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This article presents a novel simplified method to implement the finite set - model predictive control technique for photovoltaic generation systems connected to the ac network. This method maintains the advantages of the conventional finite set - model predictive control, such as fast response, simple implementation, and easy understanding; but it also eliminates the use of a cost function and hence the weighting factors, instead, it finds the optimal operating state directly from the model and the discrete number of valid states of the converter. Although the proposed algorithm does not compute a cost function, it is able to select the inverter state that minimizes the tracking error by using a hexagonal convergence region. The main advantage of this technique is to reduce the computational cost in 43% of the algorithm that selects the best state, presenting a simple and complete algorithm without compromising the predictive control performance. The proposed algorithm properly operates under various conditions such as changes in the network frequency and changes in the system parameters.

Power conversion has gain relevance because of the capacity to transform the electric energy as needed in many applications such as electrical drives, electromobility, reactive power compensation, renewable energies, among others. In this context, the proper control of the power converter may lead to improve the efficiency and protect the entire power converter system. This paper presents a deadbeat control with the capability to enhance the fast dynamic response, typical of this technique, and therefore to be used for current and voltage control applications that require slower dynamic. The proposed technique is implemented in a three-phase power converter with satisfactory results; moreover, this technique is simple and light in computational cost. Finally, to corroborate the proposal, simulations are included with satisfactory results showing an improved dynamic and making the deadbeat control softer as some applications may require.

[Background] The literature reports multiple models (or instruments) for measuring Teamwork Quality (TWQ) for Agile Software Development However, these models have different constructs and measures, and there is a lack of empirical evidence comparing them. [Goal] This study fills this gap by analyzing if two agile TWQ models yields equivalent results. [Method] First, we mapped the models’ variables given their definitions. Then, we collected data using both a BN model (Baysean Network model), TWQ-BN, and Structural Equation Modeling, TWQ-SEM, by interviewing 162 team members from two software development companies. We analyzed the collected data by applying the Bland-Altman method. [Results] We obtained enough evidence to conclude that the results for Communication, Coordination, Cohesion and Mutual Support are not equivalent. Conversely, we did not have enough evidence to claim that the models do not agree for measuring Effort and Balance of member contribution. [Conclusions] The results of this study detail how two state-of-the-art agile TWQ compare in terms of their measures as well as potential research areas for further investigation.

The transportation of large loads is still an obstacle to the productivity of some companies. To answer this internal logistics challenge, one solution with high potential is the use of several mobile robots that can execute these tasks cooperatively. This paper addresses the simulation of strategies that allow two omnidirectional robots, a leader and a follower, to coordinate their movement and cooperate in a transportation task (co-transport). This is achieved by implementing a force sensor on the mechanical structure of a support that allows the follower to grab and transport the load on the top of its chassis. Through the measurement of the forces, this robot will be able to react to the movement of the leader, whose function will be to guide the system to its final destination. The system and its cooperation strategies were idealized and then tested in the CoppeliaSim simulator. The results obtained through simulation were the target of an analysis that assessed which strategy best complemented the omnidirectional mobility of the system’s constituents and, at the same time, ensured that less forces were exerted on the load during transport.

The increase of the world population and a decrease in agricultural labour availability have motivated research robotics in the agricultural field. This paper aims to analyze the state of the art related to manipulators used in the agricultural robotics field. Two pruning and seven harvesting manipulators were reviewed and are analyzed. The pruning manipulators were used in two different scenarios: (i) grapevines and (ii) apple trees. These manipulators showed that a light-controlled environment could reduce visual errors and that prismatic joints on the manipulator are advantageous to obtain a higher reach. The harvesting manipulators were used for 5 different products: (i) strawberries, (ii) tomatoes, (iii) apples, (iv) sweet-peppers and (v) iceberg lettuce. The harvesting manipulators showed that a different kinematic configuration is required for different end-effectors, as some end-effectors only require horizontal movements and others require more degrees of freedom to reach and grasp the target. This work will support new developments of novel solutions related to agricultural robotic grasping and manipulation.

