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Belt Conveyors are essential for transporting dry bulk material in different industries. Such structures require permanent inspections, traditionally executed by human operators based on cognition. To improve working conditions and process standardization, we propose a novel procedure to inspect conveyor structures with a ground robot composed by a mobile platform, a robotic arm, and a sensor-set. Based on field experience, we introduce ROSI, a new robotic device designed for long-term operations in harsh outdoor environments. The mobile robot has a hybrid locomotion system, using wheels to reduce energy consumption while covering long distances, and also flippers with tracks to improve mobility during obstacle negotiation. A mechanical passive switch allows decoupling tracks’ traction, reducing components wear and energy consumption without raising mechanical complexity. Aiming the robot-assisted operation, control strategies help to (i) command both the mobile platform and a robotic manipulator considering the system whole-body model, (ii) adjust the contact force for touching the conveyor structure during vibration inspection, and (iii) climb stairs while automatically adjusting the flippers. Machine Learning algorithms detect conveyors’ dirt build-ups, roller failures, and bearing faults by processing visual, thermal and sound data as inspection functionalities. The algorithms training and validation use a dataset collected from running conveyors at Vale, presenting detection accuracy superior to 90%. Field test results in a mining site demonstrate the robot capabilities to stand for the harsh operating conditions while executing all the required inspection tasks, stating ROSI as a disruptive solution for Belt Conveyor inspections and other general industrial operations.

ROSI is a mobile robot designed to inspect belt conveyor machinery in the mining industry. The proposed system is a wheeled and tracked mobile platform equipped with a robotic manipulator and several sensors to allow execution of the scheduled tasks.

The development and integration of Wire Arc Additive Manufacturing (WAAM) systems is nowadays a topic of growing interest. Industries are starting to focus on deploying this technology due to its vast capability of producing different types of parts and creating new possibilities for engineering design. Measuring the process characteristics is crucial in a WAAM system, because it helps to ensure that the build up was done according as planned. In this work, it was developed a passive vision-based monitoring method to measure the metal bead width in a WAAM process. The deposition was carried out by using a carbon steel wire with GMAW process, a Motoman HP20 robot arm and a welding torch device. A Xiris XVC-1000camera was used for visual inspection and mounted in a suitable configuration to minimize arc's noise. The experimental results show that it is possible to measure the bead deposition width in real time with a satisfactory accuracy using monocular cameras. Therefore, it is a feasible solution to be used in WAAM systems with the advantage of being relatively low-cost, as compared to other active vision equipment.

The thermal-fluid control of a microchannel evaporator operating in the two-phase regime is considered. The control objective is to stabilize the fluid flow and maintain a minimal evaporator wall temperature by commanding the inlet flow rate using a pump. The first objective is achieved with a feedback controller using only mass flow rate measurement (via a lead filter). The second objective is more challenging as the achievable wall temperature depends on the heat transfer coefficient which is hard to characterize (heavily depends on the flow rate and heat load). An extremum seeking control based on sliding modes is proposed to minimize wall temperature and adjust the flow rate without considering heat transfer coefficient knowledge. Thus, considering a thermal-fluid model, the stability of the flow control loop is establish and the convergence to the extremum seeking control is analyzed via singular perturbation analysis and Tikhonov’s theorem. Simulation results demonstrate the efficacy of the proposed scheme.

In this work, it is considered an image based visual servoing control problem, for uncertain robot manipulators. Visual feedback is provided by a fixed monocular camera with uncertain parameters, for the purpose of tracking translational trajectories of a spherical target, both the trajectory on image plane and depth. Based on a cascade structure, the proposed adaptive visual servoing is combined with an adaptive motion control strategy. Stability and passivity properties are analyzed with the Lyapunov method. Simulation results illustrate and highlight performance of the proposed controller.

In this work, we consider a novel adaptive hybrid pose/force control strategy for uncertain robot manipulators capable of performing interaction tasks on poorly structured environments. A unique hybrid control law, based on an orientation-dependent term, is proposed to overcome the performance degradation of the feedback system due to the presence of uncertainties in the geometric parameters of the contact surfaces. A gradient-based adaptive law, which depends on the tracking error, is designed to deal with parametric uncertainties in the robot kinematics and the stiffness of the environment. In our solution, the effect of the uncertain robot dynamics is addressed by using an adaptive dynamic control based on a cascade control strategy. The Lyapunov stability theory and the passivity paradigm are employed to carry out the stability analysis of the overall closed-loop control system. Numerical simulations are included to illustrate the performance and feasibility of the proposed methodology.

