平面磨床工作台位移的计算机控制系统.pdf

平面磨床工作台位移的计算机控制系统?刘贵杰1,2,巩亚东1,王宛山1(1?东北大学机械工程及自动化学院,沈阳 110004;2?山东轻工业学院机电系,济南250100)摘要:本文在普通液压缸和一组通用节流阀的基础上,设计了用于控制磨床工作台升降装置运动的计算机控制系统。该系统通过控制多个具有一定开口面积比电磁节流阀的通断组合,实现对升降装置运动规律的控制。由于采用了快速启动、匀速前进和缓慢接近目标点的运动规律,大大减小了目标点处惯性对工作台位移精度的影响,并通过自学习和微调控制策略实现了工作台任意位移量的精确控制。关键词:平面磨床;工作台位移;计算机控制系统;自学习控制策略0?引言目前国内生产用机床普遍落后,数控化率极低,少数几家数控机床生产厂的数控系统仍依赖进口。为了打破垄断,国内现已开始研制具有自主知识产权的机床数控系统,并取得了成功。为了实现机床数控化升级,多数厂家开始对原有普通机床进行数控化改造。众所周知,最高质量的磨床工作台位移控制是通过伺服系统实现的。然而伺服系统制造代价昂贵,对环境条件要求高。近几年来,人们采用开关阀,用计算机对气动或液压系统的速度和位移进行控制1,2,3,其中?PCM?控制采用一般的廉价通用阀门,却能得到较高性能的控制,为采用普通阀门进行位移控制开辟了一条途径。为了实现普通平面磨床的数控化改造,本文在普通双向液压缸和一组通用节流阀的基础上,设计了用于控制磨床工作台升降装置运动的计算机控制系统。该系统通过控制多个具有一定开口面积比电磁节流阀的通断组合,实现对升降装置运动规律的控制。由于采用了快速启动、匀速前进和缓慢接近目标点的运动规律,大大减小了目标点处惯性对工作台位移精度的影响,并通过自学习和微调控制策略实现了工作台任意位移量的精确控制。实验证明工作台位移误差小于 0?02mm,可满足一般精度要求的平面磨削加工,而且具有成本低和可用高级语言编程的优点。1?系统的总体结构、硬件组成及工作原理(1)系统的总体结构及硬件组成系统的总体结构框图见图 1 所示,由图可知,整个系统控制硬件主要有辨向电路、功率放大电路和接口电路等几部分组成。?辨向电路。编码器的辨向电路图如图 2 所示,它由74LS74 和 74LS08 两块集成电路芯片组成。其中74LS74 是两路 D 触发器,其功能是当C 端上升沿到来时,Q 取D 端的值,在其余时刻,Q 保持原值,Q 是Q 的反。编码器送出的两路脉冲A 与 B是相位相差90?的方波脉冲(见图 3),向上运动时,A 波超前 B 波90?,向下运动时,A 波滞后 B 波 90?。这样,当活塞向上运动时,接入D 触发器C 端的 A 波上升沿对应送图 1?系统总体结构框图入D 端的 B 波的低电平。因此,Q 为 0 而 Q为 1,反之,当活塞向下运动时,Q 为 1而 Q 为 0。集成电路片74LS08是 4个与门组成的,将 Q 信号送入一个与门的一个输入。Q 接入另一个与门的一个输入,再将方波A、B分别接到两个与门的另一个输入,于是当向上移动时,左边与门一端输入为 Q=1。其输出将随另一输入A 方波的变化而变化。因此,向上运动时的脉冲序列由此与门输出送入CTC0。此时,右边与门的一个输入接 Q=0,无论另一输入如何变化,其输出都只能为0。同理,向下移动的脉冲序列由右边与门输出送入CTC3。图 2?辩向电路图 3?方波脉冲?功率放大电路。功率放大电路如图 4 所示。集成芯片74LS06 由6 个非门组成,其作用是使 PIO A 口发出的电压信号取反,同时增大驱动能力以使固态继电器中的发光二极管充分导通。当PIO 输出的信号为?27?机床与液压?2001?No?6?国家教委科学技术研究重点资助项目(200032)作者简介:刘贵杰,1968年生,山东轻工业学院副教授、东北大学机械工程及自动化学院博士生;王宛山,1946年生,东北大学副校长、机械工程及自动化学院教授、博士生导师。1 时,经非门后,其相应的输出为 0,固态继电器中的发光二极管正向导通,双可控硅导通,使所接的电磁阀线圈通电。图 4?功率放大电路(2)系统工作原理泵产生的高压油,经过控制阀的控制与油缸的两腔相通。由图 1 可知,当电磁铁 13 通电,电磁铁 12断电时,油缸上腔进油,下腔排油,活塞向下移动。反之,当13断电,12 通电时,活塞向上移动。活塞移动的速度,取决于进入油缸液体的流量,而流量可以通过节流阀 4、5、6、7 进行调节,由电磁铁 8、9、10、11 的通断组合确定。6 个电磁铁的通断,由计算机的输出进行控制。本系统中利用输入输出接口片PIO 的A 口作为字节输出,对其进行控制。当某一位输出为 1(高电平)时,通过反向器和固态继电器,使交流电磁铁通电。当输出为 0(低电平)时,使其断电。活塞在移动时通过附件带动光电编码器的轴转动,光电编码器的轴每转一转,可以产生960个方波脉冲。在活塞运动的过程中,光电编码器输出的方波脉冲不断经辨向电路送入计算机内的定时/计数器 CTC。其中上行的脉冲数送至 CTC0,下行的脉冲数送至 CTC3。计算机不断从 CTC得到脉冲数,感知目前活塞移动的距离,将它与指定的位移距离值比较,从而确定发出的移动速度码。一般来说,当离设定距离较远时,使活塞以较高速度移动,越接近目标值,速度越慢直至停止。活塞及推动的负载有惯性,如果位移到设定距离时,才发出停止码,实际上的距离会大于设定距离。因此,应当给出一定的提前量,此提前量在负载不同时大不相同。因此,在本系统中采用了?自学习?的方法,由计算机自动确定,并在运动过程中不断调整,以保持停止位置的精确度。2?控制策略1,2,5(1)控制码生成算法本系统中采用了自学习和微调控制策略。在本系统中,节流阀 4、5、6 的开口面积比调为 1?2?4,两位两通电磁阀 8、9、10的不同的通断组合,可形成 7 种不同速度。阀 7 的开口调整的很小,当只有阀 7 打开时,油缸活塞移动的速度很慢,因此系统实际具有 8种不同的速度。可以按照下面的控制算法产生控制码:C=CINT(yd-yyd?70?5?yd-yyd?7?710yd-yyd?7 0,则提前停止,若?y 0,则推迟停止,这样不断减小?y 值,可使误差收敛到一定范围内。当系统的负载改变时,只要停止位置有误差,计算机就能立刻觉察,并加以修正。3?实验结果分析通过实验我们发现,实验结果与文献 1 在气动方面所做的实验结果十分相似,并且油缸位移控制精度比文献 1 关于气缸位移精度更高,可达到0?02mm。系统的稳定性与两个因素有关:一是活塞与缸壁之间的静摩擦力所造成的死区非线性;二是微调阀7的节流口面积,微调节流口面积越大,对系统稳定性越不利。4?结论(1)用本系统控制平面磨床工作台位移,成本低精度高;(2)最终采用微调控制方式,可得到较高的位移重复精度(=0?02mm);(3)控制程序可用高级语言编制,具有开放性;(4)由于静摩擦力的影响,进一步提高系统精度难度较大,有待进一步研究。(下转第135 页)?28?机床与液压?2001?No?6字积分法,用中断的方式完成,两个流程间用一个标志变量来协调。