Experimental Application of H Output-Feedback Controller on Two Links of SCARA Robot

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1 INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.5 NO. Jnury 6 ISSN (Print) ISSN (Online) Experimentl Appliction of H Output-Feedck Controller on Two Links of SCARA Root Adllh Frrge * nd Ahmed S. Ali Astrct The purpose of this pper is to experimentlly investigte of H roust control technique for SCARA root in the presence of uncertinties tht rise from neglecting some of the system dynmics (e.g., motor dynmics, sensor noise). In ddition, comprison etween roust controller nd the clssicl controllers, for instnce P, PD nd PID is introduced. The experimentl results show tht the system ecomes more stle with H control which cn simply dismiss disturnces when the system is prone to uncertinties thn clssicl lgorithms. Keywords H Roust control, SCARA root, conventionl control, DOF. I. INTRODUCTION Rootic mnipultors, nd in prticulr the Selective Complince Articulted Rootic Arm (SCARA) mnipultors, hve een widely used in the industril pplictions [ 4]. They hve een used to chieve high speed nd high-precision performnce nd processes such s pick-nd-plce, pinting, rushing, nd peg-inhole. Most of pplictions re restricted in their performnces due to limit vilility of controllers in the mrket tht re sed on system models. In fct, the roust control, for instnce H, hs ttrcted ttention of mny reserchers. This control hs een extensively studied s it offer roustness nd possesses cpility of disturnce ttenution in liner control systems [5 7]. Nonliner systems hve een lso treted within the context of Hmilton-Jcoi-Iscs inequlity nd the dissiptive system control theory [8]. In this pper, the model of the SCARA root is ccommodted sed on H control which is investigted experimentlly. The contriution of this pper consists of the ppliction of the H loop shping control method for the two degrees of freedom (DOF) of the SCARA mnipultor [9], []. H loop shping control proposed in []. This pproch hs lso compred with other types of conventionl controllers PD nd PID controllers to illustrte the performnce differences when the system is sujected to uncertinty nd disturnces. The rest of this pper is orgnized s follows: Section illustrtes the system modelling. Section 3 explins the model of the used control. Results nd discussion re estlished in section 4. Finlly, section 6 contins our concluding remrks. The rootics system dynmics, on the other hnd, still present ig chllenging control prolem. This cn e ttriuted to nonlinerities, uncertinties nd strong coupling of the root dynmics so the idel performnces for most industril pplictions demnd the vilility of the complete dynmics of the root. Nevertheless, in rel pplictions, the ignoring prts of the root dynmics or errors in the prmeters of the root my result inefficiency consequences in their performnces. Even in well-structured industril pplictions, indeed, roots re often suject of the structured uncertinty due to unknown lod, friction coefficients nd so on. The one nd only solution of this would e tht control lws hve to e designed sed on n estimted model, or on the specific roust control methods. Mechtronics Section, Mechnicl Engineering Deprtment, Assiut University, 756 Assiut, Egypt * The corresponding uthor, E-mil: dllhfrg@eng.u.edu.eg II. MODELING OF THE ROBOT The SCARA root hs een used to investigte H experimentlly. Generlly, there re mny efforts which hve een mde to ccommodte the precise control of SCARA root []. There re lso mny reserch try to rech the idel model of SCARA from mny decys [3]. Fig. illustrtes SCARA root which exists in the Mechtronics L, Fculty of Engineering, Assiut University, Egypt. It hs four degrees of freedom (DOF), i.e. wist swivel, elow swivel, roll nd verticl rm. The root is equipped with feedck position nd tchometer sensors for ech xis. The model of the root, indeed, is s set of rigid links connected in series with one end fixed to the ground nd the other end free.

2 INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.5 NO. Jnury 6 ISSN (Print) ISSN (Online) The links re connected vi either revolute or prismtic joints nd torque ctutor cts t ech joint. The dynmics model eqution of n n-link root, generlly, is given y: is n vector of joint torques, is the inerti mtrix, is n mtrix representing centrifugl nd Coriolis component, is n vector representing grvity, is n vector representing friction forces, re n vectors of joint positions, velocity nd ccelertions, respectively. The elements of the dynmic eqution () for the used root re found to e s following: () () (3) where,,,, is moments of inerti of electric motor, while re fctor of reduction ger, viscous friction nd coulom friction for joint. re the torque vlues for joint nd joint, respectively. III. H CONTROLLER MODEL An importnt ppliction of H control rises when studying roustness ginst model uncertinties. The control system is roustly stle in spite of certin kind of model uncertinties which cn e expressed quntittively in terms of n H norm ound which the control system should stisfy. H control, indeed, is one type of roust controls in which cn e rejecting the effect errors represented in the form of input disturnces. In this section we we discuss riefly the model H controller. Fig. shows generlized plnt nd controller connected together in the form of liner frctionl trnsformtion. A common design method is to construct the system P(s) in (5) (6) (4) Let e prtitioned conformlly with the prtitions of the trnsfer function of the system s shown in Fig.. Fig.. () the SCARA root, () two links plnr of the root.

