This study is aimed at clarifying the mechanism of wear process for Ag plating. The samples of different hardness Ag plating on copper alloys were prepared as coupon and embossment specimens, which simulated terminal contacts. During the sliding test, the contact resistance and the friction coefficient versus sliding distance are measured. The surface observation and surface roughness of the Ag films after wear tests were investigated. As results, the hard Ag plating film (120 Hv) exhibited higher contact resistance comparing to the soft Ag plating film (80 Hv). The soft Ag film delivered wider wear trace on coupon specimens compared to the hard one. Moreover, the observation of tribofilms formed on the Ag films after wear tests suggested that a mixed-type of adhesive and abrasive wears occurred for both of soft and hard Ag films. Furthermore, the fretting corrosion resistance of Ag plating samples with different hardness was also investigated. As results, the wear resistance of hard Ag film was stronger than that of soft Ag film.

Authors previously studied the degradation of electrical contacts under the condition of various external micro-oscillations. They also developed a micro-sliding mechanism (MSM2), which causes micro-sliding and is driven by a piezoelectric actuator and elastic hinges. Using the mechanism, experimental results were obtained on the minimal sliding amplitude (MSA) required to make the electrical resistance fluctuate under various conditions. In this paper, to develop a more realistic model of input waveform than the previous one, Ts/2 is set as the rising or falling time, Tc as the flat time, and τ/2 as the duration in a sliding period T (0.25 s) of the input waveform. Using the Duhamel's integral method and an optimization method, the physical parameters of natural angular frequency ω0 (12000 s-1), damping ratio ζ (0.05), and rising and falling time Ts (1.3 or 1.2 ms) are obtained. Using the parameters and the MSA, the total acceleration of the input TA (=f(t)) and the displacement of the output x(t) are also obtained using the Fourier series expansion method. The waveforms x(t) and the experimental results are similar to each other. If the effective mass m, which is defined as that of the movable parts in the MSM2, is 0.1 kg, each total force TF (=2mTA) is estimated from TA and m. By the TF, the cases for 0.3 N/pin as frictional force or in impulsive as input waveform are more serious than the others. It is essential for the safety and the confidence of electrical contacts to evaluate the input waveform and the frictional force. The ringing waveforms of the output displacements x(t) are calculated at smaller values of Ts (1.0, 0.5, and 0.0 ms) than the above values (1.3 or 1.2 ms). When Ts is slightly changed from 1.3 or 1.2 ms to 1.0 ms, the ringing amplitude is doubled. For the degradation of electrical contacts, it is essential that Ts is reduced in a rectangular and impulsive input. Finally, a very simple wear model comprising three stages (I, II, and III) is introduced in this paper. Because Ts is much shorter in a rectangular or impulsive input than in a sinusoidal input, it is considered that the former more easily causes wear than the latter owing to a larger frictional force. Taking the adhesive wear in Stages I and III into consideration, the wear is expected to be more severe in the case of small damped oscillations owing to the ringing phenomenon.

Authors have studied degradation phenomenon on electrical contacts under the influences of an external micro-oscillation. A new micro-sliding mechanism 2 (MSM2) has developed, which provides micro-sliding driven by a piezo-electric actuator and elastic hinges. The experimental results are obtained on “minimal sliding amplitudes” to make resistances fluctuate on electrical contacts under some conditions which are three types of inputwaveform (sinusoidal, rectangular, and impulsive) and three levels of frictional force (1.6, 1.0, and 0.3 N/pin) by using the MSM2. The dynamical characteristics are discussed under the conditions. The simple theoretical model on the input signal and the output of the mechanism is built and the theoretical expressions from the model are obtained. A natural angular frequency (ω0=12600[s-1]) and a damping ratio (ζ=0.03[-]) are evaluated using experimental dynamical responses. The waveforms of inputs and outputs are obtained and the characteristics between inputs and outputs are also obtained on the theoretical model using the above. The maximal gain between the input and the output in rectangular or impulsive (24.4) is much larger than that (0.0) in sinusoidal. The difference on the output-accelerations between in sinusoidal and in rectangular (impulsive) is discussed. It is shown that it is possible to cause the degradation phenomenon in sinusoidal only when the output displacement are enlarged. It is also shown that it is possible to cause the phenomenon in rectangular or in impulsive, in addition to the above, when the external force has sharper rising and falling waveforms even if the displacement and the frequency of the force is small. The difference on the output-amplitudes between in rectangular and in impulsive is discussed. It is not clear that there is the difference between the effect in rectangular and that in impulsive. It is indicated that it is necessary to discuss the other causes, for instance, another dynamical, thermal, and chemical process.