When, in addition to stability, position synchronization is also desired in bilateral teleoperation, Time Domain Passivity Approach (TDPA) alone might not be able to fulfill the desired objective. This is due to an undesired effect caused by admittance type passivity controllers, namely position drift. Previous works focused on developing TDPA-based drift compensation methods to solve this issue. It was shown that, in addition to reducing drift, one of the proposed methods was able to keep the force signals within their normal range, guaranteeing the safety of the task. However, no multi-DoF treatment of those approaches has been addressed. In that scope, this paper focuses on providing an extension of previous TDPA-based approaches to multi-DoF Cartesian-space teleoperation. An analysis of the convergence properties of the presented method is also provided. In addition, its applicability to multi-DoF devices is shown through hardware experiments and numerical simulation with round-trip time delays up to 700 ms., 2019 19th International Conference on Advanced Robotics (ICAR)

This paper considers the pathconstrained trajectory tracking for robot manipulators optimizing a limited energy budget. The proposed strategy is based on a Nonlinear Receding Horizon Predictive Control (NRHPC) using a path parameterization of dimension one. The dynamic of the parameterized trajectory is governed by a predefined linear system, then an energy and a cost functions are defined and a NRHPC based on a Newton method is used to minimize the cost function in real time. The method is presented in both joint and task space. The proposed solution is verified on a 4 DOF manipulator with successful simulation and experimental results.

This work presents an adaptation of the Time-Domain Passivity Approach (TDPA) to enhance robustness of a cascade hybrid control scheme for interaction between a robotic manipulator and an unknown surface. A cascade control is proposed to combine a task space kinematic hybrid position/force and orientation control law in the outer loop and a joint space inverse dynamics control law in the inner loop. The proposed kinematic TDPA acts on the force control part of the hybrid scheme to ensure passivity and contact stability even in the presence of unmodeled features in the force sensor attached to the end-effector and in the control channel. Simulations and experimental results are presented to show the efficacy of the proposed method when significant force measurement delay and surface stiffness variation are introduced.

In this paper, the formation and trajectory tracking control problem for multi-agent systems is presented. A cascade control strategy for a group of nonholonomic mobile robots with non-negligible dynamics is proposed. An outer loop is a kinematic controller which has two different goals: virtual Leaders are defined for the purpose of trajectory tracking and pose regulation, and potential functions are defined for formation control. The cascade inner loop consists in a computed torque strategy. Assuming that the communication graph is always connected, a stability analysis ensures minimization of tracking and formation errors. Lastly, the control strategies are verified by simulation.

In this work, we consider the 3D visual tracking problem for a robot manipulator with uncertainties in the kinematic and dynamic models. The visual feedback is provided by a fixed and uncalibrated camera located above the robot workspace. The Cartesian motion of the robot end effector can be separated into a 1D motion parallel to the optical axis of the camera and a 2D motion constrained on a plane orthogonal to this axis. Thus, the control design can be simplified, and the overall visual servoing system can be partitioned in two almost-independent subsystems. Adaptive visual servoing schemes, based on a kinematic approach, are developed for image-based look-and-move systems allowing for both depth and planar tracking of a reference trajectory, without using image velocity and depth measurements. In order to include the uncertain robot kinematics and dynamics in the presented solution, we develop a cascade control strategy based on an indirect/direct adaptive method. The stability and convergence properties are analyzed in terms of Lyapunov-like functions and the passivity-based formalism. Numerical simulations including hardware-in-the-loop results, obtained with a robot manipulator and a web camera, are presented to illustrate the performance and feasibility of the proposed control scheme. Copyright © 2016 John Wiley & Sons, Ltd.

