Research And Application Of Trajectory Planning Method In Intelligent CNC System

High-end CNC machine tools are important equipment of a nation,and high-end CNC system is the brain of CNC machine tools.The high-speed and high-precision planning method of motion trajectory is the core key issue of high-precision CNC system.With the proposal of the "14th Five-Year" intelligent manufacturing development plan,intelligent numerical control system is an inevitable development trend.Based on the analysis of the research status and development trend of advanced intelligent CNC systems at home and abroad,the main research contents are as follows:1.Intelligent CNC system architecture.On the basis of the software and hardware platform of the intelligent numerical control system,the software architecture of the intelligent numerical control system is studied.On the basis of RCS architecture,the overall software architecture of CNC system is established.Each abstraction layer has modules for perceptual processing,world model,value judgment,and behavior generation.This paper introduces the working principle and error handling technique of the interpreter,and the realization of the world model in the interpreter software.The software architecture of intelligent numerical control system and the trajectory planning module architecture are given.On this basis,the intelligent numerical control system network platform and intelligent manufacturing process chain technology are studied.It lays the foundation for the algorithm research in the following chapters.2.Efficient trajectory planning method.In order to improve machining efficiency and real-time performance of the algorithm,an efficient trajectory planning method is proposed.One-step planning method is adopted to perform corner transition and velocity planning at the same time to improve the real-time performance.In this paper,according to different path geometry,the corner optimal transition method or the corner bisector transition method is selected in certain machining status.When G01 segments are long,the corner optimal transition method is selected;when G01 segments are short,the corner bisector transition method is selected.Then,a real-time look-ahead method is applied,adjusts corner velocity at both ends of the line segment,so that all segments are acceleration and deceleration reachable.In algorithm verification,after the methods are separately tested,they are embedded in CNC system for integral verification.When problems occurred in the actual engineering,we analyze the reasons,and improve these methods.The machining of sand molds verifies that the method proposed in this paper is suitable for high-speed machining.3.Dynamic trajectory planning method.In actual machining,sometimes emergencies and abnormal situations occur,the CNC system needs to be able to deal with emergencies and respond to external signals in real time.A dynamic trajectory planning method is proposed.Based on commonly used acceleration and deceleration methods,it can respond to external environment changes in stop mode and continuous mode and dynamically plan the velocity curve in real time.Velocity profile is adaptively adjusted in real time according to machining conditions and subsequent paths,and responds to external changes and machining conditions in real time to avoid the occurrence of abnormal and dangerous situations.The dynamic trajectory planning method for micro-line segments is based on the processing of micro-line segments,responds to external signals in real time,and modifies the velocity curve,which can respond to the adaptive adjustment of the intelligent numerical control system to external interventions.Using the linking of micro-line segments,multiple line segments form a program chain,and velocity planning is performed for all segments in the program chain,and external signals are transmitted between segments.Simulation experiments and practical results show that the proposed dynamic planning method is suitable for real-time trajectory planning.4.RTCP function and tilted plane machining.When the five-axis tool center point control(RTCP,Rotation Tool Center Point)function is applied,the CNC system firstly performs trajectory planning for the tool center point command,and then kinematically transforms the planned position in the workpiece coordinate system to generate physical axis movement in machine coordinate system.Because of the nonlinear relationship of the kinematics of the five-axis machine tool,the axis motion converted from the smooth interpolation position may have unstable speed.Therefore,a method is proposed to calculate the nonlinear mapping relationship between the actuator space of the five-axis machine tool and the cartesian space and calculate the corresponding scale factor.The speed of the actuator space is calculated according to the original programming speed multiplied by the scale factor to ensure smooth and continuous speed in actuator space.Aiming at the processing of typical "S" specimens in the aviation field,based on the existing RTCP functions,an efficient RTCP function that satisfies the constraints of speed and acceleration is designed.Then,based on the RTCP function,the tilted plane machining function is designed and implemented,which can be applied to 12 types of five-axis machine tools.5.Complex curve trajectory planning method.The high-speed and high-precision planning methods of complex motion trajectories is the core key issue of high-end CNC systems.Facing the high-speed and high-precision machining requirements of CNC systems,based on micro-line trajectory planning method,a unified complex curve trajectory planning method is studied.It includes three steps: preprocessing,curve fitting,and segmentation.First,a large number of micro-line segments are preprocessed,including isolated point correction,redundant point filtering and orientation vector correction.Second,the preprocessed data points are fitted to generate splines.Then,three basic trajectory elements: spline curve,circular arc and micro-line segments are selected for segmentation to generate workpiece programs in various combinations.Experimental verification is carried out by taking different types of cams as examples.There are three ways of cam profile expressions in CNC system: arc,micro-line and spline curve.A variety of segmentation processing methods such as spline,circular arc,micro-line segment and the combinations of these three basic expressions are given.We analyze and compare various trajectory planning methods from the aspects of time,accuracy,smoothness and continuity,and summarize the characteristics and application scenarios of various methods.