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YZC3振动压路机振动轮设计,YZC3,振动,压路机,设计
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Frame Design and Reality of On2line Quality ControlSystem for CNC Machining Center Based on MicrocomputerLiu Xiaosheng(刘晓胜) , Zhou Shuang , Wang Haoyu , Ma Yulin(School of Mechatronics Engineering , Harbin Institute of Technology ,Harbin 150001 , P. R. China)AbstractAfter giving a short review of the methods used for detecting and monitoring in general sys2tems , this paper describes the way of communication between computer and Computer NumericalControl (CNC) Machining Center (MC) . Based on these , the paper addresses the means of per2forming in2cycle measurement for manufacturing quality , provides an approach of improving thestate of manufacturing process by achieving the real2time change of control parameters accordingto the level of manufacturing process , and discusses the technique of implementing in2process di2mensional errors compensation corresponding to the in2cycle measurement. The results of the ex2periments show that the frame design is successful and the operation is reliable. The system istaking shape nowadays.Key words : Detection , Monitor , Compensation , In2cycle measurement , On2line quality con2trol , Manufacturing process1. IntroductionOn2line quality control of manufactur2ing processes is deemed essential in many ad2vancedmanufacturingsystems ,suchasFlexible Manufacture System(FMS) , Com2puterIntegratedManufacturingSystem( CIMS ) ,AgileManufactureSystem(AMS) , etc. , and it lays the technicalfoundation fortheGlobalManufacturingSystem(GMS) in the near future. In orderto carry out on2line quality control , peoplehave developed lots of detecting and moni2toring systems for manufacturing processesin the past decades , and to some extent ,some of them met the requirements of indus2trial production. Yet , some of them are justin laboratories , and few ofthem couldachieve the compensation of dimensional er2rors.As various new and advanced tech2niques appear , such as neural networks ,fuzzy control , chaos theory , Wavelet theoryand so on , some new kinds of detecting andmonitoring systems containing these newtechniques are being developed and appliedin actual manufacturing processes with bet2ter effects1 - 4. These systems usually con2sist of a detecting subsystem , a monitoringsubsystem and a faults2diagnosing subsys2tem. In this paper , a complete frame of de2tecting , monitoring , diagnosing and com2pensating the processes conducted on themilling/ boring machining center , named In2telligentInspectingandMonitoringandCompensating System Based on Microcom2puter (IIMCSBM) is given , and the meansfor its detailed implementation is also given.As a part of this system , the in2cycle mea2surement subsystem is one of the vital sub2systems ,andthein2cyclemeasurementbased on high2precise probe and linear grat2ing sensors is a feasible and effective methodfor manufacturing process in present techni2cal conditions5. In this paper , we providethe description of our efforts towards the im2plementation of in2cycle measurement forquality control. Before these , a way of com242High Technology Letters , Vol. 4 , No. 2 , December 1998Supported by the National Defense Foundation of China.Received Feb. 9 , 1998.munication between the computer for moni2toring and MC is given , which is the hard2ware foundation for the follow2up work. Onthe basisof these , we concentrate our effortsparticularly on implementing the compensa2tion of dimensional errors and the improve2ment of operating conditions by real2timechanging of control parameters , such asspindle speed(cutting speed) , feed rate anddepth of cutting , which are closely related tothe tool wear and the chatter and greatly in2fluence on the surface finish and the dimen2sional accuracy of the product. The systemframe is illustrated schematically in Fig. 1.Fig. 1Schematic diagram of on2line quality control on the boring/ milling MC2. Communication between Microcomputerand MCWith the rapid development of the soft2ware and hardware techniques , microcom2puter has been widely used in various indus2trial applications.The communication be2tween computers is the paramount founda2tion in FMS , CIMS , AMS or similar sys2tems , and it has become a relatively maturetechnique. However , the communication be2tween computer and MC is not easy becausemost of them are originally not designed forthat purpose. Although most of machiningcenters have a serial interface ( RS232C) ,which is directly connected to the numericalcontroller , the interface can be only used totransfer the parts programs and can not givecommands to the machine in most cases6.So the particular interface unit which can re2alizes the connection between the computerand MC must be found out , whose scheme isshown in Fig. 2. Our experiments are con2ducted on Hurbo CNC BMC 20L machiningcenter.The Specific Communication Inter2face Unit (SCIU) for this MC consists oftwo parts given as follows:High2performance multi2function dataacquisitioncard( AdvanTech ,PCL2818HG, with 100000 samples per secondA/D Conversion rate , 16 SE or 8 differen2tial input channels , 322channel digital input/output) : it is used to collect the sensors sig2nals of the conditions of MC in the wholemanufacturing process , transmit 32 digitalinput/output signals , and accept the inter2rupted signal of trigger probe.SpecificCommunicationInterfaceComponent (SCIC) : it is developed by us torealize many functions , such as signal isola2tion , signal transference , signal transforma2tion , etc.With this system and RS232C in themachining center , the following operations52High Technology Letters , Vol. 