Algorithm and experiments of six-dimensional force/torque dynamic measurements based on a Stewart platform

Dynamic gravity compensation; F/T-driven alignment; Precision analysis; P&O adjusting platform; Six-dimensional F/T Abstract Stewart platform (SP) is a promising choice for large component alignment, and interactive force measurements are a novel and significant approach for high-precision assemblies. The designed position and orientation (P&O) adjusting platform, based on an SP for force/torquedriven (F/T-driven) alignment, can dynamically measure interactive forces. This paper presents an analytical algorithm of measuring six-dimensional F/T based on the screw theory for accurate determination of external forces during alignment. Dynamic gravity deviations were taken into consideration and a compensation model was developed. The P&O number was optimized as well. Given the specific appearance of repeated six-dimensional F/T measurements, an approximate cone shape was used for spatial precision analysis. The magnitudes and directions of measured F/Ts can be evaluated by a set of standards, in terms of accuracy and repeatability. Experiments were also performed using a known applied load, and the proposed analytical algorithm was able to accurately predict the F/T. A comparison between precision analysis experiments with or without assembly fixtures was performed. Experimental results show that the measurement accuracy varies under different P&O sets and higher loads lead to poorer accuracy of dynamic gravity compensation. In addition, the preferable operation range has been discussed for high-precision assemblies with smaller deviations. 2016 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).