Effects Of Multiple Joint Clearances On Dynamic Characteristics Of Mechanisms

With the development of the high-precision technology,which including medical devices,aerospace technology,robot engineering,precision mechanism,and so on,engineering practical application requires the mechanical system to have more and more high accuracy,so that it is necessary for the dynamics of mechanical system to consider more and more factors,and the joint clearance is one of them.The existence of the joint clearance makes the mechanism occur vibration and shock,which increases the moving errors of the mechanism and destroys the stability of the mechanism.Therefore,it is very meaningful to study the effect of the joint clearance on dynamic characteristics of mechanisms.In this paper,a guide-bar-slider mechanism with multiple joint clearances is studied to analyze the effect of multiple joint clearances on dynamic characteristics of mechanisms comprehensively.The researches of this paper are as follows.First,the contact-impact force models based on Hertz contact theory which have been proposed over the last decades are analyzed,which summarizes the advantages and disadvantages of the force models,makes their range of application clear and provides the theory evidence to the selection of the contact-impact force models.Then,a slider-crank mechanism with all clearance joints is investigated.The ADAMS software is used to calculate the dynamic characteristic of the mechanism.The results show that all clearance joints increase the frequency of shakes of the mechanism and decrease the stability of the mechanism.Next,the dynamic characteristics of two guide-bar-slider mechanisms in which one includes a translational joint with clearance at the end of the transmission chain and the other includes a translational joint with clearance in the middle of the transmission chain are investigated.The ADAMS software is used to calculate the dynamic characteristics of the mechanisms in the two situations.The simulation result is compared with the result of ideal mechanism to figure out the effects of translational joints with clearance in different position on dynamic characteristics of mechanisms.The results show,compared to the guide-bar-slider mechanism including an endmost translational joint with clearance,the clearance of intermediate translational joint with clearance has a greater influence on output velocity,output acceleration and crank moment of the mechanism,and it increases the frequency and amplitude of shakes of the mechanism and decrease the stability of the mechanism.Finally,a guide-bar-slider mechanism with multiple joint clearances is studied to analyse the effect of multiple joint clearances on dynamic characteristic of the mechanism.The mechanism has six clearance joints except driving joint.After running through the six clearance joints in every possible combination,the effects of the number of the clearances joint,the style of the clearance joints and the location of the clearance joints on dynamic performance of mechanisms are researched comprehensively.The results show,the clearance joints in different style or location have different influences on dynamic performance of the mechanism when the clearance joints are in the same number.Besides,the effects of the number of clearance joints on dynamic performance of the mechanism are not monotonous,that is to say,the dynamic performance of the mechanism does not deteriorate with the increasing of the number of clearance joints monotonously.