Recent missions of Japanese spacecraft for space researches are briefly presented, and their requirements on the attitude control are reviewed both for three-axis controlled satellites and spin-stabilized ones. The attitude control schemes developed and the systems designed are described by putting emphases on their specific features and the problems encountered during the developments. Key technology areas which will require further attention to achieve the near-future science missions under study are identified.
The National Space Development Agency of Japan (NASDA) has developed the engineering test satellites (ETS). Five ETS have been launched already, while ETS-VI will be launched in summer of 1994 and ETS-VII has been developed for the launch in 1997. The guidance and control system about satellites is explained in general. And the perspectives of ETS is stated shortly.
The GEOTAIL spacecraft, designed and developed by the Institute of Space and Astronautical Science (ISAS) of Japan, was successfully launched by NASA's DELTA II rocket on July 24, 1992. The dual spinning satellite, equipped with two different kinds of deployable wire antenna systems, each having a pair of 50m wire antennas, will contribute to better appreciation of fundamental magnetosheric mechanisms. Due to a distinct trend towards larger space systems, deployment structures of many kinds, such as space stations, tether experiment modules, and deployment antenna configurations as well as extensible wire antennas, are supposed to play a key role in the future space infrastructure. Even at the recent stage of space activities, however, deployment of structures in space is still among the most difficult projects, showing several examples of failure and incompleteness due to technical and mechanical problems in past years. An emergency operation was in fact executed for the wire deployment of the GEOTAIL to finally obtain complete configurations. The problem is further accentuated by the fact that the dimensions of the wire antennas may lead to undesirable wire vibrations as well as satellite attitude perturbations through in-orbit events scheduled, such as antenna and mast deployment, spin-up and -down operations, and attitude and orbit maneuvers, resulting in distortion of the attitude control accuracy and the scientific observation environment. In the study, in-orbit operations exciting the wire vibrations are reviewed and some of the typical flight data of practical importance are analyzed to reveal effects of such operations on the system response.
In this paper, two kinds of mathematical models of flexible bodies connected by rotary joints are derived in a recursive form based on the method of weighted residual. The first one uses the translational and angular velocities and the modal amplitudes of the elastic deformation of the bodies as the state variables. The mathematical model derived is an extension of the model of a rigid multibody system based on the Newton-Euler method. The second one uses the translational velocity of the base body and the angular velocities and the modal amplitudes of the elastic deformation of the bodies as the state variables. The mathematical model derived is the same as the model based on the Lagrangian formulation with quasi coordinates. The algorithms of the inverse dynamics of a flexible manipulator are derived using the models obtained.
The effect of objective functions on the results of the simultaneous optimum design of structural and control systems is discussed, comparing the optimum designs obtained by minimizing several different types of objective functions. These objective functions are defined as a linear combination of the structural and control objectives. One of them is for structural weight, another is the feedback gain norm and the others are transient characteristic values which are expressed in quadratic form. A flexible cantilever beam resembling a flexible appendage attached to a large space structure is designed in the numerical example. The beam width and the controller location are optimized under initial dynamic disturbance. The results indicate that the usefulness of the simultaneous optimum design of structural and control systems depends on selection of the objective functions.
Based on the results previously reported, the authors have evaluated the performance of bang-bang vibration control methods using information on velocity, acceleration or displacement. From the results of analysis for a simple 2/3 DOF model and also from the simulation and experimental results for a beam, it turns out that the proposed bang-bang velocity feedback control equals or exceeds the conventional DVFB control in terms of vibration suppression capability, power consumption as well as robustness to system parameter variations.
This paper describes some methods to control the vibration of flexible structures based on the concept of power flow. The controllers which minimize power flow into the structure are designed using LQG, H2 and H∞ control theory about the plant modeled in modal space. Designed controllers are evaluated by simulation analysis and experiment. As the main results, the power flow control is shown to be effective for vibration control of flexible structures and a mixed H∞ control law proposed in this paper shows the best performance and robustness.
