Magnetic levitation has been studied mainly in two distinct fields of application, MAGLEV transportation and rotor bearings. A unitied overview, as it is attempted in this paper, reveals that there are many radically different types of magnetic levitation. A systematic classification of these basic levitation principles is proposed. It starts from the fundamental manner to obtain the magnetic force. The systematization derived in this manner aims at including all possible basic magnetic levitation types. As a result some little known levitation types are inc1uded, among them Lorentz-force bearings and tuned LC bearings. As a special feature, a new type of active bearing is presented, the so-called self-sensing active bearing using no gap sensor. This remarkable bearing type combines high static load and low hardware costs. Examples of realizations are given.

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The loss factor of a viscoelastic damping material is commonly measured by the half-power method using a composite beam with a viscoelastic layer. However, the method involves the problems of large measurement errors and of unusual be amshape, which does not represent practical applications. This paper discusses the relationship between vibration modes and measurement accuracy, and presents specimen dimensions which materialize the bending mode for an accurate loss factor. The vibration modes are classified as torsion, warping, torsion and warping, and bending. According to the discriminants this study derives, the beam shape must satisfy (l/b)(d₁/b)≥0.06 to materialize the bending mode. The loss factor of the viscoelastic damping material, obtained by the composite beam within the dimensional limits and the Oberst theory, had good agreement with the loss factor ofthe same material measured by the nonresonance forced vibration method, and was certified to be sufficiently accurate.

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Self-excited oscillations are often observed in a circular disk when it is rotated in air. Theoretical as well as experimental studies are conducted on these oscillations. As a preparatory study, free vibrations of the disk are discussed theoretically without taking into account the effect of air. Then, utilizing the results of this preparatory study, and taking into account the effect of air, free vibrations of the disk are studied. It is shown that self-excited oscillations can occur at a rotating speed higher than a certain value in the form of abackward traveling wave. Experiments confirm the theoretical analysis.

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When the new Shinkansen train, the series 100EC, came into service, lasting longitudinal vibration with a constant frequency arose frequently near the maximum operation speed. The lasting vibration was the first modal vibration excited by vertical track irregularities through the pitching motion of bogie trucks. This paper describes analytical results of the effects of the rubber stiffness on the longitudinal vibration characteristics. The rubber used for fixing the primary damper is a type of vibration isolator acting in series with the damper, and its stiffness must be reduced in order to allow the damper to incline with relative horizontal displacement between the truck frame and the axle box. However, when the stiffness is too low, the damping effect deteriorates. In the realistic range of reduced stiffness, the first modal longitudinal vibration increases with the decreasing stiffness, and when the stiffness is further reduced, the vibration due to truck pitching grows markedly.

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Nonstationary vibration characteristics during acceleration through a critical speed of a 1/3-order subharmonic oscillation of forward precession are investigated in a rotating shaft system. The following results are obtained : (1) A resonance curve is separated from a zero-amplitude resonance curve (a trivial solution) which is stable at any rotating speed ω. If there exists an initial disturbance at the start of acceleration, the solution jumps to the resonance curve and a subharmonic oscillation occurs. (2) The maximum amplitude during acceleration depends not only on the angular acceleration λ but also on the initial disturbance ⊿P, the initial rotating speed ω_s, and the initial angular posion Ψ_o of the unbalance. (3) For the initial angular position Ψ_o, the maximum amplitude varies periodically. (4) The amplitude grows infinitely for some values of Ψ_o when the angular acceleration λ takes a value between two critical values λ₁ and λ₂. If the angular acceleration is outside of this range, the rotor can always pass the critical speed with a finite maximum amplitude. In addition, characteristics of some other subharmonic oscillations of backward precession are discussed briefly. Finally, nonstationary vibration characteristics at various critical speeds, such as a major critical speed, a summed-and-differential harmonic resonance and subharmonic resonances, are compared.

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The phenomena of 'stick-slip' oscillations in the hydraulic drivingsystem are studied both experimentally and analytically. The system consists of a table lying on a rectilinear sliding surface, an actuator cylinder, a 4-way servo valve, a relief valve and an oil pump. The transitional friction characteristic curves are considered for increasing and decreasing velocity motions of the table. The variations of friction are modeled as fol1ows : (1) Kinetic friction varies with impressed electric current and sliding velocity ; (2) Static friction varies with the electric current passing through the servo valve and sliding velocity. The principal experimental variables are lubricant viscosity and the mass of the table. Their influences on the characteristics of 'stick-slip' oscillations are studied.

