This review focuses on instability and self-excited vibrations occurring in poppet valves used in hydraulic systems. First, the causes of the instability are considered and then studies on the local instability based on linear theory are reviewed. Second, some global behaviors of the nonlinear hydraulic systems, i. e., hard self-excitation and chaos, are described, mainly based on the author's studies by numerical simulation.

View full abstract

An active control system consists of three parts : the vibration system of the controlled object, sensors and actuators, and controllers. Control performance depends on the characteristics of the controllers. Therefore, we discuss control system design strategies and control performance for a typical design method of active structural control in detail. Although there are many control system design methods for active vibration control systems of structural control, we focus attention on a design method using modern and postmodern control theories, which is called robust control theory. We verify the control performances as benchmark problems for LQ control, LQG control, disturbance cancellation control, H² control, H^∞ control, μ control and sliding mode control. In this study, we use two vibration models : the active vibration absorber (AVA) model and the active dynamic vibration absorber (ADVA) model. Finally, we confirm that μ is superior to other control methods for linear structural control, and sliding mode is currently the best method for the nonlinear structural control system compared with other control methods in practical use.

View full abstract

The dynamic instability of a free-free column subjected to a tangential follower force in space has been investigated. The experiment of such a nonconservative system in space cannot be conducted on the ground, because the boundary conditions of the column are all free, and thus the column moves away, accelerated by the thrust. Therefore, in this paper, a suspended column on the ground is proposed to simulate the dynamic instability phenomena of a portion from the nodal point to the trailing end of an accelerated free-free column in space. One end of the model is supported by a rotational spring and the other end is free and thrusted tangentially. The mathematical model and the original one are formulated using a finite-element method, and the vibration modes are compared to discuss the equivalency of the two systems. The rotational spring constants satisfying the equivalency are obtained for the cases with and without structural damping.

View full abstract

Free vibrations of twisted cantilevered thin plates having thickness varying in two directions are investigated analytically and experimentally in this study. A numerical procedure based on the Rayleigh-Ritz method is presented using algebraic polynomials as displacement functions. To demonstrate the procedure, nondimensional frequency parameters and mode shapes are analyzed for typical twisted plates. The convergence of frequency parameters is studied and effects of plate thickness variation on vibrating characteristics are discussed. Experimental tests are carried out for three kinds of aluminum specimens. On the basis of comparison between experimentally obtained resonance frequencies and mode shapes and those obtained from the analysis, it appears that the numerical procedure proposed in the present study is useful for analyzing the free vibrations of twisted thin plates with variable thickness.

View full abstract

We discuss a new method of analyzing two-dimensional eigenvalue problems described by Helmholtz's equation. A general solution is assumed as a linear combination of plane waves which have the same wave number and travel in different directions. Nodal points are located only on the boundary of a convex domain which has an arbitary shape. A set of equations similar to finite-element equations can be derived from the general solutions. Eigenvalues obtained by this method are very close to the exact values. This method is effective in simplifying of the programming and in shortening computational time.

View full abstract

The overall aim of this research is to establish an effective method for accurately estimating the airborne noise power radiating from gear blanks. For this purpose, the basic theory for estimating the frequency response of radiating sound power was proposed in a previous paper, and was applied to a circular plate with a solid shaft subjected to an axial load, in which the circular plate was a simple model of gear blanks. In this paper the basic theory is extended to circular plates excited three-dimensionally, similar to that for helical gears. The theory includes the rigid-body modes of vibration as well as the natural modes of flexural vibration of the circular plates. The estimated sound powers agreed well with the values measured by the sound intensity method. Also, an interesting result is obtained ; sound power radiating from a circular plate with a helical tooth is proportional to sin²β, where β is the helix angle. In other words, the axial force has large influence on the sound power radiated due to the rigid-body and flexural vibrations of the circular plate.