Body divergence criteria of rocket vehicle is studied and is applied to the analysis of flight data of a small test rocket. Vibration testing showed that there could have occurred degradation of bending stiffness at the mating section of FRP solid rocket motor chamber and aluminum structure. Analysis shows that, assuming degradation at the mating section, body divergence could have occurred.
Fundamental equations governing free vibrations of curved and twisted thin plates, which are blade models of the advanced turboprop, are presented in this paper. First, exact strain displacement relationships for curved and twisted thin plates are derived based on the thin shell theory. Then, the principle of virtual work of free vibrations is formulated, which is the fundamental equation for establishing numerical procedures to analyze the vibration of the curved and twisted plate, such as the Rayleigh-Ritz method and the finite-element procedure. Since the equations are derived on the basis of shell theory, they are utilized for plates having large initial twist.
Free vibrations of curved and twisted cantilevered thin plates are investigated analytically and experimentally. A numerical method based on the Rayleigh-Ritz procedure is presented using algebraic polynomials as displacement functions and an approximate integration, dividing the plate into elements. Convergency studies of nondimensional frequency parameters are made with increase of the number of elements dividing the plate and of terms in the assumed functions. Then, effects of initial twist and curvature on vibrating characteristics are discussed for typical curved and twisted cantilevered plates. Finally, experimental tests are carried out and resonance frequencies and mode shapes obtained are compared with analytical results.
The object of this study is to determine the cause of self-excited vibrations of wire-winding-type growing equipment for silicon single crystals. From the results of experiments, we found that the form of the pulley affects the periodic change (when wire rope is not rotated) and the rate of increase of amplitude (when wire rope is rotated). These effects seem to be caused by friction between the pulley and wire rope. The easier the pulley contacts the wire rope the larger its effect becomes.
The influence of the support condition of a beam of a sandwich plate on the modal loss factor is examined. Resonant frequency and modal loss factor are calculated based on Mead's theory. While Ungar's equation, which is generally employed to estimate loss factor, is valid only for a simply supported beam, a trial of applying it to other support conditions is performed by defining the equivalent half-wavelength, and it is suggested that for support conditions other than simply supported as well, resonant frequency is well predicted by Ungar's equation. Only for the simply supported beam, can the modal loss factor be determined uniquely from frequency. For other general support conditions, loss factor depends on the mode order. An experiment is performed with the support condition of both ends simply supported and free, and a similar tendency to these finding is shown. It was demonstrated that the loss factor obtained from antiresonance for symmetrically supported beams corresponds to the modal loss factor for the clamped beam of half length. This is also verified experimentally.
The design optimization of passive vibration control mechanisms in the accelerance domain is discussed. In this study, the fixed points theory is developed which approximately minimizes the maximum accelerance in the frequency domain by equally adjusting the accelerance of two fixed points. This design method is applied to the dynamic vibration absorber (DVA) and the passive gyroscopic damper (PGD), and thus the maximum accelerances of these mechanisms are successfully reduced. The concept of the fixed points theory is reinvestigated. The accuracy and the degree of improvement compared with the fixed points design in the compliance domain are examined. The PGD realizes relatively higher damping effects, and then the accelerance reduction of the PGD by the new design method is considerably larger than that of the DVA with a moderate mass ratio.
A hybrid mass damper using a hydraulic actuator and a multistage rubber bearing has been developed and implemented in the Long-Term Credit Bank of Japan Building which has a height of 130 m, a total floor area of 62821 m2, and a total weight of 39800 t. This mass damper can work mainly as an active one to effectively control relatively small vibrations of a building caused by winds and weak earthquakes. At the same time, it can work as a passive one against strong earthquakes. The moving mass has outer dimensions of 18×6.5×4.5H m and a weight of 195 t, and heat storage tanks are utilized as a part of the mass. The active-passive mode switching rules and a variable gain control law were adopted to make the mass damper perform more effectively against frequent winds and earthquakes. Excitation tests and simulations were carried out, showing that the mass damper continued to work in the active mode for strong winds and weak earthquakes, and that, for strong earthquakes, the passive mode appeared for a certain period of the excitation with large acceleration, and then the active mode resumed and effectively suppressed the residual vibration of the building.
