Michio Nakano

Repetitive control system: a new type servo system for periodic exogenous signals

A control scheme called repetitive control is proposed, in which the controlled variables follow periodic reference commands. A high-accuracy asymptotic tracking property is achieved by implementing a model that generates the periodic signals of period L into the closed-loop system. Sufficient conditions for the stability of repetitive control systems and modified repetitive control systems are derived by applying the small-gain theorem and the stability theorem for time-lag systems. Synthesis algorithms are presented by both the state-space approach and the factorization approach. In the former approach, the technique of the Kalman filter and perfect regulation is utilized, while coprime factorization over the matrix ring of proper stable rational functions and the solution of the Hankel norm approximation are used in the latter one. >

High Accuracy Control of a Proton Synchrotron Magnet Power Supply

Abstract A linear feedback control is applied in high accuracy tracking of a periodic reference input. Asymptotic tracking of an input with a given period is achieved by locating the imaginary poles of the controllers transfer function to suit the period of the input. A frequency-domain analysis of the transient and noise characteristics leads to a simple controller design principle. The method was applied to the computer control of the 27-MVA thyristor power supply to the three main ring magnets of a proton synchrotron. The 10-4 tracking accuracy required of the exciting current control was achieved after 16 cycles of a pulsed operation.

Synthesis of repetitive control systems and its application

A new control scheme named repetitive control is proposed, in which the controlled variables follow the periodic reference commands with high accuracy. The error convergence condition for linear plants is derived by applying the small gain theorem and a synthesis algorithm using the methods of Kalman Filter and the perfect regulation is presented. We also investigate the repetitive control for a class of nonlinear systems described by x(t)=Ax(t)+Bu(t)+f(x(t)) and y(t)=Cx(t)+Du(t). The stability condition is developed using the passivity theorem. The scheme is applied to the trajectory control for a three-link manipulator.

Nonlinear repetitive control with application to trajectory control of manipulators

In this article, a new control scheme named repetitive control is proposed for a class of nonlinear systems described by x(t) = Ax(t) + Bu(t) + n(x(t)) and y(t) = Cx(t), in which the controlled variables follow periodic reference commands. The stability condition is derived by applying the passivity theorem. We show how to apply the repetitive control scheme to the trajectory control of a manipulator. A simple repetitive control scheme is developed for the trajectory control of a manipulator by using nonlinear compensation and feedbacks of position and velocity signals. Experimental results for a three link manipulator verify that the proposed repetitive control reduces the tracking error to a very low level.

Elimination of position-dependent disturbances in constant-speed-rotation control systems

Abstract This paper describes a new approach to eliminating position-dependent disturbances in constant-speed-rotation control systems. Focusing on the fact that this kind of disturbance constitutes a periodic function of the rotational angle, a new concept called the “position domain” is introduced, and the design of the proposed control system is carried out in the position domain instead of the time domain, so as to eliminate such disturbances completely, regardless of any changes in the rotational speed.

A model-based expert control strategy using neural networks for the coal blending process in an iron and steel plant

Abstract Two important aspects of the control of the coal blending process in the iron and steel industry are computation of the target percentage of each type of coal to be blended and the blending of the different types in the target percentages. This paper proposes an expert control strategy to compute and track the target percentages accurately. First, neural networks, mathematical models and rule models are constructed based on statistical data and empirical knowledge on the process. Then a methodology is proposed for computing the target percentages that combines the neural networks, mathematical models and rule models and uses forward chaining and model-based reasoning. Finally, the tracking control of the target percentages is carried out by a distributed PI control scheme. The expert control strategy proposed is implemented in an expert control system that contains an expert controller and a distributed controller. The results of actual runs show that the proposed expert control strategy is an effective way to control the coal blending process.

A model-based expert control system for the leaching process in zinc hydrometallurgy

Abstract One important step in zinc hydrometallurgy is the leaching process, which involves the dissolving of zinc-bearing material in dilute sulfuric acid to form a zinc sulfate solution. The key point in the control of the process is to determine the optimal pHs of the overflows of the continuous leach process and track them. This paper describes a model-based expert control system for the leaching process, which is being used in nonferrous metals smeltery. Specifically, steady-state mathematical models and rule models are first constructed based on the chemical reactions involved, the empirical knowledge of engineers and operators, and empirical data of the process. Then, a methodology is proposed for determining and tracking the optimal pHs with an expert control strategy based on a combination of mathematical models and rule models of the process. The results of actual runs show that the proposed control strategy is an effective way to control the leaching process.

Dead beat control for PWM inverter

Voltage source PWM inverters have been applied to such fields as power supplies and motor drivers. This is because: (1) such inverters are well adapted to high-speed self turn-off switching devices that, as solid-state power converters, are provided with recently developed advanced circuits; and (2) they are operated stably and can be controlled well. The authors have fabricated a prototype power supply unit based on a voltage-source PWM inverter to simulate harmonic trouble and power failure over the power distribution system. The prototype power supply unit has been delivered to an electric power company and is running successfully. Here, they present a summary of the power supply unit.<<ETX>>

High- speed PLL and frequency synthesizer for low frequencies

Conventional phase-locked loops (PLLs) lack speed, because ordinary phase comparators cannot achieve time-continuous phase detection, introducing equivalent time delays into the loops. This paper presents a PLL reconstructed to derive time-optimal responses. First, VCOs and filters are replaced by time-discrete ones, eliminating the stability problem caused by the time delay. Second, period rather than frequency is employed as the controlled variable for utilizing digital phase comparators as linear time comparators. A prototype consisting of about 20 ICs is tested.

Finite time settling compensation using hysteresis element

A technique of using a hysteresis element for velocity feedback in order to obtain ideal responses without the influence of the target height is proposed. The application of this control technique to actual control systems was studied through various types of simulation and experiment. It was confirmed that the control technique provides excellent compensation. It was found that the principle of posicast control which is not influenced by the input intensity can also be applied to positioning servo systems with saturation characteristics. If the hysteresis element is provided with a function for prediction, hysteresis feedback control has the same compensation effect on a high-order servo system with the behavior of a second-order damped-vibration system as on a second-order servo system.<<ETX>>