The legged robots can insert themselves in environments for which the robots with wheels are simply incapable of be inserted, as is the case of obstacles of large dimensions, terrain loose or steep slopes [1]– [5]. The objective of this work is to develop the modeling of hexapods robots and simulate them in a virtual environment of mechanical systems (according to Fig. 1), which makes possible performance analysis of several model criteria and determine the virtual path built by the robot [6]. The present work implemented the robot simulation in the Simulink simulation environment, using SimMechanics [7]. A computer program [8] was developed to make changes in the mechanical structure, in the simulation parameters, to evaluate the stability of the type of locomotion, the direct visualization of the position, speed, acceleration, and force applied to each foot of the robot. With the implementation of the stability determination algorithm, it was possible to verify that, for different locomotion patterns, there was an improvement in the stability, starting from the metachronal wave to tetrapod and tripod gaits, and there was also a consecutive decrease in the minimum torque required to the servo motors [9].

The transport of patients from the inpatient service to the operating room is a recurrent task in the hospital routine. This task is repetitive, non-ergonomic, time consuming, and requires the labor of patient transporters. In this paper is presented the design of a driverless wheelchair under development capable of providing an on-demand mobility service to hospitals. The proposed wheelchair can receive transportation requests directly from the hospital information management system, pick-up patients at their beds, navigate autonomously through different floors, avoid obstacles, communicate with elevators, and drop patients off at the designated destination.

This paper provides an overview of the development of a Sail Car within the European Project Semester (EPS), the international multidisciplinary engineering capstone programme offered by the Instituto Superior de Engenharia do Porto (ISEP). The main goal of EPS@ISEP is to offer a project-based educational experience to develop teamwork, communication, interpersonal and problem-solving skills in an international and multidisciplinary set up. The Sail Car team consisted of six Erasmus students, who participated in EPS@ISEP during the spring of 2019. The objective of the project was to design and develop a wind-powered, easy to drive land sailing vehicle. First, the team researched existing commercial solutions and considered the marketing, ethics and sustainability dimensions of the project. Next, based on these studies, specified the full set of requirements, designed the Sailo solution and procured the components and materials required to build a real size proof-of-concept prototype. Finally, the team assembled and tested successfully the prototype. At the end of the semester, the team considered EPS@ISEP a mind-opening opportunity.

Maximum Power Point Tracking (MPPT) methods have been widely discussed in many researches to improve the efficiency of the energy extraction from solar cells. On the other hand, to control process the most common way is to find a model, where the parameters are adjusted in order to achieve similarity between the model and the real plant. Solar cells have been modeled by nonlinear equations that allow to approximate the static behavior. However, the parameters evolved in these equations depend upon the construction and the type of solar cells. Thus, this paper proposes a parameter identification with a new simplified method to identify the parameters n, Rs and I0, by studying and analyzing the equations of the PV model and the information provided by the datasheets of the best-selling commercial PV panels in the world.

A domain-specific modeling language called Healthcare System Specifications (HSS) was proposed for developing clinical pathways. This high-level language was defined as a Unified Modeling Language (UML) profile. It was also proposed a model to model transformation which obtains from pathways HSS specification, a Stochastic Well-formed Net (SWN). The SWN has the capacity to model the complex healthcare system, however, it is hard to perform qualitative and quantitative analysis in this kind of nets. This paper presents a set of relaxations, abstractions and modifications to be applied in the SWNs in order to obtain subclasses of Petri Nets in which formal analysis can be performed. In particular, we obtain the classes of S4 PR and DSSP nets. The first one considers the shared resources of the hospital while the second class allows managing the interchange of information between clinical pathways.

This paper proposes a mixed linear control and model predictive control (MPC) scheme with extended horizon for a neutral point inverter topology (NPC) for photovoltaic applications connected to the AC network. The strategy is able to minimize the unbalance of the voltages of the capacitors in the DC link and to draw a sinusoidal current on the network with a unity displacement power factor. Unlike other MPCs, the resulting algorithm is easy to implement, the weighing factors of the cost function are not needed, and the computational cost is reduced. These advantages are added to the ability to operate the photovoltaic module at the point of maximum power (MPP).

