| The kinematic scheme design of NC machine tool is a complex process involving plenty of knowledge aspects.Its complexity is reflected on the huge number of design parameters and the complex relations between design parameters.In the scheme design stage of NC machine tools,the processing requirements of the machined surface are the driving force of the design process.After solving the kinematic demanding which fulfills the processing requirements of the machined surface,motions of driving axes should be obtained by decoupling the posture and position of the cutter.The kinematic scheme can be obtained by configuring the drive mechanisms and the obtained kinematic scheme will finally be evaluated considering its nonlinear error,Maintainability,manufacturing cost,operating efficiency.The contents of this paper are as follows:Solving methods of kinematic function,decoupling methods of cutter’s motion,design methods of kinematic scheme has been studied by plenty of researchers and the current state of related researches is introduced in Chapter 1.Drawbacks of the current methods are put forward,based on which the method of CNC kinematic scheme design orienting complex free-form surface machining is proposed.In Chapter 2,the tool path planning and kinematic function solving are involved as the first step of "Function-Behaviour-Structure"design method.Curvature features are analyzed and cutting stripe width is computed at each CC(cutter contact)point.Finally,the tool path is generated to make the whole surface within the scallop height requirement and the driving axes needed to drive the cutter are listed.In Chapter 3,in order to eliminate the singularity problem,the decoupling and optimization method is proposed.The DDFO(Discrete Domain of Feasible Orientation)model is constructed,based on which the movement of cutter is mapped to each driving axis.The shortest path in the solving graph of DDFO indicates the most efficient tool path without singularity problems.In Chapter 4,the kinematic scheme involving the driving mechanism configuration is generated on the basis of kinematic function scheme obtained in Chapter 2.NEMM(Non-Ergodic Morphological Matrix)model is firstly constructed to list all the possible configurations.Implicit constraints between each two driving mechanisms are found by Bayesian network analysis.At last,the configuring process is controlled by FSA(Finite State Automata)to generate all the kinematic schemes fulfilling the kinematic function requirement.In chapter 5,the obtained kinematic schemes are evaluated considering multiple kinematic performances.Cluster performances model is constructed to solve the weight of each kinematic performance.Then the evalution value of each kinematic performance is uniformly expressed by applying the Information Axiom.Each kinematic scheme is finnaly evaluated synthetically ranked according to its net flow.In Chapter 6,the design system of kinematic scheme driven by process requirements is developed,and an example is given combining the proposed technologies in Chapter 2-5 to elaborate the techonology details and validities.In Chapter 7,the research contents of this paper are summarized and the future work is prospected. |