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We consider the dynamic response of a single-degree-of-freedom system subjected to nonharmonic excitation. The model consists of a mass attached to a linear spring and a linear viscous dashpot impacting a rigid obstruction witha coefficient of velocity restitution. The amplitude and stability of the periodic responses are determined and bifurcation analysis for these motions is carried out by using the piecewise linear feature. Period-doubling bifurcations, tangent bifurcation, and crisis occur in our model. Some parameter regions which contain no simple stable periodic motions are shown to possess chaotic motions. Lyapunov exponents are computed over a range of forcing periods. Discrete mapping is used to calculate the Lyapunov exponents for the piecewise linear system due to the fact that the discontinuity occurs at impact with the Stop.

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This paper is concerned with a computer simulation of active noise control using the boundary element method for analyzing three-dimensional acoustic field problems. The active noise control under consideration is reduced to an optimum problem to determine the optimal set of parameters defining the sound pressure of a secondary source to be attached. The optimal set of parameters is selected through the conventional optimization procedure so that the sum of the sound pressure values measured at the duct exit is minimal. Computation is carried out for typical examples in which the duct is embodied in the infinite plane and the noise through the duct is radiated to the semi-infinite acoustic field, whereby the potential usefulness of the computer simulation system developed is demonstrated.

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This paper investigates H^∽ control of a flexible rotor model and suppression of spillover phenomena by modelling of reduced order. A H^∽ control system is designed such that neglected vibration modes in a high-frequency range are not excited, i.e., spillover phenomena do not occur. Simulation results are presented to demonstrate the effectiveness of the control. Since the H^∽ control problem in this paper is reformulated to a special case of the standard Ho control problem, a new method is developed to solve it.

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Recently Yano proposed a new theory of muscle contraction, termed the electrostatic linear actuator model. Based on this theory, we developed an electrostatic linear actuator as a biomimicking skeletal muscle. The fundamental actuator unit consists of a parallel plate capacitor and a slider made of dielectric material. Based on this model, we derived the theoretical formula for the thrust of the actuator. This formula revealed the following facts. The thrust can be maintained constant when the supply voltage is kept constant, and can be markedly increased by optimizing the dielectric constant of the fluid which fills the space of the capacitor. Using this formula, we designed a simple practical model expected to generate a thrust of 10 mN with the stroke of l0 mm. The surface area of this actuator was l cm².

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Output torque/force of a hydraulic actuator is generally affected by its driving speed. This may cause deterioration of the control accuracy of the system in which the plant is controlled through the driving torque/force control of the actuator. This study proposes a positive angular velocity feedback for compensation of the effect of the driving speed on the driving torque control of a rotary hydraulic actuator. The compensation scheme is experimentally applied to motion control of a one-link hydraulic robot which is controlled by means of the computed torque method. The experiments show that the compensation scheme is effective in isolating the driving torque of the actuator from its driving speed and slightly improves the tracking accuracy of the motion control.

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This paper deals with a problem of optimum structural design in which the shape for a beamlike structure that minimizes the cost for vibration control under the condition of volume constancy is determined. This is an approach to the simultaneous optimization of the structure and control functions. The objective structure is modeled by the finite-element method, and the control law obeys the optimal regulator theory. Through numerical examples, the effects of the initial state and weighting matrices on the result are discussed. Moreover, a two-step method for obtaining the optimum shape is proposed.

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The advantages of direct identification of characteristic matrices of structures are such that we can easily determine the various modal characteristics through eigenvalue analysis: those results may match automatically with the results of the curve fits in ordinary experimental modal analysis, and further, they can be used directly in numerical calculation such as that in the finite-element method. Problems in direct identification of characteristic matrices of structures lie in the accuracy of experimental data and the estimation of their errors. In this study, we allow that experimental data values themselves include errors or deviation, and for this reason, we assume that it is reasonable to deal with them as elements in fuzzy sets. Allocating a fuzzy number to each set of experimental data and extending the operation rules of fuzzy numbers, we propose a fuzzy direct identification method. The efticiency of the proposed method was demonstrated through applications to the identification of characteristic matrices of a 3-degree-of-freedom mass-spring system and a cantilever beam.

