R&D of launch vehicles, satellites and the Japanese Experiment Module to be connected to the Space Station is traced with special emphasis on their tribological problems encountered on the way of space development in Japan. Lubrication, friction and wear of rolling bearings and seals applied to turbopumps of an LE-5, the first LOX/LH₂ engine completed in Japan, are discussed. Performance on orbit of ball bearings supporting the scanning mirrors of the earth sensors launched ill 1981 is introduced including test results of candidate materials used for cages. Compared to conventional rolling bearings, magnetic bearings have the merit of no friction and wear. Results obtained from experiments of the magnetically supported flywheel brought into orbit in 1987 are described. Furthermore several tribological problems tribologists confront in designing the Japanese Experiment Module are refered.

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In the present paper, the frictional vibrations in a mechanical system are studied theoretically using the average method when the friction-velocity characteristic curves are given by several types of function. The steady-state vibrations, or limit cycles, obtained from the average method are compared with the corresponding approximate motions regarded as the positively exact solutions, which are obtained from the piecewise linear system with the friction-velocity characteristic curves approximated by a polygon having numerous segments. Moreover, the effectiveness of the use of the average method in the theoretical analysis of frictional vibrations is shown in three types of friction-velocity functions when the nonlinearities in the system are not too large. Successively, the influences of the discontinuity between the maximum static friction and the kinetic friction without slipping are investigated for the amplitude curves of limit cycles. Lastly, in the case where such a discontinuity does not exsist, an easily revisable method is offered in which almost exact solutions can be obtained by modifying the solved curves estimated from the average method.

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The paper is concerned with free flexural vibrations of connected systems consisting of linearly tapered bars and cantilever plates of infinite width and constant thickness. The frequency equations are obtained in the cases that the bars attached to the plates are of (I) constant width and linearly varying thickness and (II) Iinearly varying width and thickness. The first two natural frequencies are calculated numerically and are shown graphically.

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An approximate analytical technique is developed for obtaining the nonstationary responses of a multi-degree-of-freedom mechanical system with nonsymmetric non-linearities subjected to nonwhite random excitations with arbitrary covariance functions. The method consists of a modification of the equivalent linearization technique, in which the equivalent linear system is subjected to the equivalent forcing function with shifted mean, and the use of moment equations of the system. Numerical examples are given for single and two degree-of-freedom systems whose restoring force characteristics have both quadratic and cubic nonlinearities. In the first case, the results are compared with those of the corresponding digital simulation in order to demonstrate the validity of the present method.

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The parametrically excited oscillations in a rotating shaft system where a periodic axial force is applied are studied theoretically. The treated model is a four-degree-of-freedom system where a disk is mounted on an elastic shaft with a circular cross section. We investigate the following: the forms of parametric excitation terms in the equations of motion, the kinds of parametrically excited oscillations which occur in this system, the influences of the shaft rotating speed on the width of the unstable regions, and so on. The differences from other kinds of parametrically excited systems, such as an unsymmetrical shaft system, an unsymmetrical rotor system, and a column system under a periodic axial force, are also clarified.

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It is well known that unstable vibrations occur at a certain range of rotation speeds when the rotors are partially filled with liquid. Similar self-excited vibrations appear in large-scale and continuous flow-type ultra-centrifuges due to the formation of layers distributed from the inside to the outside in the rotor depending on increasing weight density. The unstable vibrations feature a forward-whirl rotor motion. An electromagnetic bearing control, reacting to the detected rotor displacement, can produce an artificial damping effect for this stabilization. The control to produce the damping effect is realized by a cross network combined with a tuning filter, i. e., the cross stiffness function commonly denoted by +Kxy and -Kyx. The sign of the cross stiffness depends upon the whirl direction. This control strategy using the cross effect successfully combatted unstable flow-induced forward rotor vibrations.

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In this study, a qualitative analysis of a transverse vibration of a rotor system with a crack that grows at an angle of 45 degrees toward the axis of the shaft is presented. Based on the assumption that the bending stiffness of the shaft changes synchronously with the opening/closing behavior of the crack caused by the torsional vibration of the shaft, the equation of motion of a simple rotor system with a shaft having a slant crack is represented by a differential equation with parametric excitation in the coordinate system rotating at the operating speed of the rotor. It is shown by the solution that the steady-state response of the rotor system with a slant crack on its shaft induced by imbalance contains the frequencies represented by mΩ+ nω_T/2 ; m=1, 2, ..., and n=0, 1, 2, ..., where Ω is the operating speed of the rotor, and ω_T is the frequency of torsional vibration of the rotor system.

