Contact stiffness is an important parameter for describing the contact behavior of rough surfaces. In this study, to more accurately describe the contact stiffness between grinding surfaces of steel materials, a novel microcontact stiffness model is proposed. In this model, the novel cosine curve-shaped asperity and the conventional Gauss distribution are used to develop a simulated rough surface. Based on this simulated rough surface, the analytical expression of the microcontact stiffness model is obtained using contact mechanics theory and statistical theory. Finally, an experimental study of the contact stiffness of rough surfaces was conducted on different steel materials of various levels of roughness. The comparison results reveal that the prediction results of the present model show the same trend as that of the experimental results; the contact stiffness increases with increasing contact pressure. Under the same contact pressure, the present model is closer to the experimental results than the already existing elastic–plastic contact (CEB) and finite-element microcontact stiffness (KE) models, whose hypothesis of a single asperity is hemispherical. In addition, under the same contact pressure, the contact stiffness of the same steel material decreases with increasing roughness, whereas the contact stiffness values of different steel materials under the same roughness show only small differences. The correctness and accuracy of the present model can be demonstrated by analyzing the measured asperity geometry of steel materials and experimental results.

This paper deals with the gear matching of 3K planetary gears, especially when the number of planetary wheels is more than three. The formulas of gearing ratio, concentricity condition, installation condition and adjacent condition are worked out. The concentric condition error and the adjacent condition error are set respectively in consideration of adjusting the concentricity under the condition of changing the modulus. When the error of the concentric condition is zero, the invariant bit or the height shift is indicated. When the concentric condition error is not zero, the negative shift or the positive displacement is adopted. Adjacency conditions can be given according to the designer's experience. In addition, the maximum size limit is taken into account. By giving these constraints, a computer program can be used to rapidly solve the desired number of combinations of teeth. This paper presents a typical case of seven planets.

Combining the multi-scale analysis ability of wavelet with the multi-scale self-similar feature of fractal, multi-scale wavelet decomposition of fractal contour, based on logarithmic wavelet spectrum, and then evaluating the fractal features of contour and calculating its fractal dimension, The calculation method of fractal dimension logarithmic wavelet spectrum of machined surface contour is compared with the calculation error of power spectral density method and structure function method. Finally, it is applied to the calculation of fractal dimension of actual machined surface contour, which shows its practicability.