A frame deformation estimation algorithm is investigated for the purpose of real-time control and health monitoring of flexible lightweight aerospace structures. The inverse finite element method (iFEM) for beam deformation estimation was recently proposed by Gherlone and his collaborators. The methodology uses a least squares principle involving section strains of Timoshenko theory for stretching, torsion, bending, and transverse shearing. The proposed methodology is based on staindisplacement relations only, without invoking force equilibrium. Thus, the displacement fields can be reconstructed without the knowledge of structural mode shapes, material properties, and applied loading. In this paper, the number of the locations where the section strains are evaluated in the iFEM is discussed firstly, and the algorithm is subsequently investigated through a simple supplied beam and an experimental aluminum wing-like frame model in the loading case of end-node force. The estimation results from the iFEM are compared with reference displacements from optical measurement and computational analysis, and the accuracy of the algorithm estimation is quantified by the root-mean-square error and percentage difference error.
An adaptive fuzzy network method is proposed for measuring flexible truss deformation by using situ strain in this paper. The relation matrix between strain and arbitrary deformation nodes of truss is first derived by using inverse finite element method. Based on the elements of matrix, strain measuring displacements are obtained. In addition, an adaptive fuzzy network for measuring truss deformation is developed according to the measured displacement and situ strain. Furthermore, the experiment on deformation measurement of the flexible truss modal is conducted. The experiment shows that the adaptive fuzzy network measuring method is characterized by high accuracy for measuring flexible truss deformation.
The design methodology and validation of a compliant translational joint-based force/displacement integrated sensor is presented in this article. The stiffness analysis of the large displacement high precision compliant translational joint is developed, in which the screw theory-based symbolic formulation method for structures is employed. By combining the stiffness matrix of the single compliant beams and components in this joint, the entire stiffness matrix is derived. The stiffness matrix is validated by finite element analysis (FEA) method. Finally, the compliant translational joint was fabricated with a three-dimensional printer and equipped with a linear position sensor and microcontroller. The displacement of the translational joint is measured and then the force is calculated using the stiffness matrix. A calibration is conducted so that the sub-Newton precision of the sensor is achieved.
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