Research On Related Technologies Of An Open Architecture Intelligent CNC System And Online Control

The intelligence of machine is one of an effective way in improving machiningefficiency, reducing processing cost, ensuring work-pieces’ machining accuracy andimproving the surface processing quality, and it has been accounted and studied inmany countries. At present, a kind of enclosed structure for numerical controlsystem is used, which sets process variables with fixed parameters form. Therefore,CNC is only an enclosed and open-loop actuator in the manufacturing. With thedevelopment of information, agile manufacturing mode in modern manufacturing,more and more inherent defects have been imposed. It can improve cuttingefficiency and manufacturing safety by using on-line supervision and controllingthe state of the machine. So some technologies have been deeply researched forrealization of an intelligent modular open architecture CNC system and cuttingparameters’ on-line intelligent control in milling.An open architecture intelligent milling CNC platform has been studied anddeveloped based on open modular architecture controller, which can realizeinterpolation control and external parameters’ real-time acquisition and control.Related technologies about realizing intelligent CNC system have been studied andintroduced, including hardware equipment and software supporting technologies.The software composition is divided into seven modules, including human machineinterface module, task generator module, task coordinate module, adaptive controlmodule, discrete logic control module, axis group module and axis module. At thesame time, the task for each module and logic relationships among modules havebeen planned. A scheme about external parameters’ on-line real-time acquisition andrealization of the CNC system have been studied and developed. There are severaldemands in this scheme, including the character of hard real-time in the process ofacquisition, which needs to acquire accurately and timely, to assure the tasks’coordinate and be controllable. On the other hand, it should reserve theprogramming interface for process parameters’ intelligent control. Theimplementation scheme has been studied how to feedback the actuator parameters tothe controller based on the SERCOS communication mode, and the parametersinclude the machine’s feed-rate and spindle speed. It plays an important role tostudy the intelligent CNC system platform and relative technologies for processparameters’ on-line intelligent control.Milling force is one of the most important physical parameters in the millingprocess, and it not only decides consumption power, but also directly affects the milling heat which affects the milling temperature. It is easy to cause tool’s wearand broken for high milling temperature. Finally it will affect the tool’s working life.For these reasons, relative technologies are studied about on-line processparameters’ adaptive intelligent control based on the constraint of milling force toimprove the milling efficiency in this thesis. Milling adaptive control has beenstudied in simulation on the basis of constructing machine tool’s adaptivesimulation model. At first, cutting system link based on designed BP network istrained with experimental samples. Then fuzzy controller function of automaticadjustment factor is studied and wrote. Finally the correctness of the controller andthe control algorithm are verified with simulation experiment. Secondly, to realizeon-line variable feed-rate control based on the constraint of cutting force in the openarchitecture CNC system, behavior model for the controller is established with thetechnology of finite state machine. The method of changing feed-rate override tochange the feed-rate is designed, and dual shared memory technology is raised torealize synchronization and coordination between interpolation and intelligentprocess control. At last, experiments verify the technologies of on-line variablefeed-rate to be correct and superior in the open architecture CNC system, which aredone with the step aluminum alloy work-piece.It will increase the cutting vibration and cause cutting quality unstable becauseof the cyclic changes of intermittent milling force and instantaneous cuttingthickness decided by tool’s geometry condition. On the other hand, it will formchatter due to the interaction between dynamic characters in the cutting process andmodal characteristics among machine, tool and work-piece. Chatter not only limitsthe cutting efficiency, but also reduces the quality of the work-piece surface,increases the tools’ wear rate, causes the process noise. So it is very important toavoid and suppress chatter during the metal cutting process. So relative on-linecontrol technologies about variable spindle speed suppress chatter have beenstudied in detailed in this thesis. Common sensor monitoring technologies areinvestigated in the field of chatter monitor. The time domain and frequency domainsensitive signal are studied including each component in three-component cuttingforce and acceleration sensors. Aimed at the control signal frequency characteristics,techniques including fast Fourier transform and the extraction of effectiveinformation are studied during chatter. The algorithm to suppress chatter by varyingspindle speed has been studied, and the relationship model is also set up betweenchatter frequency and spindle speed. All these provide the theoretical foundation torealize chatter suppression. Finally, Relative technologies are studied to suppresschatter by varying spindle speed in the CNC controller, and two control schemes are put forward including position mode and reconfigurable speed mode. At the sametime, the realization flowcharts are also studied about two schemes in the controllermodules. On-line chatter suppression experiments have been completed withcontinuous variable cutting depth aluminum alloy work-piece, and the experimentsverify the technologies’ correctness about on-line chatter suppression in the openarchitecture intelligent milling controller.At present, products and parts with complex curved surface are holding moreand more share in the modern manufacturing industry, and the demands ofmachining accuracy and efficiency are also becoming higher and higher. AdaptiveNURBS interpolation technologies have been studied in this thesis. AdaptiveNURBS interpolation algorithm based on chord error limited is analyzed anddeveloped, and the algorithm with trapezoid and S shape acceleration anddeceleration are studied and machined in simulation. A kind of simplified algorithmabout S shape acceleration and deceleration has been studied in the adaptiveNURBS interpolation. Because traditional algorithm is easy to break and beyond thelimited values in acceleration and jerk, an adaptive NURBS interpolation algorithmwith flexible acceleration and deceleration is presented which is based on thecharacteristics of the curvature. And this algorithm is divided into three phases,including acceleration, adaptive adjustment according to the curvature, braking inthe last. The algorithm presented is integrated into the developed controller ofintelligent CNC system, and it also has been verified its correctness with severalexperiments.