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A mathematical model of an isolated blade of a horizontal axis wind turbine generator is presented to describe coupled motions of flap, Iag and torsion of the blade. An energy approach is employed to derive Lagrange's equation of motion. The blade is considered as a pretwisted beam of variable cross section to calculate the kinetic, dissipation and strain energies. Quasi-steady blade-element strip theory is applied to compute aerodynamic forces which account for the boundary layer shear winds and wind speed reduction due to tower shadow. The resulting equations, which have time -dependent coefficients, are solved numerically to obtain the steady-state response and stability of the blade. Wind tunnel tests were conducted using a l/25 scale model to ascertain theoretical predictions.

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This paper deals with the development and analysis of a new method of measuring displacement and position by means of the variations of the sound frequency and the air column in a resonant pipe. Sound generates when compressed air is blown across an open-ended face of a small pipe. The sound frequency varies with the length of the air column in the resonant pipe. By applying this phenomena, a new, accurate and simple method for measuring the displacement and position is examined and developed. The displacement corresponds to the length of the air column and the variation of the sound frequency shows a close relationship with the displacement. The resonant frequency of the pipe can be shown by a simple equation; however, the resonant frequency does not coincide with the sounding frequency of the pipe. The difference between these two frequencies is explained in this paper as active end correction of the pipe.

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An investigation of sound generated from a ball screw was carried out in order to obtain basic information for the sound reduction of a ball screw. The test ball screws were of the single nut and single guide-tube type. Their screw shaft diameter was 20 mm and their lead was 10 mm in length. Test ball screws were set up at a ball screw sound testing machine installed in a soundproof room, and they were operated by the testing machine under the nonload condition. The sound generated from the ball screw was picked up by a condenser microphone. Using the signal thus obtained, sound pressure level measurement, sound waveform observation and real-time frequency analysis etc. were carried out. From the experimental results and considerations, the fundamental sound characteristics of a ball screw were clarified, and some basic information concerning the sound reduction of a ball screw was obtained.

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This paper presents an approximate model with an infinite number of vehicles in which an infinite number of wheels are arranged at intervals on the head of an infinitely long and straight rail installed on a distributed spring in the vertical direction. This model is very effective for the analysis of the coupled vibrations between railway vehicle wheels and a rail in the case of a large number of wheels. Using the analytical model, the contribution of rail to the coupled vibrations was examined for each section partitioned by the wheels of one Shinkansen vehicle. As a result, it became clear that rail vibration between truck wheels is dominant in the frequency region below 2 kHZ and that of the rail near a coupler between vehicles is also significant in the frequency region above 1.5 kHz.

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In the contlol systems designed on the basis of exact model matching theory, the output of the plant tracks the reference model output exactly but suffers from the errors due to continual disturbance. The effect of continual disturbance can be suppressed by inserting appropriate precompensator before the plant. The design technique is further extended to the case when the plant parameters are unknown. That is, an adaptive control system in which the effect of continual disturbance is suppressed is constructed. The theory presented here can be applied to the design of a stabilized platform which mounts a TV camera in a moving vehicle. In such case, the effect of disturbance must be suppressed thoroughly.

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A method for designing a servomechanism for a nonlinear multivariable system by sliding-mode control is proposed. The derived servomechanism is completely decoupled during sliding motion, so that a set of servomechanisms with single input-single output is obtained. The input-output relations are given by transfer functions of which the poles are arbitrarily assigned. Servomechanisms with an arbitrary system type can also be realized. The advantageous properties of sliding-mode control, such as insensitivity to parameter variations and disturbances, are preserved in this servomechanism. An example is given in order to illustrate the design procedure.

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Recently, the reduction of cost in the gear field has become a serious problem and consequently, the force-fitted gear has become the subject of attention. Although some studies on force-fitted spur gears have been presented, there have been very few studies hitherto which deal with force-fitted helical gears. In view of such a situation, the force-fitted helical gear was chosen as the subject of the author's study. That is to say, by using the three-dimensional finite element method, stresses at the root fillet of a gear tooth caused by force-fitting were calculated. Practical formulas of these stresses can be introduced.

