Exact solutions of the free vibration in a family of Duffing oscillators having hard, soft or snap-through springs with single-degree-of-freedom are solved in terms of the Jacobian elliptic functions. However, their precise numeration is rather difficult using the constant-digit computer. In our previous papers, the algorithm and program for the precise numerical computation of the exact solution for hard as well as soft spring systems were proposed. As a continuation of the previous studies, we investigate here the snap-through spring system. This system has two kinds of solutions which are referred to as the "symmetrical full-swing mode" and the "asymmetrical half-swing mode". The present paper discusses excellent algorithms/programs for the symmetrical full-swing mode. The FORTRAN program with the precision of REAL*16 is presented accompanied by the user's manual, which ensures a relative error of less than 10^-30. Numerical results of the dynamics of the present free oscillator are also discussed and demonstrated.

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Exact solutions of the free vibration in a family of Duffing oscillators having hard, soft or snap-through springs with single-degree-of-freedom are solved in terms of the Jacobian elliptic functions. In our previous papers, the algorithms and programs for the precise numerical computation of the exact solution of the free vibration with hard, soft and snap-through (symmetrical full-swing mode)spring systems were successively proposed. As a continuation of the previous studies, we here deal with the snap-through spring system in the asymmetrical half-swing mode and discuss excellent algorithms/programs to calculate the exact solution. The FORTRAN program with the precision of REAL*16 is presented accompanied by the user's manual, which ensures a relative error of less than l0^-30. Numerical results of the dynamics of the present free oscillator are also discussed and demonstrated.

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This paper deals with forced self-excited vibration accompanied by dry friction, as an example of vibrations of nonlinear systems with discontinuities. The resonance curves of harmonic, higher-hamonic and subharmonic vibrations are obtained using the direct numerical integral method presented previously by us, which is a kind of shooting method and is highly accurate. Chaos and beats are also found. Influences of amplitude and frequency of external force on the stability of solutions are discussed. It is found that bifurcation is realized from the change of the types of vibrations, mamely, change from vibration without stick to that with stick, and vice versa. Periodic solution becomes unstable due to this bifurcation and chaos sometimes occurs abruptly on the halfway through the period doubling route. In this study, a new route to chaos was found using a mechanical model.

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The response of a one-degree-of-freedom system with a parametric nonlinear vibrating system subjected to combined parametric and harmonic external stimulating forces is investigated. The characteristic of the system is analyzed using detailed numerical simulation and an averaging method. The numerical results reveal very complicated dynamic behaviors including many kinds of periodic solutions, period doubling bifurcations and chaos. A bifurcation diagram and invariant curves are also presented.

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The inverse iteration method is one of the most effective methods of eigenvalue analysis and is suited for both vibration and structural analyses. It can compute eigenvalues in the order of increasing absolute value, the convergence of iterative computation can be accelerated by applying the technique of origin shift. However, the inverse iteration method must be able to solve a large-sized simultaneous linear algebraic equation in every iterative process. In order to improve the computation accuracy and the computation speed of the inverse iteration method, we introduce the concept of the transfer influence coefficient method into the iterative process. The transfer influence coefficient method is advantageous in that it can solve simultaneous linear algebraic equations, and the memory size required in the computation is extremely decreased. The present method is applied to both the undamped and the damped systems.

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The dynamics of an overhead-crane-type one-link manipulator with a passive joint is essentially described by nonlinear ordinary differential equations including trigonometric functions. Under certain conditions, therefore, it is predicted that a manipulator performing repetitive tasks will exhibit typical nonlinear phenomena, such as the coexistence of several periodic vibrations and chaotic states of vibrations. In this paper, periodic motions of the manipulator are studied numerically, and their bifurcation diagrams in several parameter planes are calculated using the algorithms based on the geometric approach of ordinary differential equations. Period-doubling bifurcation leading to chaotic motions are observed in some parameter areas.