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This paper presents a new design method for an active suspension control system based on H_∽ optimization robust control theory. A four-degrees-of-freedom half-car model equipped with independently controlled front and rear active suspensions is analyzed. Time, frequency and spectral analyses show that the active suspension maintains the tire-road contact force for good maneuvering, stability and handling, reduces the vibration transmissibility and attenuates the passenger-perceived acceleration, improving the ride comfort. The robustness properties of the H_∽-optimization-based suspension controller are examined and compared with those of a conventional LQG-based active suspension.

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In this paper, a linear-model-following control (LMFC) method using direct digital control (DDC) to reproduce the input waveform is discussed. It is difticult to control the acceleration waveform of an electrohydraulic servovibrator because of its nonlinear characteristics. To control this acceleration waveform, the LMFC method with a reference linear model of a time-delay element is introduced. This LMFC system has a state variable feedback circuit with variable feedback gains, and the calculation of the variable feedback gains is performed by means of a digital processor. The LMFC method is applied to the analogue simulation circuit and experimental apparatus to confirm reproducibility of the input signal. The experiment shows that the performance index of waveform distortion is 11 % for a reference signal of triangular waveform with a fundamental fraquency of 30 Hz.

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Active vibration control of flexible rotor systems with gyroscopic effects is investigated in this paper. Using the finite-element formulation for the mathematical model of flexible rotors, a new rotating velocity-dependent output-feedback controller, in addition to the optimal independent modal-space control system, is proposed to suppress the vibration level and in consequence, achieve better operating conditions.This new active control loop is added in order to compensate the gyroscopic effects during rotation, especially in the higher-flexibility modes. Furthermore, stability analysis via the Kelvin-Tait-Chetdev (KTC) stability theorem for a mechanical system is presented. It demonstrates that if the placement of actuators and sensors are collocated, the fulfillment of optimality and stability for each independently controlled mode is a prerequisite to guaranteeing full-order closed-loop (FOCL) stability. Simulation results are shown in order to confirm that the proposed controller effectively promotes control performance. In addition, the significant impact of the allocation of sensors and actuators on the effectiveness of such a controller is also discussed.

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A double-pendulum-type mobile robot, which can shift laterally from one horizontal bar to an adjacent bar, has been studied. The robot is equipped with pivoted double-link arms and grippers installed on the free ends of the arms. First, one arm of the robot grasps one of several bars arranged horizontally at regular intervals with its gripper, and the second arm is immobile, hanging from its upper pivoted end. When the latter is swung by an actuator following the control path, vibratory excitation is induced in the robot. As a result of this excitation, the gripper end of the second arm is swung up to the neighboring bar, at which point the gripper grasps the bar, and the first arm's gripper releases the original bar. Then the robot moves laterally by one pitch of the bars, and shifts continuously through the bars by repeating the sequerice. It is confirmed by experiments as well as by computer simulation that the robot can shift through the horizontal bar array using excitation of the system. The concept of control paths, proposed here, is very useful. Furthermore, this mobile robot provides a unique example of dynamic interference problems between arms with and without an actuator in order to indute excitation in the entire system.

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In this paper, the kinematics of the planar multifingered robot hand is investigated for grasping and manipulation of some objects. The kinematics equations and the conditions for grasping and manipulation with rolling contact points are derived. The contact finger forces are affected by small contact point displacement, however, grasping and manipulation conditions remain unchanged. Finally, the effects of contact point displacement are illustrated concretely by numerical examples of point and rolling contact.

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In this paper, the sealing mechanism of knife-edge seals was explained and a new type of knife edge was developed. The following results were obtained: (1) The sealing mechanism of knife-edge seals was divided into three types according to the width of the flat area on the apex of the knife edge: (a) the penetration type, (b) the indentation type, and (c) the intermediate type. The P_c/l-values of the compressive force for sealing were the lowest in the case of type (a). (2) The developed knife edge had a sealing mechanism of the penetration type (a). The P_c-values of contact pressure for sealing were nearly equal to the Meyer's hardness in the sealing surface layer, regardless of both the surface roughness and the sealing surface finish. In the cases where sealing materials of copper, carbon steel and stainless steel were utilized, the P_c/l-values were approximately 15-40, 45-110 and 80-190 kN/m, respectively.

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In recent years, engine oils have contained various kinds of additives such as high-molecular-weight polymers for improved performance. Such lubricants exhibit viscoelastic behavior, but were assumed to be Newtonian fluids in most of the previous investigations on piston ring lubrication. The objective of this paper is to theoretically clarify the effect of nonlinear viscoelasticity of lubricants on piston ring lubrication by introducing a nonlinear four-element viscoelastic model which consists of two non-linear dashpots and two nonlinear springs. Numerical solutions show that the effect of viscoelasticity reduces the frictional force and the film thickness. In addition, the phase of the variations in the frictional force and the film thickness of viscoelastic fluid is delayed compared with that of Newtonian fluids.

