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Cruz-Zavala E.,National Autonomous University of Mexico | Moreno J.A.,National Autonomous University of Mexico | Fridman L.M.,CINVESTAVIPN | Fridman L.M.,National Autonomous University of Mexico
IEEE Transactions on Automatic Control | Year: 2011

The differentiators based on the Super-Twisting Algorithm (STA) yield finite-time and theoretically exact convergence to the derivative of the input signal, whenever this derivative is Lipschitz. However, the convergence time grows unboundedly when the initial conditions of the differentiation error grow. In this technical note a Uniform Robust Exact Differentiator (URED) is introduced. The URED is based on a STA modification and includes high-degree terms providing finite-time, and exact convergence to the derivative of the input signal, with a convergence time that is bounded by some constant independent of the initial conditions of the differentiation error. Strong Lyapunov functions are used to prove the convergence of the URED. © 2011 IEEE. Source

Proceedings of the IEEE International Conference on Control Applications | Year: 2010

Neural sliding mode control (NSMC) may decrease chattering of the sliding mode control (SMC) and improve control accuracy of the neural control (NC). There are some problems with the common parallel structure, such as the chattering is big at start stage. In order to overcome the above problem, we propose a new serial structure for NSMC, it is called two-stage neural sliding control. A dead-zone NC is used to make the tracking error bounded, then super-twisting second-order SMC is applied to guarantee finite time convergence. This new controllers has less chattering during its discrete realization, and ensures finite time convergence. Real-time experiments for a magnetic levitation system are presented to compare this new NSMC with regular controllers, such as PID, NC, SMC, and normal NSMC. © 2010 IEEE. Source

Yu W.,CINVESTAVIPN | Rosen J.,University of California at Santa Cruz
Proceedings of the IEEE Conference on Decision and Control | Year: 2010

An upper limb exoskeleton is a wearable robotic system that is physically linked to the arm of the human operators and its seven actuated degrees of freedom (DOF) match the seven DOF of the human arm. The stability of such a system is critical given the proximity of its human operator. A new PID controller is developed which guarantee asymptotic stability for this class of robotic manipulators. A simulation was used to assess the system performance given the theoretical results of the controller's parameters with a unique exoskeleton system (EXO-UL7). The simulation also verify the semi-global asymptotic stability of the system. The proposed methodology eliminates the need of the system's dynamics model for the purpose of designing the controller. It provides an analytical tool for the controller design that is traditionally preformed experimentally (parameter tuning). Source

Ramirez-Neria M.,CINVESTAVIPN | Sira-Ramirez H.,CINVESTAV | Luviano-Juarez A.,UPIITA IPN | Rodrguez-Angeles A.,CINVESTAV
Asian Journal of Control | Year: 2015

In this article, the problem of robust trajectory tracking, for a parallel robot is tackled via an observer-based active disturbance rejection controller. The proposed design method is based on purely linear disturbance observation and linear feedback control techniques modulo nonlinear input gain injections and cancellations. The estimations are carried out through Generalized Proportional Integral (GPI) observers, endowed with output integral injection to ease the presence of possible zero mean measurement noise effects. As the lumped (both exogenous and endogenous) disturbance inputs are estimated, they are being used in the linear controllers for on-line disturbance cancellation, while the phase variables are being estimated by the same GPI observer. The estimations of the phase variables are used to complete a linear multivariable output feedback controller. The proposed control scheme does not need the exact knowledge of the system, which is a good alternative to classic control schemes such as computed torque method, reducing the computation time. The estimation and control method is approximate, ensuring small as desired reconstruction and tracking errors. The reported results, including laboratory experiments, are better than the results provided by the classical model-based techniques, shown to be better when the system is subject to endogenous and exogenous uncertainties. © 2014 Chinese Automatic Control Society and Wiley Publishing Asia Pty Ltd. Source

IEEE International Conference on Control and Automation, ICCA | Year: 2011

This paper addresses the iterative tuning method of PID control for the robot manipulator based on the responses of the closed loop system. Several properties of the robot control are used, such as any PD control can stabilize a robot in regulation case, the colsed-loop system of PID control can be approximated by a linear system, and the control torque to the robot manipulator is linearly independent of the robot dynamic. By using these properties, a novel systematic turning method for the PID control is proposed. Simulations and experimental results of an upper limb exoskeleton give validation of this PID tuning method. © 2011 IEEE. Source

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