In order to improve the motion control performance, a new friction determination method, using the LuGre model, is proposed. The model parameters are determined by performing two-step closed-loop experiments using a proportional-integral observer (PIO). The PIO is also used to develop a robust motion controller to deal with additional uncertainties including the effect of the inaccurate estimation of the friction. The experimental results reveal improved performance compared to that of a single-PIO-based controller.

We deposited thin films of thiophene/phenylene co-oligomers (TPCOs) onto poly(tetrafluoroethylene) (PTFE) layers that were friction-transferred on substrates. These films were composed of aligned molecules in such a way that their polarizations of emissions and absorbances were larger along the drawing direction than those perpendicular to that direction. Organic field-effect transistors (OFETs) fabricated with these films indicated large mobilities, when the drawing direction of PTFE was parallel to the channel length direction. The friction-transfer technique forms the TPCO films that indicate the anisotropic optical and electronic properties.

Using frictional force microscopy (FFM), the friction surface characteristics were compared between twisted nematic (TN) mode and vertical alignment (VA) mode alignment films (AFs). The friction asymmetry was detected depending on temperature conditions on TN mode AF, but not on VA mode AF. The difference between two modes was explained by leaning intermolecular repulsion caused by the pre-tilt angle uniformity and the density of side chain. No level difference according to temperature conditions appeared when the pre-tilt angle were measured after liquid crystal (LC) injection.

The possibility of using three kinds of new type composite materials as material for high speed sliding contacts was investigated. The results of this investigation were compared with the results of the low speed tests that were reported earlier. As a result of the above, it was discovered that for high speed rotation in the range from 0.014 m/s to 2 m/s, the order of merit did not significantly change. Based on this, it was concluded that if solid lubricant is effectively supplied to the sliding surface, the influence by frictional heat generated by high speed is slight. Of the three kinds of composite material, it was clarified that composite material (CMML-1) had the lowest contact resistance and Composite Material (CMML-3) had the lowest maximum frictional coefficient of friction. 'CM' and 'ML' are initialisms for 'Composite Material' and 'Material of Lubrication' respectively. The number that is attached to the material name is a numeric value that was set by this laboratory.

The main factor determining for both friction and contact resistance is the true contact area in the contact interface. Contact resistance depends on the size of the true contact area and contaminant films interposed between the contact areas of the interface. Moreover, friction force also depends on the true contact area. In particular, the formation of metallic junctions in the true contact area strongly effects the friction force. Therefore, since both electrical contact and friction force are related to the size of the true contact area, the contact resistance and friction force are considered to be interrelated through true contact areas. For electromechanical devices with sliding contacts such as connector and sliding switches, the contact resistance and friction are important characteristics. In order to obtain low contact resistance, contact load should be higher, but the friction force increases. These are opposite-side problems. In this study, as the contact resistance and friction occur in the same true contact area, the relationship between the contact resistance and friction was expressed in an equation. Moreover, this relationship was examined experimentally on a variety of contact surfaces under different surface conditions.

The author prepared new composition of Cu-Sn based composite materials containing lamellar solid lubricants, and measured their performance with focus on contact resistance and the coefficient of friction using a low-speed tribo-meter. Among three kinds of composite materials, the composite material containing 26wt.% of total solid lubricants was lower in both of contact resistance and the coefficient of friction and showed stable characteristics compared with those containing 25wt.% and 35wt.% respectively. The author analyzed the characteristics of these materials using several techniques including BSE image, element analysis through EPMA, and mapping analysis, and examined why the composite material containing 26wt.% of total solid lubricants showed higher performance.