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This paper presents the numerical simulation for the chaotic vibration of a shallow arch having a variable cross section. The arch is excited laterally by periodic acceleration. Using the Galerkin procedure on the basic equation, the equation is reduced to that of multiple-degree-of-freedom systems. The chaotic responses are investigated by numerical integration. When the chaotic motion appears in the arch with large curvature, many natural modes of vibration of both symmetric and asymmetric modes are excited simultaneously. These modes are coupled strongly to each other. In the Lyapunov spectrum, there are more than two terms with positive Lyapunov exponents. The Lyapunov dimension increases as the curvature of the arch becomes large. Furthermore, the chaotic attractor in the Poincare section shows more complicated projection.

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This paper describes a nonlinear oscillator derived from the gear meshing vibration, which exhibits successive different bifurcations ending in chaos below the first resonance. These bifurcations are examined in detail using bifurcation diagrams, Lyapunov exponents, winding numbers, invariant curves, and Poincare maps. There are two types of sudden changes from a chaotic to a periodic attractor. One is the case, named "hysteresis", in which a chaotic attractor is transformed into a periodic one far from the chaotic one, and the other is the case in which a chaotic attractor transforms into a periodic one which lies inside the chaotic one. When an n-periodic attractor transforms into a chaotic one through period-doubling, a heteroclinic connection between the outset of a 2n-periodic inversely unstable fixed point and the inset of an n-periodic inversely unstable fixed point is necessary to generate an n-band chaotic attractor. If a directly unstable fixed point exists in the vicinity of any band attractors and the attractor touches the inset of the directly unstable fixed point on the above-mentioned sequence, the attractor expands due to "interior catastrophe", and immediately transforms into a one-band attractor.

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In this paper, a nonlinear oscillator derived from the gear meshing vibration is investigated, which exhibits successive different bifurcations ending in chaos above the first resonance. These bifurcations are examined in detail using bifurcation diagrams, Lyapunov exponents, winding numbers, invariant curves, and Poincare maps. In the bifurcation diagram, periodic subharmonic oscillations appearing nonsuccessively as a "window" belong to the same "families", which are divided into two kinds : type- I, in which fold bifurcation occurs iteratively (multifolding) in the family, and type- II, in which fold bifurcation occurs only at both ends of the family. Depending on whether both of the chaotic attractors before/after the bifurcation exist in the same area on the phase plane or not, the chaotic attractor bifurcates discontinuously according to "hysteresis" or "interior catastrophe". In the case that a 2ⁿ-band attractor transforms into a 2^n-1-band attractor without fold bifurcated directly unstable fixed points, and a periodic directly unstable fixed point exists very close to an inset of a 2^n-1-periodic inversely unstable fixed point, the unstable 2^n-1-band attractor is suddenly transformed into a one-band attractor upon touching an inset of the periodic directly unstable fixed point.

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In this paper, a single-degree-of-freedom magnetic levitation dynamical system, the spring of which is composed of a magnetic repulsion force, is numerically analyzed. The magnetic repulsion force is described by the formula : A[D/(B+x)]^P+C, where P=8. This has been reported in our previous paper [ref. (1)]. By means of the free vibration analysis, it was found that the system has soft spring properties and acts like a collision system. When the base on which the system is installed is moved harmonically, the body levitated by the magnetic force shows many kinds of vibrations upon adjusting the system parameters, viz., damping, excitation amplitude and excitation frequency. For a suitable combination of the parameters, an aperiodic vibration occurs after a sequence of doubling-period bifurcations. Several typical aperiodic vibrations are identified as chaotic by examining their bifurcation diagrams, Poincare Maps, Fourier spectra, and fractal dimension analyses.

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A method is developed for estimating the response distribution of a nonlinear system subjected to nonwhite random excitation. The method consists of the non-Gaussian equivalent linearization technique and the use of the moment equations approach. The non-Gaussian probability density for the response distribution is expressed in terms of the potential of the system and employed for determining the equivalent linear coefficients. Numerical examples are given for a single degree-of freedom system with nonsymmetric nonlinearities. The rms and mean responses and the probability density of stochastic responses are obtained and compared with the corresponding digital simulation results.

