In this paper we discuss the use of function identification and adaptive control algorithms in learning controllers for mechatronic systems. The term learning is used because the development of the algorithms is motivated by the emulation of the human ability to improve motor skills through training. The learning algorithms are based on the representation of an unknown function as a linear integral transform with a known kernel and an unknown influence function. Identification of the unknown function proceeds indirectly by identifying the unknown influence function. The application of these learning algorithms to the design of repetitive controllers for disk file systems and learning controllers for robot manipulators is also presented.

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This paper proposes a new control technique, based on the low authority control / high authority control (LAC/HAC) concept, to suppress the vibration of flexible space structures. The control system designed by the new control technique has a mechanism to adjust the HAC feedback gain between zero and one in such a manner as to enhance the effectiveness of control and to obtain global stability even when the magnitude of the LAC gain is not suitable. The paper first describes the theoretical mechanism of the new control technique and proposes a numerical method for determining the HAC feedback gain based on a neural network system. Then it shows the characteristic features of the new technique by computer simulation examples. The computer simulation shows that the new technique is quite effective in suppressing the spillover effects, and quite feasible for implementation.

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This paper proposes a new method for the vibration control of structures arranged in parallel. Recently, active dynamic absorbers have been used widely in the field of vibration control, but in the case of vibration control for several structures which stand independently this method is not advisable. In our method, both structures are controlled actively at the same time with a single actuator placed between them. Since supplementary masses are not necessary, the equipment can be simple and light. Here, the optimal design method of the controller for a 1-1 degree-of-freedom system by LQ control theory is shown. Moreover, the problem on the vibration control of the flexible structures is spillover, and this paper shows the application of the reduced-order model which suppresses the spillover in the controller design and its extension to a multi-degree-of-freedom system. Effectiveness of this method is demonstrated by the experiment.

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This paper proposes a new method for modeling flexible structures with distributed parameters as reduced-order models with lumped parameters. Both prevention of spillover and physical correspondence at the modeling points are taken into consideration. When modern control theory is employed to control the vibration of flexible structures, because of restrictions on controller design, it is necessary to make a reduced-order model of the structure. When higher modes are ignored, the reduction of the model may result in vibration instability-spillover. Because of uncontrollability and unobservability, nodes of higher-order vibration modes are selected as modeling points to prevent spillover. The effctiveness of this method is demonstrated by applying vibration control to a flexible towerlike structure.

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For the purpose of reducing the uncomfortable sway motion of high-rise buildings, induced by comparatively strong winds, a tuned active damper (TAD) equipped with a new mechanism has been developed, and installed in the Yokohama Landmark Tower. Through analysis and model tests, the effectiveness, practicality and safety of TAD have been confirmed.

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In optimal vibration control, the control characteristics of vibration depend on the criterion function and the coordinate system in the modelling, since the objective function is not necessarily described by the state variables. In this study, the relationships between the control characteristics and the criterion functions were investigated for the two cases of ignoring the dynamics of disturbance and restricting the frequency range of disturbance in the optimal control with the feedforward control due to lack of knowledge of the dynamics of disturbance. By carrying out numerical calculations, it was clarified that the optimization of the objective function can be given by feedforward control restricting the frequency range of disturbance, and that the same control effectiveness as the sky-hook damper can be obtained by choosing the absolute velocity as the objective function.

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This paper describes an experimental study on H^∞ control for vibration in multi-degree-of-freedom systems. An H^∞ controller designed by using the reduced-order model makes a closed loop system, not only causing no spillover phenomena, but also controlling the vibration on the four-degree-of-freedom experimental model. The experimental results are very similar to the simulation results, and the efficiency of the H^∞ control system is confirmed. Also experiments on frequency-shaped cost function LQG (H²) control design are performed in comparison with the H^∞ optimal control. Because the H^∞ optimal control has strong robust stability against the parameter variations, it can construct a more useful control system than H^∞ control for a real control object.

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For reduction of the low-cycle vibration of vehicles such as gondolas which are suspended flexibly, the authors studied the utilization of the control moment gyro (CMG) as an active vibration control device. The CMG is a moment generator using the gyroscopic moment effect and it is applied to attitude control of spacecraft. Particularly in the very-low-frequency region (less than 1 Hz), it is effective and requires no reaction support.

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This paper deals with the problem of control performance and optimization of the Parallel hybrid dynamic vibration absorber (PHADVA), which is a parallel combination of an active dynamic vibration absorber (ADVA) and a passive dynamic vibration absorber (PDVA). It is shown that the control force of an ordinary PHADVA with optimally tuned parameters for PDVA exceeds that of an ADVA over a certain control level. This result indicates the importance of the optimization of the spring constant and the damping coefficient of the hybrid passive elements. Their optimization is carried out, and the numerical calculation indicates that the control performance is sensitive to the variation of the spring constant, and that the optimal values become smaller as the control level rises. The effect of optimization is also investigated by numerical analysis and verified.

