机电类外文翻译【FY107】数控系统辅助液压挖掘机的概念【PDF+WORD】【中文6600字】
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.Automation in Construction 7 1998 401411A concept of digital control system to assist the operator ofhydraulic excavatorsL. Ponecki), W. Trampczynski, J. CendrowiczAbstractA concept of digital control system to assist the operators of hydraulic excavators is presented and discussed. Then,control system based on described ideas was mounted on a special numerically controlled stand, equipped with DrA andArD converters, where small hydraulic backhoe excavator K-111 fixtures were used. Experimental results shows that itfulfils all described requirements and can be used as the machine operator assist. It enables for precision tool guidance,.automatic repetition of realized movements, realization of specific tool trajectories including energetically optimal pathsand automatic improvement or optimization of realized paths. Tool trajectories can also be prescribed using the settingmodel, making excavator the machine of teleoperator class. Presented system can be used as a basis for real machine controlsystem. q 1998 Elsevier Science B.V. All rights reserved.Keywords: Digital control system; Hydraulic excavators; Tool trajectories1. IntroductionThe automation of heavy machines, including hy-draulic excavators, began in mid-1970s and waspossible due to invention of real time controllers andhydraulic elements with good dynamic properties.The first excavator equipped with several mechatron-ics systems, which was shown as a working model,was the excavator FUTURE prepared by Orensteinand Koppel for BAUMA83 Fairs. Since that time,machines equipped with systems automating the en-gine operation, pumps operation, machine fixtures,machine diagnostic, etc., are presented and offered.Such systems bring real help to the operator andclear economical profit. For example, LIEBHERRR902 excavator equipped with LITRONIC System.has for a trench digging the efficiency 40% higher)Corresponding author.and unit costs 30% lower, than similar machinewithout such automatic system. Although automation.in some case, optimization of several machine sys-tems develops quite fast, the main machine processthe shoving processhas no proper understandingand description until now. Its automation is quitelimited to systems repeating already performed.movements, laser levelling systems, etc. and sys-tems optimizing such processes are not developedyet. Quite new experimental results show clear ideafor energetically optimal tool trajectories in the caseof cohesive materials. The tool tip has to be guidedalong slip lines, which are generated from the tiptool during the previous stage of the shoving process.To realize such trajectories for practical purpose andreal machines, it is necessary to build a specialcontrol system for the tool motion, which enablesautomatic realisation of such trajectories as well asrealisation of other tasks that help the operator.0926-5805r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.PII S0926-5805 98 00045-4nts()L. Ponecki et al.rAutomation in Construction 7 1998 401411402Taking into account up-to-day heavy machines de-velopment, such system has to fit for digitally con-trolled electro-hydraulic drives. The concept of suchcontrol system, and verifying experimental results,are presented in this paper.2. The optimization of tool trajectorieswxIt was experimentally found 1,2 that in the caseof earth-moving process due to heavy machine tools,the cohesive material deforms to generate rigid zones.sliding along the slip lines well visible cracks alongwhich the material substantially changes its parame-ters the initial cohesion c decreases to the residual.value close to c s0 . In the case of the simple toolrpushing process perpendicular wall, the force-dis-placement relation shows that the horizontal forcegrows as the process advances, but in an unstablemanner. The moment of reduction of the force coin-cides with creation of a kinematical mechanism orig-inating from the tool end. Such mechanisms arecreated periodically and can be described theoreti-cally using kinematically admissible mechanisms ofwx .the theory of plasticity 48 Fig. 1 .A lot of effort was made to describe the soilcutting process within the theory of plasticity, wherethe problem of active pressure exerted by a rigidwall on a granular medium under plane strain condi-.tion can be assumed as a simplified model for soilshoving. In such case, the method of characteristicswx was used 3,9 and several theoretical solutions for.statics and kinematics were obtained under the as-sumption of rigid-perfectly plastic soil behavior. Al-though a number of boundary value problems weresolved in this manner, there exist several limitationsin obtaining complete solutions or even the kinemati-wxcally admissible ones 9 , particularly in the case ofmore advanced earth cutting processes.Another approach, based on kinematically admis-wxsible mechanisms, was proposed later 5 and appliedfor the description of more advanced earth shovingwxprocesses 6,7,1012 .Let us discuss the problem of plane strain rigidwall shoving presented schematically in Fig. 1. As-suming the material to be rigid-perfectly plastic andto obey the CoulombMohr yield criterion:11s ys q s ys sinyc coss01 . . .12 1222where: cmaterial cohesion, winternal frictionangle.The flow rule takes the form:E G s .ij sl 2 .ijEsij.where G s represents a plastic potential.ijIn the case when potential is described by the.yield criterion Eq. 1 , the associated flow rule isassumed, when another function is taken, the flowrule is non-associated.Using this approach and assuming a change ofwxmaterial parameters within the slip line 6,7 , theFig. 