View full abstract

This paper reports a study on the transient response of a head disk assembly (HDA) subjected to a half-sine shock pulse in the axial and pitching directions. The solution is obtained using the multi-modal expansion approximation and applying the Galerkin method to the resulting equations. Numerical results are obtained by the Newmark β method for a 3.5" hard disk-head system. It is found that the relative distance between the head and the disk reduces to the minimum when the input duration τ is about 1. 5 times the natural half-period of the fundamental (0, 0) mode. Results obtained also show that the shock-proof head satisfies (1/2π) (k/m)^1/2=f₀₀, where k is the stiffness of the head arm, m the head mass and f₀₀ the (0, 0) mode frequency of the rotating disk, and that the head slider should be designed so that the assembled system of the head and the disk has a high air-film stiffness.

View full abstract

The induction motor is used in many industries. These days motor noise reduction is often required due to environmental concerns. This paper is concerned with the reduction of motor noise. The relationship between exciting force and vibration mode of the stator core is analyzed. An exciting force as an electromagnetic radial force was applied to the stator core. Analysis was performed for a continuous distributed force and a discrete multipoint exciting force. The vibration behavior of the core was analyzed theoretically, numerically (FEM) and experimentally with respect to modes, frequency and phase of exciting force. It has been confirmed that : 1. in the continuous distributed excitation, the core vibrates when M=±N and the exciting frequency coincides with the natural frequency ; 2. in the discrete multipoint excitation, the core vibrates when M±N=mK. Here, N is the natural frequency mode, M is the excitation frequency mode, m is an integer, and K is the number of points at which the exciting force is applied.

View full abstract

An upright stainless steel circular cylinder with a mass attached at midlength is excited seismically in the horizontal direction using a vibration table. A well-known seismic wave called EI Centro 1940 NS is applied to excite the test specimen. Fourier components over 10Hz of the seismic wave are cut off and the duration is shortened to 30%, 40%, or 50%. The eccentricity of the center of gravity of the attached mass is varied and the amplitude of the modified El Centro 1940 NS is increased incrementally. Parametric excitation is observed for each combination of eccentricity of the attached mass and time scale of the seismic wave.

View full abstract

The dynamic behavior of vibration systems containing granular media is experimentally investigated using several models. Impact tests are performed on two different types of frame models with and without granular medium. The tests indicate that the systems containing granular medium dampen vibration. This dynamic characteristic is discussed and illustrated using the finite-element approach to calculate the dynamic behavior of the frame model. These dynamic characteristics enable vibration to be isolated in a system with rigid bodies containing granular medium. A rigid vibration-isolation system, mainly constructed from pipes and granular medium, is used to dampen a cylinder excited by electromagnetic force. The level of noise generated from the cylinder is analyzed in relation to the granular medium and the structure of the vibration-isolation system. The noise level is significantly reduced in this system.

View full abstract

This paper deals with the quenching of self-excited vibrations of a rotating circular plate subjected to a concentrated frictional force as a function of relative slip velocity exerted on its outer circumference by dynamic absorbers. Results obtained by the method of multiple scales and the shooting method showed that (1) dynamic absorbers tuned to the natural frequency of the vibration mode to be controlled and arranged at a certain angle related to the vibration mode are the most effective, (2) such mountings of not one but several dynamic absorbers for every possible occurring mode, enable us to quench self-excited vibrations perfectly, and (3) thus, the effective masses of the dynamic absorbers are on the order of 10^-3 of the mass of the circular plate. The analytical results are confirmed by an experiment concentrating on the perfect quenching of frictional vibrations of the rotating disk.

View full abstract

This paper considers the simultaneous structure/control design synthesis of a wing with an active control system called the gust load alleviation (GLA) system. The introduction of fuzzy goals for both the gust-induced stress with the control system off and the structural mass is the primary focus in the present paper. A simple wind tunnel model excited by a random gust is studied. The thickness of a FEM beam element modeling the wing spar and the feedback control gain are optimized to maximize the fuzzy decision with the prioritized design requirements, e. g., the control system's stability characteristics, and the standard deviation of the gust-induced stress and control surface deflection angle with the control system on. The sequential linear approximation method is proposed to obtain the optimum solutions for nonlinear multigoal problems with fuzzy goals.

