Abstract
To facilitate mechanics testing in special environment, in this paper, a non-contact tension testing device was developed based on magnetic levitation technology. To find a floator that facilitates the alignment of tension force, electromagnetic analyses were performed using J-Mag software and a ring floator was found to be self-aligning. In addition, since the levitated objects need to bear a tension force, which will cause the nonlinearity of the magnetic levitation system to emerge, to address the nonlinear issue, a nonlinear mathematical model was established, and a centralized feedback linearization control algorithm was proposed. Furthermore, a tuning method for the control algorithm was proposed to deal with the mismatches between the controller and the plant. Moreover, a model for estimating specimen elongation was developed using support vector machine (SVM), 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) 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 controller has stronger robustness to step disturbance than the traditional linear controller. The tension experiment results indicated that the whole control system copes well with an increasing tension force.
Highlights
The process of traditional material mechanics testing is to apply some load to a specimen on a testing equipment, remove the specimen from the testing equipment and observe it with imaging equipment, after the specimen is removed from the testing equipment, it is already in a different stress state to that during testing, so the observation results do not reflect the mechanics characteristics of the specimen when bearing the load [1]-[3]
To guarantee the alignment of the tension force, the magnetic characteristics of three shapes of floators were investigated via electromagnetic analysis
It was found that a ring floator combine the advantages of strong magnetic force, low mass, and easy alignment of the tension force
Summary
The process of traditional material mechanics testing is to apply some load to a specimen on a testing equipment, remove the specimen from the testing equipment and observe it with imaging equipment, after the specimen is removed from the testing equipment, it is already in a different stress state to that during testing, so the observation results do not reflect the mechanics characteristics of the specimen when bearing the load [1]-[3]. MLTTD in this paper allows both ends of the specimen to be contactless with the container It can be used in in-situ testing based on SEM and the testing in other sealed environment. Traditional linear control algorithms, such as PD, PID, linear state feedback, are based on the linearization around a fixed equilibrium point where the magnetic force exactly counteracts the gravity of the levitated object. Wai [20] designed a backstepping fuzzy-neural-network controller for a hybrid maglev transportation system, and the controller can maintain stability in the absence of detailed information of the plant These intelligent control algorithms were experimentally validated to perform well in dealing with non-linear, external disturbances and uncertainties. The feedback linearization algorithm proposed in this paper is for centralized control of the 2-DoF magnetic levitation.
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