Search

Large lightweight slender links mounted on mobile robots enlarge their workspace. This work presents one of these robots that has been endowed with 4 legs to improve its static stability—which is put at risk by the large link—and help in the positioning of the link. The efficiency of this system depends on its accuracy in positioning and orientating the end-effector placed at the tip of the link, which is compromised by vibrations that appear in the link during the movement and permanent deflections caused by gravity. A relatively simple control scheme that combines a feedback control of the pose of the mobile platform with a feedforward term that orientates the link is proposed. It uses three legs as actuators; and feeds back measurements of the extensions of the three legs and the orientation of the platform given by an inertial sensor placed in the upper part of the mobile platform. Based on the flatness property of a simplified dynamic model of the link, its dynamics can be easily inverted, being used to implement the proposed feedforward term. Since such feedforward term is used, extra sensors to measure the deflection of the link are not needed, and since the legs are used to move the link, extra actuators mounted on the link are neither needed. All this allows us to reduce the weight and the volume of the payload carried by the mobile platform. Results obtained through a finite elements software and experimentation of the real prototype show the good performance attained with the proposed control strategy. [ABSTRACT FROM AUTHOR]

This work addresses the robust control of processes of the form G (s) = K · e − τ · s / (1 + T · s λ) with 1 < λ ≤ 2 . A new method for tuning fractional-order P I and P D controllers is developed. The stability is assessed based on the frequency domain tuning of the regulators to control such delayed fractional-order underdamped processes. In order to analyze the closed-loop stability and robustness, the new concept of Robust High-Frequency Condition is introduced. The analysis based on that demonstrates that each controller has a different region of feasible frequency specifications, and, in all cases, they depend on their fractional integral or derivative actions. Finally, an application example, the position control of a teleoperated manipulator with a flexible link, is presented. Simulations and experiments illustrate that the region of feasible frequency specifications defined at low and high frequencies allows us to obtain robust controllers that fulfill frequency requirements. [ABSTRACT FROM AUTHOR]

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 predictor is proposed. A time delay model of the preheating zone of this process is used, obtained from an identification procedure applied in a real industrial furnace. It is shown that this process experiences very large time delay changes. A fractional-order integral controller embedded in a Smith predictor structure (FI-SP) is designed, which is robust to changes in such time delay. Simulated results of a standard Proportinal Integral Derivative (PID) controller, a PID controller embedded in a Smith predictor and the proposed FI-SP controller are compared. Six performance indexes have been used in this comparison. The analysis of these indexes shows that the designed FI-SP controller exhibits the most robust behavior (lowest indexes averaged in all the range of time delay variation) for ranges that include large time delays. Then the robustness features of the FI-SP controller outperform the other integer order controllers in the time responses both to set-point changes and to step disturbances. Therefore, this controller guarantees the best accuracy of temperature control. The designed FI-SP guarantees system stability and robust performance for a high range of plant time delay uncertainties. [ABSTRACT FROM AUTHOR]

Some insects or mammals use antennae or whiskers to detect by the sense of touch obstacles or recognize objects in environments in which other senses like vision cannot work. Artificial flexible antennae can be used in robotics to mimic this sense of touch in these recognition tasks. We have designed and built a two-degree of freedom (2DOF) flexible antenna sensor device to perform robot navigation tasks. This device is composed of a flexible beam, two servomotors that drive the beam and a load cell sensor that detects the contact of the beam with an object. It is found that the efficiency of such a device strongly depends on the speed and accuracy achieved by the antenna positioning system. These issues are severely impaired by the vibrations that appear in the antenna during its movement. However, these antennae are usually moved without taking care of these undesired vibrations. This article proposes a new closed-loop control schema that cancels vibrations and improves the free movements of the antenna. Moreover, algorithms to estimate the 3D beam position and the instant and point of contact with an object are proposed. Experiments are reported that illustrate the efficiency of these proposed algorithms and the improvements achieved in object detection tasks using a control system that cancels beam vibrations. [ABSTRACT FROM AUTHOR]