3 INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.5 NO. Jnury 6 ISSN (Print) ISSN (Online) w u System description for generl H. Using the pcked mtrix nottion, let stte spce reliztion given y: In which P(s) -K (7) Fi g.. hs miniml (8) So the stndrd H control hs the following stte-spce. (9) () () is the stte of the system, is the H output control, is the disturnce vector, is the mesured output nd is the controlled output to e minimized. y z disturnces. In ddition, it is essentil in order to gurntee stisfctory ehvior no mtter the environmentl conditions. A clssicl PID controller which represents y: nd H re synthesized nd evluted in tking of ccount of the dditive disturnce (noise mesurement). The experimentl result of PD is given in Figure 3. In tht Figure we cn see the response in Fig (, c) nd the error signl of ech joint in Fig (, d). On the other hnd, the performnce of H controller is illustrted in Fig.4. By compring the three controllers, it cn e seen tht PID Controller decresed the stedy stte error of the system nd gives minor error with compred y the PD Controller. On the other hnd, the H controller offers good performnces s well in dynmics s in sttics. In ddition, the experimentl control signls of PD nd H controllers re shown together in Fig.5. V. CONCLUSION The purpose of this pper is to experimentl implemented H on two links of SCARA root. H is implemented in the presence of disturnces which result from nonlinerity nd uncertinties. It is lso compred to PD controller experimentlly. Experimentl results hve proved tht H hs roustness ginst externl disturnces nd uncertinties of modelling. The strtegy hs ility to ensure good roustness nd stility compromise s well s very good performnces. Acknowledgment The uthors re oliged to Mechtronics L. Mechnicl Engineering Deprtment, Assiut University for providing vlule resources nd devices to crry out this study. IV. RESULTS AND DISCUSSION The H controller is implemented on the SCARA root shown in the Fig. In this section, the proposed controllers re implemented in order to evlute its performnces. Experimentl tests re crried out for two joints of SCARA root, nevertheless they cn extent to. The root movement is uncertin, nd in prticulr the uncertinty of coupling terms nd nonlinerities of the model, which cn e very distured. The implementtion of the roust H control lw overcomes these vrious

4 INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.5 NO. Jnury 6 ISSN (Print) ISSN (Online) Response of PD controller for Joint.5.5 Error of PD controller for Joint Response of PD control for Joint Error of PD.5 controller for Joint c d Fig.3. Experimentl results (, c) the response of PD controller, (, d) represent the error signl Response of H infinity controller for Joint.5 Joint..5 Error of H infinity controller for Joint Response of H infinity controller for Joint Error of H infinity controller for Joint c d Fig.4. Experimentl results (, c) the response of H controller, (,d) represent the error signl. 3

5 INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.5 NO. Jnury 6 ISSN (Print) ISSN (Online) Signl control of PD.5 Signl control of H infinity.5.5 N.m N.m Fig.5. Experimentl control signls () PD controller, () H REFERENCES [] S. Akmtsu, Position Control of -Link SCARA Root y using Internl Model Control, vol. 43, no. Jnury, pp , 9. [] M. Popescu, I. B. Ş. I, O. Olru, L. Ţ. A. Popescu, nd F. Grofu, The simultion hyrid fuzzy control of scr toot, vol. 3, no., pp. 5 4, 8. [3] Improving the Kinemtic Performnce of the SCARA-Tu PKM, IEEE, pp ,. [4] improving the kinemtic performnce of the scr-tu PKM, IEEE Int. Conf. Root. Autom., pp ,. [5] B. A. D. Mry, A. T. Mthew, nd J. Jco, Roust H-infinity (H ) Stiliztion of Uncertin Wheeled Moile Roots, Glo. J. Res. Eng. Electr. Elenc. Eng., vol., no.,. [6] M. Boukhnifer, A. Chiet, nd C. Lrouci, Experimentl H- infinity roust control of eril vehicle flight, 9th Mediterr. Conf. Control Autom. MED, pp. 4 47,. [7] K. Ales, S. Antonin, H. Jroslv, nd H. Mrtin, Automotive ctive suspension cse study on H-infinity control, Electr. Eng., pp , 3. [8] M. Yilmz, S. Mujee, nd N. R. Dhnsri, A H-infinity Control Approch for Oil Drilling Processes, Procedi Comput. Sci., vol., pp , 3. [9] S. Ddshi nd H. Tghird, H-Infinity Controller Design for A Flexile Joint Root With Phse Uncertinty, 39Th Int. Symp., pp , 8. []I. Levi, N. Bermn, nd A. Ailon, Roust dptive nonliner H<inf> </inf> control for root mnipultors, Proceeding Mediterr. Conf. Control Autom., pp. 6, 7. []P. Axelsson, A. Helmersson, nd M. Norrl, H -Controller Design Methods Applied to One Joint of Flexile Industril Mnipultor, Autom. Control, pp. 6, 4. []G. V. Ro, MODELING, SIMULATION AND ANALYSIS OF A SCARA ROBOT, ARPN J. Eng. Appl. Sci., vol. 9, no. 4, pp , 4. [3]B. S. K. K. Irhim nd A. M.. Zrgoun, Modelling nd Control of SCARA Mnipultor, Procedi Comput. Sci., vol. 4, pp. 6 3, 4. 4