INTELLIGENT INVERSE KINEMATIC CONTROL OF SCORBOT-ER V PLUS ROBOT MANIPULATOR

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    International Journal of Advances in Engineering & Technology, Nov 2011.

    IJAET ISSN: 2231-1963

    158 Vol. 1, Issue 5, pp. 158-169

    INTELLIGENT INVERSE KINEMATIC CONTROL OF

    SCORBOT-ERVPLUS ROBOT MANIPULATOR

    Himanshu Chaudhary

    and Rajendra Prasad

    Department of Electrical Engineering, IIT Roorkee, India

    ABSTRACT

    In this paper, an Adaptive Neuro-Fuzzy Inference System (ANFIS) method based on the Artificial Neural

    Network (ANN) is applied to design an Inverse Kinematic based controller forthe inverse kinematical control of

    SCORBOT-ER V Plus. The proposed ANFIS controller combines the advantages of a fuzzy controller as well as

    the quick response and adaptability nature of an Artificial Neural Network (ANN). The ANFIS structures were

    trained using the generated database by the fuzzy controller of the SCORBOT-ER V Plus.The performance ofthe proposed system has been compared with the experimental setup prepared with SCORBOT-ER V Plus robot

    manipulator. Computer Simulation is conducted to demonstrate accuracyof the proposed controller to generate

    an appropriate joint angle for reaching desired Cartesian state, without any error. The entire system has been

    modeled using MATLAB 2011.

    KEYWORDS:DOF, BPN, ANFIS, ANN, RBF, BP

    I. INTRODUCTIONInverse kinematic solution plays an important role in modelling of robotic arm. As DOF (Degree of Freedom) of

    robot is increased it becomes a difficult task to find the solution through inverse kinematics.Three traditional

    method used for calculating inverse kinematics of any robot manipulator are:geometric[1][2] ,algebraic[3][4][5] and iterative [6] methods. While algebraic methods cannot guarantee closed form

    solutions. Geometric methods must have closed form solutions for the first three joints of the

    manipulator geometrically. The iterative methods converge only to a single solution and this solutiondepends on the starting point.The architecture and learning procedure underlying ANFIS, which is a fuzzy inference system

    implemented in the framework of adaptive networks was presented in [7]. By using a hybrid learning

    procedure, the proposed ANFIS was ableto construct an input-output mapping based on both humanknowledge (in the form of fuzzy if-then rules) and stipulated input-output data pairs.

    Neuro-Genetic approach for the inverse kinematics problem solution of robotic manipulators wasproposed in [8]. A multilayer feed-forward networks was applied to inverse kinematic problem of a 3-

    degrees-of freedom (DOF) spatial manipulator robot in [9]to get algorithmic solution.To solve the inverse kinematics problem for three different cases of a 3-degrees-of freedom (DOF)manipulator in 3D space,a solution was proposed in [10]usingfeed-forward neural networks.This

    introduces the fault-tolerant and high-speed advantages of neural networks to the inverse kinematics

    problem.A three-layer partially recurrent neural network was proposed by [11]for trajectory planning and to

    solve the inverse kinematics as well as the inverse dynamics problems in a single processing stage forthe PUMA 560 manipulator.

    Hierarchical control technique was proposed in[12]for controlling a robotic manipulator.It was based

    on the establishment of a non-linear mapping between Cartesian and joint coordinates using fuzzy

    logic in order to direct each individual joint. Commercial Microbot with three degrees of freedom wasutilized to evaluate this methodology.Structured neural networks based solution was suggested in[13] that could be trained quickly. The

    proposed method yields multiple and precise solutions and it was suitable for real-time applications.

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    To overcome the discontinuity of the inverse kinematics function,a novel modular neural networksystem that consists of a number of expert neural networks was proposed in[14].

    Neural network based inverse kinematics solution of a robotic manipulator was suggested in[15]. Inthis study, three-joint robotic manipulator simulation software was developed and then a designed

    neural network was used to solve the inverse kinematics problem.An Artificial Neural Network (ANN) using backpropagation algorithm was applied in [16]to solve

    inverse kinematics problems of industrial robot manipulator.

