Masayoshi Toda

Robust Motion Control of an Oscillatory-Base Manipulator in a Global Coordinate System

This paper presents a control design method for motion control in a global coordinate system of an oscillatory-base manipulator, which can be regarded as a model system of mechanical systems installed on vessels or oceanic structures. This paper proposes a control design method for such systems exploiting H∞ control and proportional and derivative (PD) control. In order to evaluate the proposed method, tracking control simulations and experiments were conducted for both attitude control and position control with practical constraints such as sensor error and actuator saturation. Furthermore, the proposed controller was compared with a conventional proportional, integral, and derivative (PID) controller. The results demonstrate that the proposed controller is successfully effective and is superior to the PID controller. Moreover, robust control experiments and robust stability analyses using our proposed machinery show that the proposed controller has strong robustness against physical parametric perturbations. Our developed robust stability analysis machinery is based on the state-dependent coefficient form and applicable to a wider class of systems than the previous one.

Robust control for mechanical systems with oscillating bases

In this paper, robust control for manipulator robots with oscillating bases, associated with control for robots installed on either vessels or ocean structures, is considered. First, the formulation of this problem is introduced and the disturbance to the robot dynamics due to oscillation of the base is discussed. Then the control design technique, which is mainly based on scaled H/sub /spl infin// output feedback control and incorporates some other schemes to reduce the nonlinearity such as gravity, centrifugal force, etc., is presented. Once the feedback schemes to reduce nonlinearity are determined and the signals which should be regarded as disturbances are rendered distinct, then the problem becomes one of disturbance attenuation in the presence of structured model uncertainties. To acquire a controller which satisfies the control objectives and to analyze the resulting control system with respect to robustness, the structured singular value /spl mu/ theory is exploited. One of the advantages which this technique provides is that, if the frequency range of the base oscillation is known in advance, then the controller dose not require observation of the motion of the base at all. Further, robustness to physical parameter perturbations of the robot can be acquired with respect to both stability and performance.

New method for comprehensive detection of chemical warfare agents using an electron-cyclotron-resonance ion-source mass spectrometer

We developed a detection technology for vapor forms of chemical warfare agents (CWAs) with an element analysis system using an electron cyclotron resonance ion source. After the vapor sample was introduced directly into the ion source, the molecular material was decomposed into elements using electron cyclotron resonance plasma and ionized. The following CWAs and stimulants were examined: diisopropyl fluorophosphonate (DFP), 2-chloroethylethylsulfide (2CEES), cyanogen chloride (CNCl), and hydrogen cyanide (HCN). The type of chemical warfare agents, specifically, whether it was a nerve agent, blister agent, blood agent, or choking agent, could be determined by measuring the quantities of the monatomic ions or CN(+) using mass spectrometry. It was possible to detect gaseous CWAs that could not be detected by a conventional mass spectrometer. The distribution of electron temperature in the plasma could be closely controlled by adjusting the input power of the microwaves used to generate the electron cyclotron resonance plasma, and the target compounds could be detected as molecular ions or fragment ions, enabling identification of the target agents.

Motion control of an oscillatory-base manipulator in the global coordinates

This paper presents a control design method for motion control in the global coordinates of oscillatory-base manipulators, which are associated with mechanical systems equipped with such as radars and sonars installed on vessels or oceanic structures. The proposed design method exploits linear H∞ control supported by linearization and PD control schemes. Motion control simulations demonstrate that our proposed method is successfully effective and is superior to the conventional PID control.

A Theoretic Analysis of a Control System Structure of Towed Underwater Vehicles

In this paper, we present a control system analysis of towed underwater vehicles (TUVs) whose dynamics is extremely complex due to the flexible-cable dynamics and hydrodynamic forces. An explicit state-space representation of the dynamical model is given and, based on it, the fundamental properties such as controllability, observability, and stability are assessed in some details considering a degree of approximation of the cable dynamics, with a numerical and geometric approach. Additionally, we develop some machinery to assess output controllability. The analysis results clarify the significant features of a TUV as a control system and provide useful information for control-system design of TUVs.

Motion control of an oscillatory-base manipulator using sliding mode control via rotating sliding surface with variable-gain integral control

In this paper, we present a motion control method of oscillatory-base manipulators, which are associated with mechanical systems installed on vessels or ocean structures. The typical property of such systems is strong and persistent disturbance due to the base oscillation to be overcome. Therefore, we attempt to exploit the sliding mode control (SMC) concept which is known to be a powerful tool to develop a robust control system against disturbances and model uncertainties. Specifically, we propose a novel approach based on SMC by introducing a nonlinear sliding surface with variable-gain integral control. We address control system design and stability analysis for the proposed SMC, and demonstrate its control performance by simulations. The results show that the proposed control method can achieve successful control performance for oscillatory-manipulators and further exhibits advantageous features with respect to control performance and control inputs when compared with the conventional SMC.

A unified approach to robust control of flexible mechanical systems

This paper addresses a unified control design method for robust control problems of various flexible mechanical systems such as a robotic manipulator with flexible joints and/or base, a crane system, and a liquid container system. First a generic problem setting is introduced, which accommodates those control problems in a uniform manner. Then a control design technique, which is based on the generic problem setting and utilizes PD control and Hinfin control schemes, is presented. Using an illustrative example, some detailed discussions on the proposed approach are given and control simulations are performed, which provide perspectives in employing our approach and show that it is useful and widely available.

Estimation of ship oscillation subject to ship speed variation using an algorithm combining H ∞ and Kalman Filters

This paper presents an estimation method of ship oscillation subject to ship speed variation, which leads to oscillation frequency variation. Such variation will deteriorate the estimation performance particularly when relying on a model-based estimation algorithm such as the Kalman filter. To overcome the problem, we propose an estimation method of ship oscillation with a low-cost gyro rate sensor, which incorporates periodic updates of fast Fourier transform (FFT)-based model and a method of selectively combining multiple H∞ and Kalman filters according to an innovation-based criterion. The latter algorithm is the heart of our estimation method, which aims at utilizing the advantage of each filter. Some simulation results show that the proposed method is more effective than the conventional H∞ and Kalman filters.

Oscillation Reduction Control for Ocean Environment Monitoring Buoys

Abstract This study deals with oscillation reduction control based on an observer-based switching control system for ocean environment monitoring buoys, where the key idea is to switch different regulators according to the oscillation energy of the buoy to cope with saturation of the actuator torque. We have performed oscillation reduction experiments by using an experimental buoy assuming one-axis rolling control, which is equipped with an oscillation reduction actuator and a gyro sensor. Consequently, the experimental results have shown that oscillation of the buoy can be successfully reduced by the proposed control method and hence have clarified its effectiveness and feasibility.

A nonlinear disturbance observer using delayed estimates - its application to motion control of an underwater vehicle-manipulator system

This paper presents a control design method with a new nonlinear disturbance observer using delayed estimates for motion control of an underwater vehicle-manipulator system (UVMS). In recent years, application of an underwater vehicle has been expected in various fields. Since modeling unknown hydrodynamic forces is difficult, nonlinear disturbance observers have been proposed in the aim of decreasing disturbances due to hydrodynamic forces. In this paper, we propose a new disturbance observer by combining a conventional disturbance observer and time delay control, and attempt to apply it to motion control of a UVMS. Further, an analysis of ultimate boundedness and numerical simulations are conducted to evaluate the proposed control system. The respective analysis and simulation results show that the proposed disturbance observer exhibits faster convergence and less estimation errors than the conventional one and hence the control system based on it can perform successful motion control.