Dynamic modeling of a 2-dof parallel electrohydraulic-actuated homokinetic platform

Thrust vector control (TVC) is used to control the attitude of spacecraft. The most widespread method to connect the nozzle assembly and rocket consist of a gimbal joint in the case of liquid-propellant or a flexible bearing in the case of solid-propellant. Traditionally, two electrohydraulic linear actuators that are controlled by servovalves tilt the rocket nozzle. However, in this work, TVC is treated as a robotic system and the connection between the platform and the fixed base is achieved using a constant velocity joint. Instead of a servovalve, a novel proportional digital hydraulic valve is proposed. The position feedback is provided through a real-time attitude estimation based on the orientation matrix by using an inertial measurement unit (IMU). Platform kinematics modeling is performed. Dynamics modeling is developed using Newton-Euler formulation. Hydraulics modeling is presented with the description of the electrohydraulic system. Due to the linear behavior of the control valve, a simple pure proportional controller is considered. An experimental validation showed that the proposed system achieves good position tracking without instabilities.