Seung-Hi Lee

Robust Multirate Control Scheme With Predictive Virtual Lanes for Lane-Keeping System of Autonomous Highway Driving

In this paper, we propose a new approach for a robust multirate lane-keeping control scheme with predictive virtual lanes. First, the multirate lane-keeping control scheme is proposed to improve the lane-keeping performance and to reduce the ripple in the yaw rate. To improve the lane-keeping performance on a curved road, the integral of the lateral offset error is added to the state feedback controller. A multirate Kalman filter (KF) has been developed to resolve the problems caused by slow lane detection due to the vision processing system. This multirate KF estimates vehicle states at a fast rate using a microprocessor. Utilizing the estimated states, the linear quadratic state feedback control operates at the same fast update rate of the microprocessor. Thus, a multirate control scheme can reduce the ripple in the yaw rate. Second, we propose a virtual lane prediction method that compensates for the momentary failure of lane detection from unexpected problems. If the camera sensor momentarily fails while obtaining lane information, the predicted virtual lane can be substituted for the lane detection using the camera sensor in the proposed control scheme. Thus, the proposed control scheme can normally operate when the lane information is momentarily unavailable. The performance of the proposed method was evaluated via experiments.

Multirate digital control system design and its application to computer disk drives

A computationally efficient fixed order multirate digital control system is presented. Introducing a periodically time-varying gain, a multirate digital controller is designed, that works without using intersample states and delivers a stable ripple-free closed-loop with discrete-time state matching at each control update instant. Increasing the control update rate thereby tends to improve intersample behavior of the closed-loop system. The multirate controller outputs control at each control update instant, while the multirate control scheme is computed in the background during output measurement sampling period thereby reducing the computational burden for implementation. The proposed multirate scheme is applied to disk drive actuator control. Application results demonstrate the utility of the proposed multirate digital control scheme for improved disk drive actuator control.

Minimum destructive interference design of dual-stage control systems for hard disk drives

This paper presents the design of a dual-stage actuator control system consisting of a voice coil motor and a microactuator (MA). A dual-stage actuator model is developed to include a dominant MA flexible mode and the interaction between both actuators. Fundamental observations and design strategy are followed by a proposition of a dual-stage actuator control system to be used for track-seek in the MA range, track-follow, and settle. A new performance index, destructive interference, is introduced to express the degree of cooperation between both actuator systems with very different specifications and characteristics. In the dual-stage actuator control design, the measure of destructive interference is minimized to determine a MA controller so as to attain desired time and frequency responses. Robustness analysis is conducted using the structured singular value method on the resulting dual-stage actuator control system. Through an application example, it is demonstrated that minimizing the destructive interference produces a dual-stage actuator control system with desired time and frequency responses.

Dual-stage actuator disk drives for improved servo performance: track follow, track seek, and settle

This paper considers dual-stage actuator control system design and demonstrates resulting servo performance improvements. A discrete-time dual-stage actuator control system is proposed along with a design technique to attain a very small destructive interference with satisfactory time and frequency responses, which is used for track follow, track seek in the microactuator range, and settle. Application results are provided to demonstrate usefulness of the proposed dual-stage actuator control system and the design technique.

Robust Fast Seek Control of a Servo Track Writer Using a State Space Disturbance Observer

Unknown and uncertain disturbances significantly affect the servo performances of servo track writers. Therefore, the development of a robust fast seek controller that seeks using a state space disturbance observer is required. We present the design and application of a robust fast seek controller for servo track writers. Unlike some existing methods that use an explicit model for disturbance or for adjusting sensitivity using a filter, the proposed method is shown to effectively compensate for disturbances even while track seeking, which is not possible when using an integrator or a frequency domain disturbance observer. Experimental results demonstrate the utility of the proposed robust fast seek controller, which uses a state space disturbance observer, for servo track writers. The proposed servo track writer control scheme seeks tracks quickly in the presence of unknown and uncertain disturbances.

Discrete-time LQG/LTR dual-stage controller design in magnetic disk drives

This paper presents a new dual feedback loop controller design of a dual-stage actuator for hard disk drives. For precise and accurate displacement, coupled dynamic model is considered from the Newton-Euler formulation. A gain factor is introduced so that the level of microactuators contribution and the high frequency characteristics of the system can be controlled. 2.28 kHz servo bandwidth is achieved. The 6 percent settling time is 250 /spl mu/s and 3/spl sigma/ value is 0.017 /spl mu/m from the experimental result.

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.

Two degree-of-freedom dual-stage actuator controller design for hard disk drives

This paper presents a new controller design method for dual-stage actuators. The controller consists of two stabilizing controllers for VCM and MEMS actuators and two main controllers (slave and master). The slave and master controllers are used to shape the sensitivity of the closed loop system at low and high frequency, respectively. With the proposed method satisfactory sensitivity and complementary sensitivity are achieved.