View full abstract

This paper presents a new identification method which utilizes fuzzy inference in parameter identification. The proposed system has an additional control loop where a real plant is replaced by a plant model. At first, an input signal, such as a step signal, is given to both control loops. Then the parameters in the plant model are modified so that the output signal features, such as magnitude of an overshoot, of the two loops become closer. Fuzzy rules describe the relationship between comparison results of the features and magnitudes of modification in the model parameter values. This method is effective in auto-tuning because the response of the closed loop is verified. The proposed method is tested both in simulations for several plants with first-order lags and dead times, and in experiments for motor control. The results show that the proposed method is effective for practical use.

View full abstract

When an electropneumatic valve positioner is surrounded by a combustible gas, the electrical control circuit must be connected with the actuator by a long pneumatic tube. If the pneumatic tube exceeds a certain length, hunting will occur in the drive shaft of the actuator due to the time delay of the pneumatic pressure signal. Though the Smith method is known to prevent such hunting, there are some difficulties in application. Thus, a new stabilization method is proposed to realize a simpler compensating circuit. First, the approximate compensator based on the Smith method is explained. Second, the robust stability condition for such a system is derived, developing the Palmor method. Using this method, the stability margin under the identified error of time delay is clarified. Finally, through experiments, it is ascertained that the introduction of the approximate compensator makes it possible to stabilize the valve positioner.

View full abstract

A method is developed to reduce vehicle idling vibration caused by engine torque variation from individual cylinder combustion. This method is theoretically established and experimentally confirmed. Electric machine torque is actively controlled to reduce acceleration variation of the crankshaft, so that the electric machine torque and the engine torque variation cancel each other. This reduces crankshaft rotational speed variation and engine and vehicle vibration. Since the engine torque variation generally increases with engine load, it is desirable to control the electric machine torque so as not to increase the engine load. An electric machine such as a motor generator is used to provide and remove torque from the engine. This reduces vibration more than in machines that absorb engine torque, such as alternators. Experiments using test cars with four-cylinder engines validate these control concepts and clearly show that this control method reduces vibration.

View full abstract

In this paper we describe an approach for estimating unsteady flow rate through oil hydraulic pipelines and components in real time. Recently we have proposed following the three unsteady flow rate measurement approaches, RIFM, QIFM and TPFM, in which hydraulic pipeline dynamics are utilized. In this paper, we firstly propose new approaches, i.e., an interpolation method and an extrapolation method in combination with RIFM and TPFM. In the interpolation method, unsteady flow rate at an arbitrary internal location between two points along the pipeline for measuring the two-point pressure can be estimated. In the extrapolation method, unsteady flow rate can be estimated at an arbitrary point along the pipeline located in the outer region of the two points for measuring the two-point pressure. In this paper, the accuracy and the dynamic response of the interpolation method and the extrapolation method are experimentally investigated in detail.

View full abstract

One of the important ways to increase reliability of a power plant is to measure the vibration of steam turbine blades during operation. The measurement of the rotating blades is usually executed by a strain gage ; however, since the turbine has multiple stages, it is generally difficult to attach the strain gages to the rotating blades and obtain signals from the gages, especially in the intermediate stages. Furthermore, gages and wiring must endure high centrifugal force of rotating blades, steam pressure, and moisture in the turbine under operation. This paper presents noncontact measurement technology which measures the vibration of the steam turbine blades during operation using a laser beam installed in a stationary casing. Furthermore, this paper delineates technical problems in the measurement of the steam turbine blades, such as the severe environment in which light is irregularly reflected, the durability of sensors, and small amplitude due to the shroud blade.

View full abstract

Generally, a large-scale 2-D profile is obtained from the combination of a series of 1-D profiles measured by 1-D differential methods. These methods have the disadvantage that the results are affected by rolling error of the scanning stages. This paper presents some 2-D differential methods which can eliminate the datum errors including the translation error in the longitudinal direction and the pitching and rolling errors, and evaluates their basic characteristics in detail. The analysis shows that the asymmetric 2-D mixed method is superior to the others with respect to the spatial frequency resolution and the longitudinal resolution.

