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Surface description is fundamental in mechanical contact analysis. In this paper, some of the most common approaches for roughness description are first briefly described. Some models for approximating a real rough profile with parabolas that guarantee the preservation of some specific characteristics are presented. The specimens of aluminum alloy with different surface roughnesses are prepared and measured. A data analysis program is developed to identify the measured profile with quadratic functions for different approximating criteria. Based on this, the effect of the approximating criterion and the sampling interval on the surface roughness parameters and the mechanical parameters is then presented and compared. The results show that the surface roughness Ra, asperity height H, and peak radii R increase with increasing surface roughnesses for different approximating criteria. The same root mean square approximating criterion is more suitable for calculating the surface roughness Ra. The asperity height H and peak radii R increase with increasing sampling intervals for all roughnesses, while the trend is opposite for the surface roughness Ra. The sampling interval has little effect on these parameters, especially for smoother surfaces.

When spindle rotates, the stiffness and natural frequency that reflect the dynamic performances of spindle system, vary with different rotating conditions. Therefore, the measurement of stiffness and natural frequency is highly needed. However, it is difficult to apply excitation to the rotating spindle during the measurement. In this paper, a non-contact electromagnetic loading device is developed to provide desirable excitation for the measurement. Next, an experimental spindle test rig with constant pressure preload is established. With the help of the proposed loading device, stiffness and natural frequency of the experimental spindle at different rotating states are measured. Finally, the effects of rotation speed and temperature on the natural frequency and stiffness of spindle are discussed based on the measurement results. The results show that the rotation speed and temperature have the similar influence trend on the experimental spindle’s softening.

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