Modeling And Dynamic Simulation Of A Four-cable-driven Camera Robot

Due to the advantages of strong loading capacity, large working space, high response speed and the high degree of modulation, the cable-driven parallel robots have been gaining a wide application especially for the camera shooting field in the big gymnasiums. The terminal effector must be changed with the instant variations of the shooting objects when the robot moves in a large-span area. Hence, a higher requirement is put forward to the motion and control precisions for the cable-driven parallel robots. The research for the much more accurate dynamical model and effective control methods is thus becoming significantly important. Based on the dynamical analysis, this thesis mainly concentrates on the work of model simplification, optimal distribution of cable force and trajectory planning for the four-cable-driven Camera Robot. The dynamical model, which can reflect the weight, elastic deformations and force transmission characteristics of the cables, is proposed and the simulation analysis for the typical trajectory of the model is conducted with the force control mode. Furthermore, the main factors which can influence the motion and control accuracies are discussed.First, combining with the structure characteristics of a four-cable-driven camera robot, we complete the simplification of the structure model and develop the system model with the linear and the catenary cables respectively. Based on the dynamical analysis of the four-cable-driven camera robots with three degree of freedom, this thesis deduces catenary equation, in which the weight of cables has been taken into consideration, and the solution formula for the cables’ lengths. The optimal distribution of redundant cable tension is studied and the solving suggestions are presented for different models. In addition, the trajectory of the four-cable-driven camera robots is planned and the final trajectory functions are demonstrated.Second, the main idea and methods are summarized on the flexible cable structure modeling by using the ADAMS software. According to the different modeling methods, the two-cable linear model and two-cable catenary model are built and validated by the example simulations. By comparing the simulation results of the two-cable linear models with the different modeling methods, we can reach the conclusion that the spring-mass model can not only guarantee the movement of the terminal platform, butalso reflect the cable elastic deformation and force transmission characteristics, which settle a foundation for the verification and dynamic analysis of the four-cable model.Finally, the spatial four-cable-driven camera robot model with consideration of the cable weight is set up. The force control mode is applied in the motion control and analysis for the typical space trajectory of the proposed model, and we further explore the influence to the end platform motion precision from the factors such as the initial velocity and acceleration, the control time interval, the pulley deflection and the cable weight under the force control mode. After that, the results are analyzed and the suggestions on improving the motion control accuracy are proposed.