Os transportadores de correia (TCs) desempenham um papel importante no transporte de materiais em diferentes industrias. Particularmente, a sua utilizacao em processos de mineracao e extensa e vital para a operacao desta industria. Dessa forma, a inspecao dos componentes de transportadores de correia, como os rolos, e uma tarefa fundamental para garantir o correto funcionamento do equipamento. Visando apresentar uma solucao efetiva para inspecao de transportadores de correias, este artigo propoe um dispositivo robotico composto por uma plataforma movel, um braco manipulador e um conjunto de sensores para inspecao de rolos. O sistema proposto retira os operadores das areas de risco e fornece informacoes mais precisas do estado do equipamento. Alem disso, a implementacao do sistema nao exige nenhuma modificacao da estrutura existente dos TCs. Baseado no modelo cinematico do manipulador movel, e apresentada uma estrategia de controle para comandar o robo considerando seu corpo completo. Testes para prova de conceitos foram realizados em situacoes reais e as capacidades do sistema foram confirmadas em diferentes condicoes de operacao.

A autonomia de submersiveis tem sido um campo de intenso desenvolvimento na robotica submarina de levantamento e de intervencao e para tal e necessario um sistema de localizacao adequado. Propo-se neste artigo um sistema de localizacao que se baseia no uso de um simples modem acustico e em sensores embarcados: profundimetro, unidade de medicao inercial e câmeras de video. Dois estimadores de estado sao aplicados, o Filtro de Kalman Estendido (EKF) e o Unscented Kalman Filter (UKF). Simulacao sao apresentadas para mostrar a viabilidade do algoritmo e comparar a qualidade dos filtros utilizados.

Para tanto diminuir o esforco fisico de um humano, quanto aumentar a percepcao de um ambiente por um robo, um diade humano-robo pode ser usado para co-manipulacao de um objeto compartilhado. A maioria das estrategias de controle existentes atribuem ao robo a tarefa de seguidor das acoes do humano mesmo que existam situacoes em que o humano possa se beneficiar da lideranca do robo. Para emular o comportamento humano durante uma tarefa de co-manipulacao, um controle por emitância com Rigidez variavel e apresentado neste trabalho. A rigidez e continuamente variada com base em uma funcao escalar suave que define o grau de lideranca do robo. Alem disso, o controlador e avaliado por meio de simulacoes e sua estabilidade e analisada por uma funcao de Lyapunov.

This paper deals with the problem of controlling the 3D Cartesian position of an object grasped by a multifingered robot hand using the visual servoing approach. We consider that the geometry of the object is known and the contact constraints are always satisfied during the grasping motion. An RGB camera and a depth sensor are simultaneously used to provide visual positioning and depth information of the grasped object. The control design is based on the kinematic control approach and two visual servo controllers are developed in the image space, ensuring the zero-convergence of the output tracking errors and high disturbance-rejection capability. Practical tests for visual tracking tasks of a grasped object are performed with a three-fingered robot hand and a natural interface device. Experimental results are shown to illustrate the performance and feasibility of the proposed methodology.

DORIS is a mobile robot for remote supervision, diagnosis, and data acquisition on offshore facilities. The proposed system is composed of a rail-guided robot capable of carrying different sensors through the inspected area. This paper presents a general overview of the robot, and a description of the developed embedded electronics, power supply system and software architecture. The results with teleoperated navigation validate the concepts considered so far and rise several challenges for future works.

This work presents a methodology for autonomous manipulation of valves using a dual-arm robot and the visual sensing provided by cameras mounted on the head and each robot arm. A novel image-based identification and pose estimation method is devised to determine the valve to be manipulated as well as to estimate its position and orientation with respect to the robot base. The valve pose is used in the positioning and alignment of the robot end effector enabling the manipulation task to be carried out autonomously. Experimental results, obtained with a BaxterTM robot performing valve turning tasks, illustrate the feasibility of the proposed methodology. The main objective of this work is to provide capabilities to develop new solutions and innovative technologies to deal with the challenge of manipulating valves autonomously in poorly structured and harsh environments

This paper presents an accurate and computationally efficient stairway detection algorithm, robust to measurement noise. While most similar methods depend heavily on detecting three-dimensional (3D) features, this work focuses on locating two-dimensional (2D) features embedded in 3D data. The main idea is: each stair is a sequence of lines with similar domain of definition, and the staircase is a sequence of such elements. To avoid unnecessary computations, an octree is used to down-sample the environment point-cloud data. The resulting centroids are stored in n arrays, each containing points with equal height. This effectively segments the 3D data into n 2D slices. The Hough transform is used to scan each array for lines. the remainder of the algorithm detects lines with the same domain of definition and determines if sequences that may correspond to stairways exist. If these sequences meet the required tolerances, then a staircase is detected. For each detected stairway a model that contains the width, height, depth, and amount of stairs is returned. The proposed algorithm is able to efficiently locate and model staircases on different poses and is robust to noise from the measured data, as indicated by the experimental results.

