SIMULATION INVESTIGATIONS OF ELECTROHYDRAULIC DRIVE CONTROLLED BY HAPTIC JOYSTICK

Transcription

1 KOMISJ BUDOWY MSZYN PN ODDZIŁ W POZNNIU Vol. 8 nr 4 rchiwum Technologii Mazyn i utomatyzacji 8 NDRZEJ MILECKI SIMULTION INVESTIGTIONS OF ELECTROHYDRULIC DRIVE CONTROLLED BY HPTIC JOYSTICK In the paper a control of electrohydraulic drive made by human operator which ue a pecial haptic joytick i preented. On the bai of main equation decribing electrohydraulic drive, it imulation model i propoed. To thi model a implified model of human operator i added. The paper preent the ytem tability problem which can occur when in communication with operator, force feedback joytick with magnethoreological fluid brake i ued. The choen imulation reult are preented and dicued. Thee reult how that when the operator decreae hi force a a reult of drive movement reitance increae, the tability problem may occur. The advantage and diadvantage of decribed communication and control method are hortly demontrated. Key word: electrohydraulic drive, haptic joytick, imulation, tability. INTRODUCTION The term haptic i ued to indicate the preence of force feedback from the manipulated object to the operator. The aim of haptic interface i to render the mechanical featur of the object on the uer. Haptic operation can be very valuable, becaue it can help the human to perform a tak more time effectively and more reliably []. In order to achieve a good ytem everal iue have to be taken into account in the deign of haptic interface and controlled drive. The mechanical part of joytick hould exhibit low inertia and friction, but the controlled movement oppoite force hould be imultaneouly big enough. From the control perpective, tability i an important iue, becaue the preence of a human operator in a control loop include additional, not clearly and not tationary defined factor [, 3]. Thi can lead to tability problem. dditional influence on both accuracy and tability i caued by quantization of joytick and drive poition and force produced on their output. The tability of the ytem can be epecially viible when the drive contact tiff wall, then thee non-idealitie, together with limited band- Prof. dr hab. inż. Intitute of Mechanical Technology, Poznan Univerity of Technology. The tudy wa upported by Polih Minitry of Science and Education a a grant no 4T7B9.

2 54. Milecki width of the ytem can lead to ocillatory behavior, what can detroy the illuion of contact to the environment or even may be harmful to the operator. In the paper the application of joytick with force feedback to control of electrohydraulic drive i propoed. In uch joytick, controllable device able to interact with human arm, wa applied. The propertie of magnetorheological (MR) fluid enable to deign brake with controllable output force [4]. The paper preent the contruction of a joytick in which uch a brake i applied. In the paper, the apect of co-operation of electrohydraulic drive ytem controlled by human operator, which ue a force feedback joytick are conidered. To analyze the tability, the human operator and the drive are treated in the model a a linear ytem.. MODEL OF HYDRULIC DRIVE Electrohydraulic ervo drive are non-linear ytem, but in many theoretical analye they are treated a linear one. So, in mot of approache electrohydraulic ervo drive are decribed a fifth order ytem, coniting of valve decribed by econd order ytem and cylinder decribed by ocillatory element with integrative one (ee Fig. ) [5]. More tied with the hydraulic drive phyical behavior theoretical model can be made by following way. The et of equation decribing the electrohydraulic ervo drive can be written a follow [4]: Q( = Q ( + Q ( Q ( () h + where: Q valve flow (load flow), Q flow balancing the flow compreibility, Q h cylinder aborptivity, Q v leakage flow. v V V v(, y( Q Δp Q p = p p = T T x ( k z u( Fig.. Hydraulic drive Ry.. Napęd hydrauliczny Subtituting appropriate linear or linearized equation one obtain K x( K V Δ p( = E d Δ p( dy( + dt dt Qp l + K Δ p( v ()

3 Simulation invetigation of electrohydraulic drive controlled by haptic joytick 55 where: K Qp valve flow gain [m /], K l valve flow-preure coefficient [m 5 /(N )], Δp preure difference in a cylinder, E fluid bulk modulu [MPa], cylinder piton cro-ectional area, K v leakage coefficient, V average contained volume of each cylinder chamber. The motion of the ytem can be decribed by following equation d m y( dy( + D = Δp( (3) dt dt where: y piton poition [m], m ma, D vicou damping coefficient (Newtonian friction) [N m ]. The control valve can be decribed a econd order ytem decribed by equation d x dx kzωzu ζ zωz ωz dt where: x pool diplacement, k z the valve gain, ω z valve natural frequency, ζ z valve damping ratio, u input ignal [V]. = x (4) dt u Valve k z ω z +ζ z ω z +ω z x K Qp F obc Q Δ p F - y y E / V /m - - K v +K l D Fig.. Model of electrohydraulic drive Ry.. Model napędu elektrohydraulicznego Baing of preented above equation a block model i build (Fig. ). Their parameter can be obtained from catalogue (tep repone, frequency characteritic) and calculated on bai data characterizing the application (cylinder dimenion, load, friction coefficient, oil bulk modulu etc). The preented above model hould be extended by adding valve control card model. Becaue the elec-