Elastic suspension systems are widely used for vibration reduction purpose. When disturbance vibrations contain undesirable frequencies, resonances may occur and the movements of the suspensions become harmful. In order to avoid the large resonances, dynamic absorbers are used. Then the systems assume two degrees of freedom. In this paper, characteristics of these systems are treated. The spring elements for both the main suspension systems and the dynamic absorbers are assumed to be rubbers which have complex spring constants. When the main suspension systems have no damping, the fixed point theory can be used and the optimum tuning condition and loss factor are obtained. When the main systems have dampings, optimum values are derived by introducing correction factors. Vibration transmissibilities are measured experimentally. The results show good agreement with calculated ones. It is concluded that the complex spring models can be applied for calculating vibration transmissibilities of dynamic absorbers using rubber vibration isolators.
This paper describes the impact absorption characteristics of a human arm when catching an object. The impact force acting on the human arm is measured, and the time trajectory of the force is analyzed. Experimental results show that the palm of the hand absorbs the impact by reducing the peak value of the force time trajectory and the wrist and the elbow do it by reducing the force acting time. These characteristics are explained by the simulation of a catching motion model constructed of a spring-mass-damper system with the Hertz force model, by which the impact phenomenon can be simulated. It is shown that the mass effect decreases in the absorption by the palm of the hand compared with impact to a rigid object, and the damping effect decreases in the absorption by the wrist and the elbow compared with only the palm.
A new approach of finding the path to a goal automatically is proposed in this paper. For this problem, our approach uses the vibrating potential method (VPM) to provide the strategy for finding the path. The VPM is a new problem solving system we proposing, and has sufficient unity of fundamental mathematical expression to describe the movement of agents as autonomous machines. In this method, a vibrating potential field (VPF) as an environment is constructed by agents and their interaction energy. These agents interact with each other by the information from the detected wave motion from the environmental surroundings. By the VPM, each agent can decide its movement through detection of wave motion as the environmental surroundings without specific problem oriented programming. In this paper, we set moving-robot agents (RA), obstacle agents (OA) and goal agent (GA) on VPF. We show computer simulations that RA can find the path by two methods. One is position control by local-area sensoring and the other is path planning by detecting global information from GA.
This paper describes a method for the estimation of dynamic coefficients of a parallel annular seal with eccentricity based on the continuity equation and the equations of momentum in two directions. Simplified governing equations are used with the introductions of averaged axial and circumferential velocities and the Hirs turbulent friction coefficient. These equations are perturbed to obtain a set of ordinary differential equations governing the dynamic quantities with respect to the eccentricity ratio. The differential equations are integrated by the use of Adams method. The dynamic coefficients are calculated using the forces resulting from the pressure perturbation, and the results are compared with experimental data.
This paper is concerned the computer-based sliding mode control of a flexible rotor-magnetic bearing system. The reduced-order model for controller design is given by eliminating higher-order modes beyond the second flexible mode. A discrete-time sliding-mode controller for the reduced-order model is proposed, and its robust performances are evaluated in several rotational experiments up to 40000 rpm. The unstable modes can be easily controlled with good stability and the spillover phenomena due to the ignored higher-order modes are not generated. It is indicated that discrete-time sliding-mode control has robustness against the model parameter variations and external disturbances.
A dynamic analysis of free-piston Vuilleumier cycle heat pumps with friction force due to seals has been carried out by a time-stepping integration technique. This technique allows application of a discontinuous damping force caused by friction to the equations of motion for reciprocating components. Some calculations for a case study were performed taking into consideration the frictional dissipation in addition to the viscous dissipation due to oscillating flow of working gas. The dissipative work due to the friction force had a large influence on the amplitudes of a hot and a cold displacer piston and their phase difference, and had small influence on natural frequency. A mechanism to determine the amplitudes was explained based on the energy balance between the rod and dissipative works. It was found that a rod seal plays an important role in the determination of the dynamic behaviors especially in the phase difference, and the present prediction method was very effective for the free-piston Vuilleumier cycle heat pumps with frictional dissipation.
