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&...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.展开更多
Due tothe important and common problems in optimizing material processing under reduced or micro gravity, bubble dynamic behaviors under thus gravity condition attract more and more attentions.For that purpose,a pair ...Due tothe important and common problems in optimizing material processing under reduced or micro gravity, bubble dynamic behaviors under thus gravity condition attract more and more attentions.For that purpose,a pair of Maxwell-Helmholtz(M-H)coils is developed to obtain a constant magnetic force acting on ferrofluids to neutralize gravity in a certain volume,which provides a uniform gradient magnetic field as well as a magnetic fieldintensity that is big enough to reach the magnetization saturation of ferrofluids.Afterwards,a finite-element-method based numerical simulation of the M-H coils shows a 20mm×30mm zone for 90%gravity compensation exists.An initial experimentshows that gas bubble is well controlled in a closed Hele-Shaw filled with ferrofluid with the help of magnetic gravity compensation.展开更多
基金co-supported by the National Defense Basic Scientific Research (No. A2120132007)the Fund of National Engineering and Research Center for Commercial Aircraft Manufacturing (No. SAMC14-JS-15-055)
文摘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.
基金Item Sponsored by National Natural Science Foundation of China (No.59874133) Creation Foundation of Shanghai Educational Committee (No.10YZ16)
文摘Due tothe important and common problems in optimizing material processing under reduced or micro gravity, bubble dynamic behaviors under thus gravity condition attract more and more attentions.For that purpose,a pair of Maxwell-Helmholtz(M-H)coils is developed to obtain a constant magnetic force acting on ferrofluids to neutralize gravity in a certain volume,which provides a uniform gradient magnetic field as well as a magnetic fieldintensity that is big enough to reach the magnetization saturation of ferrofluids.Afterwards,a finite-element-method based numerical simulation of the M-H coils shows a 20mm×30mm zone for 90%gravity compensation exists.An initial experimentshows that gas bubble is well controlled in a closed Hele-Shaw filled with ferrofluid with the help of magnetic gravity compensation.