4 , No. 2 , December 1998Fig. 2Parallel and serial communication between PC and MCcan be performed with the microcomputer :simulating the console of MC;downloading a part program to MC;starting or stopping the machiningcenter ;setting dynamically the control param2eters for manufacturing process;driving the probe to travel to carry outin2cycle measurement ;driving the tool shifting for cutting tocompensate the dimensional errors.In general , the control mode based onthe console of the machining center can betransferred into the mode of PC , which canemulate the machine console , and programthe control procedure.Though usually themachine is not totally controllable from theSCIU based on PC , most crucial operationscan be started from the PC.3. In2cycle Measurement and CompensationSystemInspecting the dimensional informationof the product is the key step to ensure thehigh product quality.Although there aremany methods to achieve on2line or real2timedetecting in automatical systems , some de2fects usually exist in these systems. For ex2ample , the applications of the CoordinateMeasuring Machines(CMM) with a contacttrigger probe to the dimensional inspectionare restricted to the parts made of hard ma2terials, such as steel7and it is difficult toperform the on2line inspection because thecomponent must be remounted and fixed onthe table of a machine tool. The non2contactinspection means based on integrated laser orCharge2Coupled Device ( CCD) are usuallyexpensive and difficult to put into practice inactualmanufacturingconditions8.Al2though the advanced MC is often equippedwith the Touch Trigger Probe ( TTP) sys2tem , it is not easy to transmit the dimen2sional information about the product fromthe machine tool to the computer connectedwith the MC.3.1Driving the probe or the tool to travelIn order to drive a probe or a tool totravel according to the commands given bythe control computer , we have developed theSpecial Driving Card for Probe Tool ( SD2CPT) , which is the basis of implementingthe in2cycle measurement and the real2timeor on2line compensation of dimensional er2rors. It includes the following functions:selecting the X/ Y/ Z dimension for theprobe or the tool to shift ;driving the probe or the tool to travelrapidly in the direction of the selected di2mension mentioned previously;driving the probe or the tool to travelslowly in the minimum step of a pulse signalin the direction of the selected dimensionmentioned previously;changing the direction of traveling re2versibly when it accepts the probe switching62High Technology Letters , Vol. 4 , No. 2 , December 1998signal and keeps traveling reversibly for ashort distance to prevent the probe fromwearing when it leaves the measured compo2nent ;changing the spindle speed to improvethe condition of manufacturing;changing the feed rate to realize thesame goal just as the above one.The hardware structure of SDCPT isschematically shown in Fig. 3.Fig. 3Hardware structure of SDCPT3.2Inspecting for dimensionsIn2CycleMeasurement BasedMicro2computer ( ICMBM) is the automatic mea2surement or gauging of a component con2trolled by a computer while the component isclamped in the machining position whichfeeds back in2cycle quality data to the com2puter for inspecting and controlling.Thisform measurement may also include auto2matic component setting , tool setting andtool condition monitoring. Our ICMBM sys2tem consists of the following parts:contact probe sensor ( high2precisioncontactprobedevelopedbyourselves ) :sending a switching signal to SDCPT whenit touches a component ;X/ Y dimentional linear displacementgrating sensors and related second2signal2transform meter (GX2A type , manufacturedby theChineseAcademy ofSciences) :pointing out the coordinate positions of X/ Ydimension in Binary Coded Decimal(BCD) ;parallel interfaces card for grating sen2sors ( AdvanTech ,PCL2733 ,322channelIsolated Digital Input Card) : transmittingthe dimensional information from grating in2to control computer ;Special Driving Card for Probe or Tool(SDCPT) (designed and developed by our2selves) : giving means to drive the probe ortool to travel according to the commands giv2en by the computer ;microcomputer and software embed2ded in the microcomputer for measuring orcompensating programs: imitating the con2sole of MC and commanding the MC operat2ing. It is the kernel of the IIMCSBM. Thewhole in2cycle measurement system struc2ture is schematically shown in Fig. 4.From Fig. 4 , we can easily see thatwhen the probe traveling encounters theworkpiece , the trigger signal is transmittedto the probe interface , which filters the con2tact bounce noise by RS flip flop and con2verts the trigger signal into the SDCPT , and72High Technology Letters , Vol. 4 , No. 2 , December 1998the computer can read the dimensional infor2mation ofthe product immediately fromgrating sensor interface when it accepts thetrigger signal through SDCPT. At the sametime , the computer may assign the path forthe probe moving through the SDCPT , andthe computer can appoint the various veloci2ties of shifting the probe according to thedistance between the location of the probeand the location of the product. So this sys2tem can bring about two dimensional auto2matic measuring and checking functions , de2viations from tolerances , determining feedsfor finishing and so on.Fig. 4In2cycle measuring and compensating system used in the CNC machine tool3.3Compensating for dimensionsUnder the current technical conditions ,it is difficult to carry out real2time or on2linecompensation for dimension errors because itis very difficult to implement directly the re2al2time detection for dimensional errors andmodify the program