This paper presents a design for an active suspension for large-scale buses using the concept of fuzzy set theory. The model is described by a nonlinear system with six degrees of freedom subject to irregular excitation from the road surface. The active control of position type consists of principal and supplementary controls. In the fuzzy control rules, the vertical velocity and its time increment of vehicle body are treated as the input variables in the principal control, and the pitch-angle velocity and its time increment of vehicle body are done as the input variables in the supplementary control. The computer simulation indicates that the proposed active suspension provides more effective performance than the passive suspension.
In this paper we propose an algorithm for estimating the position and orientation of a polyhedral object grasped by a parallel-jaw gripper. In order to estimate the object's vertex positions, we propose a method that rotates the object around the object's vertex in contact with the external environment. The vertex positions are estimated by joint angle sensor information. We also propose an analytical method for deriving the position and orientation of the object with respect to the hand coordinate system from the vertex positions. In our formulation, the estimation problem becomes linear equations subject to the constraint that a matrix is orthogonal. A case where the data are contaminated with noise is also treated, and the optimal solution is explicitly given.
It is important to. analyze the human task in sports such as tennis games. In this paper, a fuzzy tool for evaluating of tasks in a tennis game has been proposed based on a mathematical model and questionnaires issued to players themselves. The present method is capable of calculating human performance by summing up the fuzzy-measured PSF (performance shaping factor). This elicits the two dominant PSFs with a modified fuzzy measure learning identification algorithm (FLIA) to describe the ill-defined process of human activity in tennis games. FLIA reduces a set of PSFs until human tasks are represented clearly, and groupings of tasks are illustrated on a two-dimensional map of the dominant PSF. Characteristics of groups among players of different levels are then studied via the cluster analysis.
This paper presents a system concept of a hydro-statically driven hydraulic excavator. In this system, pumps and actuators are connected each other. Then, the speed of actuators is controlled by operation of pump delivering flow rate. Herein, a hydraulic excavator has 7 actuators and 4 pumps, and the connection/disconnection of each pump and actuator is controlled by 3×4 directional control valves. Microcomputers execute the following controls : maximum pressure limiting, pump absorption power control for prevention of engine stall, transient vibration damping, maximum acceleration limiting and resolved motion rate control of the excavator's arm. Furthermore, this paper shows method for improvement of damping characteristics of the hydrostatically driven hydraulic excavator. This method does not necessarily create additional energy loss because it is controlled by operation of the pump delivering the flow rate.
In order to realize the higher throughput of semiconductor equipment, e.g. the reduction stepper, a higher-velocity X-Y stage must be developed. As for the realization of the high-speed X-Y stage, the selection of not only the driving method but also the guide mechanism for this stage are significant issues. As is well known, there are mechanical and noncontact guide systems. The former system cannot be precisely controlled due to the nonlinear friction, while the disturbance can be suppressed with the aid of the friction. On the other hand, in the case of the latter system, high-speed positioning can be expected due to the frictionless nature. Contrary to our expectation, this stage actually requires long settling time due to the lack of friction. Hence, in order to improve the positioning time, base-plate acceleration feedback was proposed as described in the literature, and the effect of disturbance rejection was experimentally demonstrated. However, an explanation for the theoretical background of its feedback was insufficient. This paper firstly shows the mathematical model of the X-Y stage including the base-plate dynamics and its validity as the control model is confirmed by comparing with the measured frequency responses. Next, based to the theoretical background using the model, the features of the positioning system with acceleration feedback, which play an important role in the suppression of disturbance, is clarified.
The driving force of an automobile depends ultimately upon the relationship between the tire and road surface. Therefore, traction control, which prevents tire slip, is becoming an important issue from the point of view of driving performance and stability of automobiles. Fuzzy traction control, developed by one of the authors and a co-worker, has excellent performance that can be adapted to any road conditions. It became clear, however, that fuzzy traction control is still poor under abnormal conditions of light vehicle load or of low tire pressure. Therefore, another algorithm for traction control carried out through the detection of the gradient between driving force and tire slip, was proposed in this paper. Relatively good results were obtained.
