Forced vibrations of rotating circular cylindrical shells are investigated. Basic equations, including the effect of initial stress due to rotation, are formulated by the finite-element method. The characteristic relations for finite elements are derived from the energy principle by considering the finite strain. The equations of motion can be separated into quasi-static and dynamic ones, i. e., the equations in the steady rotating state and those in the vibration state. Radial concentrated impulses are considered as the external dynamic force. The transient responses of circular cylindrical shells are numerically calculated under various boundary conditions and rotating speeds.

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Combination tones in a circular plate subjected to excitation having two harmonic components with frequencies Ω₁ and Ω₂ are investigated for the case in which Ω₁ and Ω₂ and one of the natural frequencies P_ll' of the plate satisfy m₁Ω₁+ m₂Ω₂≒NP<ll'> for integers m₁, m₂, and positive integers N. For theoretical analysis, the von Karman-type equation of motion of a circular plate is reduced to the modal equations using Galerkin's procedure. Then the modal equations are solved by the perturbation method of multiple scales. From the analysis, it is found that combination tones with frequencies (±2Ω₁+Ω₂), (2Ω₁-Ω₂) and (±Ω₁+2Ω₂), and subcombination tones with frequencies (±Ω₁+Ω₂)/2 can occur in multiple modes which exist in pairs for the natural frequency P_ll'. Numerical examples are given, and it is shown that the combination tones in multiple modes can take the form of a travelling wave.

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This paper presents the numerical simulation for the chaotic vibrations of a post-buckled beam with a variable cross section. The beam is clamped at both ends and is compressed in an axial direction. When the beam is deformed to a post-buckled configuration, chaotic vibration will be excited easily under periodic lateral acceleration. Applying Galerkin method, the basic equation of the beam is reduced to the ordinary differential equation of multiple-degrees-of-freedom systems. To get the steady-state response of the beam, the harmonic balance method is used. In a typical region of frequency, the chaotic response is excited. The chaotic time progress is calculated by the numerical integration. The chaotic response is examined carefully by the Poincare projection, the Lyapunov exponent and the Lyapunov dimension. The results of tapered beams are compared with that of the straight beam. The chaotic response with the asymmetric mode of vibration appears remarkably. The response shows the complicated projection to the chaotic attracter, moreover, the Lyapunov dimension takes higher value. The chaos of the beam with variable cross section shows the more complicated behavior to that of straight beam.

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One of the most important items for turbine reliability is the torsional vibration of the blade-disk-shaft system. In this paper, an effective method for calculating the torsional vibration of the blade-disk-shaft system is proposed by applying the substructure synthesis method. In this method, at first natural frequencies and mode shapes of blade-disk systems are calculated by the finite-element method, and then the torsional vibration of the blade-disk-shaft system is analyzed by the transfer matrix method using the calculated results of blade-disk systems. Because the actual turbine rotor includes many identical blade-disk systems, the torsional vibration of the whole system can be analyzed effectively using this method. In order to verify the validity of the analytical method proposed here, the results calculated using the substructure synthesis method are compared with the results calculated using the direct finite-element method. Also, a verification test is carried out and the experimental data are compared with the numerical results.

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In the screw compressor, a periodically fluctuatig torque occurs when gas pressure rises in the grooves of the rotor. An impact vibration between the male and female rotors is analyzed, in the case that movement of the male rotor is ignored. Impact occurring at both the driving and trailing sides is considered. The condition under which the periodical impact vibration occures is dependent upon the ratio of mean to amplitude of female torque. At all regions except the stable region of the periodical impact vibration, only the impact-damped vibration occurs, and the compressor is driven quietly.

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Internal resonance of cracked rotors is investigated using 2-degree-of-freedom rotor systems. Phenomena at the major critical speed and other subcritical speeds in the precritical speed range are discussed theoretically and experimentally. Phenomena in a lateral oscillation model with internal resonance and in an inclination oscillation model with no internal resonance are compared. In the former model, the two critical speeds of forward and backward whirling modes coincide. The following is clarified. (a) The vibration of the synchronous backward whirling mode changes from a steady-state oscillation to an unstable oscillation due to internal resornance. (b) The superharmonic oscillations of 2nd and 3rd order of the backward whirling mode and the super-subharmonic oscillation of 3/2-order of the backward whirling mode occur due to internal resornance.

