Stiffness Analysis Of Precision Crossed Cylindrical Roller Slewing Bearing

Precision crossed cylindrical roller slewing bearing possesses some obviousadvantages, including high slewing precision, high anti-deformation capability, highcarrying capability, and more flexibility structure design. It has been extensively usedin industrial robot joint, numerical control slewing machines, precision test turntable,optical telescope, radar antennas and other precision equipments. Bearing as the corecomponent in the precision equipment has played a vital role. The main factors whichinfluence the rotary precision of the bearing are machining precision, bearing stiffnessand so on. However, the improvement of bearing rotation accuracy just depending onimproving the precision of machine tool is very limited. Therefore, it is necessary tocarry out deep theory analysis and experiment research on the influencing mechanismof bearing stiffness, reveal the inner correlative rule, propose control strategy ofbearing stiffness, whose results provide theoretical basis for the design of the slewingbearing.Firstly, a certain type of precision crossed cylindrical roller slewing bearing as theresearch object was analyzed in this paper, the relationship of bearing deformationcoordination under combined loading condition was analyzed, mathematical model ofload distribution of the bearing was established by using the classical theory of Hertzline contact. The rollers load distribution was calculated by using Newton-Raphsoniterative procedure. By using this model and method, the relation of internal bearingclearances and the rollers load distribution was analyzed, meanwhile the influence ofclearance on maximum contact force was discussed, which laid a theoreticalfoundation for unbalance loading effect and the analysis of stiffness.Secondly, for the problem of unbalance loading effect and edge loading effect ofthe contact stress distributions between the rollers and the raceway of crossedcylindrical roller slewing bearing under combined loads, the effective method forimproving of the roller and raceway contact state was proposed, based on the research of the bearing load distribution of the slewing bearing. This method was realizedthrough the profile modification design of rollers under the premise of reasonablebearing clearance. The method based on load distribution characteristics of thebearing，then, the effects of the bearing clearance on the unbalance loading of theroller was researched by using the finite length line contact theory. Finally, under thereasonable bearing clearance, the contact stress distributions between the rollers withdifferent crowning values and the raceway were researched.Thirdly, on the basis of the finite length line contact theory, elastic approachbetween bearing rings and rollers with different crowned shape, size and external loadwas calculated by using numerical test method. Single crowned roller’s load—deformation function was got by nonlinear fitting. A mathematical model on staticstiffness of bearing considering the influences of roller modification was established.By this model, the influence of clearance, external load, crowned factors on bearingstiffness properties were analyzed．Finally, the related experimental verification on slewing bearing was researched.The axial stiffness, the radial stiffness and the angular stiffness were calculated bymeasuring the relative displacements between the inner and outer framescorresponding to different external loads. And the test results with the theoreticalcalculation results were analyzed in comparison, the experimental results show that theresearch methods was reasonable. From the perspective of engineering application,precision crossed cylindrical roller slewing bearing calculation analysis software wasdeveloped in VC++, including analysis and calculation module, the calculation resultsread module and the calculation results graphics display module.