A survey on coverage path planning for robotics

Coverage Path Planning (CPP) is the task of determining a path that passes over all points of an area or volume of interest while avoiding obstacles. This task is integral to many robotic applications, such as vacuum cleaning robots, painter robots, autonomous underwater vehicles creating image mosaics, demining robots, lawn mowers, automated harvesters, window cleaners and inspection of complex structures, just to name a few. A considerable body of research has addressed the CPP problem. However, no updated surveys on CPP reflecting recent advances in the field have been presented in the past ten years. In this paper, we present a review of the most successful CPP methods, focusing on the achievements made in the past decade. Furthermore, we discuss reported field applications of the described CPP methods. This work aims to become a starting point for researchers who are initiating their endeavors in CPP. Likewise, this work aims to present a comprehensive review of the recent breakthroughs in the field, providing links to the most interesting and successful works.     

Fe–Nx/C electrocatalysts synthesized by pyrolysis of Fe(II)–2,3,5,6-tetra(2-pyridyl)pyrazine complex for PEM fuel cell oxygen reduction reaction

2,3,5,6-Tetra(2-pyridyl)pyrazine (TPPZ) was employed as a ligand to prepare an iron(II) complex (Fe–TPPZ) that served as a precursor to synthesize carbon-supported catalysts (Fe–N_x/C) through heat-treatment at 600, 700, 800 and 900 °C under N₂ atmosphere. Both the structure and composition of the synthesized Fe–N_x/C were analyzed by X-ray diffraction and energy-dispersive X-ray microanalysis, respectively. The rotating disk and ring-disk electrode measurements showed that these catalysts have strong ORR activity with an overall 4-electron transfer process through a (2 + 2)-electron transfer mechanism, which was assigned to the catalytic function of the Fe–N_x center. A study on the heat-treatment temperature on the ORR activity showed that 800 °C is the optimal temperature for the synthesized catalysts. Furthermore, the effect of both catalyst and Nafion^® ionomer loadings in the catalyst layer on the corresponding ORR activity was also investigated. The kinetic parameters such as the chemical reaction rate between O₂ and Fe–N_x/C (adduct formation reaction), the rate constant for the rate-determining step (RDS), and the electron numbers in the ORR, were obtained. The methanol tolerance of the catalyst was also tested. To validate the ORR activity, a membrane electrode assembly in which the cathode catalyst layer contained Fe–N_x/C was constructed and tested in a real fuel cell. The results obtained are encouraging when compared with similar non-noble catalysts.     

Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode

The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe²⁺ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe²⁺ and H₂O₂ electrogenerated at the O₂-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl⁻, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe³⁺-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated.     

Electrochemical oxidation of methyl orange azo dye at pilot flow plant using BDD technology

Solutions of methyl orange azo dye were degraded by electrochemical oxidation using a 3 L flow plant with a boron-doped diamond (BDD)/stainless steel cell operating at constant current density, ambient temperature and liquid flow rate of 12 L min^?1. A 2³ factorial design considering the applied current density, azo dye concentration and electrolysis time as variable independents was used to analyze the process by response surface methodology. LC–MS analysis revealed the formation of seven oxidation products from the cleavage of the NN group of the dye, followed by deamination, formation of a nitro group and/or desulfonation of the resulting aromatics.     

Electrocatalytic properties of diamond in the oxidation of a persistant pollutant

This work is focused on the study of the role of several conductive-diamond characteristics (boron doping, sp³/sp² ratio, diamond-layer thickness) on the performance of the electrolysis of enrofloxacin (as model complex-organic pollutant). Commercial lots provided by an important conductive-diamond manufacturing company have been used. Results show that enrofloxacin electrooxidation is strongly influenced by the conductive-diamond characteristics; particularly the ratio diamond/graphite carbon was found one of the most significant parameters in this process: the higher the content in diamond-carbon the greater the TOC and COD decays in the bulk electrolyses. These results have been interpreted in terms of the oxidation mechanism involved. High graphite content favours direct oxidation of the pollutant on the electrode surface and leads to the formation of many intermediates. On contrary, high diamond content seems to favour the complete oxidation of the organic to carbon dioxide, thanks to the contribution of the oxidants (hydroxyl radicals and electrogenerated reagents) present in a region close to the electrode surface. Likewise, the oxidation rate seems to be improved with increase in the concentration of boron and decrease in the thickness of the substrate layer.     