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Probability distribution of stationary responses of a nonlinear system subjected to a random train of impulses which occur at random times and have random amplitudes is analyzed. Firstly, statistical properties of a random train of impulses are formulated, and equations for statistical moments of responses are derived. Secondly, weighted sum of several Gaussian probability density functions with various parameters is used to approximate the probability density functions of responses which are generally non-Gaussian. Computational procedure is shown and numerical examples are given for a Duffing oscillator. The usefulness of the present method is demonstrated by comparison with simulation results.

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Three-dimensional vibration analysis is proposed for determining the natural frequencies of a symmetically laminated, cross-ply thick rectangular plate with any set of boundary conditions along the edges. For this purpose, the Ritz method is used with displacement functions containing boundary indices. Numerical results are given for cross-ply laminated graphite/epoxy plates having different thickness ratios, and the validity of the solutions is established by convergence tests and comparison with other results. The range of applicability of the present three-dimensional and various two-dimensional plate theories is discussed.

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An exact-solution procedure is presented for solving free vibrations of laminated composite thin shells of revolution having meridionally constant curvature. Based on the classical lamination theory, equations of motion and boundary conditions are obtained from the minimum conditions of the Lagrangian. The equations of motion are solved exactly by using a power series expansion for symmetrically laminated, cross-ply shells. Frequencies and mode shapes are presented for shells with both ends clamped and freely supported, and the effects of various parameters upon them are discussed.

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his paper deals with the vibration and steady-state response problems for laminated composite noncircular cylindrical shells. Based on the classical lamination shell theory, equations of motion and boundary conditions are obtained from the stationary condition of the Lagrangian. The equations of motion are solved exactly by means of a power series expansion for symmetrically laminated, cross-ply shells having both ends freely supported and a load distributed uniformly in the circumferential direction and sinusoidally in the axial direction. The effects of the number of laminae and stacking sequences upon the steady-state responses of displacement and bending moment are discussed.

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An exact solution procedure is presented for solving free vibrations of laminated composite thick shells of revolution having meridionally constant curvature. Based on the thick lamination theory considering the shear deformation and rotary inertia, equations of motion and boundary conditions are obtained from the stationary conditions of the Lagrangian. The equations of motion are solved exactly by using a power series expansion for symmetrically laminated cross-ply shells. Frequencies and mode shapes are presented for shells with both ends clamped and freely supported, and the effects of shear deformation and rotary inertia are discussed by comparing the results from the present theory with those from the thin lamination shell theory.

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The damping property of aluminum honeycomb sandwich panels is discussed. Aluminum honeycomb sandwich panels are treated as orthotropic materials and parameter identification is performed based on Timoshenko's beam theory in this paper. Each parameter in the beam model is determined step by step. Namely, at first, the density is obtained by measurement of the dimensions and weights of test pieces, and the elastic constants are calculated from both experimental and analytical natural frequencies. Moreover, the modal damping ratios are determined from the acceleration for impact excitation tests. The calculated results are compared with experimental ones and the validity is confirmed. It is demonstrated that the aluminum honeycomb sandwich panel has excellent damping characteristics.

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This paper proposes a method for obtaining stresses in a rod with arbitrary cross section. The rod consists of two infinite straight portions and one two-dimensional curved portion in which the cross section varies. A twisting wave propagates from one of the two infinite straight portions to the other via the curved portion. In this analysis, fundamental equations were extended in order to apply them to the non-circular cross section by using the Fourier expansion collocation procedure, and the transfer matrix was derived. At connecting sections, solutions of curved portion and those of straight portions have been connected. Then it is possible to obtain the principal stress and the principal shearing stress at any location.