The use of mobile robots is growing every day. Path planning algorithms are needed to allow the coordination of several robots, and make them travel with the least cost and without collisions. With this emerged the interest in studying some path planning algorithms, in order to better understand the operation of each one when applied in this type of robots. The objective of this paper is to present a state of the art survey of some algorithms of path planning for mobile robots. A brief introduction on mobile robots and trajectory planning algorithms is made. After, the basis of each algorithm is explained, their relative advantages and disadvantages are presented and are mentioned areas of application for each of them. This study was developed in order to implement some of these algorithms in the near future, with the objective to find out their relative advantages and disadvantages, and in which situations their implementation is more adequate.

The increase in productivity is a demand for modern industries that need to be competitive in the actual business scenario. To face these challenges, companies are increasingly using robotic systems for end-of-line production tasks, such as wrapping and palletizing, as a mean to enhance the production line efficiency and products traceability, allowing human operators to be moved to more added value operations. Despite this increasing use of robotic systems, these equipments still present some inconveniences regarding the programming procedure, as the time required for its execution does not meet the current industrial needs. To face this drawback, offline robot programming methods are gaining great visibility, as their flexibility and programming speed allows companies to face the need of successive changes in the production line set-up. However, even with a great number of robots and simulators that are available in market, the efforts to support several robot brands in one software did not reach the needs of engineers. Therefore, this paper proposes a translation library named AdaptPack Studio Translator, which is capable to export proprietary codes for the ABB, Fanuc, Kuka, and Yaskawa robot brands, after their offline programming has been performed in the Visual Components software. The results presented in this paper are evaluated in simulated and real scenarios.

The brisk and dynamic environment that factories are facing, both as an internal and an external level, requires a collection of handy tools to solve emerging issues in the industry 4.0 context. Part of the common challenges that appear are related to the increasing demand for high adaptability in the organizations' production lines. Mechanical processes are becoming faster and more adjustable to the production diversity in the Fast Moving Consumer Goods (FMCG). Concerning the previous characteristics, future factories can only remain competitive and profitable if they have the ability to quickly adapt all their production resources in response to inconstant market demands. Having previous concerns in focus, this paper presents a fast and adaptative framework for automated cells modeling, simulation and offline robot programming, focused on palletizing operations. Established as an add-on for the Visual Components (VC) 3D manufacturing simulation software, the proposed application allows performing fast layout modeling and automatic offline generation of robot programs. Furthermore, A* based algorithms are used for generating collision-free trajectories, discretized both in the robot joints space and in the Cartesian space. The software evaluation was tested inside the VC simulation world and in the real-world scenario. Results have shown to be concise and accurate, with minor displacement inaccuracies due to differences between the virtual model and the real world.

This paper proposes an algorithm capable of estimate the global maximum power point of a large photovoltaic (PV) array system operating under partially shaded conditions. The power-voltage characteristic of a photovoltaic array is a nonlinear function that becomes more complex under partial shading conditions, in fact, the power-voltage curve may exhibit multiple local maximum power points. The proposed algorithm uses two PV reference cells, every 900 m2, one operating in open-circuit and the other one in short-circuit, to estimate the solar radiation and the ambient temperature conditions of the PV arrays. The results show an estimation error of the ambient conditions lower than 1% of the actual values. As a result, the arrays provide the maximum power possible for any distribution of irradiance and temperature conditions.

Current market demands require several degrees of flexibility, speed, and repetitiveness of manufacture and logistic processes. Considering that a fourth industrial revolution is to be expected in a near future — which is highly based on smart machines, storage systems, and production facilities that cooperate to allow dynamic businesses and engineering processes — robotics presents itself as an increasingly sought-after solution, since it is often associated with such concepts. Hence, it is of no wonder that the worldwide operational stock of industrial robots has been increasing in a steady pace for the past decades and is expected to progress in such a trend. Within the several activities for robots on industrial applications, handling operations are regarded as predominant on the European market. Subsequently, palletizing applications are amongst the handling operations that have played an important role in the end stages of modern supply chains. In this context, this work aims to contextualise and develop an application for palletizing robots. This application, together with an off-line programming software (RobotStudio), allows for automatic programming of a robot's palletizing functions. Developed in the robot's native language (RAPID), the application has a basic user interface written in XML and can provide different pallet patterns.