(1)粗插补主流程完成粗插补运算,采用改进的时间分割法,先根据事先输入程序中的信息判断探头在这一程序段中是否需要旋转及旋转的角度,然后根据插补周期和插补速度确定插补步长,计算出在每个插补周期内各轴移动的位移增量和终点坐标,如图 4所示。图 4?粗插补软件流程图 5?插补周期的分配(2)精插补精插补以中断的形式进行,主要完成脉冲分配和脉冲发送,具体地说,就是将粗插补计算出的探头在一个周期内需要旋转的角度和各个轴需移动的位移转化成均匀的脉冲信号,在 T0至T1时刻发出控制探头旋转角度的脉冲信号,在 T1至 T2时刻发出控制探头位移的脉冲信号,如图 5所示。4?插补算法中的相关问题(1)插补周期的选择采用PC586 作为控制系统的核心,其 CPU 时钟频率为500MHz,探头焦距直径为?0?5mm,进给速度为25mm/s,因 PC586 的运算速度和高速数据采集卡的频率足够,所以采样周期的选择主要考虑探头的焦点直径。让步长?L 等于探头焦点半径,即?L=0?5mm2=0?25mm,又已知扫描速度为 25mm/s,所以插补周期 T为:T=?LF=0?2525=0?01s=10ms。(2)圆弧插补方法的实现插补中另一常见的线形是圆弧插补,与通用的插补方法不同的是,超声无损检测自动扫描系统插补中要求探头始终垂直于被检测点的表面,为保证检测精度,采用角度逼近圆弧插补法,其基本思想是:在每个插补周期中,根据其相等的插补周期半径矢量移动角?=FTR值,计算出该插补周期半径矢量与某一轴的夹角?i=?i-1+?值,据此计算出在每一个插补周期内探头需要旋转的角度?i和移动位移 Xi=Rcos?i/Yi=Rsin?i,对探头的方向和位置进行控制。其它曲线也可采用类似的方法,只要CPU 运算速度足够,使粗插补在一个插补周期内完成,就能使插补顺利完成。(3)传动间隙的补偿由于是开环系统,机械间隙不可能完全消除,系统必然存在传动间隙,间隙补偿采用先实测系统的反向间隙量,转化成脉冲个数,以参数的形式储存在控制系统中,用软件的方法加到控制程序中,使系统在反向时,先完成间隙补偿,再进行插补控制。5?结束语为了验证插补方法的正确性,采用五轴超声无损检测自动扫描装置,利用水浸检测法对图 1 所示零件进行超声检测,检测时采用逐行扫描方式,通过编程控制探头运动。实验证明,该法能够实现对复杂曲面的自动扫描,扫描速度、精度均满足要求,检测效果良好。参考文献?1?毕承恩主编?现代数控机床?北京:械工业出版社,1991?2?廖效果等主编?数字控制机床?武昌:华中理工大学出版社,1995收稿时间:2001-08-16(上接第 28 页)参考文献:?1?宁?舒?气动位移系统的计算机?PCM?控制初探?液压与气动?1991(1):18-22?2?刘贵杰,丁?红,宁?舒,智能气缸设计?机械工程师?1997(5):27-28?3?刘贵杰,黄桂丛,程?强?气缸位移自学习控制研究?机械工程师,1999(6):21-22?4?程建中,张忠波,冯李合,黄效国,高精度液压微调控制系统?液压与气动,1991(2):18-21?5?刘贵杰,巩亚东,王宛山,基于交流异步电机驱动磨床进给位移的自学习控制?东北大学学报,2001?22(3):268-270?收稿时间:2001-07-05?135?机床与液压?2001?No?6MACHINE TOOL&HYDRAULICSNo?6,2001(Total Issue No?174)Abstracts and Keywords in English?Identification of dynamic coefficients of activemagnetic bearingsShen Yueet al(8)?Abstract:There is different identification means between magnetic bearing and common bearingbecause of different structure.This paperidentifies cotructuresefficients of magneticbearing-rotorsystemviamulti-frequency current excitation method andleast-squaremethod.Thesimulation proves that thisidentificationmethod is simpleand satisfactory precision is obtained.Keyword s:Magneticbearing-rotor system;Multi-frequency current excitation method;Least-square method;Parameter identificationModelingmethods forFMS distributed&hierarchical control systemZhou Binghai(10)?Abstract:A FMS distributed&hierarchical control architecturehas been constructed in this paper.On the basis of indicated above,the analysis and modeling methods of FMS distributed&hierarchicalcontrol system have been proposed.To obtain the ability of partly autonomy and the uniformcommunicational interface in each of functional entities,the software architecture model of the controlsystem is proposed ontheCORBA infrastructure.Keyword s:Distributed&hierarchical control;Modelingmethods;Control software;CORBAAnalysis of Resultant Forces C oefficientin Radial MagneticBearingS un S houqun(13)?Abstract:The precision expressions arepresented for thereultant forces coefficient KRof thegreatestcarryingcapacity Fm axunder normal and unmoral operating of radial magnetic bearing.All kinds of effectfactorsand the sensitivity are analyzed.The result of an application example indicates that