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This paper describes the effects of air and gravity on the vibration characteristics of large satellite antennas. A numerical study is presented for the large deployable antenna of the Japanese Engineering Test Satellite VI (ETS-VI). A method using effective mass is proposed to identify vibration modes. Mode identification shows that both air and gravity have little influence on vibration modes. It is also shown that variation in natural frequencies due to the air and gravity effects depends on the their modes.

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Chaotic dynamics of the Duffing oscillator with parametric and external forcing are studied. The unperturbed system, in which the damping and external forcing terms are removed and the parametric forcing amplitude or frequency is zero, has a hyperbolic saddle with a pair of separatrices. The following two cases are analyzed : (i) the parametric forcing amplitude is small ; and (ii) the parametic forcing amplitude is large but the frequency is small. The external forcing amplitude and damping coefficient are assumed to be small for both cases. Using a version of Melnikov's method, we obtain conditions under which the stable and unstable manifolds of a normally hyperbolic invariant torus intersect transversely and chaotic dynamics may occur near the unperturbed separatrices. Such chaotic motions are appropriately characterized by a generalization of the Bernoulli shift. We also describe the influence of parametric forcing on conditions for the occurrence of chaos. Numerical simulation results are given to demonstrate the theoretical results. Sustained chaotic motions wandering near the unperturbed homoclinic orbits are found.

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A new method for parameter identification of single-degree-of-freedom nonlinear vibrating systems is proposed in the time domain. The nonlinearity is approximated by piecewise linear characteristics. The nonlinear characteristics of restoring force and damping can be obtained from the linear spring constants and linear viscous damping coefficients identified on each piecewise linear section. Two experimental procedures, that is, the impact excitation method and the additional mass method without excitation, are performed. The response and excitation data for the impact excitation are required in the impact excitation method and the free vibration responses of the system with and without additional mass are required in the additional mass method. System parameters of the vibrating systems with various nonlinear characteristics, Duffing-type system and clearance system, can be accurately identified by both the procedures. It is shown that the additional mass method is valid for torsional nonlinear systems on which the measurement of excitation force is difficult.

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This paper describes a convenient method of identification of non-linear vibration system by a neural network using time series data. The neural network using suitable system of inputs and outputs are applicable for system identification of non-linear vibration by learning of impact response. By learning of only time series datas of impact response, it is possible to predict both forced vibration response and impact response in time domain by the neural network. The effectivenss of the method presented is demonstrated by numerical simulations for Duffing system and piece wise linear system.

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This paper presents a method for optimizing vibration absorbers on a flexible beam by means of a neural network procedure. Analytical results for the response of the beam with multi-absorbers have been obtained using a transfer matrix method. To achieve optimal control, a cost function composed of second-order nonlinear forms in terms of the displacement, strain, and frequencies was used. A method of minimizing the function was presented, in which input values, weights and output function were effectively controlled on the basis of the back-propagation procedure of the neural network method. Numerical calculations were carried out for an example problem. It is ascertained that the present method gives a better result than that obtained by the previously published method. The validity of the method and the analytical results was confirmed by experimental tests.

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The optimum configuration of the composite plate covered with an unconstrained viscoelastic damping layer is discussed from the viewpoint of the modal loss factor. When the configuration of a damping layer is optimized to an arbitrary mode, it's modal loss factor becomes maximum. In general, however, loss factors of the other modes are much lower than those obtained by optimization to each mode. Therefore, in this study, the optimum configuration of a damping layer is investigated under consideration of modal loss factor to some modes. The optimum distribution of the damping layer is obtained by sequentially changing the position of a section of the layer to another position to optimize the composite modal loss factor. Results are compared with the modal loss factors of (1, 1), (1, 2) and (1, 3) modes, which are optimized to their individual modes. These results indicate that although the maximum loss factor is decreased by 2∼8% compared to those optimized only to each mode, those of the other modes could be increased by 5∼23%. The results are validated by suitable experimental results.

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This paper is concerned with an inverse problem of the active control of nonsteady dynamic vibration in elastic beams. A simulation technique based on the integral equation method and the filter theory is successfully applied to such an inverse problem. The Laplace-transform integral equation method is used for the solution of dynamic bending vibration in elastic beams. Through a Taylor series expansion, the nonlinear system is reduced to a linear system for modification of the unknown parameters, and it is solved iteratively so that an appropriate norm is minimized. A few examples including continuous beams are computed and the results obtained are discussed, whereby the usefulness of the proposed method is demonstrated.