4 56. Milecki tronic control unit i uually very fat in comparion to the hydraulic part, o it could be decribed only by proportional element. 3. MODEL OF ELECTROHYDRULIC DRIVE CONTROLLED BY HPTIC JOYSTICK Different device like crane, lift, excavator are often controlled directly by human, which ue different lever or joytick to aign the drive poition or force. In mot of thi application viual and ound ignal are ued by the operator a a feedback. However, in mot cae it would be advantageou, to have additional feedback like feeling the force, produced by the controlled drive [,, 3]. It eem that having it, the operator will be able to control the ytem more accurately. Haptic device and interface became an important and popular theme in robotic with the development of the virtual reality technology. In the work of human in the virtual reality, haptic interface will enhance the full interactivity by force feedback. The goal of haptic application i to enable a uer to touch, feel, and manipulate different object the environment of the controlled ytem. In the early ninetie of XX century, ignificant progre ha occurred in ability to model and imulate haptic interaction with virtual object in real-time. Coil Gap MR fluid Fig. 3. Concept of MR brake with valve mode Ry. 3. Hamulc MR wykorzytujący tryb zaworowy Fig. 4. Photo of a joytick Ry. 4. Dżojtik In the performed invetigation, joytick with MR fluid brake i deigned, build and ued. Thi joytick ue a brake with the valve mode (ee Fig 3 and 4). In Fig. 5 model of an electrohydraulic drive controlled by haptic joytick i hown.

5 Simulation invetigation of electrohydraulic drive controlled by haptic joytick 57 The whole ytem conit of a joytick with MR brake and poition meaure element (potentiometer or rotary encoder), electrohydraulic valve with it control card, and of hydraulic cylinder. The joytick and the valve control card are linked to the control computer by input/output card. dditionally, into the model of a drive ytem, a human operator i included. He oberve the drive and it environment and by thi way create poition outer feedback. There i aumed, that operator take a input ignal the drive poition, which hould be obtained by the piton. So, thi feedback can be regarded a poition one. However, there i the quetion, how to model the dynamic propertie of an human operator. It aumed that in ome imple cae, operator can be modeled a firt order ytem, with a time contant equal to, ec. nother feedback loop i the force feedback, created by the brake in the joytick and the human operator. The dynamic propertie of thi feedback can be modeled by two erially connected firt order ytem: one for MR brake and the econd for human operator. The operator generate the electrohydraulic drive input ignal a the difference of ignal created by poition feedback linkage and force feedback linkage. Operator Feedback by obervation: Poition feedback Force meaurement Haptic joytick Force feedback Input / output card Valve control card Hydraulic upply Diturbance Obtacle Fig. 5. Model of electrohydraulic drive controlled by haptic joytick Ry. 5. Model napędu elektrohydraulicznego terowanego za pośrednictwem dżojtika typu haptic 4. ELECTROHYDRULIC DRIVE CONTROLLED BY HPTIC JOYSTICK STBILITY INVESTIGTIONS The made out in Matlab-Simulink oftware imulation model of the decribed above hydraulic drive ytem with force feedback and human operator i hown in Fig. 6. In thi model following electrohydraulic drive parameter are applied: piton cro ection area: =,8 m, flow coefficient: K Q =. m /, leakage coefficient: K v = 9 m 5 /(N ),