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A pair of hybrid mass dampers installed at both edges of the top of a six-stage structure comprising floors and pillars (approx. 3.7 m high, total weight approx. 2.5 t) was tested for its performance in reducing bending and torsional vibrations. The performance was compared between the control principles of (a) decomposing sensor signals into bending and torsion ("coupled control") and (b) separating the sensor signals ("individual control"). Both control principles proved to ensure high damping performance for bending and torsion. Between the two principles, coupled control promises better performance in general, as indicated from an example of the test results.

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For robust active vibration control for high-rise buildings, LQ control using a reduced-order model, spillover-considered control and spillover control using a low-pass filter are studied in this paper. In the numerical calculations, it is shown that the highest control performance is achieved by using a low-pass filter. In order to investigate the effectiveness of the present control methods, experiments using an 8-story model structure were carried out for the 4th-order reduced control. From the experiment results, the usefulness and feasibility of the control method for high-rise buildings are clarified.

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Modal control of magnetic bearings is applied to a shell-structured rotor to reduce the structural vibration. It is intended that the rotor be light and have a wide supporting region of magnetic flux ; hence it is made of a flexible shell structure. These structures are apt to produce shell vibrations, in addition to bending vibrations of the rotating shaft. To improve the damping property of the structure, a new control scheme for a magnetic bearing is introduced. Each magnet is controlled individually, leading to favorable structural damping, which contrasts with the traditional controller where a pair of magnets is controlled in a push-pull operation. The modal control technique is applied to the proposed magnetic bearings. The results obtained indicate a good damping property.

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To date, practical dynamic model of magnetic suspension systems using tuned LC circuits has not been established. This paper develops a transfer function model for such systems by linearizing system equations near the equilibrium state. This model not only nicely explains the inherent dynamic instability, but also provides a theoretical basis for analyzing and synthesizing system dynamic behaviors. A new dynamic stabilization method is also proposed. This method applies damping to the movable "stator" rather than to the suspended object directly, and consequently stable suspension without any mechanical contact is achieved. Experimental results are shown to confirm the theoretical analysis.

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A new active magnetic suspension system is proposed which has a displacement sensor of frequency type and uses phase-locked loop techniques for stabilization. This is termed the phase-locked magnetic suspension system (PLMS), and is studied theoretically with its basic model. It is shown that a PLMS can be stabilized with a loop filter of second or higher order. In the designed feedback system, the control input is produced from the difference in phase between the reference and feedback signals. Since phase is the integration of angular frequency, the open-loop transfer function automatically contains an ideal integration. This results in a steady-state position error of zero for step disturbances. It is also pointed out that a PLMS of self-sensing type can be realized with a switching power amplifier whose switching frequency varies with the position of the suspended object.

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This paper is concerned with the computer-based sliding mode control of flexible rotor-magnetic bearing systems (FR-MBS). The plant dynamics consisting of actuator dynamics and flexible rotor dynamics are described. The reduced-order model for controller design is given by eliminating higher-order modes of the mechanical and electrical magnetic interaction system. A discrete time sliding mode controller with reduced-order model is proposed and its robust performance is evaluated with several simulations based on a calculation model. This digital controller is implemented to replace a linear analog PID compensator. Levitation tests using the proposed digital controller are performed and compared with those of the PID compensator. With a discrete time sliding mode controller, the running test with high-speed rotation is successfully increased up to 35000 rpm without unstable vibration.

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This study is concerned with an application of H^∞ control and μ synthesis to magnetic levitation systems which have special flexible structures and the solution of the spillover problem. At first, we show the typical spillover phenomenon caused by the interaction between the control system and the flexible structure system using PID control. Next, applying mixed-sensitivity H^∞ control to the magnetic levitation system, we design the control system for it without spillover and describe in detail how to design an H^∞ controller. Finally, we analyze the structured singular value and design the μ controller using D-K iteration. In this paper, we assume the magnetic levitation system as an uncoupled system between the X and Y directions for simplicity, which is the third-order system with the exception of the guideway. As a result, it has been clarified that the H^∞ controller and μ-controller have the characteristics of two kinds of filters, a low-pass filter and a notch filter. It is found that the μ controller is superior to the H^∞ controller in terms of robust stability and robust performance. From experiments, we obtained good data on the magnetic levitation without spillover.

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The modelling of underwater vehicles in a low-speed cruising area was performed for control law design. Utilizing the model, the optimal robust control theory was applied to improve the characteristics of the system. Methods for modelling the vehicle and for designing the control system were tested, and their effectiveness was confirmed.

