Research On Kinematics Of Hybrid Serial-Parallel Mechanisms For Compensating Platform In Deep-Ocean Mining

The mining ship's motions, including heave, pitch and roll which are defined as generalized heave in this dissertation and are main motions influencing the mining system, should be compensated to keep mining platform where the hoisting system located on and load suspended, having a stable pose with respect to the inertial frame.Considering shortcomings of existing heave compensation methods and gimballed platform of mining systems in developed countries and advantages of higher overall stiffness, low inertial, and higher operating speeds of parallel mechanisms (PM), a hybrid serial-parallel mechanism used to be compensating platform is proposed in this dissertation. A translational 3-UPU PM composed of base fixed on the deck of mining ship and middle platform is used to compensate heave and conduit center shifts due to pitch and roll, and another rotational 3-UPU PM connected with the translational PM serially is used to counteract conduit inclination due to pitch and roll.The kinematical analysis and 3D simulation are worked out for the hybrid serial-parallel mechanisms used to be as the compensating platform in deep ocean mining. Forward position analysis, velocities, accelerations, singularities of mechanism, workspace and stiffness matrices are all involved in the researches of this dissertation. The unit quaternion transformation and vector algebra are applied to be analysis tools.There are two sets of closed-form direct solutions of the translational PM. For the rotational PM, although there is no closed-form direct solution generally due to its non-linearity, closed-form direct solutions can be solved on special geometric conditions. Based on known geometrical configurations of two kinds of PM, mappings of velocities, accelerations of the end-effector to its geometrical configurations are constructed, and the Jacobian matrices are derived out.Based on identifying singularity of the Jacobian matrix, the singular configuration of PM can be identified. The criteria are given out to identify singular configurations of the translational and rotational PM. A normalized method is applied to search workspace of two kinds of PM. The workspace analysis of the translational PM shows that the workspace volume is affected by all geometric and non-geometric constraints, while the average condition number is affected only by the circumcircle radius difference of the fixed base and the moving platform and there exists an optimal value of average condition number. In workspace analysis of the rotational PM, a straightforward and non-degenerate definition of orientation workspace is presented with a set of reachable unit normal vectors of moving platform and rotation angles around each normal vector. A simple criteri to identify non-compatible configurations is build up and used in determining the orientation workspace of rotational 3-UPU mechanisms.According to Jacobian matrices and results of workspace analysis, stiffness matrices of two PMs are analyzed. Comparing to the rotational PM, directions and magnitudes of the maximum stiffness of the translational PM are focused in a small range.Applying above-mentioned results of kinematical analysis of the two PMs and accordance with requirements of the compensating platform in deep ocean mining system, an optimal parameter design of the hybrid serial-parallel mechanism is carried out. A 3D simulation of compensating the generalized heave by the hybrid serial-parallel mechanism is worked out successfully. It is proved that the actively compensating platform based on hybrid serial-parallel mechanism is of kinematic feasibility for deep ocean mining.