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节能型液压挖掘机的液压装置的设计,节能型,液压,挖掘机,装置,设计
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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. q1998 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 quitelimitedto 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 00045-4()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 48Fig. 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 characteristicswxwas 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-w xcally admissible ones 9 , particularly in the case ofmore advanced earth cutting processes.Another approach, based on kinematically admis-w xsible 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:11sysqsyssinyc coss01. .121222where: cmaterial cohesion,winternal frictionangle.The flow rule takes the form:EGs.i jsl2 .i jEsi j.where Gsrepresents a plastic potential.i jIn 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 line6,7 , theFig. 1. Typical deformation of cohesive soil in the case of the advanced shoving process realised by the horizontal tool motion theoretical.solution .()L. Ponecki et al.rAutomation in Construction 7 1998 401411403different 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 shown2,6,7,10thatsuch 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 results12are shown inFigs. 2 and 4 for equal amount of dug out material.about 600 Nin 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;cadvanced 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.angleas458. 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 anglesas308, 408and 508. The valuesas408 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 ofas308, the specific unit energy is muchhigher than foras408 andas508even 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 .()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 coordinates()L. Ponecki et al.rAutomation in Construction 7 1998 401411405and 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 standwx1517enables, 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 intervalscorrespondingtoseveralsamplingperiods.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 the settingmodel was too fast for the real excavator to movesynchronously. The path nodal points, used for thecontrol systems of the fixture cylinders position, arepresented also in Fig. 4. The setting model path, themachine fixture path, and values enabling for quan-tity assessment of the reproducibility of the plannedtrajectory are presented in Fig. 5. Values markedJ, Jand Jare mean errors of the fixture cylin-lwlrll.ders positions planned and realized position during()L. Ponecki et al.rAutomation in Construction 7 1998 401411406Fig. 4. The following phases of the excavator fixture trajectory prescribed using the setting model.the motion. Values Jand Jshows maximalxMaxyMaxdifference in horizontal and vertical direction. Fig. 6shows changes of cylinder lengths of the settingmodel derived on the basis of signals coming from.positionometerssolid lineand calculated by thecontrol system cylinder lengths changes of the K-111.fixture dashed line , and the error response during.the fixture motion dotted line . The runs referring to . .the boom are marked by indexw , armrand .bucket l .The differences between the runs of signals fromthe setting model and the set points for real fixtureresult from the method of time parametrization onthe basis of the assumed feeder output motion of the.setting model exceeds the real fixture possibilities .4.3. The tool moement along straight linesIn presented case, the coordination of the fixturecylinder movement was realized by hardware, thatmeans using the setting model. It can also be realizedby software. The machine operatorusing special.buttons , can generate horizontal or vertical toolmovement preserving the constant value of the toolcutting angle in every point of the machine workingspace. The prescribed tool path is stored using thepoint method in the configuration space. Further-()L. Ponecki et al.rAutomation in Construction 7 1998 401411407.Fig. 5. The setting model path Xu, Yu and the machine fixture path X, Y for prescribed trajectory.more, the machine operator determines motion veloc-ity which is corrected by control system taking intoaccount the feeder output. In Figs. 7 and 8, results ofsuch control for the horizontal tool movement areshown. The cutting tool trajectory is presented inFig. 7. In Fig. 8, the fixture cylinder lengths calcu-.Fig. 6. The changes of cylinder lengths of the setting model solid line , calculated by the control system cylinder lengths dashed line , and.the error response during the fixture motion dotted line .