which is being run byCNC.When the dimensional errors exceedingthe tolerances by means of in2cycle measure2ments as mentioned previously is discovered ,we must decide whether a fallout comes outor not.If previous material removal is toolarge , the dimensional errors can not becompensated by any consequent operations ,so what the system can do is only to abandonthe consequent manufacturing to alleviatethe loss of work time. If not that , the sys2tem can automatically set up the manufac2turing parameters and generate the compen2sating program for dimensional errors ac2cording to the detected results and geometri2cal features of the product. After that , thesystem restarts the compensating program.When we can model the tool wear correctly ,and identify the tool wear reliable as men2tioned later , the real2time compensation fortool wear can alsobe implemented.Ofcourse , this method of compensation is onlyeffective to a certain degree.4. On2line Monitoring SystemDuringthemanufacturingprocess ,there are many factors affecting the finalquality of the product at every step of the to2tal manufacturing process. After numberousexperiments and researches were con2ductedfor productquality , we found thattoolwear , chatter and workpiece temperaturehave great influence on the surface finish andthe dimensional accuracy of the product.Hence , on2line continuous estimation of toolwear , identification of the chatter , and de2tection of the temperature are of great engi2neering importance. The on2line monitoringsystem is schematically shown in Fig. 5.They lay the foundation for compensation ofdimensional errors and change of the controlparameters.82High Technology Letters , Vol. 4 , No. 2 , December 1998Fig. 5On2line monitoring system in the CNC machine center4.1Multi2signal f usionOn the one hand , the spindle drivingcurrent signal and the feed driving currentsignal , which can be easily picked up by cur2rent sensors , usually include the informationrelated to tool wear and workpiece vibra2tion2, and vibrating signals picked up byvibration sensors also contain the informa2tion of tool wear and chatter.With thesetwo different kinds of signals , the error rateof identification of tool wear and chatter isreduced rapidly. So in our experiment sys2tem , we used three current sensors (one isfor spindle driving current , and the othertwo are for X/ Y direction feed driving cur2rent) and two vibration sensors(X/ Y direc2tion on workpiece) . On the other hand , thethermal changes caused by high2speed cut2ting sometime make the workpiece deformedto produce defective products in some de2gree10 - 11. In order to keep a stable processcondition and adjust the parameters of man2ufacturing , we monitored the change of oiltemperature in the oil bank of MC throughthe whole process. All of the three parts ofsignals are successively transferred into fil2ters , amplifiers , A/ D converters , and com2puters , and the signal feathers are extractedfrom the signals of the sensors by Wavelettransforms3, which lay the foundation ofreal2time process status control.More de2tailed software information about this will beintroduced in another paper.4.2Chatter controlChatter has a great influence on thesurface finish and dimensional accuracy ofthe workpiece , and in some extreme situa2tions it may result in damaging the machinetool and theworkpiece.Thetraditionalchatter control process usually involves thefollowing steps1:(1) stopping the feed and spindle rota2tion immediately after detecting chatter ;(2) changing the process parameters tobring the behavior to a desirable level.When the Artificial Intelligent Diagno2sis System (AIDS) in our experimental sys2tem detects the undesirable chatter existingin the manufacturing process , the abnormalcutting process is interrupted immediately bystopping the feed rapidly through SDCPT ,and the original spindle speed remains un2changed. Then AIDS resets the new processcontrol parameters (cutting speed , Feed ,Depth of cutting) to bring the behavior to anoptimal level after calculating according tothe process dynamics model.5. Concluding RemarksThis is mainly a complex experimentalsystem. We started our research and built up92High Technology Letters , Vol. 4 , No. 2 , December 1998our preliminary frame of the system in early1996. First , we built our fundamental hard2ware systems for detecting and measuringafter fully consulting about the structure andthe functions of the system. Then , we con2centrated our efforts on searching the way toachieve the process control and errors com2pensating. Next , we conducted experimen2tal studies on building the models of toolwear and chatter , and establishing the struc2ture AIDS. Although we have developed theframe of the on2line quality control system ,our research on AIDS is just started , and westill have many researches to do , while havenot reached economic viability.We hopethat they will mature soon with new theoriesand techniques through our work in the nearfuture , and could meet the needs of actualindustrial applications.References1 Bukkapatnam S T S , Lakhtakia A , Kumara SR T. Chaotic neurons for on2line quality con2trolinmanufacturing ,TheInternationalJournal ofA dvanced Manuf acturing Tech2nology ,1997 , 4(13) : 952 Soliman E , Ismail F. Chatter detection bymonitoring spindle drive current ,The Inter2national Journal of A dvanced Manuf actur2ing Technology ,1997, (13) :273 Li X L , Yao Y X , Yuan X J. On2line toolcondition monitoring system withWaveletfuzzy neural network ,Journal of IntelligentManuf acturing ,1977, (8) :2714 Malakcoti B B , Zhen Y Q , Evan C. Tandler ,In2process regressions and supervisin
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