    The inverse kinematic solution of the MOTOMAN manipulator using Artificial Neural Network wasimplemented in [17]. The radial basis function (RBF) networks was used to show the nonlinear

    mapping between the joint space and the operation space of the robot manipulator which in turns

    illustrated the better computation precision and faster convergence than back propagation (BP)

    networks.Bees Algorithm was used to train multi-layer perceptron neural networks in [18]to model the inverse

    kinematics of an articulated robot manipulator arm.This paper is organized into four sections. In the next section, the kinematicsanalysis (Forward as well

    as inverse kinematics) of SCORBOT-ER V Plus has been derived with the help of DH algorithm as

    well as conventional techniques such as geometric[1][2], algebraic[3][4][5] and iterative [6] methods.

    Basics of ANFIS are introduced in section3. It also explains the wayfor input selection for ANFISmodeling. Simulation results are discussed in section 4. Section 5 gives concluding remarks.

    II. KINEMATICS OF SCORBOT-ERVPLUSSCORBOT-ER V Plus [19] is a vertical articulated robot, with five revolute joints. It has a Stationary

    base, shoulder, elbow, tool pitch and tool roll. Figure 1.1 identifies the joints and links of themechanical arm.

    2.1.SCORBOTERVPLUS STRUCTURE

    All joints are revolute, and with an attached gripper it has six degree of freedom. Each joint is

    restricted by the mechanical rotation its limits are shown below.Joint Limits:

    Axis 1: Base Rotation: 310

    Axis 2: Shoulder Rotation: + 130 / 35Axis 3: Elbow Rotation: 130

    Axis 4: Wrist Pitch: 130

    Axis 5: Wrist Roll Unlimited (electrically 570)Maximum Gripper Opening: 75 mm (3") without rubber pads 65 mm (2.6") with rubber pads

    The length of the links and the degree of rotation of the joints determine the robots work envelope.Figure 1.2 and 1.3 show the dimensions and reach of the SCORBOT-ER V Plus. The base of the robot

    is normally fixed to a stationary work surface. It may, however, be attached to a slide base, resultingin an extended working range.

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    2.2.FRAME ASSIGNMENT TO SCORBOTERVPLUS

    For the kinematic model of SCORBOT first we have to assign frame to each link starting from base(frame {0}) to end-effector (frame {5}). The frame assignment is shown in figure 1.4.

    Here in model the frame {3} and frame {4} coincide at same joint, and the frame {5} is end effector

    position in space.

    Joint i () () Operating range

    1 /2 16 349 1 155 + 155

    2 0 221 0 2 35 + 130

    3 0 221 0 3 130 + 130

    4 /2 0 0 /2 + 4 130 + 130

    5 0 0 145 5 570 570

    2.3. FORWARD KINEMATIC OF SCORBOTERVPLUS

    Once the DH coordinate system has been established for each link, a homogeneous transformationmatrix can easily be developed considering frame {i-1} and frame {i}. This transformation consists of

    four basic transformations.

    0 0 1 2 3 45 1 2 3 4 5* * * *T T T T T T = (1)

    0 *1 1 1 10 *0 1 1 1 1

    1 0 1 01

    0 0 0 1

    C S a C S C a S

    Td

    =

    (2)

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    2 2 2 2

    2 2 2 212

    0 *

    0 *

    0 0 1 0

    0 0 0 1

    C S a C

    S C a ST

    =

    (3)

    3 3 3 3

    3 3 3 32 3

    0 *

    0 *

    0 0 1 0

    0 0 0 1

    C S a C

    S C a ST

    =

    (4)

    4 0 4 0

    4 0 4 034 0 1 0 0

    0 0 0 1

    S C

    C ST

    =

    (5)

    5 5 0 0

    5 5 0 045 0 0 1 5

    0 0 0 1

    C S

    S CT

    d

    =

    (6)

    Finally, the transformation matrix is as follow: -

    1 5 1 5 234 5 1 1 5 234 1 234 1 1 2 2 3 23 5 234

    1 5 1 5 234 1 5 1 5 234 1 234 1 1 2 2 3 23 5 2340

    5

    5 234 5 234 234 1 2 2 3 23 5 234

    ( )

    ( )

    ( )

    0 0 0 1

    S S C C S C S C S S C C C a a C a C d C

    C S S C S C C S S S S C S a a C a C d C T T

    C C S C S d a S a S d S

    + + + +

    + + + +

    = =

    (7)

    Where, = (), = () = ( + + ), = ( + + ).The Tis all over transformation matrix of kinematic model of SCORBOT-ER V Plus, from this wehave to extract position and orientation of end effector with respect to base is done in the following

    section.