Content prefetching brings contents close to end users before their explicit requests to reduce the content retrieval time, which is crucial for mobile scenarios, such as vehicular ad-hoc networks (VANETs). In order to make intelligent prefetching decisions, three questions have to be answered: which content should be prefetched, when and where it should be prefetched. This paper answers these questions by proposing a vehicle mobility prediction-based over-the-top (OTT) content prefetching solution. We proposed a vehicle mobility prediction module to estimate the future connected roadside units (RSUs) using data traces collected from a real-world VANET testbed deployed in the city of Porto, Portugal. We designed a multi-tier caching mechanism with an OTT content popularity estimation scheme to forecast the content request distribution. We implemented a learning-based algorithm to proactively prefetch the user content to VANET edge caching at RSUs. We implemented a prototype using Raspberry Pi emulating RSU nodes to prove the system functionality. We also performed large-scale OpenStack experiments to validate the system scalability. Extensive experiment results prove that the system can bring benefits for both end-users and OTT service providers, which help them to optimize network resource utilization and reduce bandwidth consumption.

In this paper, the scheduling problem of elective patients in the Orthopedic Department of the “Lozano Blesa” Hospital in Zaragoza is considered. This problem takes into account two contradictory objectives: obtain a given occupation rate of the Operation Room (OR) and respect as much as possible the preference order of the patients in the waiting list. Three different mathematical models are discussed: 1) Quadratic Assignment Problem (QAP); 2) a Mixed Integer Linear Programing (MILP) model; and 3) Generalized Assignment Problem (GAP). These models solve combinatorial problems with a high computational cost; for this reason, heuristic methods have been used to solve large instances. In particular, 1) a meta-heuristic Genetic Algorithm (GA) for the QAP; 2) a heuristic Steepest Descent Multiplier Adjustment Method (SDMAM) for the GAP; and 3) a heuristic iterative method for MILP. Finally, the models and the heuristics are compared according to the occupation rate and the preference order criteria.

This paper presents optical filters for narrow-band imaging on medical devices. Two optical filters were designed to provide an extremely narrow passband around the 415 nm (blue) and 540 nm (green) wavelengths using the Fabry-Perot phenomenon. Each filter is composed by successive thin-film layers of dielectric materials of titanium dioxide (TiO2) and silicon dioxide (SiO2). The TiO2 and SiO2 that compose the thin-films were fully characterized by ellipsometry applied within the 250–1700 nm wavelength range. The optical performance of the blue NBI optical filter (415 nm) was also measured. These filters were developed to integrate with light emitting diodes (LED) to provide the desired narrow-band imaging (NBI) bands on medical devices.

Deterministically Synchronized Sequential Process (DSSP) are modular Petri Net (PN) systems composed by a set of state machines PNs (called also agents) cooperating in a distributed way through asynchronous message passing. Messages can delay the normal execution of agents, but to not addition the resolution of conflicts. The modular structure of DSSP allows strong analytical results, (for example, the rank theorem provides necessary and sufficient condition for structural liveness). This paper considers a synthesis problem of liveness enforcing. For some particular structures of DSSP in which the rank theorem does not hold we provide a technique based on the pre-assignment of the buffers in order to ensure that the model becomes live.

To generate medium and high voltage with low Total Harmonic Distortion (THD) are used multilevel converters, through use of low voltage semiconductors devices, for applications as AC drives, PV farms and active power filters. This converter uses between the AC supply and the power cells a multipulse transformer, which is in charge of the harmonic cancellation of the input current harmonics generated by the three - phase rectifier. This transformer is expensive, heavy, bulky and must be designed according to the power, and the number of power cells. This work uses a THD minimization strategy based on a Finite Control Set - Model Predictive Control (FCS - MPC), which propose change the multipulse transformer by a simpler transformer, achieving a low THD in the input current of multi-cell AFE rectifier. The work is centered in the solution in one disadvantage of the FCS - MPC, high switching frequency. To solve this drawback, an additional objective function is used, which reduces the states changes of the power switches. Unfortunately, because of this the FCS - MPC loses an advantage, fast dynamic response to changes. In order to improve this issue, is necessary a modified control scheme, which detects the steady state and transient state to change the objectives of the FCS-MPC. Simulation results shows the feasibility of the proposed control.