In this paper we address the trajectory tracking problem of the end-effector of a single link flexible arm in which the gravity forces and the joint friction forces are taken into account. As an overall approach, a double loop cascade control is used to deal with the joint friction: in its inner loop a two-degree-of-freedom controller is responsible for the joint position in the presence of Coulomb friction disturbances, while in its outer loop an input-state feedback linearization-based controller is implemented to suppress the vibrations and track an end-effector trajectory. To highlight the benefits of the proposed controller in presence of joint friction, the controller was compared with other approaches based on feedback linearization reported in the literature, which considered only a single loop. The results of this comparison showed that our approach provides superior performance in terms of settling time, maximum overshoot and residual vibrations. The design of the controller presented relies on a non-linear single-lumped mass dynamic model that describes the dynamics of a single link arm with only one significant vibrational mode. The hypothesis of a single lumped mass model could be considered inaccurate given the distributed nature of the link mass, especially in situations in which the link mass is comparable to the payload mass held by the robot. However, for the parameters of our physical platform two studies are presented to demonstrate that the single lumped mass model is a proper description of the system even in situations in which the link mass is up twice bigger than the payload mass. The results of the paper are demonstrated with co-simulations with Matlab/Simulink and MSC ADAMS, and experimental validation. [ABSTRACT FROM AUTHOR]

Model design and motion control are considered the cornerstones of the robotic field that allow for achieving performance tasks. This article proposes a new dynamic modeling and control approach for very lightweight mechanical systems carrying payloads. The selection of the model and the design of the control are elaborated on using a fractional order framework under different conditions. The use of fractional order calculus is justified by the better performance that reveals a fractional order model compared to an integer order model of similar complexity. The mechanical structure of very lightweight manipulators has vibrations that impede the accurate positioning of their end effector. Moreover, they have actuators with high friction and sensors to measure the vibrations, which often are strain gauges, that have offset and high-frequency noise. All these mentioned problems might degrade the mechanical system's performance. Hence, to overcome these inconveniences, two nested-loop controls are examined: an inner loop that controls the motor dynamics and removes the friction effects and an outer loop implemented to eliminate the beam vibrations by adapting the input-state feedback linearization technique. Then, we propose a new fractional order control scheme that (1) removes the strain gauge offset disturbances, (2) reduces the risk of the actuator's saturation caused by the high-frequency noise of strain gauges and (3) reduces the dynamic effects of huge payload changes. We prove that our fractional controller has enhanced robustness with respect to the above-mentioned problems. Finally, the investigated approach is validated experimentally by applying it to a lightweight robot mounted on an air table. [ABSTRACT FROM AUTHOR]

This work presents a position control for a two degree of freedom flexible-beam made of a composite material, whose aim is to control the tip of the flexible-beam by decreasing the vibration when the beam moves. A mechatronic unit that uses a multi-axis force/torque sensor has been specially designed and we propose to control the system by using a reduced dynamic model. The control method makes use of an inner-loop to control the position of two servo-motors, by means of PID regulators, and an outer-loop that cancels the tip vibration. Moreover, the closed-loop motor dynamics has been reduced by using a series connection of filters that invert its dynamics. The motor controllers have proved to be fast and precise, and cancel the non-modelled components of the motor friction without the need for a previous estimation. The flexible-beam vibration has been controlled by implementing an input-state feedback linearisation which includes compensation terms for the nonlinear beam dynamics, a linear feedback control law and a full state estimator. The experimental validation of the complete control method showed a significant trajectory tracking of the tip, while vibrations were prevented. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the problem of designing controllers that are robust to a great uncertainty in a time constant of the plant. Plants must be represented by minimum phase rational transfer functions of an arbitrary order. The design specifications are: (1) a phase margin for the nominal plant, (2) a gain crossover frequency for the nominal plant, (3) zero steady state error to step commands, and (4) a constant phase margin for all the possible values of the time constant ( ): . We propose a theorem that defines the structure of the set of controllers that fulfil these specifications and show that it is necessary for these robust controllers to include a fractional-order term. Examples are developed for both stable and unstable plants, and the results are compared with a standard controller and a robust controller designed using the methodology. [Copyright &y& Elsevier]

