A novel 3-DOF cable-driven wind tunnel mechanism and its position analysis

To reduce the aerodynamic influences of rigid suspension systems in wind tunnel test, this paper describes a novel 3-DOF wind tunnel mechanism based on a cable-driven parallel mechanism. This mechanism can provide 3-DOF pure rotation by means of three actuators, especially when five single-piece sensors are amounted on the five driven cables respectively, the aerodynamic force of the scale model can be achieved directly. The main aim of the paper is to solve the forward kinematics for the mechanism. Rodridgues' parameters are applied to express the transformation matrix of the cable-driven mechanism. The closed forward kinematics model is described as three quadratic equations using three Rodridgues' parameters based on the fundamental theory of parallel mechanism. Mathematical method is used to eliminate two of the three variables, so that an eighth-order polynomial with one variable is derived., From the equation, the eight sets of Rodridgues' parameters and corresponding Euler angles for the forward kinematical problem can be obtained. In the end, numerical example of both forward and inverse kinematics is included in the paper to demonstrate the presented forward-kinematics solution method. The developed algorithm is suitable for real-time control in the future.