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This paper describes active vibration control of a vibration isolation system in a vehicle. The system consists of eight rubber springs which suppor the deadload of a sprung mass and six voice coil motors for vibration control. In order that control force acts not only in the vertical direction but also in the horizontal direction, voice coil motors have been inclined 30°. To avoid mechanical interference among the motors, rubber springs have been inserted between moving coils and the sprung mass. The spring characteristics of the rubber springs and the moving coil masses produce second-order delays. The feedback control of the acceleration of the sprung mass damps the vibration isolation system. Our controllers function as integrators in a lower-frequency region, and in order to compensate the delays, they function as differentiators in a higher-frequency region.

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In order to control flexible mechanical structures, reduced-order mathematical models are required for the computer control system. Several modeling methods have been proposed for vibration analysis and control. This paper discusses the following four modeling methods : modal method, Guyan's method, quasi-modal metod, and the reduced physical modeling method. The accuracy of calculated eigenvalues and the vibration controlling effect of each model are discussed. A thin plate having three lumped masses is used for the comparison. Regarding the eigenvalue calculation, the quasi-modal model is the most accurate of the four. However, all four methods result in the vibration control effect in our experimental tests.

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This paper analyzes the performance of neural networks to be used for identification and optimal control of active pneumatic suspensions of high speed railway vehicles. It is shown that neural networks can be efficiently trained to identify the dynamics of the nonlinear pneumatic suspensions. Neural networks can be also trained to function as optimal nonlinear controllers, which improves the suspension performance. The performance of the nonlinear suspension with a neuro-controller is compared with that of a LQ controller designed after linearizing the suspension components around the equilibrium point.

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A simulation program of vehicle dynamics for analysis of running safety of a railway vehicle was developed. Curving performance simulations were made. Original waveforms obtained from the measured 10m chord's versed sine of the track inspection car were used as the data of track irregularity for our simulation. Simulation results agreed well with measurement results. By using this simulation program, we found that an outer wheel load decreases running on an exit transition curve. The results show that the stiffness of a primary suspension is related to wheel load decrease.

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The objective of this study is to describe aerodynamic effects on vehicle dynamics. In this paper, the formulations of aerodynamic characteristics presented in the previous report are applied to the longitudinal 4-degree-of-freedom model, and used to simulate two-dimensional motions with the typical parameters of a passenger car. It is shown from the results of numerical studies that the pitching and heaving motions change their transient response characteristics with speed under high-speed conditions. Moreover, the effects of aerodynamics on the longitudinal motions are estimated as apparent changes of the spring and damping constants of the front and rear suspension systems, respectively.

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Instead of good effects on the ride comfort, the active suspension may have unfavorable effects on the wheel/rail interaction such as the increase of lateral force on the wheel. This paper deals with an analytical study about the lateral dynamics of two types of railway vehicles, in which an active suspension mechanism controls the running vibration. One vehicle type has the trucks with a bolster and side bearers, and the other type the bolsterless trucks with yaw dampers. The analytical models for the vehicles consider non-linear characteristics such as creep forces and wheel flange/rail side collision. In this study the active suspension has a controller based on the optimal control theory and assumes ideal actuators to be available. Their operations on the track with alignment irregularities are simulated up to the speed of 350km/h. The results show that the active suspension can improve the ride quality without any increase of the wheel lateral force and that the bolsterless truck has better ride quality and occurs smaller wheel lateral force than the other type truck in the higher running speed range.

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Active suspensions have been studied to improve the ride quality of railway vehicles. In many cases, pneumatic actuators were employed in these studies. This paper deals with the application of oil-hydraulic actuators, which are expected to have more control effect on the running vibration. They have been examined experimentally by using a 3 d. o. f. half-vehicle model. The LQG control law, in which state variables were estimated from measurable ones on actual railway vehicles, was adopted. The results show the possibility that the controllable frequency range is extended by the oil-hydraulic actuator under practical conditions. The addition of bogie acceleration measurement to body-related measurements provides a significant advantage for the performance. When actual body weight becomes lighter than that of the controller design value, the control performance and the stability deteriorate. Therefore, it is recommended that the empty car body weight be used for design of the active suspension controller. Moreover, the control effect can attain the maximum vibration isolation level if the sampling period is shortened to 2 ms.

