Simultaneous decoupling control of translation and rotation for a 6-DOF vibration isolator based on the Stewart platform

Measuring gravity from a ship is important in geodesy and geophysics. A 6-DOF vibration isolator based on the Stewart platform reduces the vibration on a ship. The motion coupling of the multi-DOF vibration isolator is a difficult problem. Although the translational coupling of the vibration isolator is handled by the inverse dynamic method, the rotational coupling still exists. The orientation of the top platform of the vibration isolator is described by the Euler angles. There is a nonlinear transformation between the derivatives of Euler angles and the angular velocity since the three directions of the Euler angles are non-orthogonal. Based on this relationship, a kind of decoupling controller is designed to eliminate the coupling between the rotational DOF. The translational DOF and rotational DOF of the system are controlled separately. The translational DOF is controlled by the classical computed torque control (CTC) method. As for the rotational DOF, the inverse dynamic part of the CTC is combined with the nonlinear transformation. The simulation results indicate that the proposed control method reduces the coupling between the rotational DOF to about 30% compared with the classical CTC method.