Proportional Resonant Control (PRC) is a well-known control technique applied on ac systems in order to ensure zero steady state error for sinusoidal references. However, this control technique is not suitable to operate in a variable frequency environment, which is typically found on weak micro grids and aircraft systems. Once the controller is designed, the resonant frequency is fixed, and therefore no zero steady state error can be ensured under operating frequency fluctuations. This paper extends the resonant control approach to operate in a larger frequency range in order to be applied in power inverters and achieving zero steady state error. A back-to-back topology case is studied, connected to a distorted supply (with variable frequency) feeding a critical load. The load-connected to the back-to-back topology- requires a given frequency and amplitude voltage which is easily achieved if the grid side converter successfully regulates the dc link voltage. In addition, a desired power factor at the point of common coupling can also be imposed. The approach is based in a discrete implementation of the PRC, where its resonant frequency tracks the grid frequency, independently of grid frequency variations. This issue is mathematically demonstrated and tested with accurate results.

Controlled Power Converters are extensively used in industrial applications as they can adapt the electrical energy as required by the application. However, these devices must be properly commutated in order to control voltages and currents. Indeed, power converters are known to be multivariable, coupled, and nonlinear systems; therefore, the control technique needs to be chosen carefully. There are several control techniques reported in the literature for power converters and one of them is the Resonant Control (RC) mainly used on ac based systems. Advantageously, RC guarantees zero steady state error for a sinusoidal reference with a constant frequency and, in addition, it does not need a stationary to rotating reference frame transformation. However, the conventional RC approach requires the exact ac mains frequency value to ensure zero steady state error, being a significant drawback for applications where variable frequency environments are expected. This paper proposes an enhanced RC scheme capable to work under variable frequency scenarios, as in weak and micro grid systems while guaranteeing zero steady state error. The scheme results in a simple algorithm based upon discrete mathematics whose parameters become independent of the ac grid frequency. Results show the feasibility of the proposed approach even under severe ac frequency variations (over 100%) while featuring a stable control loop operation and zero steady state error.

This paper proposes a control scheme composed by a linear control and a predictive algorithm with extended horizon for a three-level neutral-point-clamped (NPC) inverter topology for grid-tie photovoltaic applications. The proposed strategy is capable to balance the capacitor voltages at the DC link and to generate a sinusoidal current at the grid side with a unitary power factor. Differently to other approaches, the proposed scheme is easy to digitally implement, and does not need to retune the controller cost function weighting parameters, and reduces the computational effort. These advantages are added to the capability to operate photovoltaic modules at the maximum power point (MPP). Results validate the proposed control methods and the mathematical analysis.

This paper considers the operation scheduling and planning of elective patients in the Orthopedic Department of the “Lozano Blesa” Hospital in Zaragoza. We assume an ordered list of patients that should be planned for surgery in two available rooms, each room being possible to be used for a specific duration per day. Based on the average durations of surgeries that have been computed by considering historical information, we propose a Mixed Integer Linear Programming (MILP) problem to obtain a specific utilization rate per room. We have developed a Decision Support System (DSS) base on MILP that helps doctors in their daily planning. The results are tested on some real data from the hospital and some simulation results are provided.

A performance measure which is often used when evaluating systems modeled by Petri nets is the throughput of a transition in steady-state, i.e., the number of firings per unit time in permanent regime if it exists. When fluid Petri nets are considered, such measure corresponds to the continuous flow of the transitions. Its value depends on the firing rates associated to transitions and also on the initial marking of the net. In this work two properties of the steady-state throughput, monotonicity and continuity, are studied under firing rate and initial marking variations. It is shown that in certain cases there exists a kind of duality between both type of changes, that is, some property eventually holds no matter if firing rate or initial marking is varied. These results are obtained in a structural framework using the P-flows, T-flows, and configurations of the net model.

