Sensitivity-Based External Calibration of Multiaxial Loading System

Due to the nonlinear nature of coordinate transformations, evaluation and calibration of multiaxial loading systems in global Cartesian coordinates are challenging problems. This study proposes a systematic calibration method for multiaxial loading systems in global coordinates using an external measurement system. Global coordinate measurement for a multiaxial loading system is usually obtained from a geometric transformation based on internal actuator measurements. However, any misrepresentation of initial actuator configuration (e.g., origin, pin locations, etc.) introduces errors and cross-talk in the global Cartesian coordinates. Such errors and cross-talk cannot be observed or eliminated based on internal measurements. The method proposed in this paper is based on the sensitivity of the global coordinates with respect to the initial actuator length. To validate the proposed method, calibration is performed using the state-of-the-art Load and Boundary Condition Box at University of Illinois at Urbana-Champaign as the multiaxial loading system and the Krypton Dynamic Measurement Machine as the external measurement system. Experimental results demonstrate that the proposed sensitivity-based external calibration method is effective for improving control accuracy and reducing cross-talk of multiaxial loading systems in global Cartesian coordinates.