Research On Configuration Synthesis And Accuracy Control Method Of Metamorphic Mechanisms Used In Spatial Surface Flame Cutting Operation

During the manufacturing process of large hull structures on the modern ships,it is an important technical problem to cut various types holes on the complex spatial curved surface.The processing quality of those hole tasks have direct influences on the equipment performances,and the processing efficiency is also related to the manufacturing cycle of ship.With the increasing ‘high performance’ machining demand of the hole tasks on the complex curved surfaces,the traditional manual cutting method has been difficult to adapt to the modern ship manufacturing environment.Therefore,it has important theoretical significance and engineering value to study the basic theory of complex surface digital agile cutting technology,and also to develop the CNC cutting equipments with high efficiency,high precision and high quality processing performance.To process the complex spatial curved surface,both the metamorphic mechanism and the flame cutting craft are taken as the key factors for the digital agile cutting technology in this paper.Based on the innovative design theory and precision control theory,the configuration synthesis,the kinematic accuracy analysis,the pose accuracy design,and the processing accuracy compensation methods have been carried out on the spatial surface flame cutting metamorphic mechanism.Meanwhile,the validity verifications are conducted through the cutting experiments.On the theoretical level,the research framework of digital agile cutting technology has been established,of which is based on the configuration design and precision control theory of cutting metamorphic mechanism.In the physical environment,it provides a novel CNC cutting equipment to solve the engineering problems of ship manufacturing.Those studies are not confined to the machining environment of complex curved surface on the hull structures,which promotes the competitive ability of digital agile cutting technology in modern manufacturing industry.The main contents are following.A novel combination regeneration method is proposed for the configuration synthesis of the spatial surface flame cutting metamorphic mechanisms.After determining the changeable topological structure features of the metamorphic mechanism and taking the multi-tasks as the design environment,both the connotation and the synthesis framework are figured out to the combination regeneration method.For the design tool layer of the proposed method,the combination design flowchart is established to the task space.Through the functional decomposition,the sub-configuration synthesis,the sequence screening of sub-configuration,the adaptive design of the metamorphic way and the synthesis of source configuration,the metamorphic configurations could be obtained from the intuitive manner with ‘develop from nothing’.The regeneration design flowchart is established to the topological space.Through constructing the extended lower-order body matrix models,the step-description equations and the inversed extension models to refine the metamorphic characteristics,the metamorphic configurations could be obtained from the logic manner with ‘existing to updating’.Meanwhile,the evaluation criteria are constructed by setting up the kinematic performance indices of stable configurations and the change rate indices of instantaneous configurations.Combining to the complex spatial curved surface operations and the service environment of CNC equipment,12 kinds serial-parallel ‘cutting metamorphic mechanisms’ are derived from the proposed method.After selecting RPP-PRRRR metamorphic configuration as the performing kinematic chain,a metamorphic CNC flame cutting machine is developed for the spatial surface flame cutting metamorphic mechanism.The configuration results not only show the effectiveness of the proposed method,but also provides a practical and efficient processing equipment for the digital agile cutting technology.A novel configuration-complete quaternion matrix method is proposed for the accuracy analysis of the spatial surface flame cutting metamorphic mechanism.Based on RodriguesHamilton parameters,the kinematic models are established for the planar,spherical and spatial chains of metamorphic sub-configurations respectively.And then,through combining the adjacent models of the generalized kinematic variables derived from the metamorphic characteristics,the configuration-complete kinematic quaternion models are constructed.The disturbance quaternion models are also obtained for the joint variable errors,the structures errors and joint clearances of the metamorphic mechanisms.By taking those error factors to the kinematic models simultaneously,the configuration-complete kinematic error quaternion models are derived out.Theoretical calculations and physical simulations are carried on a typical hexahedral metamorphic mechanism,and the comparing results show that those established models are effective and are able to avoid the mathematical singularity,of which could figure out the changeable characteristics of the kinematic accuracy.Meanwhile,the simulations are conducted on the spatial surface flame cutting metamorphic mechanism.The obtained error influence coefficients further illustrate the rationality of the established models and the practicability of the proposed method.A novel optimal allocation method is proposed for the pose accuracy design of the spatial surface flame cutting metamorphic mechanism.Firstly,by using the causal relationships of the pose errors of the metamorphic mechanism,the main accuracy terms are determined for the accuracy design process clearly,which have been divided into the form and position tolerance of the components,the fit tolerance of adjacent parts,the driving tolerance of the control system.Secondly,based on screw theory,the error mapping models of metamorphic sub-configuration are determined through constructing the ideal pose models,the description models of the accuracy terms,the real pose models and the pose error models.Thirdly,the key tolerance factors involved in the accuracy terms are determined from establishing the error sensitivity models of the sub and the complete configurations of metamorphic mechanism.Finally,the accuracy optimal allocation models are carried out through the error sensitivity and the precision costs respectively,which could accomplish the overall accuracy design process of metamorphic mechanism.Numerical simulations are conducted on the metamorphic CNC flame cutting machine related to the cutting metamorphic mechanism,and the obtained allocation models and accuracy design results show the effectiveness of the proposed method,which also illustrate that it could accomplish the ‘best’ accuracy allocation of the spatial surface flame cutting metamorphic mechanisms.A novel error prediction and real-time compensation method is presented for the accuracy modification of the spatial surface flame cutting metamorphic mechanism.Taking the CNC flame cutting machine as the implementing device of the cutting metamorphic mechanism,the machining coordinate systems in the flame cutting process are determined as the reference frame,the machine frame,the tool frame,the measurement frame and the workpiece frame.By using the transformation matrix method,the synthesized prediction models of processing errors are established when considering 18 geometric errors,6 thermal deformations and 15 composite errors of the flame cutting components simultaneously.Based on the calibration theory,the positioning models,the POE identification models,the distance error measurement and selection procedures of the self-calibration process are constructed for the geometric elements.And also,based on the finite element analysis(FEA),the off-line test,the optimal selection of key thermal points and the thermal dynamics models are constructed for the thermal/composite elements,of which figured out the acquisition mode of those error elements clearly.Moreover,the implementation way of the real-time compensation method is figured out,where the online system through the external machine zero point shift in CNC system and the input planning principle in rapid control prototyping,the partial least squares compensation algorithm are developed respectively.Application simulations are carried out on metamorphic CNC flame cutting machine related to the cutting metamorphic mechanism,and the obtained results show the high-precision performance and the feasibility of the established real-time compensation system,which could ensure that the spatial surface flame cutting metamorphic mechanism and its CNC cutting equipment have high quality performance in the digital agile cutting technology.Finally,the application experimental verifications are conducted on the spatial surface flame cutting metamorphic mechanism.By using the configuration principle and the precision control models of cutting metamorphic mechanism,the system environment are determined for the related metamorphic CNC flame cutting machine.Then,take the eccentric hole on the cylindrical shell surface as an example,the application experiments are carried out.It is found that the cutting metamorphic mechanism and its cutting machine could achieve continuous cutting and forming of the hole task,which shows high effective performance for the spatial surface processing.Meanwhile,real-time compensation experiments of the cutting machine are carried out after accomplishing geometric calibration and thermal deformation simulations.Through comparing to the traditional teaching method,it is found that the processing quality could be improved by more than 40%,which illustrates the high precision and high quality performance for the spatial surface processing of the cutting metamorphic mechanism and its cutting machine.The results verify the practicability of the research results of metamorphic mechanism,which also provides a high performance CNC machining equipment for solving the cutting problem on the complex spatial curved surface environment.