Piezoelectric ceramics are ferroelectric, and are fundamentally nonlinear in their response to the applied voltage signal, showing a significant hysteretic loop. This paper deals with the linear drive of nonlinear piezoelectric ceramic actuators. It is shown that the expansion of a ceramic actuator can be approximated by a third-order polynomial in the applied voltage. A linear drive method is proposed for the ceramic actuators that compensates for the hysteretic loop, and then a simple nonlinear preamplifier is developed based on the drive method proposed. An experiment is conducted to verify the effectiveness of the amplifier. It is shown that the hysteretic loop disappears when the nonlinear preamplifier is installed between the d. c. amplifier and the input voltage generator.
This paper presents a study of the characteristics of a soft sensor that has the sense of human skin. The sensor is composed of two rectangular rubber sheets and a strain gauge inserted between the interface of the two sheets. The sensor is an application of Poisson's effect, which is a peculiar characteristic of the elastic medium. The normal force applied to the surface of the sensor contracts the rubber sheets in the normal direction. At the same time, the force expands the medium in the horizontal direction, which results in a horizontal strain proportional to the normal force applied. Thus, the magnitude of the applied force can be determined by measuring the output of the strain gauge that is placed horizontally between the rubber sheets. Characteristics of the sensor are measured for various combination of the two rubber sheets with different hardness and thickness. It is shown that the soft sensor proposed is effective for measurement of both concentrated and distributed applied loads. Further more, it is found that the hysteretic loop of the stress-strain curve is reduced and the linearity of the sensor is improved by placing copper foil between the two rubber sheets.
In this paper, the relationship between sound pressure and distance is described. We carried out an experiment, as a fundamental study to furnish a machine with hearing characteristics of humans, on how accurately the intensity of a sound that is audible to humans and the distance from the sound source there of can be presumed. The method employed was AHP analysis. As a result of the experiment, the relationship between the intensity of the sound which a subject heard and the distance from the sound source was found to be consistent. The sound intensity had a value similar to the theoretical value in a range where the distance from the sound source was up to 1 m. The characteristics according to the frequency were clarified by the study of six kinds of selected frequencies of the sound source. The basic data of the intensity of the human sound and the correspondence of both near and far distances were obtained.
In this paper, a piezoelectric tactile sensor designed to detect the contact point is proposed for a probe in coordinate measuring machines. The proposed sensor, which is composed of piezoelectric polymer film, resistance layer, and electrodes, is able to detect the contact point from an electric charge at electrodes, which is generated at the contact point. The sensor is sufficiently thin (100-150μm) and soft that it can be applied to a curved surface. A column-shaped probe utilizing the sensor for the detection of the θ-coordinate of the contact point is developed. A neural network is proposed as a method for the detection of the θ-coordinate from electric charge ratios at electrodes. Results of θ-coordinate detection obtained by experiment are not yet accurate enough to contribute to the improvement of measuring accuracy, however, they can be improved by uing electric signal with better S/N ratio.
Recently, the demand for moving robots working at construction sites is increasing, and research activities are in progress. Unlike industrial robots working in factories, construction robots must meet more functional requirements because they must handle a variety of complicated jobs at construction sites. The robots must also be able to locate themselves. This requires a technique that enables the robot to measure coordinates indicating its position. This paper describes a new method to enable robots working at large building sites to precisely locate themselves and describes the principle of this system and experimental results.
This paper deals with a criterion to reduce excessive communication in the Cellular Robotic System (CEBOT). While communication plays a significant role in acquiring necessary information for the decision making, we should consider its cost especially in the case when a large number of agents is involved. Therefore, we have been trying to achieve the "intelligent communication" that is defined as accumulation of knowledge enables higher performance and a lower frequency of robot communication. Acquiring information through communication, a probability model is constructed. The decision is based on the model but the risk for that is evaluated with respect to whether communication is negligible. Considering both communication cost and risk for decision making that is derived from the game theory approach, we will set a criterion for communication necessity and show that there exists a correlation between accuracy of the estimate model and communication frequency and estimated risk through the simulation results.
