| Underwater robot is one of the hot spots in the field of marine research.As an effective propulsion method,vector propulsion can obviously improve the propulsion performance of underwater vehicles.Spherical parallel mechanisms have many advantages,such as high rigidity,long service life and so on.It can realize the vector control of single propeller as well.At present,the spherical parallel mechanism is mostly symmetrical and driven by rotation.In this paper,an asymmetric parallel mechanism UPR-SPU-UR driven by linear drive is designed.The kinematics analysis and simulations are carried out,and the motion performance of the mechanism is studied,which provide a new idea for the design of the spherical parallel mechanism for the vector propulsion.Specific contents are as follows:(1)Structure description and coordinate system of UPR-SPU-UR parallel mechanism are completed.The degree of freedom is analyzed by screw theory,and it is concluded that the mechanism has two rotational degrees of freedom.The position relation of the parallel mechanism is analyzed by analytic method,and the forward and inverse solution of position is derived.Derivative of the inverse expression with respect to time is taken,and the velocity mapping matrix between input and output of the UPR-SPU-UR parallel mechanism is obtained,which is called Jacobian matrix.The multi rigid body system model of UPR-SPU-UR parallel mechanism is established by ADAMS,and the degree of freedom is verified.The kinematics and dynamics of the system are simulated in the point drive and spline driven.The results are compared with the results of the MATLAB method based on the analytical method,and the correctness of theoretical calculation is verified.(2)The singular configuration of UPR-SPU-UR parallel mechanism is determined on the basis of Jacobian matrix.Reachable workspace is solved under the integrated consideration of constraint conditions,such as the length of the driving chain,the angle of the kinematic pair,the interference of the rod and the singular position.Considered the reciprocal of the condition number of Jacobian matrix as the evaluation criteria of dexterity,the dexterity of the mechanism under different attitude is analyzed.Finally,calculate the global Jacobian matrix,then simulate and analyze local stiffness map and the global stiffness spectrum..(3)Two slender rods are used as flexible bodies.Combined ANSYS with ADAMS,the rigid flexible hybrid simulation model is established.Then the spatial spiral trajectories are drawn and the influence of the deformation of flexible chain on the whole operation of the mechanism is analyzed.The computational fluid dynamics software Fluent is used to explore the propeller driving force and deflection force when swing angle of the propeller shaft is largest,and the effects of these forces on the overall operation of AUV are analyzed.Finally,the computational fluid dynamics is used to study the open water performance of propeller in various motion modes,and the axial pressure distribution,the pressure distribution and the flow distribution on the blade surface are simulated respectively.The results of this study have important guiding significance for the dynamic analysis,size optimization and prototype fabrication of UPR-SPU-UR. |
PDF Full Text Request