Non-contact detection of polyester filament yarn tension in the spinning process by the laser Doppler vibrometer method

The precise detection of polyester filament yarn (PFY) tension in the spinning process is critical to ensure product quality. The laser Doppler vibrometer (LDV) method is proposed to achieve non-contact detection of PFY tension in this paper. By employing the Hamilton principle, the transverse dynamics differential equations of PFY are derived, which are discretized and solved by the Galerkin method and Runge–Kutta method, respectively. In the equations, the PFY between two adjacent rollers is simplified as an axially moving string to verify the generality of calculating natural frequencies. The calculated natural frequencies from the axially moving string model are compared with solved results from the transverse dynamics differential equations. It is shown that the approximation of natural frequencies can be obtained from the axially moving string model. This study attempts to establish an approximate generic model among the PFY tension, the spinning speed and the first natural frequency based on axially moving string model, from which the PFY tension can be calculated efficiently by employing the measured natural frequencies. The LDV method is used to measure the natural frequencies. A major advantage of the proposed method is to realize non-contact detection of PFY tension. The method is more useful under high-speed spinning conditions where contact tension detectors are not available. An experimental analysis is carried out to verify the effectiveness and accuracy of the proposed method. Therefore, it is believed that the non-contact detection of PFY tension in the spinning process by the LDV method is feasible.