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This paper describes the vertical dynamic characteristics of a maglev transport vehicle that has permanent magnet suspension with mechanical levitation control. First the fundamental requirements for primary suspension, magnet characteristics and mechanical levitation controller are set up. Then, the vehicle vertical dynamics are analyzed using a two-degree-of-freedom model, where the roughness averaging effect of the undercarriage with a longitudinally distributed magnet is considered. A theoretical study and simulation are carried out to evaluate the effect of the wheelbase and magnet length of the undercarriage on the vertical acceleration of the car body and the guide wheel load, which are used as performance measures. The results show that the difference in averaging effect between the wheelbase of the undercarriage and the longitudinally distributed magnet causes an increase of guide wheel load. A suitable relation between the wheelbase and magnet length is proposed by considering the roughness averaging effect and the pitching motion of the undercarriage.

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This paper presents a new design method for solving low-frequency vehicle vibration problems. Two key ideas are used. The first is the phase control on vibration transmission in hydraulic engine mounts. The other is the vector synthesis approach in treating multiple vibration input to the vehicle body.

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This paper presents dynamic characteristics of unsymmetric suspension trucks with semi-active control to achieve compatibility between high-speed stability and curving performance. According to the direction of vehicle motion, the damping coefficient is switched so that the interwheelset structure, characterized by stiffness and damping, is asymmetric fore-and-aft. It was found in a previous study using a simple calculation model that curving performance is especially enhanced in comparison with conventional symmetric trucks. In this paper, unsteady state curving behavior of the proposed unsymmetric trucks during curve entry is calculated using full car body models with nonlinear wheel profile, considering nonlinear characteristics of the contact force between wheel and rail. Calculation results were compared with those for a conventional symmetric truck. The unsymmetric suspension truck with conical wheel profile has the best curving performance while keeping adequate stability even in sharp curves. The profiled wheel tread has not only superior steering ability but also a possibility to improve high-speed stability.

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Using a new real-time signal analysis, any signal drawn from motion and vibration may be expressed in time series by a complete set of orthonormal bases with their amplitudes to reflect the signal's dynamic characteristics, such as velocity, acceleration and power. Expressing the signal dynamics from a low- to a high-frequency region becomes possible while observing the dynamic similarity expressed in power. These bases are really wavelets, whose usage is different from that in wavelet analysis. They can reconstruct the state or phase spaces in which to study the system dynamics. The bases then become various analyzing windows to observe the dynamic signal comprising many events localized in time and frequency. As a simple example of its real-time use, some fundamental analyses are first shown using the signals from an electronic oscillator. Then how an abnormal running condition of vehicles on wheels may be diagnosed is discussed. Its simulation test was done with a small mechanical rotor rotating at about 3000 rpm in an axial air flow.

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This paper considers robust motion control of uncertain systems which contain norm-bounded time-varying unstructured uncertainties. The proposed design method is based on quadratic stabilization. The feedback controller, which robustly stablizes the uncertain plant and achieves the desired performance, is constructed based on the solutions of two matrix Riccati equations with a scaling matrix. To achieve further improvement of the command response, we introduce a feedforward control based on the inverse system of the controlled nominal plant. Our method is applied to a two-inertia system which is the simplest model of a mechanical system with torsional vibration. The simulation results show the effectiveness of the proposed method.

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This paper is concerned with the practical application of PID-self-tuning control on position control of a pneumatic servo cylinder. Instead of the complicated system-equation-deriving process, a second-order mathematical model is found by the system identification method, which is used for the controller design. A PID-self-tuning controller, whose control parameters K_p, K_i, K_d are time variant and self-adjusted, is designed and implemented in a microcomputer to control the position of the pneumatic cylinder. The experimental results with the PID-self-tuning controller are compared to those from the conventional off-line PID controller.

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Mass storage systems (MSSs) with automatic mediahandling mechanisms have become widely used in the field of information processing, and faster media handling is desired. Although there are various handling mechanisms, in all cases, disturbances such as solid friction and inertia variations are major obstacles to faster handling. This paper investigates a neural-network-based controller that compensates for these disturbances. A direct-type neural controller is proposed. The capability and characteristics of the controller are numerically and experimentally investigated by testing the positioning control of a rotary storehouse mechanism in an MSS. Experimental results, compared with those obtained using a conventional disturbance observer, indicate that the proposed neural-network-based controller can compensate effectively for nonlinear disturbances in the mechanisms.

