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This paper presents an experimental study of the nonlinear characteristics of an axially moving string. An experimental system with a simple configuration, which is similar to a practical application, was built. Two laser sensors were used to monitor the vertical and horizontal vibrations of the moving string under different conditions. Using the Hilbert-Huang transform method, the detailed results of a typical measured data series, which include intrinsic mode decomposition, Hilbert spectrum and marginal spectrum, are introduced. For comparison, marginal spectra for almost all test cases are also given. Based on the results, several observed nonlinear phenomena, which include whirling motion, resonances, quasiperiodical and a beating motion, torus doublings and one chaotic motion, are presented. The quantitative nonlinear vibrating details and the observed rich behaviors help explain the great complexity of a single moving string.

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Based on the principle of the planetary transmission mechanism, we design a friction drive planetary roller-type precision linear actuator. Using the kinematic analysis, a displacement function of the linear actuator and a cutter path equation for thrust bush manufacturing are obtained. Deformations of the thrust bush under several load conditions are analyzed using the finite element method. Experiments aiming to verify the characteristics of the actuator are carried out, and the results show that the output force of the linear actuator is greater than 4500N, and the precision of the positioning reaches a micron level.

In some types of non-contact measuring systems, vibrating motion has negative effects on accuracy. Therefore, there is a need to analyze and monitor the motion state of a moving part using a low-cost scheme. This study focused on the vibration analysis and monitoring of a poly-crystalline silicon solar wafer carried by a pair of parallel moving strings, separated by a distance. Based on the sound data series picked up by a low-cost microphone and using a time-frequency analysis method, namely, the Hilbert-Huang transform (HHT) method, the low frequency features of the moving wafer could be determined quantitatively. The results showed that the motion of the moving wafer was sensitive to speed and string tension. By comparison, the average marginal spectrum should be treated as the basis for quantitative vibration monitoring, especially for a system with a strict requirement in terms of motion smoothness.

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