KRis thefunction of magnetic polesNP,bearing clearanceSOand radial displacementxof rotor departure frombalancepoint.Keyword s:Radial magnetic bearing;Electro-magnetic bearing;Resultant forces coefficient;Createst carrying capacityA numerical solution for the aeronauticbevel gearelastohydraulic lubrication problem in pointcontactWang Yanzhong(15)?Abstract:The traditional Newton finiteelement method is ameliorated.Combiningtraditional Newtonfiniteelement methodwith decliningmethod,theGauss method is applied for the calculation of elasticitydistortion in elastohydrodynamic lubrication.The practicable weighted Newton finite element method isfound.Theconvergenceof numerical calculation and thesuitabilibyof engineering deignfor point contactelastohydrodynamic lubrication is solved.Thenumerical solutionof elastohydrodynamic lubrication is givenout witin therangeof multifarious parameters.Keyword s:Point contact elastohydrodynamic lubrication;Weighted Newton finite element method;Bevel gearResearch on the high response two-degree eletrohydraulic position servo systemYeZhengmao(20)?Abstract:In order to analyze thefrequence reponse and time-domain response performance of thetwo-degree electrohydraulic position servo system of the two-stage electrohydraulic active vibrationisolation control system,thetransfer function andbond graph modeling and simulatingmethod is applied.The simulation results show that thetwo-degree electrohydraulicpositionservosystem responds veryfast.The experimental results show that both the transfer function model and bond graph model of the two-degree electrohydraulicposition servosystem are right.Keyword s:High response;Two-degree electrohydraulic position servo sytem;Two-stageelectrohydraulic active vibration isolation system;BondgraphmodelA study on ergonomics integrated method in product developmentLi Guiqin(22)?Abstract:Ergonomics activities in product development are described based on a schematicrepresentation of product design cycles.A method of integrating ergonomics with theproduct design cycleis put forward,it makes thesuccessful optimizationof products and their user interfaces possibleas it helpsergonomic aspects systematically embedded into the product design cycle.Finally,these ergonomicsactivities arediscussed formajor ergonomicdesign and evaluation tasks.Keyword s:Ergonomics activities;Product life cycle;User interfaceObject oriented inversedinematic calibration method of the variable-axes numerical controlmachine tool(VNCMT)Shi C hanghong(25)?Abstract:In this paper,theconstant zero-line of rotation error during calibration is definedbasedon the idea of error separation and theanalysis of tool path.Besides,for the position errors of the jointcenters on thebase arevery difficult to gain directly,an simple indirect mothod,named object orientedinversekinematiccalibration(OOIKC),is presented.Moreover,a new concept of gradual calibration isbrought forward.Keyword:The variable-axes numeric control machine tool;Stewart