IOSR Journal of Engineering (IOSRJEN)www.iosrjen.org ISSN (e): 2250-3021, ISSN (p): 2278-8719 Vol. 04, Issue 04 (April. 2014), ||V5|| PP 05-17 International organization of Scientific Research 5 | P a g e Novel Adaptive PID Control of Flexible Joint Robot Manipulator withBounded Disturbances Hossam N. Doghiem * Design and Production Engineering Department,Faculty of Engineering, Ain Shams University, Cairo, Egypt Abstract: - A novel robust adaptive PID control scheme is proposed with known upper bound of the external disturbances, to solve the dynamic coupling and strong nonlinearity problems in flexible joint robot manipulator control. Invoking the proposed controller, the bounded external disturbances can be compensated and the global asymptotical stability with respect to the manipulator positions and velocities is able to be guaranteed. The designed control law can enlarge the tolerable external disturbances, enhance the accuracy of trajectory tracking error, and improve the dynamic performance of the manipulator systems. The stability and convergence properties of the closed-loop system are analytically proved using Lyapunov stability theory and Barbalat's lemma. Simulation for the proposed control system is performed for a two-degree of freedom flexible joint robot, each joint modeled by two-equations of second order to illustrate its viability, and advantages. Keywords: - Adaptive PID controller, Dynamic coupling, Flexible joint robot, Bounded external disturbances, Lyapunov stability theory, Trajectory tracking error. I. INTRODUCTION Robot manipulators play an important part in modern industry by providing lower production cost, enhanced precision, quality, productivity, and efficiency. The control of robot faces significant difficulties, with regard to such a complicated system, various controllers have been developed [1], such as adaptive controllers [2-4], robust controllers [5-7] and controllers based on the theory of variable structure [8-11]. However, the applicability of these controllers to practical robot is limited because the assumption of perfect rigidity is never satisfied exactly. Since linear control methods are not suitable for strong coupled, nonlinear and time-varying flexible robot manipulator systems, many nonlinear control schemes based on conventional PID control theory have been proposed to improve the control performance. In [12], the global asymptotic stability of a class of nonlinear PD-type controllers for position and motion control of robot manipulators is analyzed, and a global regulator constrained to deliver torques within prescribed limits of the actuator's capabilities is proposed. However, it has been shown that although the PD controller is robust with respect to uncertainties on inertial parameters and the global asymptotic stability is guaranteed, uncertainties on the gravity parameters may lead to undesired steady state errors [13]. A PID control scheme can eliminate the steady-state errors, but it can only ensure local asymptotic stability. Moreover, to guarantee the stability, the gain matrices must satisfy complicated inequalities [14]. In [15], a new variable structure PID control scheme is designed for robot manipulators. Robust control laws are used for external disturbances, unstructured dynamics, and other sources of uncertainties. [16,17] present a popular approach for designing robust controller. A simple robust nonlinear control law is derived by [18] using the approach of [17] for n-link robot manipulators using the well-known Lyapunov theory to guarantee stability of uncertain systems. Other control methods developed based on [16,17] are given in [19,20]. However, disturbances and unmodeled dynamics are not considered in the algorithms in [18-20]. In [21], the method developed by [18] is modified such that the controller is robust to unmodeled dynamics and disturbances. Most adaptive algorithms may exhibit poor robustness to unstructured dynamics and external disturbances, to resolve this, a combination of robust control and adaptive algorithm is investigated in a number of literatures. In[22], adaptive controllers are designed for robot manipulators that yield robust trajectory in spite of the unwanted effects of the external disturbances and fast maneuvering of the manipulator. The algorithm presented in [23] is suitable for swift adaptation to rapidly changing system parameters. In [24], a decentralized adaptive controller is investigated for trajectory tracking of robot manipulator systems. A disturbance observer is introduced in each controller to compensate for coupled uncertainties, and an adaptive sliding mode control term is employed to handle the fast changing components of the uncertainties beyond the pass band of the disturbance observer. A novel robust decentralized control scheme by adaptive fuzzy estimation and compensation uncertainty is proposed by [25]. The controller is designed via voltage control strategy, a fuzzy system is used to