In this work steady-state throughput changes due to firing rate variations in timed continuous Petri nets with infinite server semantics are considered. Two peculiar behaviors may appear: discontinuities and non-monotonicities. None of them are possible in Mono-T-Semiflow (MTS) nets when a certain structural condition, defined on the basis of the steady-state marking, is fulfilled. This work investigates the relation between discontinuities and non-monotonicities when the mentioned condition is not satisfied. First, using a graph-based perspective, such condition is classified using structural objects of the net. Then, the system throughput under firing rate variations is studied taking advantage of this classification. The equivalence between monotonicities and the structural condition is derived, whilst a counterexample shows that for discontinuities the implication goes in one way.

This paper addresses a collision avoidance problem in a multi-robot system. Each robot has a set of possible trajectories, each trajectory fulfilling its individual task. The trajectories consist of sequences of regions to be followed, and the time for moving inside each region is known. The problem is to avoid inter-robot collisions by imposing initial time delays for each trajectory. Two solutions are developed, depending on the possibility of imposing a certain trajectory from the available set of paths for each robot. The solutions have the form of mixed integer linear programming optimizations that return the initial time delays and, when necessary, the chosen trajectory for each robot. Finally, we perform a statistical study on the proposed solutions and we conclude that one formulation is preferable to the others.

This paper proposes a control strategy for a single-stage, three-phase photovoltaic (PV) system connected to a distribution network. The control entails obtaining the maximum power point of the PV system by means of a control strategy that is based on an inner current-control loop and an outer DC-link voltage regulator. The current-control mechanism decouples the PV system dynamic from those of the network and searches for unitary power factor at the grid side. The DC-link voltage-control scheme achieves maximum active power output. The maximization of the output power is performed by operating the PV array at its maximum power point that is estimated by a proposed technique that uses two PV measuring cells, one operating in open-circuit and the other one in short-circuit.

Accurate computational simulations are highly required to properly assess the performance of power grids under high penetration levels of non-conventional generation which connects to the grid via static power converters. However, software packages that are typically used to perform power system analysis may not necessarily have the capacity to efficiently perform detailed simulations of power grids that contain, for example, hundreds of PWM converters, specially when the computational resource is limited or real-time simulation is needed. In view of this problem, this paper proposes a new modeling and simulation technique that makes use of the average of the PWM waveforms rather than their instantaneous values to simulate the converter. Two softwares packages are used to validate the proposed solution, PSIM is used to validate the proposed converter model and DigSILENT to validate the use of this model in a power system simulation tool. Results show that the proposed solution allows increasing the simulation time-step of models containing PWM converters in up to 50 times, while keeping a high level of accuracy in representing the grid related waveforms.

Power converters have been widely used in industrial applications as parallel and series compensators, UPQCs, and STATCOMs. These electronic devices can also be utilized on weak-grid or micro-grid systems, where both the supply voltage amplitude and frequency, may vary considerably from the nominal values. Micro-grid and weak-grid systems are commonly associated to distribute non-conventional power generation sources, where the voltage and frequency deviation are as a result of unbalances between generation and consumed power. This work studies and develops a Series Compensator control for a non-constant power supply. The study is focused on the rectifier control in order to get a stable closed loop system for sags and swells as well as frequency variations. In addition, an operating region study is performed in order to evaluate the capabilities and to find the maximum range of frequency variation tolerated by this topology. Finally, simulated results show the feasibility of the proposed control for a wide frequency and voltage variation.

The utilization of multi-cell converters, through the use of low voltage semiconductors, has permitted to implement medium and high voltage applications as PV farms and AC drives. In conventional AC drives, this converter requires an input multipulse transformer, which allows the low frequency harmonic cancellation that are generated by the three-phase diode rectifiers included in each cell. This multipulse transformer is bulky, heavy, expensive, and must be designed according to the number of power cells, making the transformer topology dependent. This work proposes and evaluates a harmonic minimization strategy based on a Finite Control Set — Model Predictive Control (FCS — MPC), which emulates the harmonic cancellation of a multi-pulse transformer. This feature allows the minimization of the Total Harmonic Distortion (THD) of the AC grid current of the multi-cell converter. The evaluation is focused in one disadvantage of the FCS — MPC which is its high switching frequency that causes high losses in the semiconductors. To overcome this disadvantage, an additional objective function is proposed. Simulation results prove the theory, with satisfactory results.