This paper addresses the dynamic modeling and the energy storage analysis of a wave energy hyperbaric converter, which consists of a set of oscillating bodies (named as pumping modules) linked to hydropneumatic accumulators and an electric generating unit. A mathematical model of the accumulator is presented and a model for the generating unit is proposed, including a nonlinear model of a Pelton turbine. Then, the hydrodynamic, mechanical, and electrical characteristics of the subsystems that compose the converter are discussed. With the proposed model, it is possible to evaluate the dynamic behavior of the entire system. That is, for a given incident ocean wave, it is possible to evaluate all the system state variables and the generated electric power, including the quality (fluctuation, for example) of the generated voltage and frequency for islanded or power-grid-connected operation. Simulation results considering the proposed wave-to-wire model under the action of regular and irregular incident waves are presented to illustrate the performance of the system.

This paper presents a novel control architecture for operational space control when the end effector or the robotic chain is kinematically constrained. Particularly, we address kinematic control of robots operating in the presence of obstacles such as point, plane, or barrier constraints imposed on a point on the manipulator. The main advantage of the proposed approach is that we are able to control the end-effector motion in the normal way using conventional operational space control schemes, and by re-writing the Jacobian matrix we also guarantee that the constraints are satisfied. The most challenging problem of obstacle avoidance of robotic manipulators is the extremely complex structure that arises when the obstacles are mapped from the operational space to joint space. We solve this by first finding a new set of velocity variables for a point on the robot in the vicinity of the obstacle, and on these new variables we impose a structure which guarantees that the robot does not hit the obstacle. We then find a mapping denoted the Constrained Jacobian Matrix from the joint variables to these new velocity variables and use this mapping to find a trajectory in joint space for which the constraints are not violated. We present for the first time the Constrained Jacobian Matrix which imposes a kinematic constraint on the manipulator chain and show the efficiency of the approach through experiments on a real robot.

This paper concerns the reconfiguration control of actively articulated mobile robots navigating through irregular terrains. Active mechanisms are able to accommodate for different operation conditions. The capability to influence mobility depends on the mechanism kinematic structure and the actuators velocity limitations. The robot mobility is evaluated considering ground clearance, orientation and stability. Control strategies are proposed considering the actuators bandwidth to compensate abrupt variations of the navigation trajectory and the driven terrain. The proposed solution consists on anticipating the command action by employing a predictive functional control method to adjust the robot for critical conditions faced during operation. Numerical simulations using field data, recorded while navigating on a natural terrain, are performed to verify the proposed strategies controlling a robot with two actuated DoF.

In this paper the formation and trajectory tracking control problem for multi-agent systems is presented. Initially, a control strategy for a group of holonomic robots is proposed. The proposed control is extended to the nonholonomic case. The control scheme is based on potential functions which make possible the design of decentralized formation control scheme while avoiding agents collisions. The trajectory tracking is achieved defining leaders which attract the formation to a desired trajectory. Furthermore, if at least two leaders are defined, the formation orientation tends to a desired pose (for the planar case). Assuming that the communication graph is always connected, a stability analysis using Lyapunov theory ensures the minimization of the potential function and the trajectory tracking. The control strategies are verified by simulation.

Electric lighting has not substantially changed in over 100 years. From incandescent bulbs to fluorescent tubes, the efficiency remains low and control mostly involves on/off or dimming. The new wave of solid state lighting offers the possibility of sensor-based intensity regulation, color control, and energy efficiency, under varying needs and environmental conditions. This paper formulates the lighting control problem as an optimization problem balancing color fidelity, human perception and comfort, light field uniformity, and energy efficiency. The optimization problem is solved based on the light propagation model, which is adaptively updated with color sensor feedback to account for changing ambient lighting conditions, such as daylighting. We demonstrate the proposed approach in a smart space testbed under a variety of use conditions. The testbed is instrumented with 12 color tunable lights and 12 light sensors, as well as simulated daylight. The results show substantial improvement in terms of energy usage and delivering good light field quality in the presence of varying lighting conditions. Experimental results corroborate the efficacy of the proposed algorithms.

