Robots are complex mechatronics systems where several electric drives are employed to control the movement of articulated structures. In industrial environments they must perform tasks with rapidity and accuracy in order to produce goods and services with minimal production time. These procedures require the use of flexible robots which can act in a large workspace, thus subjected to important parameters variations and nonlinear dynamics effects. This paper investigates the fractional order dynamics during the evolution of trajectories of three robotic joints, considering the complete system dynamics. Copyright © 2006 IFAC.2PART 1367372Barbosa, R.S., Tenreiro Machado, J.A., Ferreira, I.M., Tuning of PID Controllers Based on Bode's Ideal Transfer Function (2004) Nonlinear Dynamics, 38, pp. 305-321. , Kluwer Academic PublishersBoucher, P., Dumur, D., Predictive Motion Control (1995) Journal of Systems Engineering, Special Issue on Motion Control Systems, 5, pp. 148-162. , Springer-VerlagClarke, D.W., Mohtadi, C., Tuffs, P.S., Generalized Predictive Control, Part I "The Basic Algorithm", Part II "Extensions and Interpretation (1987) Automatica, 23 (2), pp. 137-160David, S., Rosário, J.M., Modeling, Simulation and Control of Flexible Robots (1998) CONTROLO'98, pp. 532-539. , Coimbra, PortugalLima, M.F.M., Tenreiro Machado, J.A., Experimental Set-Up for Vibration and Impact Analysis in Robotics (2005) WSEAS Trans. on Systems, (5), pp. 569-576. , vol. $, MayPimenta, K.B., Souza, J.P., Rosário, J.M., Dumur, D., Control of Robotic Joints with Generalized Predictive Control (GPC) (2001) RADD'2001, , Vienna, AustriaTenreiro Machado, J.A., A Probabilistic Interpretation of the Fractional-Order Differentiation (2003) Journal of Fractional Calculus & Applied Analysis, 6 (1), pp. 73-80