This work presents a case study of a modular photovoltaic (PV) plant where PV panel arrays are connected to the grid through cascaded single-phase current-source inverters. It is shown that, under non-uniform insolation conditions of the PV arrays, the output voltages of the cascaded inverters become unbalanced. Therefore, a dc voltage elimination control loop is proposed to balance the output voltage of the H bridges. Additionally a control technique called virtual synchronous generator (VSG) is applied to the PV plant in order to support the control of the grid frequency emulating an inertial response and providing damping and droop power. For the simulated cases the PV plant was always capable of performing the VSG functions, in spite of the unbalance condition of the output voltages of the H bridges. However, when the proposed dc voltage elimination control loop was in operation the maximum peak output voltage and the amplitude of its fundamental component were reduced in 13.3 % and 27 % respectively.

This paper approaches the deadlock prevention problem for the well known class of S3PR used in Resource Allocation Systems. The proposed control policy is based on inhibitor arcs and the new Petri net class will be called S3PR2. The liveness characterization of this new class is given. The main application of the approach is to robot motion for a team of robots evolving in a partitioned environment with some limited capacity regions. In a previous work it is shown that the sets of trajectories for robots can be modeled by a particular S3PR and the deadlock-free execution has been solved using a centralized approach. Based on the results in this paper, we show that a decentralized control law for robots can be implemented.

This work deals with the control of a single-phase Current Source Inverter (CSI) in a three-phase array which can be used for both power drives and PV applications. Unlike in three-phase inverters, where the Fortescue Transform or Park Transformation can be applied in order to simplify the design of the controllers, for single-phase systems they cannot be directly applied making the control a difficult task if a rotating reference frame is chosen. On the other hand, Resonant Control (RC) is a control strategy that allows working with sinusoidal references and ensuring zero steady state error. This paper studies the resonant control of a single-phase CSI in a three-phase array, considering a design in continuous as well as discrete time domain. The resonant control is justified because the current sources should not be considered equals at all times, leading to independent control in each phase, or each cell, where the current source value and the load current can be feed-forward into the controller both of them disturbances, making the load voltage control in each cell easier to accomplish. To corroborate the mathematical analysis, the proposed control scheme is tested under different conditions and disturbances, including a stability study.

The analysis and synthesis of Discrete Event “views” of dynamic Systems (DES), suffer of the so called state explosion problem. Petri net is a generic term used to designate a broad family of related formalisms for DES, all sharing some basic relevant features, such as locality of the states and actions, with consequences as temporal realism. This article deals with Place/Transition nets, by default simply called Petri Nets (PNs). A crucial property of PNs is that the global state of a system is numerically quantified, usually expressed in vector form. Among the most promising techniques to deal with the related computational problems are structural strategies as “divide and conquer”, of methodological nature, and fluidization, a relaxation. This invited contribution presents a quick overview of possibilities and problems with the last approach.

Recently the RoboCup@Work league emerged in the world's largest robotics competition, intended for competitors wishing to compete in the field of mobile robotics for manipulation tasks in industrial environments. This competition consists of several tasks with one reflected in this work (Basic Navigation Test). This project involves the simulation in Virtual Robot Experimentation Platform (V-REP) of the behavior of a KUKA youBot. The goal is to verify that the robots can navigate in their environment, in a standalone mode, in a robust and secure way. To achieve the proposed objectives, it was necessary to create a program in Lua and test it in simulation. This involved the study of robot kinematics and mechanics, Simultaneous Localization And Mapping (SLAM) and perception from sensors. In this work is introduced an algorithm developed for a KUKA youBot platform to perform the SLAM while reaching for the goal position, which works according to the requirements of this competition BNT. This algorithm also minimizes the errors in the built map and in the path travelled by the robot.