In recent years, sliding electric contacts came to be often used under very severe conditions such as high temperature, extremely low temperature, high vacuum, etc. Conventionally, solid lubricants having excellent properties in lubricating performance are generally used compositely with a metal of high electric conductivity, because of their high electrical resistivity. In the present study, we proved that more excellent sliding electrical contacts can be produced with a design made by controlling the distribution on contact surface of a solid lubricant having excellent lubricating performance and of a metal with high electric conductivity through expansion of Greenwood's theory.

The conventional describing function of Coulo-mb friction is based on the assumption that the reference input is constant. The author proposes the describing function of Coulomb friction for the ramp reference input. The experimental results for the DC servo motor control system with ramp tracking controller are shown.

A method of evaluating the gas viscous friction force acting on head/disk interface has been developed. In the past, the effect of the gas viscous friction force has been almost negligible, due to its small value compared with the contact friction force. Recently the gas viscous friction force has tended to increase with the decrease in spacing and the increase in relative speed between the slider and the disk, therefore it is becoming necessary to consider its effect on motor load or slider posture. Few experimental studies of the gas viscous friction force, however, have been performed. In this study, the measurement of the gas viscous friction force has been realized by developing a sensitive friction force sensor. Furthermore a method of evaluating the gas viscous and contact friction forces separately has been also established.

In this paper, the stress wave propagation in a coupled pendulum system with friction force is discussed experimentally and numerically. The coupled system is analogous to the one dimensional fault dynamics model in seismicity. However, we will not intend to discuss about the geophysical feature of the system. The system has rich characteristics of the spatio-temporal stress wave propagation effected by nonlinear friction force. The relation between the wave propagation and the vibration of the pendulum is mainly discussed on the standpoint of nonlinear coupled system.

Connector contact resistance may become unstable if fretting occurs. Such motions result in the formation of insulating oxides on the surface of base metal contacts or organic polymers on contacts made of platinum group metals. These degradations are termed fretting corrosion and frictional polymerization, respectively. Motion may be caused by external vibration or fluctuating temperature. The lower the frequency of movement, the fewer the number of cycles to contact failure. Increasing the contact normal load or reducing the amplitude of movement may stabilize the connection. Tin and palladium and many of their alloys are especially prone to fretting failure. Tin mated to gold is worse than all-tin contacts. Gold and high gold-silver alloys that are softer when mated to palladium stabilize contact resistance since these metals transfer to the palladium during fretting; but flash gold coatings on palladium and palladium nickel offer marginal improvement for the gold often quickly wears out. Dissimilar metal contact pairs show behaviors like that of the metal which predominates on the surface by transfer. Contact lubricants can often prevent fretting failures and may even restore unlubricated failed contacts to satisfactory service.

The applicability of composite materials containing laminar solid lubricants to sliding contacts was studied. Performances of several composite materials prepared by incorporating solid lubricants with the basic alloys of the Cu-Nb system and Cu-Sn system were investigated to test the suitability of the composite materials as sliding contacts. As a result, it was clarified that the composite materials based on Cu-Sn alloy were superior to those based on Cu-Nb alloy and those containing only WS2 and not MoS2 were more effective in reducing both the contact resistance and the coefficient of friction. Based on the relationship between the contact resistance and the coefficient of friction obtained in this experimental study, the author proposed a new model for electric contact of composite materials.

