Tsutomu Mita

An algebraic approach to H ∞ output feedback control problems

We derive an output feedback controller which stabilizes a system and satisfies a prescribed H∞ norm bound of the closed loop transfer function. The proposed design method is available for any system, i.e. there are no restrictions on D12 and D21. This approach utilizes only algebraic operations, thus proofs are simple and clear.

Optimal digital feedback control systems counting computation time of control laws

Recently, the multivariable control theory studied up to date can be applied to many practical controlling problems. However, when the time constant of the plant is short and the dynamic order of the plant is high, the time delay arising from the computation time of control laws can not be neglected. In this paper, the author treats such a problem and proposes design methods of linear optimal regulators and optimal servosystems in which the delay arising from the computation time is counted properly.

Realization of a high speed biped using modern control theory

The purpose of this paper is to propose a new controlling method of the biped locomotion composed of seven links and to show simulated and experimental data of the locomotive motion of the biped called CW-1 built in our laboratory. The control method depends mainly on the linear optimal state feedback regulator, which stabilizes the stance supported by both legs as a commanded attitude. As a result the biped successfully walks any pre-determined steps such that one step takes only one second.

Iterative control and its application to motion control of robot arm - A direct approach to servo-problems

There is a new and direct servo-control method called Learning Control which has a good advantage that the command input is not necessary a function generated from time-invariant linear systems but is required in conventional servo-theory using Internal Model Principle. Therefore, this new theory is very attractive since it may estabilish a new foundation of servo-theory in which the shape of the command is arbitrary. The idea is very simple, we determine the input function U(s) satisfying R(s)=G(s)U(s) using some iterative method. In this paper, we derive conditions on the convergence of this method and practical design procedures, and the results are applied to the trajectory control of robot arm such that the tip of the arm draws any shape with satisfactory precision in several trials.

Two-delay robust digital control and its applications-avoiding the problem on unstable limiting zeros

In the design of linear control systems, the existence of unstable zeros makes it difficult to construct many control systems. When the usual digital control scheme is used, unstable zeros appear in the discrete-time model due to the existence of limiting zeros even though the continuous-time plant is minimal phase. To avoid this unstable zero problem, two new digital control schemes, called two-delay output control and two-delay input control, are proposed. These control systems are proved to have no finite zeros. Asymptotic inverse systems, pole assignable unknown input observers, and output feedback controllers having the LTR (loop transfer recovery) property are developed using the two-delay output control. Zero assignable control systems and model matching control systems are developed using the two-delay input control. >

Self-organizing control using fuzzy neural networks

To achieve self-organizing control based on fuzzy rules, we propose a fuzzy associative memory system called FAMOUS (Fuzzy Associative Memory Organizing Units System). FAMOUS simulates the knowledge representation and inference process by using fuzzy notation and by association in neural networks. FAMOUSs learning algorithm uses training steps to generate operation skills by modifying the expert knowledge that is initially built-in. A set of fuzzy if-then rules is used for controlling variable parameter processes. The control knowledge is represented as pairs consisting of a ‘condition’ in the if-part and an ‘operation (controller)’ in the then-part. The controllers are designed for optimization and stabilization in specific conditions. The fuzzy controller described in FAMOUS recalls well-trained controllers associated with the input condition and makes the final control output by synthesizing the intermediate outputs of their controllers. FAMOUS can highly refine knowledge by using neural network learn...

Undershooting phenomenon and its control in linear multivariable servomechanisms

This paper investigates an undershooting phenomenon which occurs in multivariable feedback control systems, and a control method which suppresses the undershooting phenomenon of a type [1, 1,...., 1] servosystem is proposed. Since the linear optimal control (LOC) is not concerned with detailed specifications of the response, such studies should be useful for the design of real control systems.

A new and simple algorithm for sliding mode trajectory control of the robot arm

A simple sliding mode trajectory control of the robot arm that needs no inverse of the inertia matrix is derived. The assumptions underlying the derivation are outlined. >

On zeros and responses of linear regulators and linear observers

In the pole assignment of the single input and output regulator, there is a case where the integrated square output becomes infinite and the response of the output has an infinitely large maximal amplitude when all poles of the closed loop system are assigned to negative infinity in the numerical s -plane. This paper deeply investigates this problem from the linear structure point of view and applies the obtained results to the pole specification problem of observers.

Design of optimal strongly stable digital control systems and application to output feedback control of mechanical systems

ABSTRACT A new design method for an optimal digital series compensator is considered that is not produced by an optimal regulator incorporated with a state observer, but employs a new idea that assures total closed system optimality in one design step. However, the compensator so designed is not always stable, i.e. strong stability of the closed-loop system is not always guaranteed. For this case, the authors propose to use the inter-sample response to realize an optimal stable compensator and/or optimal output feedback control system. Especially when the given plant is a linearized mechanical system, such a strongly stable system can always be designed using only output data two samples prior to the current sample regardless of the system order and the parity interlacing property condition.