Abstract: This paper deals with the design of a predictive-integral current controller for renewable energy systems connected to the grid through PWM voltage-source converters. The control system is tailored to achieve a deadbeat-type response to set-point step changes and decoupled active- and reactive-power control. An alternative approach is designed by using a state-feedback controller. Both control systems are compared in terms of the robustness of the closed-loop dynamic response and the active and reactive-power coupling when system-modelling errors exist. Simulation and experimental results show that the predictive-integral approach is superior. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

This paper proposes the design of an IMC-PID controller with a fractional order filter (IMC-FPID) for the effective control of water distribution in a main irrigation canal pool. From real-time data and applying the system identification procedure a dynamic mathematical model of this process is obtained, which is represented by a first-order transfer function with a time delay. Based on the model obtained an IMC-PID controller with a fractional order filter was designed that behaves effectively. The simulation results compare the performance of the proposed controller with a conventional IMC-PID controller. In this comparison, the performance index of the integral of absolute error (IAE) was used. The results obtained show that the proposed controller provides lower values of this index and consequently outperforms the conventional IMCPID controller in terms of performance and accuracy. [ABSTRACT FROM AUTHOR]

In this paper, a review of the state of the art of the control strategies used for the water distribution control in irrigation systems is developed, aimed at increasing the operability of these systems, as well as reducing water losses due to operation. The historical advances of this kind of control systems are shown. Finally, some of the challenges of the international scientific community are offered to continue improving the capability and performance of the controllers used in irrigation systems. [ABSTRACT FROM AUTHOR]

In this paper, two types of fractional-order damping are proposed for a single flexible link: internal and external friction, related to the material of the link and the environment, respectively. Considering these dampings, the Laplace transform is used to obtain the exact model of a slewing flexible link by means of the Euler–Bernoulli beam theory. The model obtained is used in a sensing antenna with the aim of accurately describing its dynamic behavior, thanks to the incorporation of the mentioned damping models. Therefore, experimental data are used to identify the damping phenomena of this system in the frequency domain. Welch's method is employed to estimate the experimental frequency responses. To determine the best damping model for the sensing antenna, a cost function with two weighting forms is minimized for different model structures (i.e., with internal and/or external dampings of integer- and/or fractional-order), and their robustness and fitting performance are analyzed. [ABSTRACT FROM AUTHOR]

As a result of the exhaustion of fossil energy sources and the corresponding increase of their negative environmental impact, recent research has intensively focused on regions of alternative energy resources and, especially, on solar energy. Slow tracking of the maximum power point (MPP) and fluctuations around the MPP reduce the efficiency of photovoltaic power generation systems (PV). This study offers a novel design for the MPPT controller, which we refer to as the "hybrid IC-LQI approach", which combines the incremental conductance (IC) technique and the linear quadratic integral (LQI) controller based on the boost converter's small signal model. We conduct a comparative study of the proposed hybrid IC-LQI, and the classical one-stage IC technique in order to show the effectiveness of our proposal under three different scenarios of weather conditions and load. According to simulation findings, the proposed hybrid IC-LQI approach has a high tracking efficiency of up to 98.92%, owing to faster tracking of MPP with very large reduction of oscillations. On the other hand, the IC technique provides less efficiency, up to 96.1%, showing very slow tracking and high oscillations. The presented analysis of the results confirms the superior performance of the developed hybrid IC-LQI technique to the classical IC technique. [ABSTRACT FROM AUTHOR]

