Position Control Method For Pick And Place Robot Arm For Object Sorting System

Transcription

1 Poston Control Method For Pck And Place Robot Arm For Object Sortng System Khn Moe Mynt, Zaw Mn Mn Htun, Hla Myo Tun Abstract: The more ncrease the number of ndustres n developng countres, the more requre labourers or workers n that. To reduce the cost of labour force and to ncrease the manufacturng capacty of ndustres, the advanced robot arms are more needed. The am of ths journal s to elmnate the manual control for object sortng system.robot arm desgn n ths research uses two jonts, three lnks and motors to drve. Mcrocontroller s used to generate requred PWM sgnal for motors. In ths research the poston control of robot arm was desgned by usng knematc control methods. There are two types of knematc control methods whch are forward and reverse knematc methods. In forward knematc method, the nput parameters are the jont angles and lnk length of robot arm and then the output s the poston at X,Y,Z coordnate of tool or grpper. In nverse knematc, the nput parameters are poston at X,Y,Z coordnate of grpper and the lnk length of robot arm and then the output parameters are the jont angles. So, knematc methods can explan the analytcal descrpton of the geometry moton of the manpulator wth reference to a robot coordnate system fxed to a frame, wthout consderaton of the forces or the moments causng the movements. For sortng system, Metal detector s used to detect the metal or non-metal. Ths poston control of pck and place robot arm s fully tested and the result s obtaned more precsely. Keywords: knematc analyss, Mcrocontroller, motors, Robot arm, sortng system. I. INTRODUCTION A robot s an electromechancal devce connected wth jonts and lnks, drven by motors or actuators, guded by sensors and controlled through a software program, to manpulate and handle parts, tools for preformaton varous operatons n many dfferent knds of work envronment. Followng the Karel Capek s drama, R.U.R. (Rossum s Unversal Robots), n whch automatons n human form carred out arduous tasks, robots made ther ndustral debut n 1960s. Snce ths advent of robots n the ndustry, numerous and multfaceted research and development strdes n robotcs have been wtnessed. Also, as the world contnues to engage n ntense and sophstcated technologcal operatons and actvtes, and n many specfc applcatons, robot arm has ncreased sgnfcantly.[1] And then, robot arm s very useful n many dfferent applcaton areas such as ndustry; some dangerous works ncludng radoactve effects. There are four manly robot confguratons such as 1.Cartesan robot, 2. Cylndrcal robot, 3.Polar robot or Sphercal robot and 4.Jont arm robot or artculated robot. And several types of robot manpulators have been developed n tmes past; examples of these are the Tomorrow Tool (T3), ntroduced by Cncnnat Mlacron, Inc. n 1974, the Programmable Unversal Manpulator for Assembly (PUMA) developed by Vctor Schenman at the poneerng robot company Unmaton, the Selectve Complant Artculated Robot for Assembly (SCARA), the AdeptOne robot by Adept Technology, Inc., the Shuttle Remote Manpulator System (SRMS), etc. One of the vtally mportant functons of a robot manpulator n the ndustry s a pck-and-place operaton, such as, lftng a payload from wthn ts work space, carryng t to a predetermned poston and then releasng t. For nstance, Sanjay Lakshm Narayan who worked on[2] Poston Control of Pck and Place Robotc Arm, whch s a 5-DOF artculated robot arm for real-tme moldng machne operaton; Karl Berntorp proposed the applcaton of a moble robot wth knematc redundancy for future pck-and-place operaton n the grocery stores; [3] Bnbn Lan showed how the dmensonal parameters of a 2-DOF parallel manpulator could be optmzed to realze hgh-performance pck-and-place operaton; n order to obtan effectve pck-and-place operaton, Altuzarra O proposed two desgn methods for a mechancal drve whch would yeld an ncreased end-effector angular range; and Bn Lao et al. carred out an optmal desgn of a three-degree-of-freedom planar revolute-chan parallel manpulator wth a vew to mprovng ts operatonal velocty and accuracy for pck-and-place tasks.