Performance Analysis And Dimension Parameters Optimizition Design Of Parallel Metamorphic Cutting Mechanism

In the manufacturing process of different types of ships,cutting holes on the complex-surface of the hull has been a key technology,and the current cutting equipment is based on the series mechanism,which has inherent defects such as poor rigidity,accumulated error and poor dynamic performance.Therefore,the study of the parallel mechanism for the cutting of the holes on complex-surface,form a useful supplement to the existing cutting equipment,has a very important research and application value.In this paper,a kind of parallel metamorphic cutting mechanism facing to complex-surface cutting is studied.The workspace,kinematic model and performance evaluation index are studied around the evaluation of mechanism performance and dimension synthesis.And the dimension parameters optimization design is carried out on the basis of the established performance index.Firstly,a parallel metamorphic cutting mechanism for complex-surface hole cutting tasks on the hull is designed.Study on the freedom of the source and sub-configuration,as well as the reasonableness of the drive input are conducted based the POC theory.The study verifies the requirements of the mechanism to meet the different degrees of freedom of the cutting task.Based on the geometrical characteristics of the mechanism,using the POE formula to establish the motion constraint equation,and the position inverse solution model of two configurations is obtained.Then,the workspace of two configurations is finded by Matlab,and the initial design dimension is determined according to the analysis result.To solve the kinematics problem of the mechanism,we use the screw theory as a mathematical tool to obtain the generalized Jacobian matrix and the explicit form of the Hessian matrix expressed by the Lie bracket,and then the velocity and acceleration model are established.The kinematic model,differential method and ADAMS software were used to validate the inverse kinematics simulation.The curves of angular velocity and angular acceleration over time obtained by three methods mentioned above are completely consistent,that verified the correctness of the kinematic model.To analyze the performance of the parallel metamorphic cutting mechanism,we formulate the dimentionally homogeneous Jacobian matrix of source configuration and the velocity Jacobian matrix and the Hessian matrix,that with only the driving information of sub-configuration.Then the algebraic features are used as the mathematical basis and the local performance indexes of dexterity,force and torque transmission performance,acceleration and inertia force in the workspace are calculated by Matlab software.The global performance map of each performance index is drawnt,too.In order to get the size parameters with excellent performance,the size parameter design of parallel variable cell cutting mechanism can be divided into two steps.In the first step,the objective function of the full-configuration global dexterity,acceleration and inertia force is taken as the objective function,and the objective function is optimized by the improved MOPSO algorithm.The multi-group optimal solution is obtained.The second step,according to the requirements of low speed and high precision in cutting process.The dexterity index which expresses the precision of motion is taken as the performance target.The solution when the dexterity index is biggest is chosen,from the group of optimal solutions,as the final solution.Compared with the the previous optimization,the dexterity performance indexes of two different configuration are improved,that verifies the correctness of the optimization results and the validity of the optimization method.