| Multibody system with spherical clearance joints is widely used in precision mechanism,ships,aerospace vehicles,robots and animal skeleton systems.With the development of technology and the increase of demand,more and more researchers pay attention to the problems related to the high precision,high stability and high efficiency of various multibody systems.However,the clearance,which exists in the actual spherical joint,may cause the impact force,it will affect dynamic characteristics of multibody system,and reduce motion accuracy and stability of the whole system.Therefore,analysis of the dynamic characteristics of multi-body system with spherical clearance joint and reduction of the influence of clearance on the dynamic performance,motion accuracy and stability of multibody system have become the focus of relevant research.In order to reduce the influence of spherical clearance joint on the dynamic characteristics of multibody system,a new flexible spherical clearance joint model with an elastic bushing was proposed in this dissertation.Then,a rigid-flexible coupling model of the four-bar mechanism was established by using this flexible spherical clearance joint.And,dynamic characteristics of this mechanism were analyzed.These results of this mechanism with flexible spherical clearance joint were compared with the case of the rigid spherical clearance joint.It is concluded that flexible spherical clearance joint with elastic bushing can greatly reduce the impact force caused by clearance,and can greatly improve the dynamic characteristics of multibody system with clearance.This dissertation lay a fundation for the design,high precision analysis and reliability analysis of multibody system with clearance joint.The main contents and results of this dissertation are as follows:1.Several contact models and friction force models had been compared,and the dynamic equations of multibody system with rigid spherical clearance joint were also established.The influence of clearance,clearance size and driving speed on the dynamic response of multibody system with rigid spherical clearance joint was analyzed.Simulation results shown that the existence of clearance will affect the displacement,velocity and acceleration of multibody system,and change the ball center trajectory and contact force of the spherical joint.Moreover,clearance size and driving speed have great influence on the dynamic response of the imperfect multibody system.2.To reduce the influence of clearance on dynamics of multibody system,a new flexible spherical clearance joint model with elastic bushing was established,and then this new joint model was introduced into the spatial four-bar mechanism to establish a rigid-flexible compling model.The dynamic response of this multibody system with flexible spherical clearance joint was analyzed,and results were compared with those of multibody system having traditional rigid spherical clearance joint.These results shown that this new flexible spherical clearance joint can regularize the motion modes of the spherical clearance joint,greatly reduce the impact force and impact frequency of spherical clearance joint,and significantly eliminate the negative influence of clearance on the dynamic response of multi-body systems.3.Influence of clearance on the dynamic response of clearance multibody systems under different clearance sizes,driving speeds and friction coefficients was discussed.The results shown that the flexible spherical clearance joint can reduce the negative effect of clearance on the dynamic response of multi-body system under various conditions,especially under large clearance size,high driving speed and low friction coefficient.The flexible spherical clearance joint can also greatly reduce the influence of clearance size on the dynamic response of multibody system.4.The effect of flexible spherical clearance joint on improving the motion stability of multi-body system was studied.The effect of flexible spherical clearance joint with different clearance sizes,driving speeds and friction coefficients on the stability of imperfect multibody system was discussed.These results shown that the flexible spherical clearance joint can improve the stability of motion for multibody system having spherical clearance joint.When the imperfect mechanism has large clearance size,high driving speed or low friction coefficient,flexible spherical clearance joint can greatly improve the motion stability of this system.5.Some researchers used the flexible connecting rod to reduce the effect of the clearance.Here,the scheme of the flexible spherical claearance joint was compared with this scheme of the flexible connecting rod.Results shown that flexible connecting rod has some limitations,it will reduce the motion stability of impefect multibody system.Compared with the flexible connecting rod,flexible spherical clearance joint can reduce the influence of clearance on the dynamic characteristics of multi-body system directly and completely,and it can rapidly improve the motion stability of multi-body system having spherical clearance joint. |
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