View full abstract

A cellular robotic system (CEBOT) is a system composed of many kinds of units called "cells". A cell has a simple function and limited intelligence. In task executions, many cells are required to carry out a same task cooperatively to supplement their functions each other. If some cells have malfunctions, the total performance of the system can maintained by exchanging the malfunctioning cells. Therefore, CEBOT is expected to be adaptable to any kinds of tasks and environments. It is important to study self-organization and self-evolution of CEBOT, because both the hardware and software of CEBOT consist of many kinds of cells which are autonomous agents as mentioned above. This paper addresses self-organization of the hardware and self-evolution of the software based on the Genetic Algorithm. An outline of cells developed by the authors is reported. A self-evolutional knowledge base addressed in this paper is based on the Genetic Algorithm. The self-evolutional knowledge base is applied to a simple task planning system installed into a manipulator system and is verified. The effectiveness of the knowledge base is demonstrated by showing a learning capability of the manipulator in experiments.

View full abstract

This research concerns a new method for the learning control of robotic manipulators based on self-tuning of computed torque gains using an artificial neural network (ANN). We consider some ways to use ANNs in learning control schemes so that ANNs become simplified for multi-input/output systems. We discuss two important issues in ANNs : the first concerns a sigmoid unit function used to achieve flexibility in ANN structure and the second is a learning algorithm for the sigmoid function that is similar to the popular back-propagation algorithms. It is shown that this algorithm has an excellent generalization property which is superior to back propagation in error minimization capability. Two kinds of sigmoid functions are most widely studied and applied to neural network structure today : one is bipolar (hyperbolic tangent function) with a range from -1 to 1 and the other is unipolar with a range from 0 to 1. However, in our proposed neural network structure, the sigmoid unit functions are changeable in shape depending on the training data. The proposed neural network structure has more than one linear unit at the input layer, only one bipolar unit with changeable shape at the hidden layer, and more than one unipolar unit with changeable shape at the output layer. Such a structure, in comparison with conventional structures, becomes very simple and can be utilized in large-scale elaborate systems. A simulation is demonstrated to evaluate the newly proposed structure by applying the method to construct an adaptive computed torque controller for a two-link manipulator.

View full abstract

The need for a compact and high-capacity memory storage apparatus has generated much interest in recent years. Due to the increased track density made possible by recent developments, there has been an ongoing attempt to provide an actuator capable of rapid accessing time. To reduce the average accessing time of a memory storage device, a newly developed moving-magnet actuator using an air-core solenoid and multiple permanent magnets is implemented and tested. In a servo-control mechanism, hybrid control which consists of bang-bang, velocity and position controls is used. An advanced servo-control scheme which uses an analog state observer and a disturbance observer is applied to increase the tracking and focusing accuracy. A new linear actuator which theoretically can achieve an accessing time of less than 20ms at the accuracy required for a 3.5-inch-disk magnetooptical drive is presented.

View full abstract

Generally, peristaltic and syringe pumps have been used to feed liquids at about 2(ml/min). However, since continuous and low-fluctuation flow cannot be easily realized simultaneously with either of these two types of pumps, a new type of microquantity pump is required in the field of pharmaceutical manufacturing. Therefore piezoelectric elements were applied to fabricate a 2-dimensional pump suitable for multichannel and multistage pumps. Experiments demonstrated that the pump worked successfully and its maximum head was 18(kPa).

View full abstract

A generalized solution of levitation control, applicable to the PM (Permanent Magnet) rotating motor, has been obtained. It is assumed that the rotor has sinusoidally distributed magnetic poles, while the stator has a current sheet to produce arbitrarily distributed magnetic flux. The levitation force can be independently controlled using the proposed PM² (Plus Minus two) pole algorithm. A simple experimental apparatus is constructed and tested to clarify the validity of the proposed method.

