International Journal of Engineering Trends and Technology   (IJETT)   –   Volume   10   Number 4   -   Apr   2014  ISSN:   2231 - 5381   http://www.ijettjournal.org   Page   176  Optimization and Design of a Laser - Cutting Machine using Delta Robot  1 B.Moharana,   2 Rakesh Gupta,   3 B ashishth Kumar Kushwaha  1 DR. B.B.A GOVT.POLYTECHNIC, Karad, India  2,3 Roorkee Engineering & Management Technology Institute, Shamli, India  Abstract:   -  Industrial   high - speed laser operations the use of delta  parallel robots potentially offers many benefits, due to their  structural stiffness and limited moving masses. This paper  deals with a particular Delta, developed for high - speed  laser cutting. Parallel delta robot has numerous advantages  in comparison with serial robots:   Higher stiffness, and  connected with that a low er mass of links, the possibility of  transporting heavier loads, and higher accuracy. The main  drawback is, however, a smaller workspace. Hence, there  exists   an   interest   for   the   research   concerning   the  workspace of robots.in industrial cutting tool maximum   do  not have more prescribe measurement to cut so that in This  paper is oriented to parallel kinematic robots definition,  description of their specific application of laser cutting,  comparison of robots made by different producers and  determination   of   velo city   and   acceleration   parameters,  kinematic analysis   –   inverse and forward kinematic. It  brings information about development of Delta robot.   The  production of laser cutting machines began thirty years  ago. The progress was very fast and at present time ev ery  year over 3000 laser cutting machines is installed in the  world. Laser cutting is one of the largest applications of  lasers in metal working industry.  Keywords:   Delta robot, parallel kinematic structure, Laser  robot, control system.  I.   INTRODUCTION  Par allel   architectures   have   the   end - effector   (platform)  connected to the frame (base) through a number of kinematic  chains (legs). Their kinematic analysis is often difficult to  address. The analysis of this type of mechanisms has been the  focus of much recen t research. Stewart presented his platform  in 1965 [1]. Since then, several authors [2], [3] have proposed  a large variety of designs.   The interest for parallel manipulators  robot (PMR) arises from the fact that they exhibit high stiffness  in nearly all   configurations and a high dynamic performance.  Recently, there is a growing tendency to focus on parallel  manipulators with 3 translational   [4, 5,]. In the case of the three  translational parallel manipulators, the mobile   platform can  only translate with r espect to the base. The DELTA robot (see  figure 1) is   one of the most famous translational   parallel  manipulators robot [5, 6, 7, 11, and 12].  Figure 1 Delta robot sketch model with three degree angle  freedom  Laser beam device should connect to mechanic al systems that  allow a rigid body (called end effector) to move with respect to  a   fixed   base   play   a   very   important   role   in   numerous  applications. A rigid body in space can move in various ways,  in translation or rotary motion. These are called its degrees   of  freedom (DOF). The position and the orientation of the end -  effector (called its pose) can be described by its generalized  coordinates. As soon as it is possible to control several degrees  of freedom of the end - effector via a mechanical system, this  sys tem   can   be   called   robot.   [4]   From   this   aspect,   robot  represents an integrated Mechatronic system   consisting of three  subsystems:   sensorial,   control   and   decision - making,   and  actuation subsystem. The sensorial subsystem establishes a  feedback with the enviro nment.   The control and decision -  making subsystem represents the 'thinking' centre of the robot,  its 'brain'. Together, the sensorial and control subsystems make  up a cognitive system. Finally, the actuation subsystem is used  to affect the environment, maki ng such an impact on it that the  environment changes [2].   It was concluded that the serial  robots   are   inappropriate   for   tasks   requiring   either   the  manipulation of heavy loads, or a good positioning accuracy,  or to work with high dynamic parameters.  II.LASER CUTTING MACHINES  Laser   machines for   contour   cutting thin sheet   present   the  product of high technology. They are composed of: laser, beam