This paper addresses the feedback control of a vapor compression cycle for electronics cooling at different operating conditions including near the critical heat flux (CHF) condition. The control objective is to maintain the temperature of the heated wall below a safe threshold during large transient heat loads. The lumped-parameter model developed for this system is used to design the control strategy. Our experimental testbed is used for evaluation and validation. Linear controller design is applied based on the linearization about specific operating points. The controllers are tuned to achieve good robustness margins to guard against nonlinearity and other modeling errors. When the system traverses through multiple operating points, a gain-scheduling approach is used to switch between the controllers. For heat load changes which would lead to CHF, a dual-input gain-scheduling controller, using both expansion valve and compressor speed, is designed using the evaporator wall temperature as the feedback variable as well as the scheduling variable. Comparison between open-loop and closed-loop experiments for the same operating conditions shows that a 80 °C rise in the wall temperature is avoided with the gain-scheduling controller.

This work addresses the visual tracking problem of robot manipulators with non-negligible dynamics using a fixed camera, when the camera-robot system parameters are uncertain. An adaptive strategy is developed for visual servoing systems based on the image-based look-and-move structure to allow the tracking of a 2D reference trajectory, without using image velocity measurements. The adaptive visual servoing problem free of image velocity information is formulated as a relative degree two MIMO adaptive control problem. As a solution, we employ a recently proposed Lyapunov/passivity-based adaptive control scheme based on the SDU factorization method. From a cascade control strategy, the resulting online camera calibration scheme is combined with a direct adaptive motion controller for the robot manipulator, which takes into account its uncertain nonlinear dynamics. The overall stability of the adaptive visual servoing system can be proved thanks to the explicit Lyapunov-like functions of both adaptation schemes.

In this work, the bilateral teleoperation of a Multi-Master Multi-Slave (MM/MS) robotic system able to perform object manipulation tasks is presented. A multi-agent formation control strategy is considered to control the object's velocity. The velocity and interaction forces are provided by the master robots while the object is manipulated with a bounded force by the slave robots. Stability and transparency are guaranteed by two-layer passivity strategy using the energy tanks approach. The stability and convergence analysis is carried out by using the Lyapunov stability theory and the passivity formalism. Numerical simulations are included to illustrate the performance and effectiveness of the proposed control scheme.

In this paper the control allocation problem is revisited in the context of quadrotor unmanned aerial vehicles (UAVs). Two control allocation strategies are presented, both aiming to avoid output saturation. The first strategy is based on the optimization of a weighted least squares (WLS) criterion subject to boundary constraints. The second, called direct control allocation (DCA), aims to maintain constant the direction of the desired virtual efforts vector. As a modification of this strategy, we introduce the partial control allocation (PCA) scheme. In the latter, only the direction of a fraction of the desired virtual efforts vector is kept constant. It is also presented a discussion on the performance of the DCA and PCA schemes.

In this work the problem of remote calibration and trajectory replanning for a subsea robotic manipulator is considered. Because the trajectory planning is normally done in a structured environment, several uncertainties arise when the robot is placed on the seabed and these need to be compensated for to guarantee that the task specifications are fulfilled. We address the particular problem of configuration errors in the robot base with respect to the configuration used during the off-line trajectory planning. A calibration method based on both internal and external sensors is presented in order to estimate the uncertainty in the location of the robot. Moreover, a trajectory replanning strategy in the Cartesian velocity space is proposed to guarantee that the originally planned trajectory is followed. Simulation and experiments performed with a 6-DoF robot manipulator and a real calibration grid show the viability of the proposed planning and control schemes.

