Stability Analysis Of A Four-wire-driven Camera Robot

The wire-driven camera robots can fly over the stadium with a span of about 250 meters. The unsteadiness of the camera platform, which is caused by factors such as wind disturbance, frequent change of speed and inertial impaction from fast startup and shutdown, can lead to blurred images. Camera robots face more severe challenges in terms of the stability than any others. However, there is lack of qualitative and quantitative indicators to describe the stability of the wire-driven camera robots at present in domestic researches. This thesis, on the basis of stability analysis of other systems, proposes indicators for evaluating the stability of wire-driven camera robots, as an attempt of the application of multi-aspects stability enhancement technology of the wire-driven camera robotics system, to guarantee the successful shooting of cameras under the conditions of disturbance of environmental factors and frequent starts and stops as well as frequent going back and forth.Firstly, the kinematics model of common wire-driven parallel manipulators is established by vector theory and derivation method. With structural features of a four-wire-driven camera robotic system in view, the simplified kinematics model of the camera robot is obtained on the basis of the kinematics model of common wire-driven parallel manipulators. The simulation analyses of the inverse solution of position, velocity and acceleration are further presented with analytical method.Secondly, the dynamic model of the four-wire-driven camera robot is established. And the redundant wire tension problem is converted to a convex programming problem by reverse solving the dynamic equation. Then optimizations of redundant wire tension with different objective functions are adopted. With other ways compared, the method possessing with the minimum variance is chosen as the final strategy from the perspective of improving stability and stiffness.Thirdly, on the definition of workspace of the four-wire-driven camera robot, similarities between wire-driven camera robots and fixed-point contact without friction grasping system are investigated. The convexity condition of force-closure grasp is introduced to the wire-driven parallel manipulator system. According to the vector closure theorem and the dimension reduction techniques, a uniform solution strategy isproposed. Numerical simulations demonstrate the effect of the maximum wire tension and quality of the end effector on workspace. The results provide theoretical reference for physical design of the four-wire-driven camera robot.Finally, as a reference to the stability analysis of other systems, this thesis introduces two original indicators, the minimum wire tension in the four wires and the minimum singular value of the static stiffness matrix, to evaluate stability of the four-wire-driven camera robot. And independent numerical simulations are made for analyzing stability of the whole workspace. Based on the discussion of advantages and disadvantages of the two original indicators, a comprehensive performance criterion is proposed to measure stability by normalization and weighting processing. And reasonable weighting coefficients are selected on the basis of the analyses of the influence of different weighting coefficients on the comprehensive performance criterion. And then a steady workspace with the proposed indicators is constructed. This thesis provides theoretical references to enhance the multi-aspects stability of the camera robot and to guarantee the successful shooting of cameras under complicated conditions.