1. Typical deformation of cohesive soil in the case of the advanced shoving process realised by the horizontal tool motion theoretical.solution .nts()L. Ponecki et al.rAutomation in Construction 7 1998 401411 403different kinematically admissible solutions for arigid wall shoving process can be proposed and thesolution predicting minimum energy is searched.Kinematically admissible solution for rigid wallshaped as letter L is presented in Fig. 1. It showsmain effects observed experimentally. As the processadvances, the horizontal force grows in unstablemanner and the moment of reduction of the forcecoincides with creation of a kinematical mechanismoriginating from the tool end. Such mechanisms arewxcreated periodically. It was shown 2,6,7,10 thatsuch theoretical predictions describes quite well themain effects observed experimentally.Taking into account experimental observations andtheoretical solutions, it is possible to show experi-mentally that as soon as slip lines are created withincohesive material, the energetically most effectiveway of the tool filling is to follow previously createdwxslip line by the tip of the tool 12 . Experiments werewxperformed on a special laboratory stand 1,12 underplane strain conditions, using an artificial material,imitating a clay and its parameters. It consisted of:cement50%, bentonite20%, sand18% andwhite vaseline12%, and was characterized by thefollowing parameters: ws248 internal friction an-.3gle , gs18.4 kNrm . Application of white vase-line, as one of the components, resulted with obtain-ing a cohesive soil, which parameters were not influ-enced by air humidity and liquid flow. It also en-sured that those parameters were stable during allexperimental program.wxTypical experimental results 12 are shown inFigs. 2 and 4 for equal amount of dug out material.about 600 N in a following way. The L-shaped.Fig. 2. Experimental program for slope sample: a model of the.tool and slope; b initial stage of the processhorizontal move-.ment; c advanced stage of horizontal movement and various.trajectories; d the final stage of the process.Fig. 3. Values of specific work for different inclination of thewithdraw lines in the case of two-phase piece-wise trajectory.tool, inclined at an angle of 58 simulating the cess, LAs180 mm was first pushed into slope.to a certain position Fig. 2b . When the tool wasadvancing, the slip lines were created periodicallyfrom the tool tip to the material free boundary, at the.angle as458. In the next phase withdraw phase ,the tool tip was moved along three different straight.lines Fig. 2c , with simultaneous rotation of the tool.Fig. 2d to have it filled with the material. Thosestraight lines were inclined at angles as308,408and 508. The values as408 and 508 were close tothe inclination of slip lines created during the tool.horizontal pushing process Fig. 2c . It means that insuch case, the end of the tool was moved almostalong the slip line, where material cohesion c sub-stantially dropped as a result of material softeningduring the slip process.Specific energy of those processes for differentpreliminary horizontal displacements, chosen to en-sure similar amount of dug out material in every test.600 N , is shown in Fig. 3. It can be seen, that inthe case of as308, the specific unit energy is muchhigher than for as408 and as508 even over.100% . Hence, conducting the tool tip along the lineinclined at the angle similar to the angle of slip linesinclinations, the specific energy of the earth-fillingprocess can be significantly reduced.Experimental results shows that in the case of.cohesive soil earth-moving process: 1 material de-forms as rigid zones sliding along the slip lineswhere material substantially changes its parameters. .cohesion ; 2 moving the machine tools along pre-viously created slip lines, one can substantially save.energy used for earth-moving processes tool filling .nts()L. Ponecki et al.rAutomation in Construction 7 1998 401411404This observation can be the basis for the optimiza-tion of the filling process.3. The basic concept of the computer aided con-trol systemIt was shown before that analyzing the mechanicsof the soil deformation during the shoving process, itis possible to determine energetically optimal cuttingtool trajectories. Hence, the automatic tool move-ment along slip lines generated in cohesive materialhas to be a quite important option of proposedsystem. It should also enable precision tool guidance,automatic repetition of already realized movements.for example, teach-in , realization of some toolmovements impossible to realize manually, etc.Taking into account to-day experience with au-tomation of heavy machines, such system should beconstructed to assist machine operator, who stillplays a main decisive and control role. Hence, theproper separation of tasks, between the control sys-tem and the operator, is necessary.Such control system for excavators was built onlaboratory scale. Its basic assumptions can be statedwx .as follows 13 : 1 operation of the central controlsystem is based on cooperation of two digital sys-tems. The first one controls directly the motion ofthe machine fixture using the control system of thehydraulic cylinders position. The second one works.out control signals for the first one. 2 Under thestandard work conditions, action of the proportionalhydraulic valves of the fixture cylinders is controlledthrough the computer. The direct operator control is.possible only in case of emergency conditions. 3The feedback between the machine environment andcontrol system is realized through the operator. Heparticipates continuously in the process of the con-.trol of machine fixtures motion. 4 For realization ofthe tool motions which are impossible for manualcontrol, the operator has a possibility to coordinatedisplacement of separate cylinders by means of hard-.ware or software. 5 The operator has a possibilityto switch into automatic control of the fixture motionto realize a special tool trajectories. For example, itcan be energetically optimal tool trajectory wheretool tip moves along slip lines or specific trajectory.realized and stored previously. 