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The steady-state response of a disk-beam coupled system having cyclically symmetric structure subjected to a sinusoidal point force is investigated analytically. The orthogonal polynomials generated using the Gram-Schmidt process and the eigenfunction of a uniform disk are employed as admissible functions, and artificial springs are introduced between the components to satisfy their continuity condition. The equations for steady-state response are derived by means of the Lagrange equation. The response curves of the system are calculated numerically to examine the effect of damping factors, the location of the driving point, the existence of the shroud, and the stiffness ratio of the disk and beams.

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This paper describes the theoretical modal analysis of a thick circular plate with a solid shaft and a solid cylinder. For the modal analysis the circular plate is divided into three pieces : a circular plate with a solid shaft and two cylinders, namely, the left cylinder and the right cylinder. Using the solutions of flexural vibration of the circular plate with a solid shaft and those of the two cylinders with given boundary conditions, the natural modes of vibration of the circular plate with a solid shaft and a solid cylinder are solved. The calculated natural frequencies and mode shapes coincide with those obtained by the experimental and FEM modal analyses.

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The importance of viscoelastic materials has been increasing in engineering applications such as vibration-absorbing devices and shock-absorbing devices. The author has studied the dynamic behavior of silicone gel which is an important vibration-and shock-absorbing viscoelastic material. This material shows high performance in absorbing vibrations and shocks from the mechanical systems to which the material is applied. The measured complex shear moduli of the silicone gel have suggested that the silicone gel can described by a generalized Voigt model. The objective of this paper is to elucidate the fundamental characteristics of the oscillator composed of the silicone gel and a mass. The fractional time-derivative Voigt model of the silicone gel and the equation of motion of a single-degree-of-freedom (SDOF) oscillator having the fractional derivative term are derived. The fundamental characteristics of the equation of motion are studied through frequency response functions and characteristic roots. Transient analyses of the equation of motion are also conducted by the discrete Fourier transform and by a new time integration method.

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This paper describes a method of modal analysis in the time domain. Which belongs to the inverse problem. This analysis is used to determine modal parameters which characterize dynamic properties of the system concerned. The theory is developed on the basis of the assumption that the motion of vibrating systems is governed by the equation of motion. By applying this method to the time histories of response data obtained during earthquakes, satisfactory results were obtained. In general, such analysis is treated by Fourier transformation. However, it is difficult to understand characteristics of the system from Fourier spectra, because earthquake records contain much influencing noise.

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This paper proposes an expression for design of optimal dynamic absorbers attached to damped linear systems. The classical expressions were derived from the assumption that the primary system has no damping. There are two optimization criteria in the design of the dynamic absorber : the fixed-points theory and the minimum variance criterion. In the fixed-points theory, the dynamic absorber is optimally tuned and damped with respect to the primary system so that the two resonant amplitudes of the main mass are equal. On the other hand, in the latter criterion the area under the power spectrum density curve of the main mass is adjusted to take the minimum value. The new expression proposed in this paper is based on the fixed-points theory. However, there are no fixed points in the resonance curves of the damped linear systems, so the analytic procedure becomes impossible. Therefore a perturbation method is used to obtain the expression, and the accuracy of the solution is discussed.

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When a rocket is launched by a rail launcher, the rocket receives tip-off angular velocity caused by the moment due to engagement of the tail hanger of the rocket on the rail after clearance of rocket C.G. from the tip of the rail. This paper analyses one occasion, when small test rocket launched from a rail launcher experienced unexpected large pitch-down tip-off angular velocity. The rocket had two hangers, one of which was constrained by a detent mechanism prior to launch. When the rocket motor was fired, detent action caused torsional deflection of the shaft, which supported teh rail launcher. When the hangers got free, the shaft started oscillatory motion, which amplified the tip-off angular velocity of the rocket. Analysis of the dynamics of the rail launcher and the rocket was performed and numerical calculation was made to simulate the tip-off velocity. Measures for improvement were summarized.