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It is empirically known that a railway vehicle is by nature, characterized by contra-dictory behaviors on a tangent track and on curves. Hence, it becomes clear that the Z-link-equipped vehicle, which is intended to improve the passing performance on curves, has a slight forward expansion of the unstable region of body hunting in comparison with traditional vehicles. In order to improve this hunting unstability, the steering truck with a unique mechanism, Z-N-link suspension device mechanism, has been developed, which contributes to enhancement of good running performance both on the tangent track and on curves. On the basis of the theoretical analysis, it is recognized that adequate supporting stiffness at the point of connection between N-links is an effective means of increasing the hunting velocity, and that there exist two limit cycles, that is, one is an unstable limit cycle and the other is a stable one. In this paper, a new concept of the steering truck is given, which provides guidelines of future design of high-speed trucks.

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The purpose of this study is to achieve decentralized processing of the finite-element method (FEM) by making use of matrix decomposition. For structural analysis of FEM, generally, the global stiffness matrix is a very large matrix which reflects the physical properties of the structure. The matrix decomposition can be used to transpose the global stiffness matrix with simple band matrices. The object of analysis in this study is a truss. The matrix decomposition is effective for the high-dimensional equation which decomposes a reduced-order equation. The computational process with analysis of FEM can be optimized such that the time complexity is minimized due to parallel processing. In this study, the matrix decomposed algorithm is derived for the analysis of a truss, and the time complexity and the arithmetic complexity are compared numerically. Results show that, the time complexity and the arithmetic complexity can be reduced to 29% and 26%, respectively.

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It is very important to estimate the damage rate of machines and structures caused by low cycle fatigue under dynamic loading, from the point of view of guaranteeing their safety and developing the scheme of their maintenance. Therefore, the in-service health monitoring system to monitor the damage rate of machines and structures by low cycle fatigue is proposed to assure the safety of the structures. In this paper, the use of wavelet transform is proposed to extract the fatigue signals from the noisy detected signals. The model of fatigue is considered to be that of reducing stiffness of members of machines and structures having impulse forces occurring at random intervals. The response of machines and structures excited by these impulse forces is analyzed under noisy conditions. The wavelet transform is applied to the analyzed responses, and extraction of the assumed signals of fatigue from these responses is proven.

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Non-stationary signals must be represented in a time-frequency plane because frequencies of those signals evolve with time. For the time-frequency analysis, representative methods, such as spectrogram, Wigner distribution and wavelet transform (WT), have been investigated. WT, in particular, has attracted much attention, because it can detect discontinuous points in signals, and the frequency resolution of WT is similar to that of a human ear. In the case of wavelet analysis, if the admissibility condition is satisfied for the analyzing wavelet applied, the time-frequency distribution can be inversely transformed to the original time series. In this study, comparisons are made between original signals and the inversely transformed time series of the time-frequency distribution obtained by WT for several kinds of signals. It is clarified that the signal reconstruction by means of inverse wavelet transform (IWT) is a very potent method in the field of signal analysis.

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In the steam generators (SG) of LMFBR, it is necessary to detect the leakage of water from tubes of heat exchangers as soon as it occurs. The active acoustic detection method has drawn general interest owing to its short response time and reduction of the influence of background noise. In this paper, the application of the active acoustic detection method for SG is proposed, and sound attenuation by bubbles is investigated experimentally. Furthermore, using the SG sector model, sound field characteristics and sound attenuation characteristics due to injection of bubbles are studied. It is clarified that the sound attenuation depends upon bubble size as well as void fraction, that the distance attenuation of sound in the SG model containing heat transfer tubes is 6dB for each two-fold increase of distance, and that emitted sound attenuates immediately upon injection of bubbles.

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A 3-port regulator valve, actuated by a linear solenoid, has been used increasingly in advanced automatic transmission. This paper presents a study of the stability of such a valve. By using a static model, which includes notches and inner leakage, and a dynamic model, where air in oil considered, good agreement between calculated and experimental results is shown. This model was linearized and reduced to generate the pole configuration. Variance analysis of simulated step responses in the nonlinear condition indicates that there are some factors which strongly influence stability. It can be concluded that decreasing the sensitivity of regulator valves improves stability. In addition, it is shown that inner leakage has a significant effect on the stability, and notches affect the sensitivity of regulator valves.