Intersection of microwire electrodes with proximal CA1 stratum-pyramidale neurons at insertion for multiunit recordings predicted by a 3-D computer model

It is of broad interest in the context of neuronal multiunit extracellular recordings to understand electrode-tissue interactions in order to maximize the number of recordable units and to minimize experimental artifacts due to mechanical tissue alteration. Toward this goal, a computer model of microwire electrode insertion in hippocampus CA1 area was developed, firstly to provide estimates of the number of electrode-neuron intersections affecting recordable (local) neurons and, secondly, to determine optimal insertion/electrode parameters that minimize the number of intersections. The model predicts that in hippocampus CA1 area, using an electrode 50 microm in diameter, only 10% of the recordable neurons (those within 50 microm of the electrode), would remain collision free. Moreover, the model also predicts that inhibitory neurons are less prone to be intersected by the electrode, resulting in a 2 to threefold higher percentage of collision-free interneurons than expected from the relative densities of pyramidal cells and interneurons. Furthermore, the model confirms, in agreement with experimental observations, that electrode tilting with respect to the main neuronal axis increases the number of intact neurons (fourfold for a 50-microm electrode at 45 degrees when compared to 0 degrees , i.e., an insertion normal to the cell body layer).     

Modeling of switching frequency instabilities in buck‐based DC–AC H‐bridge inverters

In this paper, the dynamical behavior of a full bridge DC–AC buck inverter controlled by fixed frequency and PWM is studied. After showing that the system can undergo both period‐doubling and Neimark–Sacker bifurcation at the fast scale (switching period) by using the exact switching model, an exact solution discrete‐time model able to predict both instability phenomena is derived. The model is obtained without making the quasi‐static approximation and it can be used to obtain the useful operation region in the multi‐dimensional design parameter space from time domain simulations in a very fast and accurate manner. Based on the study of the system, some design guidelines are provided. Copyright © 2010 John Wiley & Sons, Ltd.     

Multi-leader coordination algorithm for networks with switching topology and quantized information

This paper analyzes the stability and convergence properties of a proportional–integral protocol for coordination of a network of agents with dynamic information flow and quantized information exchange. In the setup adopted, each agent is only required to exchange its coordination state with its neighboring agents, and the desired reference rate is only available to a group of leaders. We show that the integral term of the protocol allows the agents to learn the reference rate, rather than have it available a priori, and also provides disturbance rejection capabilities. The paper addresses the case where the graph that captures the underlying network topology is not connected during some interval of time or even fails to be connected at all times.     

Ground measurements for the validation of land surface temperatures derived from AATSR and MODIS data

An experimental site was set up in a large, flat and homogeneous area of rice crops for the validation of satellite derived land surface temperature (LST). Experimental campaigns were held in the summers of 2002-2004, when rice crops show full vegetation cover. LSTs were measured radiometrically along transects covering an area of 1 km². A total number of four thermal radiometers were used, which were calibrated and inter-compared through the campaigns. Radiometric temperatures were corrected for emissivity effects using field emissivity and downwelling sky radiance measurements. A database of ground-based LSTs corresponding to morning, cloud-free overpasses of Envisat/Advanced Along-Track Scanning Radiometer (AATSR) and Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) is presented. Ground LSTs ranged from 25 to 32 °C, with uncertainties between ± 0.5 and ± 0.9 °C. The largest part of these uncertainties was due to the spatial variability of surface temperature. The database was used for the validation of LSTs derived from the operational AATSR and MODIS split-window algorithms, which are currently used to generate the LST product in the L2 level data. A quadratic, emissivity dependent split-window equation applicable to both AATSR and MODIS data was checked as well. Although the number of cases analyzed is limited (five concurrences for AATSR and eleven for MODIS), it can be concluded that the split-window algorithms work well, provided that the characteristics of the area are adequately prescribed, either through the classification of the land cover type and the vegetation cover, or with the surface emissivity. In this case, the AATSR LSTs yielded an average error or bias of − 0.9 °C (ground minus algorithm), with a standard deviation of 0.9 °C. The MODIS LST product agreed well with the ground LSTs, with differences comparable or smaller than the uncertainties of the ground measurements for most of the days (bias of + 0.1 °C and standard deviation of 0.6 °C, for cloud-free cases and viewing angles smaller than 60°). The quadratic split-window algorithm resulted in small average errors (+ 0.3 °C for AATSR and 0.0 °C for MODIS), with differences not exceeding ± 1.0 °C for most of the days (standard deviation of 0.9 °C for AATSR and 0.5 °C for MODIS).