International Journal of Engineering Trends and Technology   (IJETT)   –   Volume   10   Number 4   -   Apr   2014  ISSN:   2231 - 5381   http://www.ijettjournal.org   Page   177  guiding,   cutting head,   coordinate table,   system for   energy  supply and control unit. It is based on vaporize   the material in a  very small area by focused laser beam. Process characteristics  are: uses a high energy beam of coherent light; beam is focused  on a small spot on the work piece by a lens; focused beam  melts, vaporizes, or combusts   material; molten   materi al   is  ejected out from the melt area by pressurized gas jet. Laser  cutting is the high speed cutting with a narrow kerf width that  results in superior and enhanced quality, higher accuracy and  greater flexibility. The optical quantum generator generates th e  light beam that presents a tool in working process. By optical  system in cutting head the laser beam is focused in diameter  from 0.2 mm with the power density over 10 8   W/cm2. Since  our desire is to remove the evaporated and molten material  from the affec ted zone as soon as possible, the laser cutting is  performed with a coaxial assist gas. The gas blowing increases  the feed rate for as much as 40 %. Cutting process along  contour is realized with the movement of laser beam or work  piece. Machine for moveme nts is accordance with necessities  of laser machine. [14] Laser cutting robots have totally flying  optics architecture. All movements are made by the focusing  head and the work - piece remains stationary. Laser robot takes  the laser beam along any continuous   pre - programmed path in  three - dimensional space, and then cuts with accuracy, speed  and quality. The speed and acceleration on the main axes of the  new generation of robotic systems are 60 m/min and 23 m/s2.  Integration of the laser beam guiding in the rob ot arm structure  offers great advantages compared to conventional systems with  external laser beam guiding. In case to design more accuracy  beam guiding in work space so that we are going to design  some new method to implementation tool to developed   in  ch allenging to problem.  III.CHALLENGING PROBLEM  A   more   challenging   problem   is   designing   a   parallel  manipulator delta robot for a given workspace. This problem  has been   addressed   by Boudreau and   Gosselin [5, 6],   an  algorithm has been worked out, allowing the determination of  some parameters of the parallel manipulators using a genetic  algorithm method in order to obtain a workspace as close as  possible to a prescribed one. Kosinska et   al.   [7] presented a  method f or the determination of the parameters of a Delta - 4  manipulator, where the prescribed workspace has been given in  the form of a set of points. Snyman et   al.   [8] propose an  algorithm   for   designing   the   planar   3 - RPR   manipulator  parameters, for a prescribed (2 - D) physically reachable output  workspace.   Similarly in   [9] the   synthesis   of   3 - dof   planar  manipulators with prismatic joints is performed using GA,  where the architecture of a manipulator and its position and  orientation   with   respect   to the prescribed work space were  determined .  a.   KINEMATIC ANALYSIS  If we want to build our own Delta robot, we need to solve two  problems. First, if we know the desired position of the end  effector (for example, we want to catch some object in the  point with coordinates X,Y , Z), we need to determine the  corresponding angles of each of the three arms (joint angles) to  set motors (and, thereby, the end effector) in proper position  for picking. The process of such determining is known as  inverse kinematics.  And, in the second   case, if we know joint angles (for example,  we have read the values   of motor   encoders), we need to  determine the position of the end effector (e.g. to make some  corrections   of   its   current   position).   This   is   a   forward  kinematics   problem. [10]  To be more fo rmal, we can look at the kinematic scheme of a  delta robot. The platforms are two equilateral triangles: the  fixed one with motors is green, and the moving one with the  end effector is pink. Joint angles are   θ 1 , θ 2   and θ 3   and point E is  the end effector   position with coordinates (x 0 ,y 0 ,z 0   ). To solve  inverse kinematics problem we have to create the function with  E coordinates (x 0 ,y 0 ,z 0 ) as parameters which returns( θ 1 , θ 2,   θ 3 )  Forward   kinematics   functions gets   ( θ 1 ,   θ 2,   θ 3 )   and returns  (x 0 ,y 0 ,z 0 ).  b.   INVERSE   KINEMATICS  The Delta robot consists of a moving platform connected to a  fixed base through three parallel kinematic chains.   Each chain  contains a rotational joint activated by actuators in the   First;  let's determine some key parameters of the robot’s geometry.  Let's designate the side of the fixed triangle as f, the side of the  end effector triangle as e, the length of the upper joint as r f   ,  and the length of the parallelogram joint as r e, . Th ese are  physical parameters which are determined by the design of  Delta robot. The reference frame will be chosen with the origin  at the centre of symmetry of the fixed triangle, as shown  below, so z   - coordinate of the end effector will always be  negative.  Because of the robot's design the joint F 1,   J 1   (Fig. 3) can only  rotate in YZ plane, forming a circle with the centre in point F 1  and radius r f . As   opposed to F 1 ,   J 1   and E 1   are so - called  universal   joints,   which   means   that   E 1 J 1   can   rotate   freely  relativel y to E 1   , forming a sphere with the centre in point E 1  and radius r f   .
