Research On Chaotic Motion Of Mechanism With Clearance Actuated By PM Brushless DC Motor

As one important element in mechanism, kinematic pair ensures certain relative movement between jointed links, which compose a mechanism. When the links are connected through movable fit, there is always clearance in kinematic pair which changes the relative position and motion accuracy between links. The clearance makes the dynamics of mechanism with clearance a non-linear system to represent rich non-linear dynamic phenomenon.Permanent magnet (PM) brushless direct current (DC) motor is also strong non-linear system, which is sensitive to the change of initial condition and input.A slider-crank mechanism with clearance driven by PM brushless DC motor is studied in this thesis. The purpose of this study is to find out something about the chaotic motion arising from these two coupled nonlinear dynamic system.The major contents and results of this study are as follows:1. The continuous contact model is employed to establish the dynamics model of the slider-crank mechanism with the clearance existing in the kinematic pair between the crank and the floating link and that between the floating link and slider respectively. It is simulated as the crank rotate with a constant angular velocity and the clearance existing in the kinematic pair between the crank and the floating link. The results show that the bigger the clearance size is, the more intense the chaotic motion will be.2. The mechanical characteristics and controllable characteristics of PM brushless DC motor are presented and the dynamitic model for analysis is established. The parameters for both stable motion and chaotic motion are determined by simulation.3. The dynamic model of the slider-crank mechanism with clearance driven by PM brushless DC motor is established. Taking the parameters of the motor for stable motion, simulations are carried out. The effects of the location of clearance, the clearance size and input voltage of motor on the chaotic motion of the system are analyzed. The results show that although there is a few exception the intensity of chaotic motion is proportional to the value of input voltage or/and clearance size in general, especially in the case when the clearance size is smaller. On the other hand, the effect of variation of input voltage on the intensity of chaotic motion is not obvious if the clearance size is larger. It is also shown that the chaotic motion is more intense if the clearance exists in the kinematic pair between the crank and floating link than that between the floating link and slider under the circumstance that both the input voltage and clearance size are same. That is to say that the closer to the axle of motor the kinematic pair with clearance is, the more intense the chaotic motion will be.The work and the results presented in this thesis pave the way for chaos controlling.