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A modified Reynolds equation for nonlinear viscoelastic fluids based on a nonlinear four-element model was derived, and the effects of viscoelastic behavior on the performance of parallel circular squeeze bearings oscillated sinusoidally was clarified by comparing the theoretical results with the experimental ones, in the previous paper. This paper presents two applications of the modified Reynolds equation to fluid film lubrication problems. Firstly, by applying the modified Reynolds equation to a finite-width journal bearing which is oscillated sinusoidally, the analytical procedure for viscoelastic lubrication problems under three-dimensional flows of lubricants is clarified, and good agreement is shown between the experimental results and the theoretical predictions based on the four-element model. Secondly, to clarify the effects of viscoelastic behavior on the performance of parallel circular bearings under irregular squeeze motion, theoretical and experimental studies of parallel circular plates in normal approach are shown.

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The fretting wear properties of copper, SUS316L steel, epoxy and polyimide were examined at room temperature (293 K) and with liquid nitrogen (77 K) . Fretting conditions were a frequency of 8.3 Hz, a peak-to-peak slip amplitude of 100 μm, normal loads of 4, 10 and 20 N, and 5×10⁴ fretting cycles. The frictional properties against the fretting cycles were qualitatively independent of temperature for like-metal combinations. Temperature dependence was observed for metal and polymer combinations, that is, coefficients of friction increased after certain cycles at 293 K and were maintained constant at 77 K. Mean coefficients of friction at 77 K were higher than those at 293 K for like-metal combinations, while they were lower than those at 293 K for polymers against metals. Wear volumes at 77 K were less than those at 293 K for all combinations. These properties were affected by the change in mechanical properties of materials, the change in the oxidational process and the cooling effect by liquid nitrogen.

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In a crowned gear pair, which is employed to prevent end-tooth bbearing, the load distribution in the tooth trace direction is elliptical. This paper describes the effects of crowning on the antiseizure capacity of a gear base oil. The experiments were carried out by two-cylinder tests at high specific slidings comparing the results under uniform bearing. The antiseizure capacity of the gear base oil in the tests with crowned cylinders was higher than that in the tests with uncrowned cylinders. Though the contact width in the axial direction at seizure became small and the Hertzian stress at seizure became high as the radius of crowning was decreased, the radius of crowning hardly affected the antiseizure capacity. Finishing the surface roughness finely is an effective means to decrease the friction coefficient and to increase the antiseizure capacity of the gear base oil in the higher range of sliding velocity.

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Based on Bassani yield criterion, a computer simulation of axi-symmetrical pure stretch-forming is attempted. A method for estimating the coefficient of friction necessary for the calculation is presented by extending Hill's method. The results calculated for four kinds of metal sheets are compared with the experimental data. The strain distribution and the fracture position are found to be sensitive to the shape of the yield locus, that is, anisotropic yielding, and it is concluded that the Bassani function is much more useful for the simulation than Hill's old criterion.

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The true root stresses of internal spur gears with various numbers of teeth and addendum modification coefficients are calculated by means of 2-dimensional elasticity theory and mapping function, and the position of the critical section on the compressive side of the internal spur gear tooth is indicated. The stress concentration factors at the position of the critical section are calculated under different loading conditions. A practical formula for the compressive true root stress of the internal spur gear tooth is derived on the basis of these calculated results. Furthermore, the root stresses calculated by this practical formula are compared with those calculated by the theory of elasticity and FEM, and with measured stresses, and the validity of the practical formula is thereby confirmed.

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This paper presents a study on the effect of standard pressure angle on the bending fatigue strength of helical gears. The root stresses of meshing helical gears with various pressure angles, helix angles and whole tooth depths were calculated by using the approximate equations for deflection and bending moment due to a concentrated load on gear teeth of full depth and long teeth with various pressure angles and Kubo and Umezawa's method. Bending fatigue tests were performed on helical gears of full depth teeth with various pressure angles and helix angles. On the basis of these results, the effects of pressure angle, helix angle, and whole tooth depth on the root stresses and bending fatigue strength of helical gears were clarified to a considerable extent.

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In this paper, the method by which an autonomously guided vehicle tracks a white-line course using image processing is described. There are three peculiarities in this method. The first is that the input images of the white-line course are all segmented and are treated by serial pattern numbers. The second is that each input image has the output value of the steering calculated in advance and all the output tables according to the input images are stacked in the data files. The third is that the path is approximately tracked by connecting the several arcs which occur. We confirmed the effects of this method using a simulator which replicated the motion of an autonomously guided vehicle.

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