The increasing demand for safety and ride comfort, especially at high speeds, has led to the development of actively controlled suspensions in ground vehicles such as automobiles, railways and maglev vehicles. The active or semi-active suspension replacing passive elements with controlled actuators or variable elements can theoretically and practically improve vehicle vibration isolation properties, dynamical responses of pitch, roll and yaw motions, and road holding and guideway tracking performances. This paper reviews basic suspension problems, suspension control types, theoretical approaches to active suspension control and applications to practical systems.

View full abstract

Self-induced manometer oscillation was observed in a test tank connected to a larger downstream tank by a short duct. Water flowed into the thin rectangular test tank horizontally and flowed out vertically through a duct located at the bottom center. The other end of the vertical duct opened to a lower part of the downstream tank where the water level was controlled by overflow. At a certain water level and flow rate, the free surface of the test tank oscillated upward and downward periodically, causing the oscillation of the outlet flow rate. The period of the oscillation was found to be that of liquid oscillation in a U-tube under gravity. Namely, the oscillation occurred in the multi-free-surface system composed of the test tank, the overflow tank, and the connecting duct. The flow pattern in the test tank was visualized by small particle tracers. The oscillation growth model based on the flow pattern transformation was proposed.

View full abstract

Tooth mesh frequency sound generated aerodynamically in the region of meshing was investigated to determine the general characteristics of the sound emission as well as its detailed source locations. Sound pressure response measurement for various facewidths revealed that emission is expressed in terms of a similarity law as a function of a parameter b/λ, the ratio of facewidth to wavelength of the sound. The effect of dimensions such as the module and number of teeth were derived by means of a dimensional analysis with respect to pumping action of the cavity between driving and driven gears. Throughout several kinds of experiments, one source was located at the middle of the meshing exit, which becomes prominent as the axial air flow reaches a certain speed. Another source is estimated to spread over both faceends, of which the radiation characteristics are closely related to the distribution and the solid boundary of the gear pair.

View full abstract

This paper discusses the regulator problem with the zero terminal state for a multi-input linear digital system. First, for a general additive performance index, the fundamental structure of the regulator which drives the state to zero within a finite time is obtained. This problem is divided into three phases : the new free-end-point problem in the first phase, the new free-end-point problem for the new time-variant system with the time-variant structure of the new inputs in the second phase, and the constant gain special deadbeat control in the third phase. That is, the new optimality condition of the fixed-end-point regulator is expressed by the special deadbeat control and the optimality condition of the induced free-end-point regulator. Furthermore, the closed-loop expression for the quadratic performance index is obtained to show the effectiveness of the new optimality condition.

View full abstract

A robust stabilization condition which guarantees the robust stability of multivariable uncertain discrete-time systems under state feedback with a class of nonlinear actuators is derived in the time domain. A simple method recently developed for synthesizing controllers for robust pole assignment of linear uncertain systems is extended to obtain the robust stabilization condition. In this paper, the plant is not restricted to the stable case. Moreover, based on the robust stabilization condition, an algorithm is proposed for determining the tolerable operational sectors of nonlinear actuators for the case where the robust controller is designed first in order that the feedback system without nonlinear actuators is asymptotically stable. As long as the nonlinear actuators lie in the determined tolerable operational sectors, the linear multivariable uncertain discrete-time systems with these nonlinear actuators and the designed robust controller are still asymptotically stable. An example is given to demonstrate the use of the proposed approach.

View full abstract

In this paper, we present some results on robustness of eigenvalue distribution in specified complementary regions for perturbed systems. If some eigenvalues of the nominal system are located in a specified region, the proposed sufficient conditions guarantee that the same number of eigenvalues of the perturbed system lie inside the same region. The characteristics of a linear time-invariant system are influenced by the eigenvalue location of the system matrix. Due to uncertainty or parameter variation, all mathematical descriptions of dynamic systems are approximate models at best. The effect of uncertainty will move the eigenvalues of a real system away from the designed ones. Therefore, it is significant to guarantee that the same number of eigenvalues of the perturbed system lie inside the same region as that of the nominal system. By the analysis of eigenvalue distribution, we can explore the locations of dominant eigenvalues, specified eigenvalues or even individual eigenvalues of perturbed systems. Consequently, more properties of perturbed systems such as stability margin, performance robustness and so on can be examined. The proposed theorems can be applied to both continuous- and discrete-time systems. In addition, the analysis of stability robustness can be dealt with as a special case in our study. Two examples are given to show the applicability of the proposed theorems. Finally, some conclusions are presented.

View full abstract

This investigation presents a way of modeling complex structures by the modal force technique (MFT) and its application for structure control. A structure can be divided into substructures and the frequency response function (FRF) of the original structure can be obtained from the FRFs of its substructures by applying this technique. The synthesized FRF is transferred through the process of realization to the state space equation for designing an active vibration controller. The optimal control theory (LQG) is employed to design an active vibration controller with piezoelectric film (PVF₂) as the distributed-parameter actuator. At the same time, a Kalman filter is also designed. The exact solution for the modal parameters of an L-shaped cantilever beam structure is obtained by using MFT. The L-shaped cantilever beam structure is used to illustrate the application of the method proposed to vibration control. Numerical simulations reveal that the active vibration controller provides appropriate damping to suppress the tip point vibration when the structure is under random excitation. The Kalman filter can estimate accurately the states of the system and reduce the effects of disturbance and noise.

View full abstract

This paper presents a method for sensitivity analysis of undamped, viscously damped and proportionally damped structural systems based on modal parameters. The method involves the usage of eigenvalues, eigenvectors and theory of adjoint structures to enable the study of the sensitivity of complex mechanical structures. The modal parameters are determined from the experimentally measured vibrational data, and later will be used to select the optimal locations for structural modification to reduce the vibration. They can also be used to determine the dynamic behavior of the structure before and after modification. In the present study, an example is provided to demonstrate the applicability and validity of the method.