This paper discusses an optimization method of multi-agent system. A method for optimization called "evolutional programming" based on genetic algorithms is proposed and addressed. Evolutional programming can be applied to optimization of ill-structured systems such as multi-agent systems. As an example of multi-agent systems, the intelligence system of cellular robotic systems called CEBOT which has been previously studied by us is discussed. The intelligence system of CEBOT consists of many kinds of knowledge sources, which have simple levels of data and intelligence, together with some blackboards, which dynamically organize a hierarchical structure in order to optimize its own performance index. To realize optimal self-organization and self-evolution, evolutional programming is applied. The efficiency of the algorithm is shown by some simulations of self-organization and self-evolution of the intelligence system.
It is difficult to control large complex systems by centralized control. Therefore, autonomous decentralized systems which have variety, flexibility and fault tolerability, have been studied recently. In this paper, we propose an autonomous decentralized system comprised of classifier systems. Classifier systems are parallel, message-passing, rule-based systems that learn through credit assignment and rule discovery (the genetic algorithm). In our method, each subsystem is controlled by an individual classifier system, and it generates production rules autonomously by exchanging information with adjacent subsystems. We test the system on a 6-legged robot, in computer simulations, which learns how to coordinate its legs so as to walk forward, as a practical example.
A legged robot should be able to walk through an unknown environment and avoid unpredictable breakage. To realize this capability, the robot should learn to control its legs without being precisely informed of its internal and external environments. Since the worst condition is the situation where no environmental model is given and where only sensory input that informs the success or failure of walking is available, it is necessary to establish a learning mechanism to developing rules for walking under this situation. This paper proposes a reinforcement-learning-based method to realize this adaptive gait acquisition with minimal information. It was shown by computer simulations that the 6-and the 8-legged wall-climbing robots could successfully establish their gaits without any initial knowledge. It was also demonstrated that the simulated 8-legged robot could establish a new gait after one of its legs was broken.
This paper proposes a new regularization procedure for inverse analyses using hierarchical neural networks and computational mechanics. The present regularization method, named here as the generalized-space-lattice (GSL) transformation, transforms localized learning data points onto lattice points in a generalized multi dimensional lattice space. This procedure improves the geometrical structure of the learning data sets. The method of inverse analysis using the hierarchical neural networks with the GSL transformation consists of the following three phases : (1) preparation of learning data, which are produced through many finite element computations and then converted by the GSL transformation, (2) training of neural network, and (3) utilization of the trained neural network. Fundamental performances of the GSL transformation are clearly demonstrated through its application to the structural identification of a vibrating non-uniform beam in Young's modulus.
In this paper, the solution of the two-point boundary value variational problem is improved to solve problems with some constraints. The objective function consists of two parts, the original one and the other, named a potential function, connected by a weighting coefficient. The potential function is described as a quadratic function corresponding to constraints. The optimum solution of the variational problem is obtained as a set of control points of a uniform B-spline by parallel and iterative computation. The algorithm is very simple and easily applied to various engineering problems. As an application, trajectory planning of a manipulator with redundant degrees of freedom is considered under the conditions that the end effector path and the constraints of the control or the state variables are specified. The validity of the algorithm is confirmed by numerical examples.
Planar cams are typically machined by NC machine tools using linear and circular interpolation functions. This causes polygon-shaped cams. The misshaping of a cam causes poor dynamic characteristics at higher speed operation. Recently, industries have demanded higher-quality cams to achieve higher speed and higher accuracy. To meet those requirements, it is necessary to obtain a very smooth contour of the cam over the entire cam surface. One of the ways to obtain such a smooth contour is to use a circular arc for the segment between two control points which has a common normal vector with adjacent segments at the end points of the segment. In this study, the basic concept of a contour constituted by circular arc segments is introduced. Then, the calculating procedure to obtain the intermediate point which is the contact point of two circular arcs is shown. With this method, a smooth contour of the cam without edge can be obtained.