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We present a practical method of numerical analysis for optimization problems of domains in which natural vibration problems of linear elastic bodies are defined. In this paper, we apply the traction method that was proposed as a solution to the domain optimization problems to elliptic boundary value problems. The treated problems are those which determine the domain that maximizes a specified vibration eigen value, which is defined by the squared natural frequency, and that moves several specified vibration eigen values in a specified direction. Using the Lagrange multiplier method, we obtain the shape gradient functions for these domain optimization problems from the optimality criteria. We show the successful resolution of the problems of beamlike plates clamped at one end and at both ends.

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In this paper, we consider the handling of a vibrating flexible structure by a robot. We suppose that the robot is rigid and the object is flexible. The robot consists of links and two end-effectors at its ends ; one end-effector is for fixing the robot on a base such as a satellite bus and the other for handling the object. The aim of this work is to realize position control of the flexible object while suppressing its vibration. The problem taken up here concerns the control system design to realize the active control of the flexible object. For this purpose, we propose a numerical modeling method of the system consisting of the robot and the object. The model is derived based on the torque requirements at the handling point. Next, we linearize the model with an identification method before designing a robust servo system using an H^∞ controller to handle the flexible object actively.

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Decentralized simple adaptive control (decentralized SAC) which can construct controllers for feasible division of subsystems with little knowledge with respect to information about the plant and disturbances shows good vibration absorbing performance for the active vibration control of a multi-degree-of-freedom structure. However, when we limit the plant, for example, to a high-rise building, we can utilize the special features of the construction of the plant and obtain even better control performance. In this paper, we discuss active vibration control of a special multi-degree-of-freedom structure by the use of decentralized SAC. Also, when actuators can directly generate output force, we can utilize decentralized robust SAC which can reduce the negative effects of interactions between subsystems and disturbances. The effectiveness of the proposed methods is shown by the simulations and the experiments.

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Characteristics of viscoelastic resin for a vibration damping composite steel sheet (VDCS) were studied numerically using the Ross-Kerwin-Ungar model. The following three conclusions were obtained : i ) magnitude of shear modulus of the resin determines frequency where the VDCS shows the maximum loss factor ; ii ) although there is a limitation of loss factor, the magnitude of loss factor is proportional to tangential loss of the resin ; and iii) loss factor is independent of frequency if the shear modulus of the resin is proportional to frequency. Characteristics of an actual resin for VDCS were shown to agree with the calculated results. The same trends were observed for the calculated results as for the characteristics of the actual resin. Therefore, the results obtained might be useful in the developement of new resin for VDCS. The results obtained are also useful for understanding the behavior of loss factor in terms of frequency dependence and temperature dependence.

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This paper deals with a control algorithm based on an optimal control theory for a hydraulic active mass damper (AMD) system, which is used to suppress vibrations of high-rise buildings caused by winds or earthquakes. A low-order linear approximation of the AMD system and a control algorithm are derived. In this control design, the damping ratio of the dominant pole is taken as an index of the control system, and modelling error does not have a significant effect on the stability of the system. This design algorithm was verified by experiments on a small-scale model.

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An approach for simultaneous optimum design of the structure and H^∞ control system is proposed. H^∞ cootrol theory enables the design of a control system robust and stable against the parameter change of the structure, while maintaining the ability of frequency shaping. The objective function in this approach is the liner sum of the structural mass and the H^∞ norm, that is, the performance index of control. As the definition H^∞ norm depends on existence of solution, the objective function sometimes becomes discontinuous with respect to design variables. Hence, the complex method which can optimize the discontinuous objective function is adopted in this approach. Effectiveness and practicability of the approach are verified by both simulation and experiment on the vibration control of planar plate.

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This paper deals with a problem of vibration isolation control for multi-degees-of-freedom systems by applying the optimal control theory using a Kalman filter and H^∞ control theory. A four-degees-of-freedom system for an experimental model is reduced into a two-degees-of-freedom system in order to control vibrations of the fundamental and second modes. As a result of numerical calculations and experiments, it is shown that the spillover problem occurring from the model reduction dose not affect the vibration isolation performance for multi-degees-of-freedom systems and it is important to determine how to reduce the vibrations of low modes of which vibration levels are high. Furthermore, it is demonstrated that the control characteristics depend on the adopted objective functions and the vibrations of the low modes are effectively reduced by introducing a frequency-shaped function in H^∞ control theory.

