International Symposium on Devices MEMS, Intelligent Systems & Communication (ISDMISC) 2011 Proceedings published by International Journal of Computer Applications® (IJCA) 5 Comparison of Robustness of PID Control and Sliding Mode Control of Robotic Manipulator Jyoti Ohri Associate Professor National Inst. of Technology, Kurukshetra, Haryana Dhaval R. Vyas M.Tech Control System National Inst. of Technology, Kurukshetra, Haryana Pretty Neelam Topno M.Tech Control System National Inst. of Technology, Kurukshetra, Haryana ABSTRACT High accuracy trajectory tracking is challenging topic in robotic manipulator control. This is due to nonlinearities and input coupling present in robotic arm. This paper is concerned with the problem of modelling and control of two degree of freedom robotic manipulator. PID controller and sliding mode controller is derived so that actual trajectory tracks desired trajectory as close as possible despite of highly nonlinear and coupled dynamics. The goal is to determine which control strategy exhibit more robustness. Simulation study has been done in Matlab/Simulink environment shows that both the controllers are capable to control robot manipulator successfully. The result shows that Sliding Mode Control (SMC) produce better response compared to PID Control strategy when payload is changed. Keywords Robotic manipulator, PID controller, Manipulator control, Sliding mode control 1. INTRODUCTION The dynamic of robots is described by coupled second nonlinear differential equations and inertial parameter depends on the payload which is often unknown and changes during the task. Usually in a classical control we must have an accurate model, classical control cant compensate accurate model and robust model such as sliding mode control. So effort has been made for comparison of classical control such as PID control and sliding mode control in sense of robustness. The theory of Variable structure control has been developed firstly in Soviet Union by Emelyanov[11], introduced after by Utkin[10] and more recently studied by several authors. The robust nature of VSS is proved by the sliding mode. When the sliding mode occurs, the system will be forced to slide along or near the vicinity of the switching surface. The system became then robust and insensitive to the interaction, disturbances and variations. In addition, this does not require an accurate model of the robot. 2. ROBOT MANIPULATOR The dynamics of robot manipulator describes how the robot moves in response to these actuator forces which apply torques at the joint of robot. For simplicity, we will assume that the actuators do not have dynamics of their own and arbitrary torques can be commanded at the joint of the robot[4]. Fig.1 shows a two link planner robot arm manipulator. This arm simple enough to simulate, yet has all the nonlinear effects common to general robot manipulators. Fig.1 Two Link Planner Robotic Arm To determine the arm dynamics, we assume that the link masses m 1 and m 2 concentrated at the ends of links of lengths l 1 and l 2 , respectively. We define the angle of first link q 1 with respect to the inertial frame as depicted in fig.1. The angle of second link q 2 is defined with respect to the orientation of the first link. Torques τ 1 and τ 2 are applied by the actuators to control the angles q 1 and q 2 , respectively. The complete dynamics of two links arm[1,2] described as, M(q)q + N(q,q) = τ (2.1) Where the symmetric inertia matrix, α + β + 2ηcosq 2 β + ηcosq 2 M(q) = β + ηcosq 2 β (2.2) and nonlinear terms, N(q,q) = V(q,q) + G(q) (2.3) Where,