    2.4. OBTAINING POSITION IN CARTESIAN SPACEThe value of, , is found from last column of transformation matrix as: -

    1 1 2 2 3 23 5 234( )X C a a C a C d C = + + + (8)

    1 1 2 2 3 23 5 234( )Y S a a C a C d C = + + (9)

    1 2 2 3 23 5 234( )Z d a S a S d S= (10)

    For Orientation of end-effector frame {5} and frame {1} should be coincide with same axis but in our

    model it is not coincide so we have to take rotation of 90 of frame {5} over y5 axis, so the overall

    rotation matrix is multiplied with 90 as follow: -

    cos( 90 ) 0 sin( 90 )

    0 1 0

    sin( 90 ) 0 cos( 90 )

    yR

    =

    o o

    o o

    0 0 1

    0 1 0

    1 0 0

    yR

    =

    (11)

    The Rotation matrix is: -

    1 5 1 5 234 5 1 1 5 234 1 234

    1 5 1 5 234 1 5 1 5 234 5 234

    5 234 5 234 234

    0 0 1

    0 1 0

    1 0 0

    S S C C S C S C S S C C

    R C S S C S C C S S S S C

    C C S C S

    +

    = +

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    5 234 5 234 234

    1 5 1 5 234 1 5 1 5 234 5 234

    1 5 1 5 234 5 1 1 5 234 1 234

    C C S C S

    R C S S C S C C S S S S C

    S S C C S C S C S S C C

    = + + (12)

    Pitch: Pitch is the angle of rotation about y5 axis of end-effector

    2 3 4 234pitch = + + = (13)

    2 2234 a tan 2( 13, 23 33 )r r r = + (14)

    Here we use atan2 because its range is [, ], where the range of atan is [/2, /2].Roll: The = 5 is derived as follow: -

    5 234 234tan 2( 12 / , 11/ )a r C r C = (15)

    Yaw: Here for SCORBOTyaw is not free and bounded by 1.

    2.5. HOME POSITION IN MODELING

    At home position all angle are zero so in equation (1.7) put 1 = 0, 2 = 0, 3 = 0, 4 = 0, 5 = 0So the transformation matrix reduced to:-

    1 2 3 5

    1

    0 0 1 0 0 1 603

    0 1 0 0 0 1 0 0

    1 0 0 1 0 0 349

    0 0 0 1 0 0 0 1

    Home

    a a a d

    Td

    + + + = =

    (16)

    The home position transformation matrix gives the orientation and position of end-effector frame.From the 33 matrix orientation is describe as follow, the frame {5} is rotated relative to frame {0}

    such that 5 axis is parallel and in same direction to 0 axis of base frame; 5is parallel and in same

    direction to 0 axis of base frame; and 5axis is parallel to 0but in opposite direction. The position is

    given by the 3 1 displacement matrix 1 2 3 5 10 .T

    a a a d d + + +

    2.6. INVERSE KINEMATICS OF SCORBOT-ERVPLUS

    For SCORBOT we have five parameter in Cartesian space is x, y, z, roll () , pitch ().For jointparameter evaluation we have to construct transformation matrix from five parameters in Cartesian

    coordinate space. For that rotation matrix is generated which is depends on only roll, pitch and yaw of

    robotic arm. For SCORBOT there is noyaw but it is the rotation of first joint 1.So the calculation ofyaw is as follow: -

    1 tan 2( , )a x y = = (17)Now for rotation matrix rotate frame {5} at an angle about its x axis then rotate the new frame {5} by an angle with its own principal axes , finally rotate the new frame {5} by an angle with

    its own principal axes ''. = ( ) ( ) ()

