A Modified 6-DOF Hybrid Serial–parallel Platform for Ship Wave Compensation

This study proposes a modified six-degrees of freedom (6-DOF) hybrid serial–parallel platform (HSPP) for ship wave compensation. This HSPP is proposed based on the three universal-prismatic-universal_universal-prismatic (3UPU_UP) parallel module (PM), constructed by three UPU limbs and one UP limb. The serial module (SM) consists of a XY table and a rotational table. First, to better understand the compensation motions of the 6-DOF HSPP, the position and orientation of rotational axes and translational axes in this system are analyzed in detail by using the screw theory. Second, the position and velocity of the HSPP are systematically analyzed. Third, differences between the HSPP and its PM in singularity and reachable workspace are analyzed. The results show that the PM includes three characteristics: larger workspace, poorer orientation adjustment ability, and stronger coupling in the position and orientation. The HSPP inherits the characteristics of PM and adds SM to improve the deficiency of PM. The proposed HSPP can use PM for coupling compensation and can also use PM and SM for decoupling compensation. Compared with the Stewart platform, the HSPP has more advantages in terms of workspace and decoupling, which provides a new idea for the study of wave compensation.