View full abstract

Previous studies on space robots have assumed a relatively small object as the manipulated target, but in space, a target object can be relatively large, e.g., a space station or a solar-powered satellite. In these cases, manipulation by several vehicle-type robots or vehicles, hereafter, which have thrust engines is superior to that by arms mounted on spacecraft. In manipulation by vehicles, fuel consumption in a thrust engine is related to the norm of force generated by the vehicle. The norm of the force depends on the positions of contact points. Therefore, contact points of the vehicles are important in view of the fuel consumption. In this paper, the optimal contact points are defined as the points which minimize the norm of force needed for the acceleration of the target object or maximize DMM (dynamic manipulability margin) according to the nature of the task. Experiments to verify the validity of this optimal contact points determination method will also be shown.

View full abstract

This paper deals with a study on the problem of minimizing each single objective function in two different design spaces. Whereas designers of automobile suspensions require that automobiles provide a comfortable ride during all automobile speed ranges, designers of humps require that humps induce an uncomfortable riding condition when driving at speeds greater than the hump design speed in order to indicate to the driver that he is speeding. Thus from the former standpoint, the maximum acceleration of the driver should be minimized at a speed greater than the hump design speed under adequate constraints for other maximum accelerations, and the optimum damping coefficients of the shock absorbers can be found. From the latter standpoint, the maximum acceleration of the driver should be minimized at the hump design speed under adequate constraints, and the optimum dimensions of the hump can be properly designed. The above two optimization processes are alternately repeated and the optimum dimensions of the hump are confirmed.

View full abstract

The behavior of elastohydrodynamic lubrication(EHL) films formed between a steel ball and an oscillating glass disk is examined by means of the optical interferometry technique, and the results obtained are compared with those of tests conducted under unidirectional conditions. The surface traction is also measured. The film profile in the contact area breathes cyclically because the wedging and squeezing actions are not in phase. In reciprocation under pure sliding, the thick oil film entrapped between both surfaces at the stroke end moves towards the exist side at about half the velocity of the glass disk. Under conditions of a short stroke and a high frequency, air bubbles produced in the downstream result in oil starvation in the next stroke, so that the EHL film collapses. In the full EHL regime, the central oil film thickness and the surface traction at the stroke center are almost the same as those under unidirectional conditions. It is also found that the oil behaves like a non-Newtonian fluid, and as a result the behavior of EHL films varies with oil and type of motion.

View full abstract

The frictional traction behavior of elastohydrodynamic contacts under pure sliding reciprocation with and without cyclic impact loading is studied using an optical interferometry device. In the full elastohydrodynamic lubrication regime, the traction under simple reciprocation is almost constant in a wide range of sliding velocity, and its value can be estimated from that under unidirectional conditions. It is also found that the thick oil film entrapped between the contacting surfaces by impact loading can reduce the traction. The reduction ratio of traction depends on the frequency of impact loading and the length of reciprocation.

View full abstract

The behavior of elastohydrodynamic lubrication(EHL) films formed between an optical flat and a normally vibrating steel ball is examined by means of the duochromatic optical interferometry technique. The film entrapped between the ball and flat plate forms an envelope at the end of the loading process. The maximum height of the film, which depends on the non-Newtonian response of oils and the squeeze number, remains constant during the cycle. Under conditions of short strokes and high frequency, air bubbles produced in the unloading process result in the collapse of the entrapped EHL film.

View full abstract

On-line estimation of the wear rate of materials subjected to abrasion has been accomplished using acoustic emission(AE) sensing. The energy in the AE signal is directly related to the energy required for material removal in the abrasion process. The technique has been successfully applied to monitoring the wear of magnetic recording head materials using lapping tapes over a wide range of wear rates. A methodology has been developed to calibrate the AE monitoring system on-line, and to estimate the total wear volume. Such a system provides a very powerful, quantitative measurement technique for tribological studies, as well as for on-line machine or process diagnostic applications.