This paper addresses the posture control problem for robotic systems subject to kinematic constraints. The key idea is to consider the kinematic constraints of the mechanisms from their structure equations, instead of explicitly using the constraint equations. A case study for parallel robots and cooperating redundant robots is discussed based on the following concepts: forward kinematics, differential kinematics, singularities and kinematic control. Simulations results, obtained with a Four-Bar linkage mechanism, a planar Gough-Stewart platform and two cooperating robots, illustrate the applicability and versatility of the proposed methodology. Este artigo considera o problema de controle de postura para sistemas robóticos com restrições cinemáticas. A ideia principal é considerar as restrições cinemáticas dos mecanismos a partir de suas equações estruturais, ao invés de usar explicitamente a equação de restrição. Um estudo de caso para robôs paralelos e robôs cooperativos é discutido baseado nos conceitos de cinemática direta, cinemática diferencial, singularidades e controle cinemático. Resultados de simulação, obtidos a partir de um mecanismo Four-Bar linkage, uma plataforma de Gough-Stewart planar e dois robôs cooperativos, ilustram a aplicabilidade e versatilidade da metodologia proposta.

A novel output-feedback sliding mode control strategy is proposed for a class of single-input single-output (SISO) uncertain time-varying nonlinear systems for which a norm state estimator can be implemented. Such a class encompasses minimum-phase systems with nonlinearities affinely norm bounded by unmeasured states with growth rate depending nonlinearly on the measured system output and on the internal states related with the zero-dynamics. The sliding surface is generated by using the state of a high gain observer (HGO) whereas a peaking free control amplitude is obtained via a norm observer. In contrast to the existing semi-global sliding mode control solutions available in the literature for the class of plants considered here, the proposed scheme is free of peaking and achieves global tracking with respect to a small residual set. The key idea is to design a time-varying HGO gain implementable from measurable signals. Copyright © 2010 John Wiley & Sons, Ltd.

This work addresses the 3D visual servoing problem for robot manipulators in the presence of uncertainties in the camera-robot system parameters. From a fixed and uncalibrated camera, the cartesian motion is decomposed into a 2D motion on a plane orthogonal to the optical axis and a 1D motion parallel to this axis. An adaptive visual servoing scheme based on a kinematic approach is developed for image-based look-and-move systems to allow both depth and planar tracking of a reference trajectory, without using image velocity and depth measurements. A cascade control strategy based on direct/indirect adaptive method is applied to consider the uncertain robot kinematics and dynamics in the presented solution. The stability properties and the convergence analysis are discussed from the Lyapunov-passivity formalism. Simulation results are shown to illustrate the performance of the proposed control scheme.

In this paper an adaptive formation control for nonholonomic mobile robots with curvature constraints is proposed. The proposed control strategy is based on a saturated potential function which makes possible the design of a decentralized formation control scheme and avoids agents collisions considering its dimensions. Provided that the communication graph is always connected, the control strategy guarantees the formation will achieve a configuration that minimizes the potential function.

In this paper, a solution for the formation control of a group of nonholonomic uncertain agents is proposed. The configuration pattern is generated from a given potential function, which may also incorporate a strategy for collision avoidance. The system parametric uncertainties are compensated by a robust adaptive control algorithm named binary adaptive control which combines the good transient properties and robustness of Sliding Mode Control with the desirable steady-state properties of parameter adaptive systems delivering continuous control signals, thus avoiding chattering. First, a static formation (regulation) scenario is considered. Conditions for semi-global stability of the multi-agent system are established using Lyapunov theory for decentralized control schemes. Then, the control scheme is extended for trajectory tracking to be performed by the group of agents while maintaining a desired geometric pattern. In the case of regulation, only the relative position information with respect to neighboring agents and individual velocity are available for the control implementation for each agent. In the case of tracking, also the velocities of the neighbors are needed. Simulations are presented to validate the theoretical results.

A hybrid control scheme based on adaptive visual servoing and direct force control is proposed for robot manipulators to perform interaction tasks on smooth surfaces. The camera parameters, as well as the constraint surface, are considered to be uncertain. A fixed camera with optical axis non-perpendicular to the robot workspace is used for position control, while a force sensor mounted on the robot wrist is used for force regulation. In order to solve the interaction problem on unknown surfaces, a method is developed to estimate the constraint geometry and keep the end-effector orthogonal to the surface at the contact point, during the task execution. Experimental results are presented to illustrate the performance and feasibility of the proposed scheme.

This note presents a solution to the problem of global exact output tracking for uncertain linear plants with arbitrary relative degree using output-feedback sliding mode control. The key idea to overcome the relative degree obstacle is to introduce a hybrid compensator by combining, through switching, a standard lead filter with a robust exact differentiator, based on higher-order sliding modes, achieving uniform global exponential practical stability and asymptotic exact tracking.