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This paper deals with a new and simple method of optimum design of dynamic vibration absorbers which consist of viscoelastic springs and auxiliary masses. If the usual method of design of dynamic absorbers is applied to an absorber with a viscoelastic spring, the stiffness and the loss factor of the spring are determined as optimum values corresponding to the given ratio of the auxiliary mass to the principal mass. The actual value of the loss factor, however, cannot be chosen arbitrarily, because it depends on the material of the visco-elastic spring. In the proposed method, the optimum condition can be found for any combination of values of the mass ratio and the loss factor of the viscoelastic spring. Therefore, dynamic absorbers can be realized for springs of arbitrary viscoelastic materials.

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An analytical procedure for implementing the wave-absorbing controller is presented and experimental verification for the procedure is performed. The ideal controller transfer function H(s) from the sensor output to the control force is a complex function with respect to s, i. e., it contains i=√(-1) explicitly, so that H(s) cannot be implemented by convolution of the output with h(t)=L^-1[H(s)]. To solve this problem, the ideal controller transfer function is expressed as a real irrational function with high precision. Parameters of the digital convolution algorithm and convolution integration range length, which are needed for the implementation within the prescribed error, are determined analytically. Experimental results show that the digital algorithm can control many modes without causing instability to any higher mode, and that controlled responses are in good agreement with the theoretical results. Moreover, robustness is ascertained experimentally for structural parameter variation in all portions except between the sensor and actuator at the boundary.

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This paper proposes a novel technique for the dynamic characterization of microstructures by generating motion in them. Here, microstructures refer to microsensors and microfabricated mechanical components. The method satisfies the requirements for the dynamic characterization of microstructures. Motion is triggered by the reflection of pulse elastic waves propagating in a metal bar. The microstructure to be characterized is fixed to the end surface of the bar and dynamic displacement generated is measured by an argon-ion-laser-based interferometer. The motion of the end surface of the bar generated by the reflection of a pulse elastic wave is measured by either strain gages bonded on the side of the bar or directly by the argon-ion-laser-based interferometer. There is a simple mathematical relationship between the measured strain and the acceleration at the end of the bar. The validity is verfied by the characterization of several kinds of microstructures : a silicon doubly supported beam, an accelerometer and an AE-transducer.

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A simplified adaptive boundary mesh construction scheme is proposed for the eigenvalue analysis of the scalar-valued Helmholtz equation by boundary element method. The scheme estimates effect of each local mesh refinement (h-version here) on the eigenvector not on the eigenvalue, which makes it possible to apply the strategy developed earlier for the boundary-value problem while the eigenvalue is global value. The local reanalysis for eigenvector determination corresponding to each mesh refinement is employed for simplicity and improvement of computational efficiency. Sample computations in the two-dimensional problems prove higher utility compared with the previous methods.

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This paper reports the kinematic characteristics of the center of mass of the entire human body while ascending and descending stairs, using large force plates which can measure both three-dimensional force components between the feet and the stair and the point of application of the force. Kinematic characteristics in terms of the velocity and displacement of the body center in the three-dimensional space can be obtained by numerical integration of the force components with respect to time after proper calibration of measured data. For the calibrations, two methods were used : the first one compensates the measured force according to the sensitivity of the force plates due to their size were large ; the second one tunes integration constants to avoid drifting features in integrated data. The following results are obtained : our new method, i. e., obtaining kinematic characteristics for stair gait using force plates, gives reliable results in the three orthogonal directions in space ; characteristics in the sagittal and vertical directions change depending on gait cadence ; characteristics in the lateral direction are similar to those observed in level walking.