View full abstract

This paper presents a method to be used for correction of finite-element models by referring their modal parameters to experimental modal data. The proposed method is based upon both the sensitivity analysis and the least square method, and gives us the physically realistic solution of design variables, in contrast with the methods based on pseudo-inverse. Numerical simulations of finite-element models of a beam and a plate are presented to demonstrate the effectiveness and the validity of the proposed method in comparison with the pseudo-inverse method with respect to physical meaning of structures. Further, the correction of a finite-element model of an actual structure is carried out by referring its modal parameters to experimentally extracted modal data.

View full abstract

Impact/collision is a fast and non-linear phenomenon, so it is difficult to control a robotic manipulator undergoing collision phenomena. Therefore, in the past, manipulators were moved slowly in order to avoid collision. But with the recent increase in the amount of high-speed tasks, control of the manipulator undergoing collision has become indispensable. In such a situation, it is effective to use learning control in the forward manner. In this paper, we propose a new learning control method to optimize the weighted least-squares criterion of learning errors. This method can be applied to obtain a unique control gain, and it is shown here that the convergence of learning error can be readily assured. Using this learning control method, we carried out experiments on force control with collision phenomena, and proved the convergence of the output error. The robotic manipulator was made of an air-driven rubber actuator with no reduction gears to avoid damage due to impact.

View full abstract

In this paper, a methodology using the Lyapunov direct method is proposed for analyzing the stability of an n-D.O.F. linear manipulator system, which is positioned on a flexible wall, using the collision phenomena. A methodology for determining the control law which guarantees the stability of the manipulator is also discussed. As collision is a phenomenon involving energy dissipation, it is used in industry for such purposes as suppressing vibrations. On the other hand, in the field of robotics, this phenomenon is considered ought to be avoided, because the controllability of the system becomes poorer at contact. However, in the case where the demand for rapid manipulation in the environment increases, collision becomes an essential problem which must be addressed. In our previous reports, some approaches using the Lyapunov method were discussed. In this report we expanded the manipulator complexity to n-D.O.F. and proved the stability of the system even in the case of collision. Some numerical simulations were also executed to demonstrate the transient behavior of the system and to allow comparison with the results of the theoretical analysis.

View full abstract

A method is developed to simulate fatigue crack growth in a carburized gear tooth based on two-dimensional linear fracture mechanics. In the simulation, the stress intensity factor is calculated by means of a finite-element method (FEM) which takes into account the effect of residual stress. The fatigue crack growth rates in the case layer are estimated experimentally, and they are expressed by an experimental formula. A strength evaluation procedure for carburized gears is then proposed on the basis of the developed method of simulation. In the procedure, the critical length of the initial crack which is obtained from the fatigue strength is assumed to be equal to the crack length evaluated from the threshold stress intensity factor, and the basic load capacity is estimated. The critical lengths are evaluated for variously treated gears and illustrated as a function of surface condition.

View full abstract

Recently, plastic gears have been used in water, but depending on the kind of plastic, there are some gears which show a great deal of wear when they are used in water. However, it is important to note that in water or in places where moisture exists, water functions as a lubricant, and wear decreases as compared with the case without lubrication. To date, some reports have addressed this phenomenon but few have presented data on the design of plastic gears for use in water. In light of this situation, in this study, nylon gears and polyacetal gears, which are widely used plastic gears, were operated in water and with a small number of water drops, and various characteristics such as the wear of the teeth, the change in the tooth profile, the tooth surface roughness and so on, due to the difference in the quantity of bathing water were examined.

View full abstract

This paper describes the variations in stiffness and damping coefficients in bearing oil films under the influence of large dynamic loads. A rotor-journal bearing system in which large dynamic loads act on the rotor is nonlinear, so it is analyzed as a coupled problem of the equations of motion for the rotor combined with Reynolds equations for all the bearings. By making use of the displacements and velocities of the rotor center obtained through analysis, the stiffness and damping coefficients have been numerically calculated as an unsteady state along the locus of the rotor center. The variations in these coefficients over one rotor revolution are shown for the journal bearings in a rotary compressor. Our results demonstrate that most of the coefficients for all the bearings vary by more than one order of magnitude, and that oil film nonlinearities seriously influence the rotor motion.

View full abstract

Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the power plant, has been used in severe conditions where high loading is in effect. Therefore, for the purpose of increasing plant reliability, we must establish a precise calculation method and optimal design procedure of the blade, taking its specific characteristics into consideration. In this paper, an effective autotuning technique of the blade's natural frequencies by combining sensitivity analysis with nonlinear programming is presented, and its application is shown. In the blade design, many natural frequencies must be tuned between engine order frequencies, satisfying various constrained conditions which result from such requirements as thermal efficiency and manufacturing. The new optimal technique in this paper is very useful for such blade design because a blade profile having the required natural frequencies can be obtained automatically.

View full abstract

High concentration of active grains and low bonding strength are important features for increasing the removal rate and reducing the subsurface damage in lapping of brittle materials. Thus, high-concentration lapping discs with low bonding strength have been developed. First, the finishing characteristics using the lapping discs were investigated, varying the concentration of bonding agents and thereby determining that a high removal rate could be obtained at a low concentration. Next, soft abrasives, which may undergo a mechanochemical reaction with workpiece materials, were adopted as the abrasive material of the lapping discs, and colloidal silica which may undergo a chemomechanical reaction with workpiece materials was applied as a coolant in finishing. A mirror-surface finish of less than 10 nm Ra was obtained for various brittle materials, and a smooth-surface finish with no dropout of grains was achieved for aluminum nitride substrates.

View full abstract