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The effect of shape error on the rotational accuracy of an externally pressurized air journal bearing with point sources is analyzed theoretically. The shape errors taken into account are roundness errors of both the journal and bearing, and the roundness profile is assumed to be of a sinusoidal lobe shape. The rotational accuracy is studied by investigating the amplitude of the journal center locus calculated by nonlinear analysis of the Reynolds equation for compressible fluid. The mass unbalance effect on rotational accuracy is not considered in this paper. It is shown that roundness errors, frequency of roundness pfofile, feeding parameter, and load significantly affect the rotational accuracy of an externally pressurized air journal bearing.

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The objective of this study is to propose a methodology by witch to establish the CAE (Computer Aided Engineering) system for assisting product development. In general, for new product development designs, the design objects are frequently redesigned on the basis of experimental results. This paper describes a method to establish the CAE system, which possesses an engineering model of a design object in the model database, and refines the model on the basis of experimental results. We have utilized the blackboard inference model to infer the model retinement and the redesign countermeasure. The validity of the proposed CAE system has been verified by developing an active magnetic bearing for a turbomolecular pump.

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Actual design methods are multiobjective design satisfactions with heterogeneous objective functions such as performance and cost, and with dimensionaL design variables such as part size and distance. To materialize the actual designs in computer-aided design, this paper presents a new method which determines structural dimensions (design variables) in order to make all objective functions accomplish their respective functions. Heterogeneous objective functions can be described in the same form (a new concept termed attainability), which apparently indicates the satisfied functions by a positive sign or zero. The sensitivity coefficient matrix provides the most successful variables which can improve a minimum, as well as a negative, attainability to positive or zero, and simultaneously keep all positive attainabilities positive or zero. Values of the variables are revised iteratively for this purpose. In an agricultural transmission gear design, the method produced significant and practicable results in short CPU time.

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An intelligent translating system which is under development extracts the CAD (Computer-Aided Design) data from mechanical drawings. The system consists of three modules: image processing, image recognition and image understanding. By scanning the geometric structure of the drawing, the image recognition module tries to identify visible lines, dimension lines, extension lines, broken lines and center lines. In the image understanding module, vector data are modeled on the chemical bond. Feature points and vectors are interpreted as atoms and molecules, respectively, and the degree of understanding is equivalent to the coupling force. The representation of the drawing is a hierarchical structure composed of end points, segments of lines, and front, side, and top views. Expert rules detect and correct errors in recognition to arrive at complete understanding.

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A new method of finish rolling is proposed to finish tooth surfaces and fillets at roots of gears in one pass, using a screw-shaped tool. A preliminary experiment of finish rolling of only tooth surfaces of spur gears is conducted with a trial constructed apparatus. Gears with good tooth profile accuracy and good surface finish are produced without any modification of the tooth profile of the tool or the work by this method. The rolled tooth surface of the work is markedly hardened.

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At present, the accuracy of a deteriorated lapping plate may be recovered by cutting and grinding, or by using a correcting carrier. A correcting carrier is simpler to use than the grinding method and is generally employed at many factories. How-ever, as the deteriorated condition of the lapping plate changes with machining conditions, optimal correcting conditions must be selected in order to recover the deteriorated lapping plate. In this paper, the wear characteristics of a lapping plate with a correcting carrier are analyzed theoretically and confirmed experimentally. It is confirmed that deteriorated lapping plates can be restored by means of this method.

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Modular tools have the potential to offer a more economical solution to the problem of designing FMS lines for machine shops. However, the coupling of a cutting tool edge and a cutting holder is achieved manually and takes 5 to 10 min. It is suggtsted that an automatic assembly device for modular tools would be very useful, especially for machine tools with many cutting tools. We designed a system and named it ATASS (R) (Automatic Tool Assembly and Supply System). This system consists of a magazine for the cutting edge, an assembly device, a supply device, and a controller. We also designed a new modular tool that is easy to assemble automatically, and in which coupling can be completed within 0.5 sec. The new modular tool has cutting performance equivalent to that of the conventional tools. By applying ATASS to machine tools, we can reduce the total cutting tool expense by 14-70% and cutting tool space by 20-75%. As practical examples, this paper describes 3 types of ATASS for turning center, lathe, and machining center.

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