Design and Analysis of a Non-Contact Tension Testing Device Based on Magnetic Levitation

Abstract

This paper proposed a non-contact tension testing device using magnetic levitation technology, where a specimen can be tested while being levitated. To guarantee the alignment of tension force, the magnetic characteristics of three shapes of floators were investigated via electromagnetic analysis, and a ring floator was selected according to the electromagnetic analysis results. Also, the number of the coil turns, and the dimensions of all the device parts were minimized while ensuring sufficient magnetic force. Furthermore, to realize the levitation of the system, which belongs to two-degree of freedom (2-DoF) magnetic levitation system, a nonlinear mathematic model was established, and a centralized feedback linearization control algorithm was proposed. A tuning method for the centralized feedback linearization control algorithm was proposed based on control simulation results. The control simulation results implied that the centralized feedback linearization control algorithm allows the device to withstand the disturbances caused by the tension force even in the case of mismatches between the controller and the plant. Moreover, a model for estimating specimen elongation was developed employing a support vector machine (SVM). Also, the estimation simulations were performed, and the estimation results demonstrated that the range of the estimation error was between -0.1988mm and 0.2269mm, the root mean square error (RMSE) and coefficient of determination (R 2 ) were 0.0843mm and 98.76% respectively. Ultimately, a levitation experiment and a tension experiment were successfully performed, the levitation experiment results demonstrated that the proposed tuning method is effective and the centralized feedback linearization control algorithm has stronger robustness to step disturbance than the traditional linear control algorithm. The tension experiment results indicated that the whole control system cope well with an increasing tension force.