    1 0 0 0 0

    0 0 1 0 0

    0 0 0 0 1

    C S C S

    C S S C

    S C S C

    =

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    C C C S S

    C S C S S C C S S S C S

    S S C C S S C S C S C C

    = + + (18)

    Now rotate matrix by 90 about y axis: -

    (90 ) 0 (90 )

    ( 90 ) 0 1 0(90 ) 0 (90 )

    y

    COS SIN

    RSIN COS

    =

    o o

    o

    o o

    0 0 1

    ( 90 ) 0 1 0

    1 0 0

    yR

    =

    o

    (19)

    After pre multiplying the equation 19 with equation 18, one will get following rotation matrix: -

    S S C C S S C S C S C C

    C S C S S C C S S S C S

    C C C S S

    +

    = + (20)

    So, the total transformation matrix is as follows: -

    0 0 0 1

    S S C C S S C S C S C C X

    C S C S S C C S S S C S Y T

    C C C S S Z

    +

    + = (21)

    After comparing the transformation matrix in equation (7) with matrix in equation (21), one can

    deduce: -

    1 = ,

    234 = ,5 = ,

    Now, we have 1 and 5 directly but 2, 34 are merged in 234 so we have separate them, toseparate them we have used geometric solution method as shown in Figure 1.6

    Here for finding 2, 3, 4, we have X, Y, Z in Cartesian coordinate space from that we can take:-

    2 21 1( )X X Y andY Z = + = (22)

    We have pitch of end-effector 234 = , from that we can find point 2, 2 is calculated as follows: -

    2 1 5 234

    2 1 5 234

    cos

    sin

    X X d

    Y Y d

    =

    = +(23)

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    Now the distance 3and 3can be found: -

    3 2 1

    3 2

    X X a

    Y Y

    =

    =

    From the low of cosines applied to triangle ABC, we have: -2 2 2 23 3 2 3

    32 3

    ( )cos

    2

    X Y a a

    a a

    + =

    23 3 3tan 2( 1 cos , cos )a =

    (24)

    From figure 1.6 2 = or

    2 3 3 3 3 2 3tan 2( , ) tan 2( sin , cos )a Y X a a a = + (25)

    Finally we will get: -

    234 2 3 = (26)

    III. INVERSE KINEMATICS OF SCORBOT-ER V PLUS USING ADAPTIVENEURO FUZZY INFERENCE SYSTEM (ANFIS)

    The proposed ANFIS[7][20][21] controller is based on Sugeno-type Fuzzy Inference System (FIS)

    controller.The parameters of the FIS are governed by the neural-network back propagation method.

    The ANFIS controller is designed by taking the Cartesian coordinates plus pitch as the inputs, and the

    joint angles of the manipulator to reach a particular coordinate in 3 dimensional spaces as the output.The output stabilizing signals, i.e., joint angles are computed using the fuzzy membership functions

    depending on the input variables. The effectiveness of the proposed approach to the modeling isimplemented with the help of a program specially written for this in MATLAB. The information

    related to data used to train is given inTable 1.2.

    Sr.

    No.

    Manipulator

    Angles

    No. of

    Nodes

    No. of Parameters Total No. of

    Parameters

    No. of

    Training

    Data Pairs

    No. of

    Checking

    Data Pairs

    No. of

    Fuzzy

    RulesLinear Nonlinear

    01. Theta1 193 405 36 441 4500 4500 81

    02. Theta2 193 405 36 441 4500 4500 81

    03. Theta3 193 405 36 441 4500 4500 81

    04. Theta4 193 405 36 441 4500 4500 81

    The procedure executed to train ANFIS is as follows:

    (1) Data generation: To design the ANFIS controller, the training data have been generated by usingan experimental setup with the help of SCORBOT-ER V Plus. A MATLAB program is written to

    govern the manipulator to get the input output data set. 9000 samples were recorded through the

    execution of the program for the input variables i.e., Cartesian coordinates as well as Pitch. Cartesiancoordinates combination for all thetas are given in Fig.1.7

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    (2) Rule extraction and membership functions: After generating the data, the next step is to estimatethe initial rules. A hybrid learning algorithm is used for training to modify the above parameters after

    obtaining the Fuzzy inference system from subtracting clustering. This algorithm iteratively learns theparameter of the premise membership functions and optimizes them with the help of back propagation

    and least-squares estimation. The training is continued until the error minimization..The input as wellas output member function used was triangular shaped member function.The final fuzzy inference

    system chosen was the one associated with the minimum checking error, as shown in figure 1.8.it

    shown the final membership function for the thetas after training.

