Characteristic Of Friction Research Articles

弾性変形要素を付加したすべり送りねじによる超精密位置決め １ 摩擦特性と弾性変形機構

The sliding leadscrew is a machine element used most generally in positioning technology. However, because of excessively discontinuous characteristic of friction between a male screw and a female one, it becomes an improper element for ultra-precision positioning. This study aims at improving such negative situation by a new technique. In the technique, axial displacement caused by deformation of an elastic element attached in series to a sliding lead screw is utilized for minute positioning motion under a full-closed displacement control. The deformation generated is adjusted by friction torque within maximum static friction. As the first report, this paper deals with friction characteristic in a sliding lead screw which must be basically known for this technique, and the structure and design of the elastic element. From experiments simulated to the case, it is confirmed that usable state of static friction exists clearly in use of lubricants for positioning. Experiments about function of the elastic elements equipped in a positioning apparatus show good results nearly as expected and possibility of ultra-precision positioning at nano-meter level.

Rigid body analysis of the indeterminate grasp force in power grasps

This paper analyzes the indeterminate grasp force in power grasps with a rigid body model. A power grasp overconstrains an object with multiple contact points using the surfaces of finger links and palm. It is known that the overconstrained grasp results in the static indeterminacy of the grasp force. This paper shows that it also results in an infeasible combination of the sliding directions at the contact points. A static friction force acts only in the opposite direction of the trend of sliding. This characteristic of friction restricts the grasp force in power grasps although it is indeterminate. We first show an example to illustrate the restriction on the grasp force, and then formulate it formally. This analysis leads to a special case where the grasp force is unique.

Disturbance Observer-Based Nonlinear Friction Compensation and Application to Table Drive System

Nonlinear friction in machine elements is one of the inherent nonlinearities, which causes stick-slip motion in very low velocity control range and tracking errors in trajectory control due to the break-away friction and Stribeck effect. Since those greatly affect the control accuracy of servo drive systems, the appropriate modeling and/or compensation for friction is indispensable to achieve the higher performance motion.The authors have already proposed the compensation scheme for nonlinear friction by using a remarkable disturbance observer which is designed on the basis of Coulomb friction characteristic. In this paper, the dynamic characteristic of nonlinear friction is examined by means of a friction model with elastic bristles between sliding surfaces. The analysis reveals that the nonlinear friction behaves in Coulomb friction under the dynamic motion at velocity reversal and, as a result, it is concluded clearly that the proposed disturbance observer is quite useful to estimate the instantaneous friction. Experimental results using a table drive system show the significant performance improvement of the proposed scheme in precise trajectory control.

切りくず接触長さの拘束によるエンドミル加工のびびり振動抑制

The paper presents a new method for preventing chatter vibration in end-milling operation. Natural contact length between chip and rake face of end mill is reduced artificially by grinding. It is found experimentally that end-mill with the reduced contact length enables to prevent onset of the vibration and raises the stability threshold up to 70% in lower cutting speeds. Computer simulation of the chatter occurrence is also carried out, in which three models of dynamic cutting with variable undeformed chip thickness and energy methods for predicting the cutting force are developed and utilized. Through the simulation, it is revealed that the reduced contact length suppresses the cutting force variation when some disturbance is introduced in undeformed chip thickness, ilence it would reduce excitation of the vibration system. The suppression of the force vibration could be attributed to the stress characteristic of friction on the restricted rake face.

Effect of alloying recrystallized molybdenum with nickel on the amplitude characteristic of internal friction and on microdeformation

A study was made to determine the effect of alloying recrystallized molybdenum with nickel on the amplitude characteristic of internal friction and on microdeformation. Industrial grades MCh and MS of molybdenum were examined. Microdeformation, which is responsible for the amplitude dependence of internal friction in these grades of molybdenum within the 100–500‡K temperature range, has been found to be a thermally activated process and to be associated with the formation of double kinks. The activation energy, calculated from the temperature characteristic of the slope ∂δ/ ∂γ, is equal to (0.060±0.005) eV and does not change with alloying. It appears from the results of this study that the plasticizing action of nickel in recrystallized molybdenum is not related to the higher mobility of dislocations within the grain volume but, instead, is caused by the changing state of grain boundaries and manifests itself, only under conditions where strain is transmitted from grain to grain, in lowering the proportional limit Τ1 and extending the second stage of the microdeformation process (γpl,II).

Effect of aqueous solutions of cuprammonium complexes on the machinability of brass

Thermodynamic analysis of the conditions under which the environment has a physicochemical effect on the mechanical properties of solids (the Rebinder effect) gives grounds for the view that fracture in solids may be facilitated by irreversible chemical reactions taking place on their surfaces [1, 2] as well as by the action of related (similar in molecular nature) liquid media. This permits examination from a common viewpoint of an extensive series of processes in which the environment affects the mechanical properties of solids: from purely physical adsorption to purely chemical reaction, for example, during the stresscorrosion cracking of metals and alloys. It is an essential condition for these processes that the energy of the solid-environmen t reaction should be commensurate with the surface energy [3], similar to the situation occurring when a solid is in contact with a related environment [4]. The purpose of our work was the experimental study of the effect of a chemically active environment on the mechanical properties of a solid material under conditions as favorable as possible for fracture to be facilitated as a result of surface reactions. Forced localized fracture (scratching with a diamond point) makes it possible to compare the results obtained with the facilitation of metal machining in the presence of metallic fusions previously studied in [5], a classic example of a reduction in strength resulting from a crop in surface energy; the system studied (brass solutions of ammonia and its derivatives) provides an opportunity for comparing the facilitation of fracture discovered with the patterns of stress corrosion. The investigation was carried out with a specially designed pendulum-type scratch sclerometer. The linear dimensions of the scratch (its width for the most part) were recorded at a constant level of dissipated energy (identical initial amplitude of pendulum swing), as was the speed of pendulum oscillation damping, which is proportional to the coefficient of friction (the linear reduction in amplitude with time characteristic of dry friction was established by preliminary experiments). The relative percentage increase in scratch width was taken as the measure of the effect of the environment on strength. During the experiments, the concentration of ammonia and of bivalent copper in the solution was varied over a wide range. The test agent was prepared by mixing solutions of ammonia and of copper salt of identical percentage concentrations in specified proportions. The liquid obtained was applied by pipette to the carefully polished surface of a brass plate on which a diamond cutting tool connected to the pendulum had made a scratch in about 100 consecutive passes; the cutting tool was pressed against the plate by a constant force. The test results showed that solutions of cuprammonium complexes in specified concentrations could greatly facilitate the fracture of alpha brass (Fig. 1). In these circumstances an increase in the coefficient of friction can be detected in this concentration region. Pure ammonia does not facilitate fracture; what is more, at high ammonia concentrations there is a considerable drop in friction and a reduction in the depth of the scratch as a result of tool slippage. It was necessary to study the connection between the data obtained by us and the composition of the solutions used in the experiments, because contradictory opinions are expressed in the literature on stress corrosion of alpha brass in cupramm0nium solutions as to precisely which ammonia complex is responsible for the fracture.

Contribution of original dislocations to the amplitude characteristic of internal friction

The amplitude characteristic of internal friction is calculated here, with two kinds of internal barriers taken into account. The initial stage of this curve has a peak whose profile is determined by the density of dislocations as well as by their movement and retardation. The factors are analyzed which contribute to a transition to the second stage of the characteristic, and its trend is considered in the case when the displacement of original dislocations increases jumpwise but the number of dislocations remains the same.