International Journal of Engineering Trends and Technology   (IJETT)   –   Volume   10   Number 4   -   Apr   2014  ISSN:   2231 - 5381   http://www.ijettjournal.org   Page   178  Figure 2 Delta robot joint moving parameters   sketch  Intersection of this sphere and YZ plane is a circle with the  centre in point E 1 ' and radius E 1 ' J 1 , where E 1 ' is the projection  of the point E 1   on YZ plane. The point J 1   can be found now as  intersection of two circles of known radius with centres in E 1 '  and F 1   intersection point with smaller   - coordinate). And if we  know J 1 , we can calculate angle θ 1   [10].  Figure 3 coordinates of end effector (E 0   calculation)  c.   FORWARD KINEMATICS  In this case the three joint angles   θ 1 , θ 2,   θ 3   are given, and we need  to find the coordinates (x 0 ,y 0 ,z 0 ) of end effector point E 1   . As we  know angles theta1, we can easily find coordinates of points J 1 ,  J 2   and J 3   (Fig. 3). Joints J 1 E 1 , J 2 E 2   and J 3 E 3   can freely rotate  around points J 1 , J 2   and J 3   respectively, forming three spheres  with radius r e .Now let's do the following: move the c entres of the  spheres from points J 1 , J 2   and J 3   to the points J 1 ', J 2 ' and J 3 ' using  transition vectors E 1 E 0 , E 2 E 0   and E 3 E 0   respectively. After this  transition all three spheres will intersect in one point E 0 .So, to  find coordinates (x 0 ,y 0 ,z 0   ) of point E 0 , we need to solve the set  of three equations like (x   –   x j ) 2   + (y – y j ) 2   + (z – z j ) 2   =r e 2   , where  coordinates of sphere centres (x j ,y j ,z j ) and radius r e   are known.  IV.DESIGN A CONTROL SYSTEM  For   the control of the machine the   commercial  motion   controller   ROBOX RBXE has been chosen  (up to   3   axes,   Intel Atom   microprocessor, 1.2G Hz,  endowed with   teach pendant). It offers the user the  possibility to   implement her/his own defined model  based control laws   and coordinates transformation  between the world   Cartesi an coordinate system and  the robot internal   coordinate system minimizing the  effort of writing   interpolating algorithms   [13][15] .  All the control algorithms are   written in C++ and the  control state variables’ references   updating is made  every   2.5   milliseconds.   The   programming  environment runs on Windows NT based   personal  computers and, besides allowing to write,   compile  and debug the application software, it permits to  evaluate the behaviour of the controlled machine and  then   to choose the best solution. Particular attention  has been paid to the robot working   safety. Special  safety   measures   have   been   integrated   into   the  control system including digital watch dog modules  with the aim to   assure intrinsic safety (Fig. 4 ).  Th e safety watchdog process in the design's safety  layer provides an overall health check on the system.  It   performs   two   major   functions:   resetting   the  hardware   watchdog timer and monitoring to ensure  that other   software processes are still running. At  regul ar intervals, all processes are required to send a  pulse to   the   safety   watchdog process: failure in  receiving the signal within   the specified time period  causes   a   corrective   action   to   occur.   Corrective  actions may vary depending on which   process has  failed   and the severity of the failure.  Figure 4   design of the robot control system  V. CONCLUSION  The overall performance and industrial feasibility of a laser  cutting system with parallel kinematics structure have been  assessed. The limited moving masses that characterise this type  of   mechanical   system   allow   obtaining   high   speed   and