6 58. Milecki linearization coefficient: K l =.7 m 5 /(N ), cylinder tiffne: E /V = 8 Pa/m 3, dynamic friction coefficient: D = N /m, ma: m = kg. Servovalve wa decribed a econd order ytem with damping coefficient ζ z =.5 and with natural frequency ω z = Hz. There are few additional important quetion regarding the human being included into the drive feedback: how will the operator behave when the force on the joytick arm will increae? Will he increae or decreae hi reaction (force and joytick arm movemen on thi change? In the firt cae (operator increae hi force), a poitive feedback loop will be created, what can lead to intable behavior of the whole drive ytem. nother problem, concern to the control principle, which will an operator in force feedback loop follow. In imple cae he can act imilarly to PID controller, with not clearly defined non-linearity. Thi nonlinearity i omitted and in preented below imulation, linear PID controller are ued to model human operator behavior. The firt of them repreent the poitioning control, and the econd one the force control. In Fig. 7a the diturbance force generated according to the firt order ytem tep repone curve i hown. The generation of thi force tart one econd after the tart of imulation. In Fig. 7b, the curve how the tep repone (poition change) of the drive with only poition feedback linkage. The curve and 3 preent the drive repone with poition and force feedback loop. In the firt cae (curve ) the operator decreae hi force when the drive meet an obtacle. In the econd cae (curve 3), the operator increae hi force, when he feel that the drive oppoite force increae. One can note, that when the operator decreae hi reaction on drive oppoite force appearance, the ettling time decreae. In otherwie cae, the drive repone i fater but the ytem can eay became intable. In preented above imulation invetigation, human operator wa modeled a PI controller in poition loop and a only D controller in force feedback loop. In Fig. 8 the imilar invetigation reult are preented, but here operator in force feedback loop wa modeled a PD regulator. In thi cae, when the operator decreae hi reaction, the drive doe not reache the aumed poition (curve ) but when the operator increae hi force, the output ignal i bigger than the aumed on. In intuitive behavior operator will probably decreae hi force when he feel the increae of the joytick force, but after a while, when he recognize that there i nothing dangerou, he will increae it in order to overcome problem with the movement. Thi can lead to intability.

7 Simulation invetigation of electrohydraulic drive controlled by haptic joytick 59 Clock 5.5+ To Workpace Step Diturbance Force To Workpace F.8 PID Operator poition controller 3.+ Human Fop Human-Force +4+ Tranfer Fcn To Workpace3 Operator force controller KQ MR brake -K- -K- E/V Integrator3 Kl+Kv -K-.5 /m D 5 Integrator Integrator.3.+. PID.+ Scope Poition meaurement Fig. 6. Made in Simulink imulation model of electrohydraulic drive controlled by haptic joytick Ry. 6. Wykonany w programie Simulink model napędu elektrohydraulicznego terowanego za pośrednictwem dżojtika typu haptic t

8 6. Milecki a) b) F. y Fig. 7. Simulation reult: a) diturbance force, b) ytem tep repone Ry. 7. Wyniki badań ymulacyjnych: a) iła zakłócająca, b) odpowiedź napędu Fig. 8. Step repone obtained when operator wa modeled a PD controller Ry. 8. Odpowiedzi kokowe uzykane podcza modelowania operatora za pomocą regulatora PD 5. CONCLUSION The invetigation have hown the baic feature and propertie of control of electrohydraulic drive, made by human operator which ue force feedback joytick. In uch application, the main quetion i how thi operator will behave when the drive will meet an obtacle and the movement oppoite force uddenly occur. In dependence of thi, the ytem can became intable or the poition error can be increaed. However, thi obervation are made when human operator wa modeled only a linear PID controller, what can be truth only partially. In fact, human operator hould be regarded a complicated intelligent ytem, able to overcome mentioned above problem.

9 Simulation invetigation of electrohydraulic drive controlled by haptic joytick 6 REFERENCES [] dam R. J., Hannaford B., Stable haptic interaction with virtual environment, IEEE Tranaction on Robotic and utomation, 999, vol. 5(3), p [] Harward V., Haptic ynthei, in: Proc. 8th International IFC Sympoium on Robot Control, SYROCO 6. [3] Li P. Y., Toward Safe and Human Friendly Hydraulic: the Paive Valve, SME Journal of Dynamic Sytem, Meaurement and Control,, vol., no. 3, p [4] Milecki., Ławniczak., Ciecze elektro- i magnetoreologiczne oraz ich zatoowania w technice, Poznań, Wydawnictwo Politechniki Poznańkiej 999. [5] Milecki., State pace model of electrohydraulic ervo, rchiwim Technologii Budowy Mazyn i utomatyzacji, 3, vol. 3, no.. Praca wpłynęła do Redakcji Recenzent: dr hab. inż. Zbigniew Kęy BDNI SYMULCYJNE NPĘDU ELEKTROHYDRULICZNEGO STEROWNEGO DŻOJSTIKIEM Z SIŁOWYM SPRZĘŻENIEM ZWROTNYM S t r e z c z e n i e W artykule opiano terowanie napędem elektrohydraulicznym przez operatora za pośrednictwem dżojtika typu haptic. Na podtawie równań opiujących właściwości napędu tworzono jego model ymulacyjny. Dodano do niego uprozczony model operatora. Wyniki badań ymulacyjnych pokazują, że ytem może być nietabilny podcza terowania za pomocą dżojtika z iłowym przężeniem zwrotnym. Zamiezczono i omówiono przykładowe rezultaty ymulacji oraz wkazano wady i zalety terowania napędem za pomocą dżojtka. Słowa kluczowe: napęd elektrohydrauliczny, haptic dżojtik, ymulacja, tabilność