[5] The confguraton of robot arm n ths journal s smlar to artculated robot arm whch has three revolute jonts and rregular workspace.the advantages of artculated robot arm are hgher reach from base, useful n contnuous path generaton, appled to weldng operaton and reachng the congested small openngs wthout nterference. The rest of journal s presented as Secton (II) explans Methods usng n research and Secton (III) show Analytcal calculaton. After that Secton (IV) buld system block dagram and next Sectons are testng expermental results and observaton. Fnally, Secton (VIII) presents the concluson of ths journal. II. METHOD USING IN RESEARCH Robot knematcs method s the study of the moton (knematcs) of robots. In a knematc analyss, the postons of all the lnks are calculated wthout consderng the forces that cause ths moton. In the knematc analyss of manpulator poston, there are two separate problems to solve: drect knematcs and nverse knematcs. Robot knematcs s the study of the moton of robotc mechansms. Snce the performance of specfc manpulator tasks s acheved through the movement of the manpulator lnkages, knematcs s the fundamental mportance n robot desgn and control. A knematc equaton provdes the relatonshp between the jont dsplacement and the resultng of end effector poston and orentaton. The problem of fndng the end-effector poston and orentaton for a gven set of jont dsplacements s referred to as the forward knematcs problem. That s, the forward knematcs problem allows one to specfy n a unque manner the relatonshp between the (n x 1) jont vector θ. rmally; the forward Knematc equaton can be obtaned from the spatal geometry of the manpulator or by solvng certan matrx algebrac equatons. [4] The more ncrease the number of degrees of freedom (n), the more complex knematc equaton becomes. Hence, the requred amount of computaton to compute the poston of end-effectors can become qute large. Drect knematcs s for solvng the forward transformaton equatons to fnd the locaton of the grpper n terms of the angles and dsplacements between the lnks. Inverse knematcs means for solvng the nverse 57

2 transformaton equatons to fnd the relatonshps between the lnks of the manpulator from the locaton of the grpper n space. Table 1: lnk parameters used n calculated desgn Lnk d α θ a cos(α ) sn(α ) 1 d 1 90 θ θ 2 d θ 3 d θ = rotaton angles of each jonts d = dstance along Z axs α = twsted angle between successve jonts a = twsted length between successve jonts After assgnng all lnk parameters of robot arm, table 1 can construct. The lnk lengths as shown n Fg. 2 are L 1 = 6cm, L 2 = 12 cm, and L 3 = 21.5cm. Fgure 1: Structure of artculated robot arm desgn () Forward Transformaton Matrces Once the table1 s ready, the transformaton matrces are easy to fnd. Generally, the matrx of transformaton can be establshed from the relaton between successve frame to +1. Input Angles Forward Knematc Poston of Grpper Rotaton and translaton of arm matrx s A +1 =H(z,θ ). H tran (0,0,d ). H tran (a,0,0).h(x,α ) Lnk Parameters cos A +1 = sn 0 0 cos sn cos cos sn 0 sn cos cos sn cos 0 a cos a sn d 1 output Angles Inverse Knematc Fgure 2; Block dagram of knematc methods Fgure2 shows the operaton of knematc control methods. So we need robot arm desgn to defne the lnk parameters of robot arm. III. Analytcal calculaton of research And then, the ndvdual transformaton matrces for =1, 2 and 3 can be easly obtaned. Thereafter, the complete transformaton 1 H 4 s found from: 1 H 4 = 1 A 2 2 A 3 3 A 4 Upon the determnaton of, 1 H 4 we can fnd the global coordnates of the end effector. The tp pont of the arm s at the orgn of frame 3 (Fg. 3),.e. t s at [ ] T. So, ts poston n the global frame becomes: 1 H 4 = 1 H 4 [ ] T = [dx dy dz 1] T Analytcally from knematc method, poston of the grpper wll obtan dx =cos(θ 1 )((L3(cos(θ 2 +θ 3 ))+L2cos(θ 2 )) (1) dy=sn(θ 1 )((L3(cos(θ 2 +θ 3 ))+L2cos(θ 2 )) (2) dz=l1+l3(sn(θ 2 +θ 3 ))+L2sn(θ 2 ) (3) () Inverse knematc transformaton We end up wth a set of three nonlnear equatons wth three unknowns. Solvng these equatons algebracally, known as the nverse knematcs, requres that we need to know the jont varables (θ 1, θ 2, θ 3 ) for a gven grper poston (dx, dy, dz). We get from equatons (1) to (3), by dvdng, squarng, addng and usng some trgonometrc formulas: Fgure 3; Lnk parameters of artculated robot manpulator θ 1 = tan -1 (dy/dx) θ 2 =cos -1 [(cosθ 1 dx+snθ 1 dy)(a 3 cosθ 3 +a 2 ) a 3 snθ 3 (d 1 +dz) (a 3 cosθ 3 +a 2 ) 2 +a 2 2 sn(θ 3 ) 2 ] θ 3 =cos -1 [(cosθ 0 dx+snθ 0 dy) 2 +(d 0 +dz) 2 (a 1 2 +a 2 2 )] 2a 2 a

