Choo Chung

Nonlinear control of a swinging pendulum

We propose a nonlinear controller to regulate the swinging energy of the pendulum for a cart and pendulum system. Roughly speaking, the controller is designed to regulate an output (the swing energy) while providing internal stability (regulating the cart position). It is difficult to apply many of the standard nonlinear control design techniques, since the output zeroing manifold does not contain any equilibrium points and the relative degree of the system is not constant. In contrast to controllers that use a command generator and possibly a time-varying feedback, our control law is a simple autonomous nonlinear controller. We analyze the stability of the closed-loop system using an Lv small-gain approach on a transverse linearization of the system about the desired periodic orbit. One can easily extend this approach to analyze the robustness of the control system with respect to disturbances and parameter variations. Experimental results demonstrate the effectiveness of the nonlinear controller.

Microstepping Using a Disturbance Observer and a Variable Structure Controller for Permanent-Magnet Stepper Motors

The application of a disturbance observer (DOB) and a variable structure controller (VSC) to current control of microstepping for permanent-magnet stepper motors (PMSMs) is studied. This is a recent approach to the current regulation of PMSM that results in improvement of position tracking performance of microstepping using only current feedback. We designed the DOB to estimate back electromotive force (EMF) in the form of a high-pass filter. Since the PMSM is a two-input one-output minimum-phase nonlinear system, the asymptotic convergence of the currents to the desired currents guarantees the asymptotic convergence of the position to the desired position in microstepping. Therefore, in order to compensate for the estimation errors of back EMFs and to guarantee the desired currents required for microstepping, the VSC is designed with a state feedback controller. The current tracking error and the integral of the current tracking error are proven to asymptotically converge to zero. Since the proposed method does not require any transformations or the calculation of sinusoidal terms, its structure is simple. The least lower bound of the absolute steady-state position tracking error during a constant-velocity period is estimated in order to analyze the performance of the proposed method. Our experimental results validate the performance of the proposed method.

High-Gain Disturbance Observer-Based Backstepping Control With Output Tracking Error Constraint for Electro-Hydraulic Systems

We propose a high-gain disturbance observer (HGDOB)-based backstepping control with position tracking error constraint for electro-hydraulic systems to improve the position tracking performance in the presence of disturbances. The HGDOB is designed to estimate the disturbances that include the friction, the load force, and the parameter uncertainties. Auxiliary state variables are proposed to avoid amplification of the measurement noise in the HGDOB. To compensate for the disturbances while guaranteeing tolerance of the position tracking error, the backstepping controller is proposed by using the barrier Lyapunov function. As a result, the proposed method satisfies the output constraint and improves the position tracking performance in the presence of disturbances. Its performance is validated via simulations and experiments.

Disturbance-Observer-Based Position Tracking Controller in the Presence of Biased Sinusoidal Disturbance for Electrohydraulic Actuators

A nonlinear position tracking controller with a disturbance observer (DOB) is proposed to track the desired position in the presence of the disturbance for electrohydraulic actuators (EHAs). The DOB is designed in the form of a second-order high-pass filter in order to estimate the disturbance. The nonlinear controller is designed for position tracking as a near input-output linearizing inner-loop load pressure controller and a backstepping outer-loop position controller. Variable structure control is implemented in order to compensate for the error in disturbance estimation. The desired load pressure is designed to generate the pressure using the differential flatness property of the EHAs mechanical subsystem. The disturbance within the bandwidth of the DOB can be cancelled by the proposed method. The performance of the proposed method is validated via simulations and experiments.

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.

Control Methods in Data-Storage Systems

The recording performance of data-storage devices, in which write/read elements move relative to a storage medium to reliably store and retrieve information, depends on the capability of servo mechanisms to provide the necessary positioning accuracy. The desired characteristics of servo mechanisms for data-storage systems include robustness against variations of environmental parameters, high resolution, accuracy, stability, and fast response. This paper presents a comprehensive overview of advanced servo-control methods for data storage. The applications are to well-established recording technologies, including magnetic tape and magnetic disk systems as well as CD/DVD/Blue-Ray optical data-storage systems. Moreover, newer holographic and near-field optical systems and the emerging probe-storage technology are also addressed. Emphasis is given to the potential exhibited by the technologies considered for achieving ultra-high storage capacity, as required by the exploding demand in data-storage capacity for archival systems and massive multimedia data storage.

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

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.

Design and Implementation of Simple Field-Oriented Control for Permanent Magnet Stepper Motors Without DQ Transformation

In this paper, a simple field-oriented control (FOC) without direct quadrature (DQ) transformation is proposed for position tracking of permanent magnet stepper motors (PMSMs). Conventional FOC methods require DQ transformation to linearize the mechanical dynamics for PMSMs. In this paper, a proportional-integral-derivative controller with velocity feedforward is developed to obtain the torque modulation required to track the desired position. In addition, a new commutation scheme is proposed to generate the desired currents with the torque modulation; this commutation scheme is equivalent to the microstepping where the desired currents have time-varying amplitudes with π/2 electrical phase advance. The proposed controller method is in the form of an FOC even though DQ transformation is not used. The proposed commutation scheme likens the PMSM to a two-phase permanent magnet synchronous motor. Experimental results validate the effectiveness of the proposed method.

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.