()L. Ponecki et al.rAutomation in Construction 7 1998 401411408Fig. 7. The cutting tool trajectory for horizontal motion.lated for prescribed velocity are drawn with solidline. Their calculated lengths assumes the feederoutput are drawn with dotted line. The way of thetool path time parametrization was similar to thatusing the setting model. It is seen that velocitiesgiven by the operator are too high and system cor-rected cylinder motion timing to keep assumed feederoutput. The example of the tool motion along theinclined line is presented in Figs. 9 and 10, whereFig. 9. The cutting tool trajectory for inclined motion.the tool trajectory and corresponding cylinder lengthsare drawn. Such movement is realized as a sum ofhorizontal and vertical tool motions the line inclina-tion depends on proportions between horizontal and.vertical velocities . For example, the tool trajectoryalong inclined line can be realized during the.withdraw stage of the shoving process Fig. 2 tofollow the slip line or for automated, making the soilscarps.Fig. 8. The fixture cylinders calculated lengths for prescribed velocity solid line and calculated lengths assuming the feeder output dotted.line .()L. Ponecki et al.rAutomation in Construction 7 1998 401411409.Fig. 10. The fixture cylinder lengths calculated for prescribed velocity solid line and calculated lengths assuming the feeder output dotted.line .4.4. Automatic tool moement along a slip lineAnalysis of experimental results of the soil shov-ing process shows that it is possible to predict theo-retically the slip lines positions and energeticallyoptimal tool trajectories. It can be done for homoge-neous material under laboratory conditions. In realsituations, when material is not homogeneous andFig. 11. The horizontal force vs. horizontal displacement and tool trajectory for the model slip line detection.()L. Ponecki et al.rAutomation in Construction 7 1998 401411410Fig. 12. The magnified fragment of Fig. 11.not well-defined, the material sleep lines has to bedetected automatically.The procedure of automatic slip line detection isbased on the observation that when cutting toolbegins to penetrate more dense material, then theincrease of the horizontal force acting on the tool isobserved. Such situation takes place also when thetool tip moves from the slip linewhere material.density is quite small to the virgin material material.not deformed beforebehind the slip line . Hence,the observed increase of the pushing force can beused for slip line detection. Such procedure, whichsimplified version is described below, can be real-ized as follows.Cutting tool motion is realized as a sum of hori-zontal, vertical and rotational movements and hori-zontal reaction of the soil is measured and followed.Firstly, the tool moves horizontally up to the momentwhen the horizontal force drops, that coincides withcreation of slip lines system originating from the tool.end Fig. 1 . If such slip lines cannot be created as aresult of horizontal pushing, a special procedure for.example tool rotation can be applied. Then, tool ismoved vertically by prescribed displacement valueand then moves again horizontally rotation of the.tool can be added up to the moment when horizon-tal force begins to increase and exceeds definedvalue. If so, tool is moved once more vertically by.described displacement , and then horizontally, andso on. This way, the tip of the tool automatically.follows in a step way the slip line.Results of such preliminary tests are presented inFigs. 11 and 12. As a simplified model, the possibil-ity of automatic tool movement along the soil scarpinclined with 0.61 rad. was investigated. For definedvalues of maximum horizontal force and definedvertical displacement, the control system automati-cally followed the tool along the scarp. The horizon-tal force vs. horizontal displacement and tool trajec-tory are shown in Fig. 11. The magnified fragmentof Fig. 11, which shows the way in which system isacting, is presented in Fig. 12.5. ConclusionsExperimental results show that presented controlsystem fulfils all described requirements and can beused as the machine operator assist. It enables forprecision tool guidance, automatic repetition of real-ized movements, realization of specific tool trajecto-.ries including energetically optimal paths and auto-()L. Ponecki et al.rAutomation in Construction 7 1998 401411411matic improvement or optimization of realized paths.Tool trajectories can also be prescribed using thesetting model, making excavator the machine ofteleoperator class. Presented system can be used as abasis for real machine control system.AcknowledgementsThis research was sponsored by the Project KBN7T07C00412 Optimization of the soil shoving pro-cess due to heavy machines of an excavator typerealized at Kielce University of Technology.Referencesw x 1 D. Szyba, W. Trampczynski, An experimental verification ofkinematically admissible solutions for incipient stage of a . .cohesive soil shoving process, Eng. Trans. 4231994243261.w x 2 A. Jarzebowski, J. Maciejewski, D. Szyba, W. Trampczyn-ski, Experimental and theoret
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