    -0 . 5 0 0 . 5

    0

    0. 5

    1

    in pu t1

    D

    egree

    of

    m

    e

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    b

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    in 1 m f1 in 1 m f2 in 1 m f3

    -0 . 4 -0 . 2 0 0 .2 0 . 4

    0

    0. 5

    1

    inp u t 2

    D

    egree

    of

    m

    e

    m

    b

    ers

    in 2 m f1 in 2 m f2 in 2 m f3

    -0 . 2 0 0 . 2 0 . 4 0 . 6 0 .8

    0

    0. 5

    1

    in pu t3

    D

    egree

    o

    f

    m

    e

    m

    b

    ership

    i n 3 m f1 in 3 m f2 in 3 m f3

    - 4 - 2 0 2 4

    0

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    inp u t 4

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    egree

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    m

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    b

    ership

    in 4 m f1 in 4 m f2 in 4 m f3

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    0

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    egree

    of

    m

    em

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    in 1 m f1 i n 1 m f2 i n 1 m f3

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    0

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    (3) Results: The ANFIS learning was tested on a variety of linear and nonlinear processes. The

    ANFIS was trained initially for 2 membership functions for 9000 data samples for each input as wellas output. Later on, it was increased to 3 membership functions for each input. To demonstrate the

    effectiveness of the proposed combination, the results are reported for a system with81 rules and a

    system with an optimized rule base. After reducingthe rules the computation becomes fast and it alsoconsumes less memory. The ANFIS architecture for 1 is shownin Fig. 1.9.

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    Five angles have considered for the representation of robotic arm. But as the 5 is independentof other angles so only remaining four angles was considered to calculate forward kinematics. Now,

    for every combination of1, 2, 3 and4 values the x and y as well as z coordinates are deduced usingforward kinematics formulas.

    IV. SIMULATION RESULTS AND DISCUSSIONThe plots displaying the root-mean-square error are shown in figure 1.10. The plot in blue representserror1, the error for training data. The plot in green represents error2, the error for checking data.

    From the figure one can easily predict thatthere is almost null difference between the training error aswell as checking error after the completion of training of ANFIS.

    0 2 4 6 8 10 1 2 1 4 1 6 1 8 2 00 . 5 5

    0. 6

    0 . 6 5

    0. 7

    0 . 7 5

    0. 8

    0 . 8 5

    0. 9

    E poc hs

    RM

    SE

    (RootM

    ean

    Squared

    Error)

    E rror C urves

    0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 200 . 2 2

    0 . 2 4

    0 . 2 6

    0 . 2 8

    0. 3

    0 . 3 2

    0 . 3 4

    E pochs

    RM

    SE

    (RootM

    ean

    Squared

    Error)

    E rror C urves

    0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 00 .45

    0 .5

    0 . 55

    0 .6

    0 . 65

    0 .7

    E p oc hs

    RM

    SE

    (R

    ootM

    ean

    Squared

    Error) E rror C u rve s

    0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 00 .3 2

    0 .3 4

    0 .3 6

    0 .3 8

    0 .4

    0 .4 2

    0 .4 4

    E p o c h s

    R

    M

    S

    E

    (R

    ootM

    ean

    S

    quared

    E

    rror)

    E rro r C u rve s

    1 2

    3 4

    In addition to above error plots, the plot showing the ANFIS Thetas versus the actual Thetasare given

    in figures1.11,1.12,1.13 and 1.14 respectively. The difference between the original thetas values and

    the values estimated using ANFIS is very small.

