Showing papers by "Vicente Feliu-Batlle published in 2019"

Stable force control and contact transition of a single link flexible robot using a fractional-order controller.

Abstract: The control of robots that interact with the environment is an open area of research. Two applications that benefit from this study are: the control of the force exerted by a robot on an object, which allows the robot to perform complex tasks like assembly operations, and the control of collisions, which allows the robot safely collaborate with humans. Robot control is difficult in these cases because: (1) bouncing between free and constrained motion appears that may cause instability, (2) switching between free motion (position) controller and constrained motion (force) controller is required being the switching instants difficult to know and (3) robot control must be robust since the mechanical impedance of the environment is unknown. Robots with flexible links may alleviate these drawbacks. Previous research on flexible robots proved stability of a PD controller that fed back the motor position when contacting an unknown environment, but force control was not achieved. This paper proposes a control system that combines a fractional-order D tip position controller with a feedforward force control. It attains higher stability robustness and higher phase margin than a PD controller, which is the integer-order controller of similar complexity. This controller outperforms previous controllers: (1) it achieves force control with nearly zero steady state error, (2) this control is robust to uncertainties in the environment and motor friction, (3) it guarantees stability (like others) but it also guarantees a higher value of the phase margin, i.e., a higher damping, and a more efficient vibration cancellation, and (4) it effectively removes bouncing. Experimental results prove the effectiveness of this new controller.

Maximum Power Point Tracker Based on Fuzzy Adaptive Radial Basis Function Neural Network for PV-System

Abstract: In this article, a novel maximum power point tracking (MPPT) controller for a photovoltaic (PV) system is presented. The proposed MPPT controller was designed in order to extract the maximum of power from the PV-module and reduce the oscillations once the maximum power point (MPP) had been achieved. To reach this goal, a combination of fuzzy logic and an adaptive radial basis function neural network (RBF-NN) was used to drive a DC-DC Boost converter which was used to link the PV-module and a resistive load. First, a fuzzy logic system, whose single input was based on the incremental conductance (INC) method, was used for a variable voltage step size searching while reducing the oscillations around the MPP. Second, an RBF-NN controller was developed to keep the PV-module voltage at the optimal voltage generated from the first stage. To ensure a real MPPT in all cases (change of weather conditions and load variation) an adaptive law based on backpropagation algorithm with the gradient descent method was used to tune the weights of RBF-NN in order to minimize a mean-squared-error (MSE) criterion. Finally, through the simulation results, our proposed MPPT method outperforms the classical P and O and INC-adaptive RBF-NN in terms of efficiency.

Smith predictor based fractional-order integral controller for robust temperature control in a steel slab reheating furnace:

Abstract: In this paper, a new strategy for robust control of temperature in a steel slab reheating furnace with large time delay uncertainty based on fractional-order controllers combined with a Smith predi...

Passivity-based control of a single-link flexible manipulator using fractional controllers

Abstract: This work presents a new methodology for the design of passivity-based controllers of fractional order for single-link flexible robots. In this work, some previously developed passivity-based controllers, which have robust stability to parametric uncertainties and spillover effects, are extended by using phase-lag controllers of fractional order. The extra degree of freedom supplied by these controllers is used to enhance the phase margin robustness of these systems and the sensitivity to sensor high-frequency noise. These controllers are applied to the position control of a single-link flexible robot. Experiments show that fast and precise vibration-free movements of a flexible robot are achieved. Also, the property of phase margin robustness to changes in the payload using this new controller is experimentally assessed.

Two-degrees-of-freedom PI2D controller for precise nanopositioning in the presence of hardware-induced constant time delay.

Abstract: This work was supported in part by the Spanish Agencia Estatal de Investigacion (AEI) under Project DPI2016-80547-R (Ministerio de Economia y Competitividad) and in part by the European Social Fund (FEDER, EU), and in part by the Spanish FPU12/00984 Program (Ministerio de Educacion, Cultura y Deporte).

A Fractional-Order Partially Non-Linear Model of a Laboratory Prototype of Hydraulic Canal System.

Abstract: This article addresses the identification of the nonlinear dynamics of the main pool of a laboratory hydraulic canal installed in the University of Castilla La Mancha. A new dynamic model has been developed by taking into account the measurement errors caused by the different parts of our experimental setup: (a) the nonlinearity associated to the input signal, which is caused by the movements of the upstream gate, is avoided by using a nonlinear equivalent upstream gate model, (b) the nonlinearity associated to the output signal, caused by the sensor’s resolution, is avoided by using a quantization model in the identification process, and (c) the nonlinear behaviour of the canal, which is related to the working flow regime, is taken into account considering two completely different models in function of the operating regime: the free and the submerged flows. The proposed technique of identification is based on the time-domain data. An input pseudo-random binary signal (PRBS) is designed depending on the parameters of an initially estimated linear model that was obtained by using a fundamental technique of identification. Fractional and integer order plus time delay models are used to approximate the responses of the main pool of the canal in its different flow regimes. An accurate model has been obtained, which is composed of two submodels: a first order plus time delay submodel that accurately describes the dynamics of the free flow and a fractional-order plus time delay submodel that properly describes the dynamics of the submerged flow.

Feasible frequency robustness conditions for PI α controllers: Laboratory hydraulic canal system as an example of analysis

Abstract: For delayed fractional order processes, fractional order controllers of the form $PI^{\alpha }$ are designed to fulfil an iso-phase margin constraint and two design frequency specifications: gain crossover frequency and phase margin. In this paper, regions of robust frequency specifications to gain changes are developed and are approximated in function of the fractional orders of the plant and the controller. For the obtained regions, every two frequency specifications could be satisfied and the controller is designed respecting to an added iso-phase margin constraint. Numerical simulations in the time and frequency domains clearly justify the utility of the developed regions and the performances of the designed controllers.