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This paper describes an optimum motion control method for robotic serial manipulators with multiple redundant degrees of freedom. The manipulability measure, which is given by a function of the Jacobian matrix concerning the position and posture of the end effector of a serial manipulator, is proposed as the index to evaluate the dexterity of the manipulator, and it is defined as most dexterous when the manipulability measure takes the maximum value. New methods to drive serial manipulators most dexterously, namely the optimum CP control methods with and without consideration of the posture angle of the end effector, are proposed and experimentally examined for planar 3R-, 4R- and 5R-redundant manipulators. Consequently, a better result was obtained by the optimum CP control method with consideration of the posture angle than by the method without consideration of the posture angle : the manipulators were driven most dexterously over most of the driving range, and high response was obtained.

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This paper deals with the active control of power flow of a vibrating plate. It is the purpose of this paper to present a wave control method for suppressing vibration of a distributed parameter system such as a beam or a plate. Unlike a conventional modal-based control method, this method has the potential to suppress all vibration modes of a structure. First, from an analytical point of view, this paper presents three kinds of flow patterns appearing in controlled vibration intensity : (1) straight flow patterns from the excitation point to control point, (2) S-shaped flow patterns and (3) vortex flow patterns around the excitation point and control point. Then, the existence of these patterns is verified experimentally. Next, relationships between vibrational and acoustical intensities are discussed, and the acoustic power and acoustic pressure in terms of these patterns are also investigated. Furthermore, the characteristics of the rotational patterns are clarified and a means to generate the vortex of vibration intensity at an arbitrary position on a plate is presented.

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We present in this paper a rule-based control system which effectively suppresses liquid sloshing by injecting air bubbles into the sloshing liquid. We show that the most important control parameter is air-bubble injection timing, which is determined by the control laws established from the knowledge on characteristics of slosh suppression by air-bubble injection. The control experiments carried out using an 800-mm-long, 500-mm-high, and 150-mm-wide rectangular tank reveal that (1) the control laws that delay the air bubble injection timing with decrease in the sloshing amplitude and adjust the zero-level crossing timing of sloshing can successfully suppress sloshing oscillation, (2) the effectiveness of the control algorithm is experimentally demonstrated for earthquake-induced sloshing, and (3) the visualization of slosh circulation flow reveals a unique flow pattern when the sloshing is effectively suppressed and can offer an insight towards understanding the mechanism of slosh suppression by air-bubble injection.

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The chatter suppression described in this paper is based on the application of active dampers to a slender boring bar. Chatter vibration signals detected by a pickup are fed to a computer. After calculating the chatter frequency and the corresponding phase shift parameter, the computer supplies the amplified signals to piezoelectric actuators with the same phase as that of the vibration velocity of the boring bar. As a result of this, the actuators generate damping forces ; that is, they act as active dampers. It has been confirmed in cutting tests that the active damping system adapts to change and fluctuation of the chatter frequency and suppresses chatter well. Furthermore, it has become clear that there is an optimum position of the active damper for chatter suppression.

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A new active adaptive feedback control algorithm (F. B. LMS) was developed in this paper mainly for the purpose of reducing aerodynamically self-oscillating noises. This is an algorithm which reconstructs the Filtered-X-LMS to a feedback type and which needs only error signals. A simple experiment using a straight duct proved that this method could increase acoustic damping in a closed sound field by controlling the secondary source just like a sound-absorbing wall. This method was also proven to be effective for reducing periodic noises which had periodic causality. This method was applied to reduce a cavity tone and a resonant noise of a model tube bundle which were typical self-oscillating noises, and satisfactory results were obtained. It was also successfully applied to reduce periodic noises such as those in a cab of a construction machine radiating from engine, cooling fan and oil hydraulic pump.

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To reduce noise radiated from vibrating surfaces of mechanical systems, it is important to know the acoustic radiation efficiency of vibrating surfaces and radiating modes by externally applied forces. However, it is difficult to evaluate the acoustic radiation efficiencies of large systems because of their complicated structures. The reciprocity method, which is developed for evaluating ship structures, is a useful tool for the investigation of sound transfer functions from a particular system to its surrounding medium. In this paper, the application of the reciprocity method for evaluating the acoustic radiation efficiency of the hull plate is described.

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An active noise control technique for prevention of howling is studied in this paper. A 2-Microphone system is often employed in a long-sized duct, where the propagation wave is the main component. However, in a short-sized duct, the reflected waves must be considered. In this case, the authors introduced the acoustic condition that the component of the reflected wave should be absorbed at the end opposite the opening end. The authors called this system the 2-Microphone delay system. The acoustic property of the duct for the 2-Microphone delay system was examined. The effect of this active noise control system with a howling canceler was compared with a 1-Microphone system. Their characteristics were examined by comparing theoretical results with the experimental results. The features of the individual systems have been determined. It was found that the digital filter in the 2-Microphone delay system implements the control filter characteristics except the frequencies determined by the distance between two microphones. On the other hand, the implementation of the 1-Microphone system was poor.

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