查看更多>>摘要：The friction stir lap welding(FSLW)of metal to polymer is a challenging work due to the unavoidable polymer overflowing.Facing this problem,a novel seal-flow multi-vortex friction stir lap welding(SM-FSLW)technology based on the subversively-designed multi-step pin was put forward.Choosing 7075 aluminum alloy and short glass fiber-reinforced polyether ether ketone(PEEK)as research subjects,the welding temperature,material flow,formation and tensile shear strength of dissimilar materials lap joint under the SM-FSLW were studied and compared with those under traditional FSLW based on the conical pin.The multi-step pin rather than the conical pin effectively hindered the polymer overflowing due to the formation of vortexes by the step,thereby attaining a joint with a smooth surface.Compared with traditional FSLW,the SM-FSLW obtained the higher welding temperature,the more violent material flow and the larger area with high flow velocity,thereby producing the macro-mechanical and micro-mechanical interlock-ings and then heightening the joint loading capacity.The tensile shear strength of lap joint under SM-FSLW was 27.8％higher than that under traditional FSLW.The SM-FSLW technology using the multi-step pin provides an effective way on obtaining a heterogeneous lap joint of metal to poly-mer with the excellent formation and high strength.
查看更多>>摘要：This article focuses on asymptotic precision motion control for electro-hydraulic axis systems under unknown time-variant parameters,mismatched and matched disturbances.Different from the traditional adaptive results that are applied to dispose of unknown constant parameters only,the unique feature is that an adaptive-gain nonlinear term is introduced into the control design to handle unknown time-variant parameters.Concurrently both mismatched and matched distur-bances existing in electro-hydraulic axis systems can also be addressed in this way.With skillful inte-gration of the backstepping technique and the adaptive control,a synthesized controller framework is successfully developed for electro-hydraulic axis systems,in which the coupled interaction between parameter estimation and disturbance estimation is avoided.Accordingly,this designed controller has the capacity of low-computation costs and simpler parameter tuning when compared to the other ones that integrate the adaptive control and observer/estimator-based technique to dividually handle parameter uncertainties and disturbances.Also,a nonlinear filter is designed to eliminate the"explosion of complexity"issue existing in the classical back-stepping technique.The stability analysis uncovers that all the closed-loop signals are bounded and the asymptotic tracking performance is also assured.Finally,contrastive experiment results validate the superiority of the developed method as well.
查看更多>>摘要：Passive binocular measurement systems are being increasingly utilized in the in-situ industries of automobiles,aviation,and aerospace,etc.due to their excellent qualities of accuracy,efficiency,and cost performance.Whereas the barrier of evaluating the accuracy of measured objects resulted from the unequal equivalent focal length and quantization of pixels,has limited their further development and application of high requirements for in-situ machining,e.g.,the mea-surement of machining reference points for the positioning of robotic drilling in aerospace manu-facturing.In this paper,an accuracy evaluation method is proposed to address the problem.Firstly,the unequal equivalent focal length is considered to improve the accuracy of 3D reconstruc-tion.Next,the credibility probability model is developed to calculate the probability of the observed error in the public view of the binocular measurement system and indicates the direction of improvement.Finally,the in-situ experiment is carried out to validate the method within the effec-tive public view range of 300 mm × 300 mm.The experiment results show that the RMSs of observed errors are superior to 0.035 mm,and the credibility probabilities are all higher than 0.91;the maximum 3D reconstruction accuracy improvement is 60.3％,with the error reduced from 0.078 mm to 0.031 mm.
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