Even in a macroscopically 2-dimensional contact situation, existence of surface roughness causes a 3-dimensional stress field in the vicinities of asperity contacts. Although several methods for stress analysis in the contact of rough surfaces have been established so far, the possibility of analysis was limited to the cases of 2-dimensional asperity contact or macroscopically 3-dimensional contact in which contact area is comparatively small. In order to elucidate the mechanism of pitting or rolling fatigue, it is necessary to develop a method of calculation of the 3-dimensional stress field near the asperity contact, which would occur in contact of cylindrical bodies having surface roughness. In this study, one method of such analysis is shown. This method can be applied to calculate the stress intensity factor of a crack in rolling contact of rough surfaces. which will be presented in another paper.
In this paper, the dynamic behavior of a perfectly rigid rotating shaft supported by hydrodynamic journal bearings is examined theoretically by considering the combined effects of turbulence and fluid shear stress acting on the journal surface. In the theoretical analysis, the fluid film reaction forces in the normal and tangential directions, which include the effect of fluid shear stress on the journal surface, are derived based on the turbulent lubrication theory under the assumption of a short bearing. Applying the Routh-Hurwitz stability criterion [Hashimoto, et al., Trans. ASME, J, Trib., 109 (1987), 307] to the equations of motion for the rotor-bearing systems, the whirl onset velocities are obtained. Moreover, the journal center trajectories are calculated by the Runge-Kutta method. From the numerical results, the effects of fluid shear stress on the stability of turbulent journal bearings are clarified.
The frequency responses and traction forces between the driver roller and the follower flat plate in the traction drive of reciprocating motions are studied experimentally. The traction oil Daphne 7074 and paraffinic mineral oil VG 32 are used. There is a marked discrepancy in the shape of the traction curves which are obtained from the increase and decrease of the relative velocity of the roller and the plate. The critical frequency, below which stable transmission could be performed, is presented theoretically. Maximum traction coefficients are obtained at the critical frequency and are influenced by the limiting shear stress of the lubricants and the surface roughness of the specimens.
To solve the tribological problems such as wear and loosening in existing knee prostheses composed of ultrahigh molecular weight polyethylene (UHMWPE) and metal or ceramics, a new design was attempted to realize adaptive multimode lubrication in the artificial joint. For this purpose, artificial articular cartilage is required, which has a similar structure and function to natural articular cartilage. In this study, PVA (polyvinylalcohol) hydrogel was used as artificial cartilage in the total knee prostheses. A PVA hydrogel layer was placed on an articulating surface of the tibial component, and their lubrication property during walking was evaluated by the knee joint simulator test. Silicone rubber (another compliant material) and UHMWPE were also tested and their frictional behaviors were compared with that of PVA hydrogel. As a result, PVA hydrogel showed suitable frictional behavior as artificial cartilage.
Experiments on the transmission error caused by service time of polyurethane synchronous belts were carried out under initial tension when the center distance of the experimental apparatus was fixed. The experimental results were compared with the computed results on the fracture of the belt. It was confirmed that uneven wear of the belt flanks and root lines for one revolution of the belt due to running fatigue tests was caused by production errors in the belt as a single pitch error, a change in cross-sectional area of the tension members and a change in modulus of elasticity. As the experimental results agreed quite well with the computed ones, the transmission error due to belt running was increased by the uneven wear in the belt flanks and it was hardly affected by uneven wear in the root lines. In addition, it was found that the change in the transmission error due to the service time can be reduced when production errors of the belt are lessened.
In order to study the effect of lubricating oil temperature on tooth surface strength, the temperature of three kinds of oils which have very different viscosities at room temperature was changed between 60°C and 105°C under the condition that the viscosity is kept constant. It was shown that the tooth surface strength of case hardened gears is not affected much by the temperature change, but in the case of tempered gears, the tooth surface strength decreased remarkably with increasing oil temperature. Further, so as to study the effect of hardness on tooth surface strength, the effect of the hardness of tempered gears (HV≒285∼550) and the effective case depth of case hardened gears (heff≒0.2∼1.1mm) on the tooth surface strength were examined and discussed.