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The enveloping grasp is a stronger grasp than others. This grasp has a disadvantage in that it is difficult to determine contact points and contact forces. In this paper we discuss the identification of unknown parameters, which are contact points and contact forces, in the enveloping grasp, and show a necessary and sufficient condition of identification. It requires more than three joints between adjoining contact points.

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In order to manufacture micromachines, development of micromanipulation is indispensable. This paper treats micro handling tools as end-effectors of a micromanipulation system, and introduces three prototypes of nontweezing tools : air-sucking, electrostatically charged, and surface-tensional ones. These three can handle microparts (l0 to 500 μm in length). In particular, they can perfectly release the microparts with several methods, such as ultrasonic vibration. Through theiractual usage, we confirm the validity of the tools for micromanipulation.

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In order to clarify the destabilizing mechanism of the head to flexible disk interface, we investigate the destabilizing mechanism caused by the coupling effect of the transverse and pitch stiffnesses. The eigenvalue analysis is carried out for two analytical models : the coupled suspension stiffnesses model and the coupled contact stiffnesses model. It is shown that instability of the head-disk coupling system is primarily caused by the instability of the head-suspension system due to the frictional force and the coupling effect of stiffnesses. Thus the unstable region of the head-suspension system due to the coupling effect of suspension stiffnesses is examined in term of the stiffnesses, frictional coefficient and head mass ccenter position. It is found that the natural mode of vibration of the head-disk coupling system is strongly destabilized under the unstable conditions of the head-suspension system, There exists a similar unstable region of the contact stiffness and strong instabilities when the coupling effect of transverse and pitch contact stiffnesses is taken into account. This instability is weak when the unstable natural frequencies of upper and lower head-suspension systems are greatly separated.

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This paper describes motion analysis of vehicles damaged due to collision. Various parts of vehicles are damaged in collisions in general. In this paper, the damages to body and wheels are picked up. The center of gravity of the vehicle and the polar moment of inertia are changed by deformation of the body. Furthermore, the wheelbase, treads and wheel steering angles are changed by the damage to the wheels. Thus the vehicle loses symmetry with respect to the vehicle axis. In this paper, the motion analysis for the vehicle is carried out by extending the four-wheel vehicle model to examine the influence of vehicle damages due to collision on the vehicle motions after impact. Then, the motions of damaged vehicles are compared with those of undamaged vehicles. It was found that damage to vehicles has a significant influence on vehicle motion after impact.

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In the previous paper, in order to emulate a human riding a unicycle by a robot, a new model with two closed-link mechanisms and a controlling rotor (turntable) was proposed. By analyzing that model, we showed through simulation that both longitudinal and lateral stability of a human riding a unicycle can be satisfactorily emulated. In this study, we designed and manufactured a unicycle robot based on an idea proposed in the previous paper. Using the new method for detecting the posture of the robot in three dimensions, we conducted experiments on this robot under the proposed control method. The robot's posture was stabilized successfully in both longitudinal and lateral directions in three dimensions, and driving control was realized. The experimental results tell us that the proposed model and control method are effective in emulating the human riding a unicycle system by a robot. We believe that this is the first completely successful study in emulating a human riding a unicycle by a robot.

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Ocean development has been advanced for a long time in order to obtain ocean resources and energy, but its working environment is very severe for human beings, so underwater working robots which can be used instead of human beings have came into demand. This paper deals with attitude control of the main body of an unconstrained underwater robot using a movable counterweight controlled by the optimal servo system and trajectory control of a manipulator using disturbance compensation control(DCC). From the result obtained by computer simulations, it was made clear that the attitude of the main body can be controlled without steady-state error by means of controlling the position of the counterweight using the optimal servo system. In addition trajectory control of the manipulator can be carried out by using DCC which regards the reaction force due to the movement of the counterweight as a disturbance.