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High pressure pulsation generated by vane pumps causes serious vibration or noise in oil pressure systems. As vibration or noise reduction by increasing the stiffness of the system is difficult, reduction by decreasing the pulsation is required. This paper presents an interferential method to decrease the pulsation and a simulation of the interference. The interferential device is composed of tandem vane pumps, dual pipelines and an interferential chamber, and is supplied with pulsation flows of phase difference 180°. The interference effect occurs in the upper stream of the chamber because of the flow speed of the pulsations ; both the pulsation and the phase difference decrease gradually. The simulation clarifies the effect seen in the experiment. We also indicate the similar effect in flows separated by an elastic film.

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Multiple elevator doors are driven with one servomotor through a multi-degree-of-freedom linkage system. This paper deals with the derivation of the equation of motion of the door mechanical system. The movement of the doors is described by giving various constraint conditions to multiple single-chain and multi-degree-of -freedom rigid body systems. The door motion was simulated based on this formulation. The conclusions are as follows. (1) It is clarified by computer simulation that the change in the constraint condition caused by integration error is extremely small. (2) The method of obtaining the motor driving torque, in which a given movement of the door or the motor is regarded as a constraint condition, is proposed. (3) The conversion of joint torques to motor torque can be obtained by converting these joint torques into a single-degree-of-freedom system which is motor rotation.

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Power match control of hydraulic power systems involves continuous control of the output power of the hydraulic pump so as to agree with the power of the load actuator. In a previous report, we investigated the dynamic performance of pressure match control, employing an electrohydraulic power match system driven by the differential-PWM method. The result showed that the system had good control performance. The feature of this system is different from that of a conventional type ; that is, pressure, flow rate or power of the load actuator can be controlled without the need for any control valves such as a load-sensing valve and a flow control valve. In this report, the performance of flow rate match control is evaluated by experiment and computer simulation. It is verified that the system has good control performance.

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In the sterilization process for foods packed in cans or retortable pouches, it is of importance to reduce quality deterioration of packed foods, achieving a certain level of sterilization. For this purpose, the optimum retort temperature profile is investigated in this paper. The optimal control theory was used to determine the optimum retort temperature profile for maximizing quality retention for a given final sterility value during the heat sterilization of conduction heating foods in flat containers. This is a constrained optimal control problem with an unspecified terminal time. The conjugate gradient minimization method is applied to this problem. The results show that the best profile can nearly be approximated by a ramp function.

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This paper proposes a design method of the minimum energy controller in the z-domain for a multiinput, linear, time-invariant, discrete-time system. The controller is expressed by the dynamic state feedback, and induced from the open-loop expression (or the closed-loop expression with time-varying gains) in the t-domain, using the property that the state of the controlled object settles to zero within a finite time. Since this controller has constant parameters which do not depend on the initial state of the system, it is more useful to analyze, synthesize and implement the feedback system. Furthermore, the stability and the finite-time settling property of the feedback system are guaranteed.

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An active acoustic power control method for three-dimensional space was investigated both theoretically and experimentally. This paper focuses on the typical case of a single primary and multiple secondary point sources, and methods of minimizing the power output using the exisiting Filtered-X LMS algorithm are presented. Suitable arrangements of the sources and microphone are proposed on the basis of theoretical estimations. The authors call this the acoustic nodal point method. The power reducing performance was verified by applying the method to the noise radiating from a duct opening. Considerable noise reduction was achieved both at the error microphone and in the whole area around the noise source.

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The basic idea of the prediction is founded on our previously published theory, in which the vapour lock is mainly caused by the bubble growth below the brake-fluid boiling point. According to this theory, a brake pedal becomes spongy due to the bubble growth, and fluid pressure may be lost upon further growth. Hence it is most important for drivers to be able to determine the beginning of the bubble growth in a hydraulic brake because they can predict the vapour lock. Therefore, we developed an alarm device for vapour lock, which can sense the bubble growth, using a simple sensor with 2 short conducting wires embedded in disk calliper housing. Using this device, we are altered to bubble growth in the disk calliper housing by the light of the alarm lamp. In this report, the outline of this alarm device and the significance of the adoption of the device in automobiles are explained.

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High-level noise induced in MRI equipment has been a main obstacle for their wide application in medical diagnosis. The noise is caused by the vibration of the cylindrical shell used to support the gradient magnetic field coils in MRI. In this study, a reduced-size model of the coil drum is constructed using polymer films and piezoelectric films. The piezoelectric films are divided into several patches and two patches of them are used as integrated bending actuators in the control of the shell vibration so that no external actuators are needed. The disturbance cancellation method is used since the shell is excited by predetermined forces. The relationships between the size, position and output magnitude of the actuators and control effect are also discussed. Experiment and simulation were carried out for the cases where the shell was excited at resonance frequencies of three main modes. The results show that the disturbance cancellation method in combination with the piezoelectric film actuators can successfully suppress the forced vibration of the shell and that the minimum amplitude of controlled vibration varies with the resonance mode.