Recent advances in mobile robotic technologies have enabled significant progress to be made in the development of Stair-Climbing Mobility Systems (SCMSs) for people with mobility impairments and limitations. These devices are mainly characterized by their ability to negotiate those architectural barriers associated with climbing stairs (curbs, ramps, etc.). The development of advanced trajectory generators with which to surpass such architectural barriers is one of the most important aspects of SCMSs that has not yet been appropriately exploited. These advanced trajectory generators have a considerable influence on the time invested in the stair climbing process and on passenger comfort and, consequently, provide people with physical disabilities with greater independence and a higher quality of life. In this paper, we propose a new nonlinear trajectory generator for an SCMS. This generator balances the stair-climbing time and the user's comfort and includes the most important constraints inherent to the system behavior: the geometry of the architectural barrier, the reconfigurable nature of the SCMS (discontinuous states), SCMS state-transition diagrams, comfort restrictions and physical limitations as regards the actuators, speed and acceleration. The SCMS was tested on a real two-step staircase using different time-comfort combinations and different climbing strategies to verify the effectiveness and the robustness of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper a two-input, two-output (TITO) fractional order mathematical model of a laboratory prototype of a hydraulic canal is proposed. This canal is made up of two pools that have a strong interaction between them. The inputs of the TITO model are the pump flow and the opening of an intermediate gate, and the two outputs are the water levels in the two pools. Based on the experiments developed in a laboratory prototype the parameters of the mathematical models have been identified. Then, considering the TITO model, a first control loop of the pump is closed to reproduce real-world conditions in which the water level of the first pool is not dependent on the opening of the upstream gate, thus leading to an equivalent single input, single output (SISO) system. The comparison of the resulting system with the classical first order systems typically utilized to model hydraulic canals shows that the proposed model has significantly lower error: about 50%, and, therefore, higher accuracy in capturing the canal dynamics. This model has also been utilized to optimize the design of the controller of the pump of the canal, thus achieving a faster response to step commands and thus minimizing the interaction between the two pools of the experimental platform. [ABSTRACT FROM AUTHOR]

This sequential paper aims to present studies on modelling and tip tracking control of a flexible single beam. It first outlines the flexible-beam robotic mechanism that was designed and built to be used for the force and torque sensory information-based modelling and control. It then details the vibration suppression controller strategy that is applied to this robotic system. The controller is designed with respect to a simple lumped model describing the dynamics of the system. Here the dynamics of the closed-loop controlled motor is inverted in order to obtain a system with unity dynamics. Further, the flexible-beam dynamics is input state linearized. Finally, a simple external feedback control, which is based on the measurements of beam deflections using a force and torque sensor, is implemented. The complete experimental setup was positioned by two servo-motors controlled by a proportional-integral-derivative controller for each axis. The proposed controllers allow the flexible beam to move continuously in a precise manner, so that it could be treated as an accurate positioning sensor. Simulation and experimental results provided at the end illustrate that the controllers designed and implemented produce a satisfactory control performance and adequate robustness to model uncertainties and system nonlinearities. [ABSTRACT FROM AUTHOR]

We deal with the online identification of the payload mass carried by a single-link flexible arm that moves on a vertical plane and therefore is affected by the gravity force. Specifically, we follow a frequency domain design methodology to develop an algebraic identifier. This identifier is capable of achieving robust and efficient mass estimates even in the presence of sensor noise. In order to highlight its performance, the proposed estimator is experimentally tested and compared with other classical methods in several situations that resemble the most typical operation of a manipulator. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a detailed study of a method of rotor-resistance estimation for indirect-field-oriented control of induction machines based on the reactive-power reference model. It will show how the estimation procedure can be carried out independently of the stator frequency and the load torque. The stability of the estimation procedure will also be demonstrated. Simulation and experimental results will be presented to validate the main contributions of this work. Finally, the sensitivity of the algorithm to errors in other machine parameters will be investigated. [Copyright &y& Elsevier]