In this paper we focus on distributed control of timed continuous Petri nets (TCPN). We assume that subsystems are connected by places modeling buffers. The problem we handle here is to drive all the subsystems to their desired final states, which is similar to the classical set-point control problem in general continuous-state systems. We first propose a centralized MPC controller, in which asymptotic stability is guaranteed by means of adding constraints to force the state trajectory to be inside an interior convex subset of the reachability space. Then, we apply this controller to a distributed setting, and for this aim we use a particular strategy to maintain the positiveness of the markings of buffer places. We prove that, by using the proposed algorithm, the desired final states of all subsystems can be reached in finite time (even if at different time instants). In our method, no high level coordinator is needed and only limited communication occurs among neighboring subsystems.

This work shows the design and implementation of a new neural network design based on trigonometric series expansion proposed by Dr. P. Ponce that was applied to control a non linear system (hexapod). In order to prove the capacity of the topology simulation and experimental results are shown. The new topology of the neural network genereted excellent response under new situations presented to the hexapod. A complete description of the topology proposed is presented and explained in detail.

In recent years there has been an increasing introduction of industrial robots in the manufacturing industry, with several studies that predict the increased dissemination of robots in industrial and service sectors. On the other hand, there is often the lack of people able to plan the introduction of these equipments in manufacturing environments and to operate it after its inception. This leads to the need to train undergraduates in the operation and programming of industrial robots. Due to the Portuguese economic situation, there is a lack of funding for the higher schools, leading to the need of finding innovative ways to teach these subjects. Bearing in mind these ideas, in this paper is described a course on industrial robotics, which is based in the achievement of the practical training using commercial off-the-shelf robot simulation software for off-line programming.

The European Project Semester at ISEP (EPS@ISEP) is a one semester project-based learning programme addressed to engineering students from diverse scientific backgrounds and nationalities. The students, organized in multicultural teams, are challenged to solve real world multidisciplinary problems, accounting for 30 ECTU. The EPS package, although focused on project development (20 ECTU), includes a series of complementary seminars aimed at fostering soft, project-related and engineering transversal skills (10 ECTU). This paper presents the study plan, resources, operation and results of the EPS@ISEP that was created in 2011 to apply the best engineering education practices and promote the internationalization of ISEP. The results show that the EPS@ISEP students acquire during one semester the scientific, technical and soft competences necessary to propose, design and implement a solution for a multidisciplinary problem.

In this paper, we consider the decentralized fault diagnosis problem of discrete event systems modeled by time Petri nets (TPNs). Our approach is based on the fault diagnosis graph which is obtained from the time reachability graph by removing the irrelevant nodes. A coordinator computes the diagnosis states of the global system using information from subsystems. Local systems send small amounts of information to the coordinator for the computation of diagnosis states of the global system.

Legged robots are being the target of several studies and research. The idea is to develop machines that present characteristics approximate to the ones observed in biological living creatures. However this objective is still relatively far away and the development of prototypes for these studies is expensive and time consuming, which leads to the creation of models that allow the realization of the intended studies in software. These models should include the main characteristics of biological creatures relevant for locomotion studies. Given this, the presented work describes the development of a quadruped robot model in MATLAB/Simmechanics TM. This model is intended to be used in the development of gaits for legged robots based on Central Pattern Generators. With this purpose in mind, the model was developed in a way to accept different gaits by direct introduction of the angular positions of the knee and hip joints. Various parameters of the robot are also easily changed through a configuration file that accompanies the model. This paper presents the model of a robot with flexible body, its legs and its hip and knee joints. The model of a feet-ground interaction was also modelled using a theoretic model described in the literature.

This paper presents optical filters for integration on stereoscopic image sensors. The filters must cover each one of primary colors within the visible, in order to yield a passband around the respective wavelengths. Dielectric materials based on SiO2 and TiO2 were used due to their compatibility with silicon. The best simulation with only 3 dielectric layers resulted in optical filters with full width at half maximum (FWHMs) of 79, 95 and 124 nm and central wavelengths of 456, 529 and 605 nm, respectively.