Coulombs law of friction, in which the coefficient of friction is constant independently of apparent area of contact and applied load, is deduced from the modern adhesion theory. That is, the friction resistance is caused by shearing of solid/solid junctions which are formed through plastic deformation of surface asperities of mating solids. In so-called point contact, on the other hand, different experimental results from Coulombs law have been sometimes reported. In these cases, coefficient of friction is not constant, but reduces with increasing normal load. A weighty interpretation for these facts developed formerly is that Hertzian contact area acts as an effective zone to generate the friction resistance. This interpretation has, however, an important doubt, as the Hertzian contact area is not formed through plastic but through elastic deformation of solids. If the friction resistance is generated in an elastic contact area, the adhesion theory of friction would be shaken at its standing basis. To give an explanation of this inconsistency between the experimental facts reported previously and the adhesion theory of friction, the authors propose a new idea in this paper. The plastic deformation occurs at surface asperities even in Hertzian contact. If the rubbing condition is kept dry, the friction resistance would be generated only at those plastically deformed zone dotted in the elastic contact area, so that Coulombs law is realized. If the rubbing condition is kept wet, the clearance between mating surfaces in the elastic contact zone is filled with any lubricant or contaminant molecules, the friction resistance would be generated through shearing of them within the Hertzian area. In this case, the coefficient of friction would be proportional to(load)-1/3, which is close to observational facts reported previously. An experimental verification made in this study can describe the authors proposal.

Bifurcation Phenomena observed in a circuit containing two Josephson junctions coupled by a resistor are investigated. This circuit model has a mechanical analogue: Two damped pendula linked by a clutch exchanging kinetic energy of each pendulum. In this paper, firstly we study equilibria of the system. Bifurcations and topological properties of the equilibria are clarified. Secondly we analyze periodic solutions in the system by using suitable Poincare mapping and obtain a bifurcation diagram. There are two types of limit cycles distinguished by whether the motion is in S1R3 or T2R2, since at most two cyclic coordinates are included in the state space. There ia a typical structure of tangent bifurcation for 2-periodic solutions with a cusp point. We found chaotic orbits via the period-doubling cascade, and a long-period stepwise orbit.

The superconducting magnet on a maglev vehicle vibrate and heats up inside under the influence of various disturbances in running. We have investigated the characteristics of heating in the superconducting magnet vibrating under the electro-magnetic disturbance from the ground coils. This magnetic disturbance has a frequency component ranging widely from 0 Hz to several hundred Hz which is proportional to the speed of the maglev vehicle. It was revealed that an extreme increase of heat load on the inner vessel of the energized magnet occurred at a particular frequency and it surpassed the capacity of the refrigerator installed in the tank of the superconducting magnet. As a result of the investigation, we could identify broadly three factors of heating, and now we have good prospects of largely suppressing the heating by reducing the disturbance through the folded arrangement of the ground coils and a structural improvement of the magnet.

A new electrostatic wobble motor design and fabrication method were proposed, and micromotors were successfully fabricated and operated. The advantages are (1) thicker structural size, resulting in larger torque, (2) simple and safe fabrication process and (3) needle-shaped bearing to support the rotor. Needle-shaped bearing used here is expected to have lower friction comparing with the existing motor, since the load is smaller for this kind of bearing structure. Two major sources of the load, electrostatic force and capillary force, were considered to prove this tendency. Diamond-like Carbon (DLC) film was employed as a solid lubricant for its bearing. The friction of DLC and that of ilicon-dioxide were compared by experiment.

Composite materials of solid lubricants, such as graphite, MoS2, WS2, etc., and metals are being used as the sliding electrical contacts. However, few reports have so far been presented on the detailed characteristics of such composite materials. It is shown in this report that contact resistance and coefficient of friction of the sliding contact of the composite material of Cu-Nb system against Cu were higher than those of the sliding contact of the composite material of Cu-Sn system against Cu. It was, further, found that composite materials of Cu-Sn system were superior to those of Cu-Nb system being both contact resistances and coefficients of friction lowered. At the same time, it was found that performances of composite materials of Cu-Sn alloy base containing exclusively WS2 were superior to those containing both WS2 and MoS2. It was, therefore, suggested that proper samples suitable for the service conditions should be selected from the composite materials of Cu-Sn system which contain exclusively WS2 for the practical applications.