Landing Gear Tolerance Design Planing For The Robustness Of Mechanisms

The safety of the landing gear is strongly associated with the quality of the mechanism kinematic precision.The robustness of the kinematic deviation and the tolerance design are the key to keep the safety of the landing gear.The original jacobian model is derived from the robotics theory,and with it,three dimension tolerance models are easy to be established compared with the traditional dimension chain method.In this paper,the focus is to improve the original jacobian model,apply it in the motion deviation analysis,and introduce Taguchi theory to carry out the sensitivity analysis of tolerances,in order to get a robust tolerance design.Aiming at the complexity of the dimension chain method in three-dimensional analysis,the kinematic jacobian tolerance model is put forward and established based on the original Jacobian model and traditional dimension chain,in this way,kinematic accuracy can be analyzed through the tolerance analysis.A crank-slider is taken as an example to verify the validity and effectiveness of the kinematic Jacobian tolerance model.There are two limitations to the approach of the kinematic jacobian tolerance model,therefore,the order of screws in original Jacobian model is adjusted.Meanwhile,two coordinate frames are introduced and established in each functional elements’ pair,one is local tolerance frame,while the other is local directional frame.With the transformation matrix,the tolerance in a local tolerance frame can be transferred into the corresponding local directional frame.The local tolerance frames are used to establish the tolerance screw models,while the local directional frame is served for the establishment of Jacobian tolerance model.Based on the adjustment of the screw order in a Jacobian matrix and two local frames in each functional elements’ pair,the original Jacobian tolerance model is modified,it is named as screw Jacobian tolerance model.Two linkages are taken as examples to verify the feasibility and availability of the screw Jacobian tolerance model.For the robustness of the kinematic accuracy in a mechanism,Taguchi method is introduced into the tolerance design for mechanisms.The robustness of the kinematic accuracy is taken as the objective,tolerance ranges are control factors,experiments are carried out and based on Taguchi theory,sensitivities and contributions can be analyzed.In this way,the robustness of the precision for mechanisms is guaranteed.A linkage with three joint clearances is taken as the study case and the results show that this method improve the robustness of the kinematic accuracy distinctly.The methods introduced above are applied to carry out the tolerance design of an aircraft landing gear.Firstly,according to equal accuracy method and traditional experiences,initial tolerance design is completed.Then the screw Jacobian tolerance model is applied to analyze the initial tolerance design,and Taguchi method serves to analyze the sensitivities and contributions of tolerance ranges.Thirdly,the tolerance design is revised based on the analysis above.At last,the tolerance analysis of the revised tolerance design is implemented and the results show that the robustness of the kinematic accuracy is apparently improved.