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The present paper shows an analysis for stability and dynamic responses of a rarefied gas lubricated slider bearing on a magnetic recording disk. Knudsen number of the air film under the head slider is close to 1/5, i. e., the limit of continuum, so a modified Reynolds equation is adopted for this problem. The other, more crucial problem is stability of the head accelerated by air lift which is rather random due to up-down motion of the rotating disk. The problem is reduced to a coupling problem of the vibrating system subjected to random fluid pressure. FEM and FDM are adopted for the modified Reynolds equation and the method of Duhamel integral is applied to equations of motion. The result shows the adequacy of the computation and the method. Results of analysis for random acceleration are shown by dynamic response diagrams of the head slider and power spectra of the response.

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The optimal setup condition for camera calibration is clarified in this paper. In order to obtain general results, the camera model is first normalized. Then, the setup constraints for fiducial marks are proposed to reduce the number of parameters to be considered. Errors of calibrated camera parameters and those of visual angles are given by applying the law of error propagation for measurement errors of image coordinates of fiducial marks. The visual-angle errors are calculated under different setup conditions, and the optimal setup condition giving the minimum visual-angle error is obtained. Furthermore, the visual-angle error under the optimal setup condition are quantified for some cameras with different intrinsic parameters. Finally, a formula is derived which can provide visual-angle errors for any camera.

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The sensation of touch and force is generated or conducted through the phenomenon of contact. This fact make us aware of a new force feedback method, which was named the concept of Surface Display. In this concept, we are remarking not on the force between the user and the object but on the surface and existence of the object. The force feedback device based on this concept presents the surface of an object, the user interact with the surface. Force is caused only as a result and it is measured by the device for the simulation of the behavior of the object. In this paper, the application of this device into a shape forming task is discussed. We have developed a kind of the virtual clay modeling environment, in which the shape of the surface can be changed by pushing directly on the surface. Sensation of making contact with the surface and the sensation of force caused by the elasticity of the clay is fedback by using the device. From an experiment in the environment, the importance and effectiveness of force feedback was made clear.

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This paper presents generation and adaptation mechanism of the swarm strategy for a multi-agent system in a dynamic environment. The approach for the adaptation of the swarm strategy is based on the clonal selection theory of the biological immune system. The immune system possesses a homeostasis maintenance mechanism which allows for recognition of self and non-self, and removal of foreign substances from the body. In this paper, we adopt some of the immune mechanisms for each agent and for interaction between agents. "Tactics cloning", the mechanism we present here, is one method to search and adapt the optimal swarm strategy in a dynamic environment. By using this tactics cloning, individual tactics or a set of individual tactics generates the most optimal swarm strategy.

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This paper deals with an optical servo system using a bimorph PLZT actuator which has relatively large displacement. This optical actuator works by controlling the intensity of irradiated U. V. beam using the feedback controller. An optical actuator servo system is proposed as a mathematical model of the optical actuator, and the transfer function of the optical servo control system is identified. Optical servo control experiments are conducted. To improve the response of the bimorph PLZT actuator, U. V. beams are irradiated on both sides of it. We also show the experimental results of the double-sided U. V. beam irradiation.

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This paper describes a new visualization technique for three-dimensional large-scale finite-element analyses, whose visualization speed is independent of mesh size. Once an analysis shape is defined, a small-scale mesh with uniform distribution of element sizes is created using an automatic mesh generation technique. The mesh is named here a virtual finite-element model and used only for the purpose of visualization. Then the mapping between the virtual FE model and the analysis shape and the mapping between the virtual FE model and an actual FE model are established. Analysis conditions and analysis results can be visualized using the virtual FE model interactively on any graphics hardware. We developed a postprocessor, and applied it to a large-scale heat conduction problem. It was demonstrated that this technique can provide a fully interactive visualization environment.