International Journal of Engineering Trends and Technology   (IJETT)   –   Volume   10   Number 4   -   Apr   2014  ISSN:   2231 - 5381   http://www.ijettjournal.org   Page   179  acceleration with   a relatively low power consumption. The   direct   and   inverse   kinematic   equations   that   describe   the  robot   behaviour   can   be   implemented   on   a   commercial  motion controller for robotic applications,   the past, one of  the main hindrances to the diffusion of parall el robots was  the computational heaviness of kinematics; this problem has  been   overcome   thanks   to   the   impressive   progress   in  computer technology of the last years.  REFERENCES  [1]   D. Stewart, 1965,”A platform with 6 degrees of freedom”, Proc.  of the   Institution of mechanical engineers, Vol. 180 (Part 1,  15),pp. 371 - 386, 1965.  [2]   Clavel,   R.   1986.   Une   nouvelle   structure   de   manipulation  parallèle pour la robotique légère.R.A.I.R.O. APII, Vol 23, N o  6.  [3]   Griffis, M., and Duffy, J.,”A Forward Displace ment Analysis of  a Class of Stewart  Platforms,”   Trans.   ASME   Journal   of   Mechanisms,  Transmissions, and A automation in Design, Vol. 6, No. 6, June  1989, pp. 703 - 720.  [4]   Zhang, D. Parallel Robotic Machine Tools. Oshawa: Springer  Science and Business Media,   LLC 2010, ISBN 978 - 1 - 4419 -  1116 - 2, e - ISBN 978 - 1 - 4419 - 1117 - 9  [5]   R. Boudreau and C. M. Gosselin 1999, ”The synthesis of planar  parallel manipulators with a genetic algorithm”, ASME Journal  of Mechanical Design, Vol 121, pp 533 - 537.  [6]   R. Boudreau and C. M.   Gosselin 2001, ”La synthèse d’une plate  forme de Gough - Stewart pour un espace de travail atteignable  prescrit”, Mech. Mach. Theory 36 (2001) 327 - 342.  [7]   Kosinska, A, Galicki, M. and Kedzior, K. 2003,”Design and  optimization of parameters of Delta - 4 Paral lel Manipulator for a  Given Workspace”, Journal of Robotic Systems 20 (9), pp 539 -  548.  [8]   J. A. Snyman and A. M. Hay 2005, ”Optimal synthesis for a  continuos   prescribed dexterity interval of 3 - DOF parallel planar  manipulator   for   different   prescribed   output   workspaces”,  Proceeding   of   CK2005,   12th   International   Workshop   on  Computational Kinematics Cassino May 4 - 6.  [9]   M. Gallant and R. Boudreau 2002, ”The synthe sis of planar  parammel manipulators with prismatic joints for an optimal,  singularity - free workspace”, Journal of Robotic Systems 19 (1),  pp 13 - 24.  [10]   Zavatsky,M.   Delta   robot  kinematic2009.http://forums.trossenrobotics.com/tutorials/introd  uction - 129/ delta - robot - kinematics - 3276/.  [11]   Xie, S.Q., Wang, G.G. and Liu, Y. (2007) ‘Nesting of two -  dimensional   irregular   parts:an   integrated   approach’,  International   Journal   of   Computer   Integrated  Manufacturing ,Vol. 20, No. 8, pp.741 – 756.  [12]   Xie, S.Q., Tu, Y. L., Liu, J.Q. and Zhou, Z.D. (2001) ‘Integrated  and concurrent approach for compound sheet metal cutting and  punching’,   International Journal of Production Research , Vol.  39, No. 6, pp.1095 – 1112.  [13]   Liu, X. - J., Jeong, J., and Kim, J.: 2003, A three tran slational  DoFs parallel cube - manipulator, Robotica   21 , 645 – 653.  [14]   Pierrot, F., Reynaud, C., and Fournier, A.: 1990, DELTA: A  simple and efficient parallel robot, Robotica   8 , 105 – 109.  [15]   Ryu , J. and Cha, J.: 2003, Volumetric error analysis and  architecture optimization for accuracy of HexaSlide type parallel  manipulators,   Mechanism Machine Theory   38 , 227 – 240.  ABOUT THE AUTHORS  Bhimsen Moharana received the B.Tech degree in  Mechanical   Engi neering  from   Utkal   University,  Udisha, India in 1990.   He  Persuining   M.Tech   degree  from   NITTIR,   Chandigarh ,  India.During   his graduation  work,   he   esearched   on  various,   Robotics,   tools  designing, materials.   He is  currently   working   as   Lecturer   in   DR.   B.B.A  GOV T.POLYTECHNIC, Karad, India .  Rakesh   Gupta   received   the   B.E.   Degree   in  Electrical   and   Electronic  Engineering   from   Anna  University,   Chennai,   In dia.  During   his   Graduation   he  held   several   workshop   and  summer training program. He  is   currently   working   as  Assistant   Professor   in  Roorkee   Engineering   And   Management  Technology Institute, Uttar Pradesh, India. He  has   research   interest   in   low   power   system  d esign, Robotic, Embedded s ystem, VHDL.  Bashishth   Kumar  K ushwaha   born in deoria,India.He  received   the   B.Tech   degree   in  mechanical   engineering   from  United   College   of   Engineering  and   Research nainee, Allahabad,  India in 2008.During his Graduate  Studies   time   he   held   many  research   training   program.   He   is   currently  working   as   Assistant   Professor   in   Roorkee  Engineering   And   Management   Technology  Institute, Uttar Pradesh, India. He has research  interest in Material, Tool cutting and robotics .