3 Table 2: analytcal calculaton result of robot arm IV. SYSTEM BLOCK DIAGRAM Ths research uses dual-swtched power supply as a source power. It can be used the source of power to both mcrocontroller and motors. Metal detector s used for sortng system.mcrocontroller s used to generate the pulse to drve the motors. Servo motors are used as actuators for robot arm s jonts. The controller unt: Ths s the most mportance of the robot system, because t performs all vtal calculaton of knematc analyss. The controller unt used n ths research s on Atmega328 mcrocontroller and has 6 analog nputs, 14 dgtal nput/output pns (6 of whch can be used as PWM outputs). The unt receves sgnals (feld nformaton) from the sensors (such as metal sensor and other object sensor) and then processes t based on the already-programmed software n ts memory. Actually, a pn (confgured as an nput pn) on the mcrocontroller s connected to the sensor condtonng crcut, and the mcrocontroller responds dependng on whether ths pn s HIGH or LOW. When the pn s LOW, t means there s absence of an object, and the mcrocontroller mantans the robot at ts home poston, but when the pn s HIGH, t means there s presence of an object, and the mcrocontroller uses a pulse wdth modulated sgnal to control the jont motors to drve the robot to an approprate locaton (the object poston n ths case) n the workspace. The actuatng unt: The actuators that are beng mplemented for the jont operaton are motors. Because the robot s a revolute manpulator, t means all the jont varables are angle rotatons, and therefore, the motors are very sutable. Conventonal RC motors consst of 4 prmary parts: a DC motor, a gearbox/system, a potentometer, and a control crcut. The motor s controlled by a pulse wdth modulated sgnal (control sgnal) from the controller unt through ts control wre. Snce there are two types of s wth dfferent specfcatons n the arm robot, the results obtaned from the smulaton on Proteus dffer n terms of pulse wdth, angle and motor behavor. Accordng to Table3 and Table4, the smulaton consders the rotaton angle wth respect to the generated pulses wth the pulse wdth ranges from 600μs to 2400μs for Tower-Pro SG-5010, and from 400 μs to 2400 μs for Tower-Pro SG-90. Table3; specfcaton of SG-5010 motor Table 4; specfcaton of Tower pro SG-90 motor Power supply Mcrocontroller Metal detector Fg 4: System block dagram of research Fgure 5; SG-5010 PWM smulaton by usng proteus software 59

4 In ths smulaton, all angles are 90 command. So, all pulses wdth s 1.5 ms. Metal detector; Metal detector s used to detect the object s metal or not. When the object s metal, sgnal s sent to controller to pck up the robot arm. If the object s not metal, the robot arm s not operated the pck and place operaton. In ths research Metal detector s used for sortng system. V. FLOW CHART OF RESEARCH START Intalze the nput/output Move the robot arm to home poston All angles are 90 Mantan the home poston Fgure 8; expermental testng the robot arm to reach at poston 1 Move the object to poston 1 Pck the object from poston1 Detect the object s metal at poston 1 Is the object metal? Check the object at poston 2 Is the object n poston 2? Move the object to poston 2 Robot arm to reach at poston 1, nverse knematc method s used. Dstance of poston 1 s appled to nverse knematc equaton, the angles of motors (θ 1 =45, θ 2 =130, θ 3 =80 ) s obtaned. Other postons are also calculated as above descrpton. The result angles are appled to motors that are connected to robot arm jonts by usng Arduno software. Return to home poston Place the object to poston2 End? End FIGURE 6; FLOW CHART OF PICK AND PLACE ARTICULATED ROBOT ARM VI. POSITION TRACKING OF ROBOT ARM EXPERIMENTALLY Accordng to flow dagram, home poston of robot arm s assumed at dx=0cm,dy=21.5cm and dz=12cm.after that poston 1 s at dx=-18cm,dy=-18cm and dz=4cm.and then, let poston 2 to be at dx= 18cm,dy=18cm and dz=4cm respectvely. Orgnal object poston s set at poston 1 and the fnal object poston s set at poston 2. Fgure9; expermental testng of pck up object condton Fgure 7; testng the robot arm at home poston (all angles are 90 appled) Fgure 10; expermental testng the arm reachng at poston 2 60