6 The optimal cut-ting tool trajectories can also be realized as correc-tion of trajectories given by the operator. Such cor-rection is done mainly during the time parametriza-.tion of the tool path. 7 The trajectories given by theoperator can be corrected by the system to take intoaccount such limitations as geometrical ones, maxi-mal power of the pump, maximal output of thepump, maximal pump efficiency, etc.Presented concept is based on such cooperationbetween the operator and control system that thefixture movements are controlled by the operatorwhile the control system corrects him or, whenordered, can act automatically.4. Examples of the control system functioningThe control system based on described aboveideas was mounted on a special numerically con-trolled stand, equipped with PC computer havingCrA and ArC converters, where small hydraulicwxbackhoe excavator K-111 fixtures were used 1417 .The control system of the fixture motions utilizes thecontrol system of the cylinder positions. The fixturecylinder displacement is controlled by the propor-tional hydraulic valves fed by the variable outputmulti-piston pump.The control system for fixture cylinders is basedon three control systems, each to control differentcylinder displacement using PID or state controllerswx14 . It enables control of the fixture motions usingdifferent methods of the tool trajectory planning,measuring of acting forces and displacements anddetermining other magnitudes related to the fixturemovements. Experimental data acquisition is alsopossible.One of quite important problems, which should betaken into account when building the control system,is the way of the tool trajectory planning. It is. wxrealized as usually in two steps 15 . In the firstone, the trajectory shape is planned and determined.In the second one, the trajectory curve is parametrizedin time in a determined manner, what defines thetrajectory within the generalized coordinate space.On this basis, the time runs of the generalized coor-dinates describing the configuration space of themachine are determined. In the case of an excavator,lengths of hydraulic cylinders are those coordinatesnts()L. Ponecki et al.rAutomation in Construction 7 1998 401411 405and then they are used as signals for control systemto reproduce planned trajectory. Some system abili-ties are described below.4.1. The tool moement along prescribed lineThe control system build for experimental standwx1517 enables, among others, programming thework motion in the excavator work space, or in itsconfiguration space, using point to point technique.In this method, the coordinates of the initial and finalpoints, and sufficient number of the characteristicnodal points, are defined. Values describing thispoints are then introduced to the system, whereremaining points of the trajectory are calculated us-ing interpolation methods. Linear or the third degreepolynomial interpolation is used. The trajectoryparametrization in time can be realized through:determination of the total trajectory run-time andits division into individual segments of the path.System calculates the velocities of cylinders,determination of the run-time between followingnodal points, taking into account some limitations.or conditions for optimization .In the case of standard excavator construction, itis quite difficult to precisely realize trajectories,where simultaneous movement of two or three cylin-ders is necessary.4.2. The tool moement using the setting modelAnother method of controlling the fixture motionis to control using the setting model. It is somehowsimilar to the manipulator unit in robotics. The con-wxtrol is carried out by means of the phantom 18 ,understood as a kinematic duplicate or the model ofthe machine kinematics, equipped with systems mea-suring the motion parameters. The excavator con-trolled in this manner becomes the machine of tele-wxoperator class 19 .The setting model is the model of K-111 excava-tor fixture, situated on the plate, made in scale of1:10. Three potentiometers are located on the rota-tion axes of the model element. Signals from thesepotentiometers allow us to determine the configura-tion of the fixture. Mechanical end stops are pro-vided to the model, to limit the rotation angles ofindividual fixture elements to the values obtained inthe K-111 excavator fixture. The special switch acti-vates the system.The setting model is used only for planning of thetool path and during its movement the tool trajectoryis registered using the point method. The trajectorypoints are registered when:the sum of the cylinder length increments, com-paring with former position, is higher than as-sumed,time of data registration is later compared withformer registration time.Points of the path are registered at constant timeintervals, excluding the fixture stoppage. The pathnodal points are defined by the corresponding fixturecylinder lengths. Other path points are calculated bycomputer applying the linear interpolation in theconfiguration space. Deviation of the path calculatedin this way from that marked by the setting modelcould be disregarded at the nodal point intervalscorresponding to several sampling periods.Parametrization of such path is realized on the basisof the assumed output of the hydraulic feeder. Hence,the system operates through nodal point registrationand determination on the basis of the already de-scribed nodal points and assumed output of the.feeder of the set points for the control system of thefixture cylinder positions. If the motion of settingmodel is slow, for the properly assumed feederoutput, the real excavator fixture moves like itsmodel. For faster motions, the path planning ad-vances its realization by the real excavator fixture.Experimental results for the fixture motion con-trolled by setting model are presented in Fig. 4,where following phases of the excavator fixture tra-jectory prescribed using the setting model are shown.Dashed lines refers to the setting model, solid linesrefers to the real excavator fixture and points refersto the path nodal points. In that case, with theassumed feeder output, the motion of
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