platform;Object oriented;CalibrationComputercontrol system for displacement of worktable of plane grindingmachineLiu Guijie(27)?Abstract:An approach of improvinggeneral grindingmachinebycomputerwas presentedand thePC-basedcontrol systemwas designed in this paper.Computer control system for displacement of worktableof planegrindingmachine is designed by using usual fluid cylinder and aset of general throttles in thispaper.This system can control worktable to move according to definite moving disciplinarian throughcontrolling electromagnetism throttlewith definite opening area to open or close.By fast startup,evenvelocitymoving andslowlyneartarget point,theinfluenceof inertiacanbededuced,andthedisplacementprecision can beincreased greatly.The precision control of arbitrariness displacement of worktablecan berealized by the self-studying control principle andslender adjustment strategy.Keyword s:Plane grinding machine;Worktable displacement;Computer control system;Self-studying control strategy.Parametrized converted cam-contour and automatically generatedNC codeTan Zheli(29)?Abstract:Themotion formula of driven part was converted into cam-contour by the autolisp,thentheNC codewas generated in the mastercam.It couldget rid of the error and trouble caused by manualpoints drawing and curve fitting,which provided apractical method for cam designing and manufacturingthat is complicated,precise and high speed,and for cam parameterized design.Keyword s:Cam;Contour;Parameterization;ManufactureAnalysis and optimization of gyro moment in nutation drive of bevel differentialYu Yibin(32)?Abstract:Nutation is introduced into gear drive.On the basis of dynamics,computing method ofgyromomment in nutation drive of bevel differential is presented.Furthermore,a new kind of optimalmetbod is given usingMATLABOptimization Toolbox.Keyword s:Bevel gear;Differential teeth;Nutation drive;Gyro moment;MATLAB;OptimizationToolboxNumerical calculation and analysis of flowfield forhydraulic integrated blockGao Dianrong(34)?Abstract:In this paper,finite element method is used to simulate the flow field of hydraulicintegratedblock which is widely used inhydraulictechnique,and thestructureof theflow fieldis given inthevisualized picture,withproviding thetheoretical basefor the analysis of energyloss andtheoptimizeddesignof flow channel.Keyword s:Integrated block;Finite element method;Flow channel;Flow fieldDesigning line-incision programmingsystem on AutoC AD by using DelphiL?u Wenge(36)?Abstract:This paperrecommends themethodthat how touseDelphi languageto second-design line-incision programming system on AutoCAD.Keyword s:AutoCAD;Delphi;Line-incision programmingsystemA forward force(Moment)recursive equation of roboticmanipulatorbased on 6-dimensionwristforcesensorGan Fangjian(38)?Abstract:TheNewton-Euler backward force(moment)recursive equation of robotic manipulator isinvalidatedwhen Robotic Manipulator acts on unknown environment because of unknown acting force(moment).Inthis