| In order to improve the positional viability and adaptability,a certain type of vehicle-borne radar is required to complete the withdrawal operation with high accuracy and stability.The lifting device is an important component of the withdrawal system,with complex structure and high technical requirements.The error of lifting mechanism directly affects the performance of the entire radar.This paper uses the lifting mechanism of a certain type of vehicle-borne radar as the research object,its structure composition and movement characteristics are introduced,the position error of the output point of the lifting mechanism are analyzed by integrating the effect of the clearance of revolute joint and component size parameters.The main contents are as follows:(1)The structure and main actions of a certain type of vehicle-borne radar's mechanical structure are introduced,focusing on the lifting mechanism's structure and working principle.The constraint spiral theory is used to analyze the degree of freedom of the lifting mechanism and find redundant constraints out.Then a formula is proposed to calculate the degree of freedom for flat complex mechanisms,and the mobility analysis method is advanced for mechanisms with redundant constraints.(2)According to the structural characteristics of the lifting mechanism,the spatial position expression of each component is given.Based on geometric constraint relationships according to the basic parameters of each component,the equation of motion is set up with the amount of screw elongation as the independent variable,the position of the lifting mechanism's output point and the mechanism angle of each component as dependent variables.Finally,the equation is imported into MATLAB to get results.(3)The structural composition of the revolute joint is analyzed in the lifting mechanism,and the error transmission path of the clearance of revolute joint is constructed.Solving the coupling problem of the error transfer path,the direction of revolute joint clearances is analyzed by static method.The value of each component error is stimulated to calculate by using the Monte Carlo method.The ranges and distribution probability of the value of revolute joint clearance are obtained.Finally,the sensitivity and contribution of each component error of revolute joint are analyzed.(4)Combining with the clearance model of revolute joint and the dimension parameters of the components,the end position error expression of each branch in the lifting device is given.The calculation steps for the position error of lifting mechanism's output points is proposed,then it's divided into two cases according to whether consider redundant constraints or not.The position error of lifting mechanism's output points is analyzed and calculated,and their results are compared.The sensitivity and contribution of each constituent error of the lifting mechanism's position error is analyzed by considering the influence of redundant constraints.The method of freedoms calculation and mobility analysis in this paper has engineering reference and application value to analyze mechanisms which contain redundant constraints.The model of revolute joint clearance and position error model of the lifting mechanism can be used to guide the tolerance design of vehicle-borne radar,and has certain reference value for error analysis of mechanisms with redundant constraints. |
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