    0 50 100 150 200 250 300 350-4

    -3

    -2

    -1

    0

    1

    2

    3

    Time (sec)

    Theta1 and ANFIS Prediction theta1

    Experimental Theta1

    ANFIS Predicted Theta1

    0 50 100 150 200 250 300 350-1

    -0.5

    0

    0.5

    1

    1.5

    2

    Time (sec)

    Theta2 and ANFIS Prediction theta2

    Experimental Theta2

    ANFIS Predicted Theta2

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    0 50 100 150 200 250 300 350-3

    -2

    -1

    0

    1

    2

    3

    Time (sec)

    Theta3 and ANFIS Prediction Theta3

    Experimental Theta3

    ANFIS Predicted Theta3

    0 50 100 150 200 250 300 350-3

    -2

    -1

    0

    1

    2

    Time (sec)

    Theta4 and ANFIS Prediction Theta4

    Experimental Theta4

    ANFIS Predicted Theta4

    The prediction errors for all thetas appear in the figures 1.15, 1.16, 1.17, 1.18 respectively with a much finer

    scale. The ANFIS was trained initially for only 10 epochs. After that the no. of epochs were increased to 20 for

    applying more extensive training to get better performance.

    0 50 100 150 200 250 300 350-3

    -2

    -1

    0

    1

    2

    3

    Time (sec)

    Prediction Errors for THETA 1

    Prediction Error Theta1

    0 50 100 150 200 250 300 350-1.5

    -1

    -0.5

    0

    0.5

    1

    Time (sec)

    Prediction Errors for THETA2

    Prediction Error Theta2

    0 50 100 150 200 250 300 350-3

    -2

    -1

    0

    1

    2

    Time (sec)

    Prediction Errors for THETA3

    Prediction Error Theta3

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    0 50 100 150 200 250 300 350-2

    -1.5

    -1

    -0.5

    0

    0.5

    1

    1.5

    Time (sec)

    Prediction Errors for THETA4

    Prediction Error Theta4

    V. CONCLUSIONFrom the experimental work one can see that the accuracy of the output of the ANFIS based inverse

    kinematic model is nearly equal to the actual mathematical model output, hence this model can be

    used as an internal model for solving trajectory tracking problems of higher degree of freedom (DOF)robot manipulator. Asingle camera for the reverse mapping from camera coordinates to real world

    coordinateshas been used in the present work, if two cameras are used stereo vision can be achieved

    andproviding the height of an object as an input parameter would not be required. The methodologypresented herecan be extended to be used for trajectory planning and quite a few tracking applications

    with real world disturbances. Thepresent work did not make use of color image processing; makinguse of color image processing can helpdifferentiate objects according to their colors along with theirshapes.

    ACKNOWLEDGEMENTS

    As it is the case in almost all parts of human endeavour so also the development in the field of robotics has been

    carried on by engineers and scientists all over the world.It can be regarded as a duty to express the appreciation

    for such relevant, interesting and outstanding work to which ample reference is made in this paper.

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    AuthorsHimanshu Chaudhary received his B.E. in Electronics and Telecommunication from

    Amravati University, Amravati, India in 1996, M.E. in Automatic Controls and Robotics

    from M.S. University, Baroda, Gujarat, India in 2000.Presently he is a research scholar in

    Electrical Engineering Department, IIT Roorkee, India. His area of interest includes

    industrial robotics, computer networks and embedded systems.

    Rajendra Prasad received B.Sc. (Hons.) degree from Meerut University, India in 1973. He

    received B.E.,M.E. and Ph.D. degree in Electrical Engineering from the University of

    Roorkee, India in 1977, 1979 and 1990 respectively. . He also served as an Assistant

    Engineer in Madhya Pradesh Electricity Board (MPEB) from 1979- 1983. Currently, he is a

    Professor in the Department of Electrical Engineering, Indian Institute of Technology

    Roorkee, Roorkee (India).He has more than 32 years of experience of teaching as well as

    industry. He has published 176 papers in various Journals/conferences and received eight

    awards on his publications in various National/International Journals/Conferences Proceeding papers. He has

    guided Seven PhDs, and presently six PhDs are under progress. His research interests include Control,

    Optimization, System Engineering and Model Order Reduction of Large Scale Systems and industrial robotics.