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We developed an electrostatic linear actuator for use as an artificial muscle which consists of parallel plate capacitors and a slider made of dielectric material. The most effective method to increase the output force of the actuator is optimizing the dielectric constant of the gap-filling medium, which fills the space between two electrodes of the capacitor, and increasing the dielectric strength of the medium for supplying high voltage to the capacitor. We chose liquid crystal as the gap-filling medium. Its maximum dielectric cnstant is 23 and the dielectric strength is 5.5 MV/m. The maximum output force of 56.5 mN was generated by the actuator filled with liquid crystal. This value is seven times as large as that generated by the same actuator filled with pure water used as the gap-filling medium in previous experiments.

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Force control using a hierarchical structure is discussed, which consists of upper force control and lower joint position control. The force controller calculates the joint position corrections necessary to control the force in the desired manner. These correction signals from the force controller are output to the lower controller and added to the nominal joint position command. In this paper, we apply mixed sensitivity design of H_∞ control theory to a force control system. The nominal model is discussed, and the robustness against modeling errors is analyzed. Owing to joint torque feedback control, the change of the controlled plant is reduced, so high gain force control can be achieved. Experimental results and eigenvalue analysis are also presented.

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Adaptive control seems to be effective for force control of robot manipulators, where the dynamics of the total system varies in a wide range or becomes unknown in some cases according to the change in the environment around the manipulator. In this report, aiming at practical usage of force control, the problems that were discussed first were those which would be fatal in the application of the theory of model reference adaptive control to actual industrial robots using a cross-type robot manipulator. Then effective solutions were drawn based on the robust adaptive control strategy. As the result, a force control system with excellent performance could be designed with carefull tuning of the design parameters which are complexly related with each other.

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An artificial rubber muscle has attracted much attention to features of light weight and mechanical flexibility, thus it is anticipated to be applied to a robot which can operate kindly against or with human. However, there are few reports on the multi-d. o. f. manipulator using this actuator. In this study, a hybrid-type position and force control is carried out by using a 2 d. o. f. manipulator comprising this actuator, of which fundamental control performances are investigated. This actuator has a nonlinear characteristic in terms of structure and air compressibility, which makes accurate position control difficult. To cope with these problems, a position controller using a two d. o. f. PID controller is realized by adding a feedforward compensator. As a result, a satisfactory position tracking control performance can be obtained. Also, hybrid control of force control and tracking speed can be accomplished with sufficient accuracy.

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This paper presents a robust control scheme for robot manipulators with flexible joints. By the analysis of the properties of the model of the manipulator and the presented lemma, exponential convergence is ensured which dose not make any assumption on stiffnesses of joints. The uncertaity bounds of parameters are needed to derive the control law. The control input is always continuos and can guarantee global exponential stability of tracking errors. The control scheme is applied to an one link flexible-joint manipulator as an illustrative example.

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A new algorithm is proposed to generate a collision-free trajectory for a robot manipulator. In this method, joint trajectories are described by uniform B-spline curves and the control points which represent initially specified joint trajectories are improved by the nonlinear optimization technique called Complex Method. The algorithm makes use of two advantages. The first one is that control points of B-spline curves uniquely, continuously, and locally describe joint trajectories. The second one is that the Complex Method does not require the gradient of performance index which represents the interference between manipulator links and obstacles and which evaluates the goodness of the trajectories. The proposed algorithm is simple and easily applicable. The effectiveness is also confirmed by examples for the trajectory generation of multijoint manipulators.

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In general, a semiclosed loop method which utilizes the signal obtained from an encoder mounted on a servomotor, is adopted in the control of industrial robots. In this method, the position of the end-effector is not controlled very accurately. Therefore, we aim to apply a closed loop control which uses the absolute position measured directly at the end-point. However, it is very difficult to control the arm based on this method because of the flexibility of the driving system. In this study, a robot arm with the damper using electrorheological fluid is developed in order to improve the stability. Then the closed loop method is applyed to the positioning of the end-point of the arm. The feedback-controller is derived by using the mixed sensitivity problem of H_∞ control theory.

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This paper presents analytical and experimental studies on dynamic characteristics of a horizontal robot arm composed of high-and low-rigidity links. Two links are connected by a passive joint that has a brake system. To drive the robot arm at high speed with less power, this system harnesses elastic strain energy of the low-rigidity arm and inertia of the system itself. The low-rigidity arm is modelled as a cantilever beam in the analysis, and the robot arm is driven by a D. C. motor in the experiment. Experimental results show the same tendency as analytical ones in regard to the relationship between the time taken to release the brake and the rotating speed of the arm.

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