View full abstract

In reciprocating internal combustion engines, one of the most important issues is to clarify the complicated frictional characteristics between the piston ring and the cylinder liner because of the demand for reduced frictional loss, as well as a solution of problems such as scuffing and wear, that has accompanied the recent progress in engine performance. In the present study, the floating liner method, in which the cylinder liner was supported by means of hydrostatic bearings, was developed to measure accurately the frictional force of the piston assembly as a function of the crank angle in an operating diesel engine. The influences of engine operation conditions (engine speed, cylinder wall temperature, and gas pressure in the cylinder), lubricating oil viscosity, polymer-containing multigrade oils, and a friction modifier on the frictional characteristics were evaluated on the basis of the experimental results obtained using this equipment.

View full abstract

It is well known that magnetic levitation using permanent magnets without control is impossible. However, just as in the case of a sleeping top, if the body to be levitated has rotational velocity, the situation will be changed. In this paper, a new type of system which utilizes both magnetic force of permanent magnets for vertical levitation and a null-flux coil system for axial or radial restoring force is proposed. A method of decreasing the required restoring stiffness for the null-flux system is given. Asymptotic stability of the top is discussed using eigenvalue analysis. Damping methods for the asymptotic stability of two conical vibration modes using eddy current dampers and the null-flux system are proposed. From preliminary experimental results, the possibility of constructing the all-passive-type rotary magnetic bearing is clarified.

View full abstract

A new numerical scheme for calculating the interface phenomena of VCR, namely between magnetic tape and head or drum, is presented. To enable estimation of the characteristics of the designed VCR system and effects of design parameters on the performance, it is necessary to reduce the CPU time and memory storage without sacrificing accuracy. We divide the area to be analyzed into two sub-areas : entire drum area and head area. These are analyzed separately, with the result for the former being used in the analysis of the latter. The results obtained are in good agreement with experimental ones.

View full abstract

A new type of shrink fitter, 'a hybrid shrink fitter', containing liquid such as a fusible alloy is proposed. The specimen materials are Al₂O₃ and Si₃N₄ for the shafts, SUS 304 for casings of the hybrid shrink fitters and SUS 403 for the metal rings. Fitting strengths were measured up to 600°C. The fitting strengths decreased with temperatures up to 200°C or 300°C and increased at higher temperatures. It was found that the hybrid shrink fitter had a higher apparent coefficient of thermal expansion than the monolithic shrink fitter. The effect of the number of slits on the fitting strength at elevated temperatures was also studied. The slit was essential for improving the fitting strength. The number of slits did not affect the fitting strength-temperature relationship if the number was 2 or more. The longevity of the hybrid shrink fitter was less than that of the monolithic shrink fitter at elevated temperatures.

View full abstract

Due to the asymmetric features of this control system, the STR strategy with a fixed reference model is no longer valid. Thus, the LQG self-tuner incorporated with the simplified 1st-order ARMAX model is proposed. By minimizing the cost function, this proposed scheme not only provides a tuned optimal reference model, but also avoids concealing the additional zero and transient oscilation. In addition, an implicit integrator is deduced from the cost function to reduce steady-state error and the effect of disturbance. Thus, by verification of robustness measurement, it is proven that the LQG self-tuner is always superior to the classical STR and insensitive to various operating conditions.

View full abstract

The macrofunction in the computer aided manufacturing (CAM) system is executed based on the macrocode which is transformed by a series of operations input by the user. By the use of this function, operations which should be performed by the user can be simplified. Therefore, if the transformation from mechanical drawings to NC code can be changed directly into macrocode, NC machining can be achieved easily. In our study, a function for transforming macrocode from data of CAD drawing to CAM data is developed. However, drawing data of a CAD system ("CAD-drawing") does not always coincide with drawing data of a CAM system ("CAM-drawing"), because in a CAM system, restricted conditions, such as machining conditions, must be considered. Consequently, drawing data must be represented by a structure and function which include information about restricted conditions. Thus, the concept of the relationship between "master and servant" for definitely expressing structure and function in an object model is specifically incorporated. As a result, even in the case where structure and function are changed, the knowledge base can be consistently maintained. This paper describes representation of knowledge in the knowledge base and method for generating a macrocode using the knowledge base.

View full abstract