technique for disk drives with dual-stage actuators.

Design of a multi-rate estimator and its application to a disk drive servo system

Considers multi-rate estimator design and proposes very simple and practical methods to improve the performance of multi-rate estimators. The proposed methods are applied to disk drive servo system design. Experimental results are presented to show applicability of the proposed design techniques. Noticeable performance improvement is observed with the proposed multi-rate estimator especially during seek motion of a disk drive actuator.

Vibration rejection control for disk drives by acceleration feedforward control

Considers accelerometer based vibration rejection control for disk drives using acceleration feedforward. A very simple and practical acceleration feedforward control algorithm is proposed to reject the effect of external vibration for improved tracking accuracy. No transfer function from the base frame to the actuator is introduced, while the phase delay of accelerometers is considered. Noticeable improvement in tracking accuracy is observed with the proposed acceleration feedforward control. Through the results of simulation and experiment, it is shown that the proposed simple algorithm is very effective to attain tracking accuracy in the existence of vibration.

Design and control of a robotic finger for prosthetic hands

Considers design and control of a robotic finger for prosthetic hands. A linkage driven robotic finger actuated by single motor is developed such that the motion of the robotic finger is very close to the motion of a human finger. The signal measured from strain gauges attached to the tendon of the hand is used as a position command to control the motion of the robotic finger. The results of simulation and experiment are presented to show that the proposed robotic finger is fit for a prosthetic hand.

Modeling and control of a dual-stage actuator for hard disk drive servo systems

This paper presents modeling and control of a dual-stage actuator for disk drive servo systems. Parametric modeling of MIMO and MISO dual-stage actuator is presented along with a method to find the parameters. Based on the model, a MISO dual-stage servo algorithm in the form of discrete-time LQG with feedforward control is proposed. Issues in the design of state space dual-stage actuator servo are also addressed. As an example, a MISO servo system is designed for a dual-stage actuator with a piezoelectrically driven microactuator. Through the results of simulation, it is shown that the proposed dual-stage actuator servo system yields considerably improved output disturbance rejection and very fast step response.

Modeling of pivot friction using relay function and estimation of its frictional parameters

One way of modeling frictional effects that arise from pivot ball bearing in rotary disk drive actuator requires a special experimental setup. In this paper, a revised model from two-slope and three-slope model with omission of first slopes from both position and velocity feedback and an addition of relay, is presented. The hysteresis characteristics of ball bearing are much more accurately described by a relay added on the velocity feedback. For parametrization, a mathematical description of the frictional relay is obtained, and both linear and nonlinear terms in the friction model are treated simultaneously by using conventional recursive-least-square method incorporating a new technique that extracts V/sub th/ threshold parameter. The effectiveness of the new friction model is tested by a parameter estimation scheme, and simulation and experiment of the estimation algorithm are also demonstrated for overall performance.

A new seek servo controller for minimizing power consumption in micro hard disk drives

Recently, the demand for micro hard disk drive that provides high-capacity removable storage for handheld electronic devices is increasing very rapidly. The major concern in the design of seek servo controller in micro disk drives is to reduce power consumption. The input power delivered to the seek servo system is consumed by the transistors of power amplifier and motor coil resistance. In this paper, we present a new seek servo controller for minimizing the power consumption. We use a Fourier decomposition and constrained nonlinear programming to determine the optimum seek profile that minimizes the power consumption. Finally, we present some experimental results using a commercially available micro disk drive.

Discrete-time robust tracking control using a state space disturbance observer

This paper considers the design of a discrete-time robust tracking control system which consists of a state space disturbance observer, a state estimator, and a state feedback controller. A new discrete-time state space disturbance observer is proposed not requiring modeling of disturbances. Through the results of applications, it is shown that the proposed method is very effective to compensate a variety of disturbances and to improve the performance of a tracking control system in the existence of external disturbances. It is also observed that the proposed state space disturbance observer allows more accurate state estimation in the existence of modeling error and disturbances.

Kinematic/dynamic analysis of a 6 DOF parallel manipulator with 3-PPSP serial subchains and its implementation

In this paper, the kinematic analysis for a 6 degree-of-freedom parallel manipulator with 3-PPSP type serial subchains is performed and its kinematic characteristics are investigated via isotropic index of the first-order kinematic influence matrix. Also, dynamic analysis of the manipulator is performed and its dynamic characteristics is examined via the isotropic characteristics of the output effective inertial matrix. From the analysis results, it can be concluded that the manipulator has an excellent kinematic and dynamic characteristics required for high precision manipulators. Lastly, a prototype manipulator system is implemented and the joint position servo-controller is applied to the system. Noting the manipulator has closed-form forward/reverse position solutions, it is expected that more advanced controller requiring heavy computational burden can be applied to the system in real time to further enhance the performance of the system.

Robust velocity tracking using sign-observation with its application to computer disk drives

This paper presents a control strategy for velocity tracking in mechanical systems with unknown constant disturbance, using only the sign information of the tracking error. The behavior of the closed-loop system including the error convergence is analyzed via relay feedback system theory and nonsmooth Lyapunov argument. Additionally, it is shown that an arbitrary nonlinearity can be allowed as long as it is smooth and positive. The proposed control strategy is applied to the so-called dynamic ramp loading/unloading scheme in computer disk drives, which requires an additional servo action that must take place before the existing digital servo system comes into play. The application illustrates that the proposed strategy provides this problem with a feedback control solution more cost-effective than any other conventional solution. Simulation is conducted to verify the theoretical performance and further to predict the practical performance under nonideal implementation. Also provided are experimental results based on the actual implementation, which demonstrate the practical efficacy of the proposed strategy.