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Many industrial robot manipulators are driven by d. c. servomotors, where, in addition to gears, springs are used to connect each manipulator arm axis with the corresponding motor axis. In control aspects, the gear in those transmission parts is a positive factor because it suppresses nonlinear dynamics of the manipulator. However, the spring is a negative one ; it makes the joint flexible and causes residual vibration in the end point of the manipulator when the manipulator has to stop abruptly. In this paper we show that the H_∞ controller is very effective to eliminate, or minimize to an acceptable level, the residual vibration. The robot manipulator considered in this paper is one with revolute joints (i. e., so-called PUMA type). First we describe the method of designing the H_∞ controller, and then we confirm the effectiveness of this controller through experiments by comparison with a PD controller. The experimental results show that the H_∞ controller can make the settling time of residual vibration much shorter than the PD controller, although the overshoot is rather large.

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This paper presents a simple method for controlling both the motion and contact force of a flexible manipulator without calculating inverse dynamics. The contact force is converted into a velocity vector according to the proposed force/velocity conversion law considering the flexibility of the manipulator. The velocity vector which is tangent to the constraint surface is calculated using velocity control law. The desired velocity vector is obtained as a sum of the above two velocity vectors, and is converted into angular velocity vectors considering deflectional velocity of the flexible links. The desired angular velocity vector is obtained as a sum of the above angular velocity vector and strain feedback term. Motion and force control is performed using DC motors whose desired values are the above desired angular velocity vectors. Computer simulations and experimental analyses are carried out to clarify the validity of the proposed method.

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This paper describes the design of digital control based on predictive control for an underwater manipulator. The discrete time model of the manipulator becomes an uncontrollable system which has nonlinear terms and zero of unstable and/or near by the stability bound zero. Hence, the conventional adaptive control method cannot be directly applied. Kaynak and Hoyer have proposed simple predictive control method. This adaptive control system based on the predictive control method is directly applicable to nonminimum phase systems. However, the stability and convergency of the control system cannot be guaranteed. In this paper, it is shown that the adaptive control system guarantees the stability for most 2nd-order stable systems. Experimental results from a underwater manipulator demonstrate the effectiveness of the adaptive control system.

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We have been developing an electrohydraulically operated manipulator for open-air handing of a medium-heavy load for the past 5 years. Open-air manipulators require both downsizing and integration of control components. The newly designed manipulator consists of three independent units which provide 6 degrees of freedom. Each unit has a 2 degrees of freedom in yaw and pitch motions which are controlled by two servocylinders of 170 mm in stroke and 35 mm in diameter integrated with fully bridged PWM switching valves and position sensors. The three-unit jointed manipulator is 2050 mm tall with a dead mass of 92 kg, and controls an inertia load of 35 kg at a working pressure of 10 MPa with position precision of 3 mm at a maximum tip speed of 1.42 m/s.

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The purpose of this work is to realize highly accurate trajectory tracking control of a real position for a wheeled mobile robot (WMR). The authors have been conducting a dynamical study of a theory on trajectory tracking control based on kinematics for WMR. This tracking theory has been proven in the estimated environment using an internal sensor (similar to an encoder). In this paper, in order to apply the aforementioned theory in a real environment, an extended theory of trajectory tracking control is proposed. All of the estimated parameters (directional angle, velocity, position) of WMR are modified at short sampling time using real position data measured by external sensors. We conducted experiments using a laser beacon measuring system as external sensors and found that this extended theory provides satisfactory results in terms of accuracy of trajectory tracking.

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In recent years, the automatic planning method of the collision-free manipulator path among obstacles is reported in many papers to increase manipulator capability. However, path planning among moving obstacles has been studied in only a few papers, in which some difficulties such as the necessity for assumption of the ideal path or necessity for transformation of real-space coordinates of the obstacles to the joint angle space have made it almost impossible to apply the methods to a multi-DOF manipulator. We propose an algorithm in order to solve these difficulties, while adopting the potential method of fuzzy reasoning. As the result of simulations, this work proved this method effective and that if the information not only the deviation from the target and proximity to the obstacles but also the rate of change of these quantities is known, the planning time of the collision-free path among moving obstacles is shortened.

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