Presently, we often hear the phrase "plastics friendly to the global environment", and that a biodegradable plastic is being developed. However, no case has been reported up to now of mechanical parts being made of such plastics. Therefore, focusing the characteristics of this plastic, we have carried out a study to utilize this plastic for gears. In the study, first, biodegradable plastic gears were formed by injection molding similarly to commercial plastic gears, and their operation tests were carried out to investigate operating life, wear of teeth, tooth profile change, and tooth surface roughness. The results were compared with those of commonly used polyacetal gears, and the practicability of biodegradable plastic gears was examined.
Determining the load distribution on a contact line of a bevel gear and root stress distribution is very important on strength design. However, it is not easy to request them, because the mesh is three-dimensional and tooth thickness and height of tooth become large from the toe through the heel unlike a cylindrical gear. Therefore, before load distribution and root stress distribution are requested, approximate equations of deflection-in-fluenced functions and the bending moment-influenced functions of a tooth of a bevel gear were determined by using the three-dimensional finite-element method in a previous report. In this report, integral equations including the approximate equation of the deflection-influenced functions are solved, and the load distribution on the contact line of a tooth of a bevel gear is calculated. Furthermore, tension-side root stress is calculated by using these load distribution and approximate equations of the bending moment-influenced functions. These calculated values were compared with measured values, and validity of this calculation method was examined.
A global local finite element method (GLFEM) is a numerical technique for three dimensional elastic analysis in which a conventional finite element solution and an analytical one are combined on the basis of the energy principle. In this method, an analytical domain is divided into two parts ; in one domain, the analytical and the finite element solutions are superposed, and in the other one, only the finite element solution is used. Hence, a constraint must be introduced to ensure a continuity of displacement on their boundary. In the present paper, Lagrange multipliers and penalty functions are applied for the constraint. As a result, it is revealed that the constraint of displacement creates another problem, which is how the analytical domain should be divided. Hence, the analytical solution should be superposed on the finite element one over the whole analytical domain. This method brings another merit such as flexibility in change in loading point.
Dynamic motion of the work by vibration cutting, whose process is suitable for precision machining, is theoretically analyzed on a linear tool-work forced vibration system. The purpose of this study is to analyze the nonlinear vibration phenomena on vibration cutting. Previously nonlinear vibration phenomena during 2-dimensional vibration cutting at 20-500 mm/min low cutting speed are shown on a Poincare map. It is found that the profile of a machined surface can be analyzed by using the Poincae map. In this report, the experiments are carried out using 3-dimensional vibration cutting at 25-50 m/min practical cutting speed. It is confirmed that the nonlinear phenomena due to vibration cutting are remarkably influenced by changing the tool amplitude and the natural frequency of a work vibration system, and that in such a case, randomlike oscillations excited by vibration cutting force exhibit chaos.
Three-point bending creep tests were conducted on a resinoid cutting grinding wheel from room temperature to 180°C. The Young's modulus of the wheel, which was determined from the instantaneous displacement, was about 2.0 GPa at room temperature which decreased with increasing temperature. The creep displacement of the wheel was increased with the increase in stress and temperature. The displacement vs time relationships can be approximated by logarithmic curves except for the high-stress regime at 180°C. This behavior can be ascribed to the creep of resin in the bonded region of the wheel.
The micro-route grinding system was developed for efficient micro-cutoff and micro-slotting of fine ceramics. However, because of the use of a very thin electroplated diamond quill, it has several problems in the machining performance : elastic deflection and fracture of the quill, and chipping and large cutoff-surface roughness. To solve these problems, ultrasonic vibration was applied to the workpiece perpendicularly to the machining direction. The obtained results from some cutoff experiments of Sr-Ferrite ceramics are summarized as follows. (1) By means of ultrasonic vibration, the grinding force is decreased by about 30% at the maximum, and the number of large-size chippings on the upper edge of the cutoff workpiece surface is decreased. Furthermore, the ten-point average roughness Rz of the cutoff workpiece surface measured in the quill axis direction is decreased by about 30%. (2) In the case that a quill cuts off a workpiece while rotating in a clockwise direction, the quill deflects backward to the left of the cutting direction. Here, the deflection size is decreased by ultrasonic vibration, and the cutoff accuracy is enhanced. (3) In the case of the use of an eccentric quill, the width of the obtained cut-out groove is increased by ultrasonic vibration.