This paper presents the detailed design, analysis, and application of the controller for a shunt active power filter based on a pulsewidth modulation dc-to-ac voltage source converter. The controller is mainly tailored to compensate harmonic currents of nonlinear loads connected to the mains. However, it can also achieve reactive-power compensation and mains-current balancing when required. The controller has a two-layer structure. The outer layer generates the current references for the inner layer. The former uses a plug-in discrete-time repetitive algorithm for current-harmonic compensation, a proportional-integral algorithm to maintain the dc-capacitor voltage in spite of unmodeled losses and a reactive-power-reference generator. The inner layer uses state-feedback with integral action for current control. The repetitive controller is justified to improve the tracking of the periodic current references required by the active filters. The stability of the resulting closed-loop system is studied and some indication of the system robustness is given. The proposed controller has been tested in a prototype with balanced and unbalanced nonlinear loads. A discrete-time model of the filter has been used from the beginning. The microcomputer delay when calculating the controller output and the delay due to the anti-aliasing filters have been included in the inner system state-variable model. [ABSTRACT FROM AUTHOR]

Conventionally, the parameters of a fuzzy logic controller (FLC) are obtained by a trial and error method or by human experience. In this paper, the problem of designing a FLC for maximum power point tracking (MPPT) of a photovoltaic system (PV) that consists of a PV generator, a DC-DC boost converter and a lead-acid battery is studied. The normalization gains, the membership functions and the fuzzy rules are automatically adjusted using a particles swarm optimization algorithm (PSO) in order to maximize the criterion based on the integration of the PV module power under standard temperature condition (STC) (T=25°C and S=1000 W/m²). The robustness test of the optimized fuzzy logic MPPT controller (FLC-MPPT) is carried out under different scenarios. Simulation results of the system clearly show that the proposed optimized FLCMPPT controller outperforms in terms of maximum efficiency the FLC-MPPT controller not optimized, the FLC-MPPT controller with optimized normalization gains and the FLC-MPPT controller with optimized normalization gains and membership functions. [ABSTRACT FROM AUTHOR]

The design and application of sensing antenna devices that mimic insect antennae or mammal whiskers is an active field of research. However, these devices still require new developments if they are to become efficient and reliable components of robotic systems. We, therefore, develop and build a prototype composed of a flexible beam, two servomotors that drive the beam and a load cell sensor that measures the forces and torques at the base of the flexible beam. This work reports new results in the area of the signal processing of these devices. These results will make it possible to estimate the point at which the flexible antenna comes into contact with an object (or obstacle) more accurately than has occurred with previous algorithms. Previous research reported that the estimation of the fundamental natural frequency of vibration of the antenna using dynamic information is not sufficient as regards determining the contact point and that the estimation of the contact point using static information provided by the forces and torques measured by the load cell sensor is not very accurate. We consequently propose an algorithm based on the fusion of the information provided by the two aforementioned strategies that enhances the separate benefits of each one. We demonstrate that the adequate combination of these two pieces of information yields an accurate estimation of the contacted point of the antenna link. This will enhance the precision of the estimation of points on the surface of the object that is being recognized by the antenna. Thorough experimentation is carried out in order to show the features of the proposed algorithm and establish its range of application. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Incremental Conductance (IncCond) algorithm based on direct control mode is one of the highest Maximum Power Point Tracking (MPPT) algorithms ensuring multiple performances compared to some other classical methods. Unfortunately, these performances can deteriorate, especially in the case of sudden changes in weather conditions and load variation., Preventing these drawbacks will form the basis of a new IncCond-MPPT scheme based on indirect control mode in which a smooth electrical power response generated by photovoltaic (PV) panels is well ensured, regardless of quick changes in solar irradiance, absolute temperature and load variation. The proposed MPPT approach uses two stages of control. The first one is used to provide the reference PV-module voltage. The second control loop is formulated as a transfer function that is then controlled using an appropriate Integral controller. Its integral gain is well tuned by applying the Routh's stability criterion on the characteristic equation of the obtained closed loop transfer function. This allows providing the proposed new guideline, which represents the main contribution of this paper. The proposed IncCond-MPPT scheme is compared with the standard one in terms of MPP tracking accuracy and electrical power ratio, which exceeds 97 %, where quick changes of weather conditions and load variations are considered. [ABSTRACT FROM AUTHOR]