paper,aforwardforce(moment)recursiveequationof roboticmanipulator is givenbasedon6-di mensionwrist force sensor,and,a kinetic behavior is analyzed and investigated based on 6-di mensionwrist forcesensor.Keyword s:Roboticmanipulator wrist force sensor;Force(moment);Recursive equationThetheoretical research on steam promoting burning in coal-fired boilerWang Wenkui(41)?Ab stract:The paper presents the theory of steam to promote burning,reduce pollution and save energy.The establishment of chemical and physical models of steam promoting burning proves that the theory isfeasible.Keyword s:Boiler;Steam;Promotingburning;Reducing pollution;Saving energyVariablestructurecontrol of PMBDCLi Jiangcheng(48)?Abstract:In this paper,aiming at large load inertia and variable electromotive parameter of theelectric vehicle,variablestructurecontrol is used in thespeed and acceleration control of PMBDC.whichimproved therobusticityof thesystem.Computer simulation provedthat this kind of control has not onlyexcellent control performance,but also rapid running speed andreal-time performance.Keyword s:PMBDC;VSC control;Electric vehiclePID control with2 degrees of freedomin electrohydraulicservo systemCao Jian(54)?Abstract:This papaer describes the filter type incomplete differential PID control algorithm with 2degrees of freedom and carries out simualtion analysis in accordance with the characteristic of hydraulicservosystem in flight simulationswivel-table.Results show that it is superior to traditional PID controllerin performance and improves greatly system performance.Keyword s:Flight swivel-table;ElectrohydraulicservoPID with2 degrees of freedom?Design of the ultrasonicrotatinghead with air bearingChen X uemei(56)?Abstract:Becausegas viscosity is very small,air hydrostatic bearing has such advantages as lowfrictions,high rotational accuracy of spindle,stability,reliability,nowear either pollution,and long lifeetc.For use in high speed ultrasonic rotating head and CNC ultrasonic rotating machine tool,airhydrostaticbearing is advantaging and applicable.This paper describes mainly operation principle anddesignmethodof theultrasonic rotatingheadwith air bearing.Keyword s:Air bearing;Ultasonic rotating;DsignReal-timemanufacturingbased on reverse engineering and rapid prototypingXu Xianliang(65)?Abstract:This papers show anew manufacturing system named RealtimeManufacturing,which is akindof digit manufacturingsystem that integrate3-Ddigit measuring technologyand modeling technologywith rapid prototyping.And byapplying it,thedesign andmanufacturing of product not onlywould be avery flexibleintelligent progress highly integrated and automated,but alsowouldbecome soshort that thecorporations could havea very quick feedback to themarketplace.Keyword s:Realtimemanufacturing;Reverse engineering;RapidprototypingThedesign of numerical control systemforNC curling machineZhu Huayuan(68)?Abstract:The basic frame,the software and controlling features of the numerical control curlingmachine are intro