5 After testng the robot arm,there s lttle error occurred.the poston of X, Y and Z coordnate are not equally smlar to the calculated result from nverse knematc method. Error = ((calculated dstance-expermental dstance) /calculated dstance)*100% For example, Let dx=dy=18.6cm and dz=4cm are appled to nverse knematc equatons. The output angles θ 1 = 45, θ 2 =130, θ 3 =80 are obtaned. After applyng these angles to motors of robot arm, there s a dfferent between the calculated result and the expermental out dstance dz=0.1cm at Z coordnate and dx and dy are 0.6 cm dfferent between the calculated result and the expermental result. Table 5; Error calculaton of expermental testng VII. DISCUSSION Knematc control methods are useful for robotc system. In ths journal forward and reverse knematc methods has been fully explaned and calculated wth mathematcally.from the result of ths, artculated robot arm has been tested by Arduno Software wth expermentally. When testng the robot arm for pck up and place operaton, there s lttle error occurs. The occurrence of ths error s because of the lmtaton of selected motors and some mechansm structure of robot arm. Whenever, the maxmum rotatng angle of the chosen motors cannot exactly rotate 180. VIII. CONCLUSIONS The nverse knematc analyss of 3-DOF Robot s nvestgated. The mathematcal model s prepared and solved for angles of jonts. The calculated result and the testng expermental result are absolutely the same. Ths artculated robot arm s fully tested the operaton of pck and place object at the research group centre of our unversty. Ths journal consders the hardware, software and mathematcal calculaton parts and have been dscussed and tested n the practcally. As the future of advanced robot arm, t can be desgned to get an optmum grp on the desred object, t s recommended that a pressure sensor be ncorporated on one of the end-effector s fngers. Moreover, a camera and a computer, whch has mage processng capablty, can be used to know locatons of the object (nstead of the pre-programmed postons operated n ths research). Electronc Engneerng, Mandalay Technologcal Unversty, accomplshed gudance, hs wllngness to share hs dea and, helpful suggestons and for hs patence, contnuous supervson and encouragement durng the perod of ths paper. REFERENCES [1] Jolly Shah, S.S.Rattan, B.C.Nakra, End-Effector Poston Analyss Usng Forward Knematcs for 5DOF Pravak Robot Arm, Internatonal Journal of Robotcs and Automaton (IJRA),Vol. 2,. 3, September [2] Sanjay L., Shweta P., Poston Control of Pck and Place Robotc Arm, Internatonal Conference on Engneerng Innovaton and Technology, Nagpur, 1st July, [3] Bnbn L., Ymn S., Gang D., Tao S., Yang Q., Dmensonal Synthess of a Planar Parallel Manpulator for Pck-and-Place Operatons Based on Rgd-Body Dynamcs, Intellgent Robotcs and Applcatons/Lecture tes n Computer Scence, Sprnger, Vol. 7506, pp , [4] Altuzarraa O., Şandru B., Pnto Ch., and Petuya V., A Symmetrc Parallel Schönfles-Moton Manpulator for Pck-and-Place Operatons, Robotca, Vol. 29, Issue 06, October 2011, pp [5] Bn L., Yunjang L., and Zexang L., Knematcs and Optmal Desgn of a vel 3-DoF Parallel Manpulator for Pck-and-Place Applcatons, Internatonal Journal of Mechatroncs and Automaton, Vol.3,.3, pp , [6] Ayokunle A.Awelewa, Samuel O. Majekodunm, Isaac A. Samuel, Development of a Prototype Robot Manpulator for Industral Pck-and-Place Operatons, October 2013 IJENS [7] Mohammad D. Abdul Hakeem, Desgn and Comparatve Assessment of State Feedback Controllers for Poston Control of 8692 DC Servomotor, Publshed by August 2015 n MECS. [8] Jolly Shah, End-Effector Poston Analyss Usng Forward Knematcs for 5DOF Pravak Robot Arm Internatonal Journal of Robotcs and Automaton (IJRA),Vol. 2,. 3, September Acknowledgment The author wshes to acknowledge especally to Dr.Mynt Then, Rector of Mandalay Technologcal Unversty, for hs gudance, help and sharng frutful deas. The author s deeply grateful to Dr.Hla Myo Tun, Assocate Professor and Head, Department of Electronc Engneerng, Mandalay Technologcal Unversty for permttng all necessary electronc components has been used from lab centre. The author also wshes to U Zaw Mn Mn Htun, Lecturer, Department of 61