S.F. Ermakov, E.A. Khrabrov, V.V. Mulyarchik, V.E. Minin

High-accuracy and sensitivity measurements in triboengineering usually employ the methods based on oscillation processes. These oscillations are performed by a physical pendulum in which the friction joint under study is located either in the supporting point of the pendulum or outside it in the case the frictional interaction of the pendulum itself or its point with the environment is estimated. During such measurements the pendulum amplitude is recorded to obtain its kinetic dependencies that carry information on the character of frictional interaction. It has been established that variation of amplitude per period is as informative characteristic as the oscillation amplitude itself. Variations of the amplitude during a period or a cycle of oscillations of the pendulum is nothing but a measure of the friction force in the bearing unit during the same time period, while the dependence of these variations of the amplitude on the number of cycles is in its essence the dependence of the friction force value on sliding velocity in the baring joint. Since the variations in the amplitude are much less in value than the very amplitude, so its variations are by far more sensitive to the changes occurring in the bearing friction joint. Consequently, named approach may provide for the same sensitivity like in the method of the inclined-plane pendulum. Simultaneously, the present approach makes grounds for conducting precision testing of the real friction joints by the pendulum method. Nevertheless, since the amplitude variations recorded per cycle are very small, there appears a necessity of a more thorough account and estimate of disturbances and noise always present in a useful signal. In this connection, the aim of the present work was to develop such an investigation method and a measuring system thereof, which are able to ensure reliable estimation of small-scale measurements or amplitude variations of the pendulum that carry important information on frictional interactions between solid bodies. The essence of the method proposed consists in the gated integration of the input signal. This function is performed by transforming the analogue signal into the frequency of succession of pulse trains, calculation of their number per time corresponding to the length of the oscillation half-wave, and determination of the values proportional to the areas of the even or odd oscillation half-waves. Based on the results obtained, the oscillation amplitudes and their variations are determined per period as well as the friction coefficients and their time dependencies for the studied friction joints. These operations exercise digital averaging of obtained experimental data to ensure high accuracy and validity. The present work also describes a logic diagram of the pendulum measuring system that realizes above-proposed electronic cou8nting method of recording small-scale variations of oscillation amplitude, and stress diagrams in characteristic points of the diagram. The measuring system allows for an ideal gated integration of the input sinusoidal signal and determination of required values. Proceeding from above, we may conclude that the proposed electronic cou8nting method of estimating small-scale variations of oscillation amplitude and the measuring system for its realizing display high information capacity in respect to tribological characteristics, ensure high accuracy and reliability of the data obtained. In this connection, they can be recommended for application in pendulum tribometry, including evaluation of frictional behavior of different by nature and properties solids in conditions approaching the actual friction joints.