DYLEMA: Using walking robots for landmine detection and location

Detection and removal of antipersonnel landmines is an important worldwide concern. A huge number of landmines has been deployed over the last twenty years, and demining will take several more decades, even if no more mines were deployed in future. An adequate mineclearance rate can only be achieved by using new technologies such as improved sensors, efficient manipulators and mobile robots. This paper presents some basic ideas on the configuration of a mobile system for detecting and locating antipersonnel landmines efficiently and effectively. The paper describes the main features of the overall system, which consists of a sensor head that can detect certain landmine types, a manipulator to move the sensor head over large areas, a locating system based on a global-positioning system, a remote supervisor computer and a legged robot used as the subsystems’ carrier. The whole system has been configured to work in a semi-autonomous mode with a view also to robot mobility and energy efficiency.This work has been funded by the Spanish Ministry of Science and Technology under Grant CICYT DPI2001-1595 and DPI2004-05824.Peer reviewe

A perception system for accurate automatic control of an articulated bus

This paper describes the perception system for an automatic articulated bus where an accurate tracking trajectory is desired. Among the most promising transport infrastructures of the autonomous or semi-autonomous transportation systems, the articulated bus is an interesting low cost and friendly option. This platform involves a mobile vehicle and a private circuit inside CSIC premises. The perception system, presented in this work, based on 2D laser scanner as a prime sensor generates local terrain maps, where the major concern lies in detecting and tracking a tunnel guide rail built-in the circuit, by using a hybrid-efficient line extraction algorithm and the obstacle detection to guide the vehicle down the lane.The authors acknowledge partial funding of this research under: Robocity2030-II S2009/DPI-1559 and IMADE PIE/62/2008 (Comunidad de Madrid, ALDESA CONSTRUCCIONES SA, MAXIMASDE); FORTUNA D/026706/09 (Agencia Española de Cooperación Internacional para el Desarrollo, AECID). Dr. Héctor Montes acknowledges support form Universidad Tecnológica de Panamá and from CSIC under grant JAE-Doc.Peer reviewe

A perception system for accurate automatic control of an articulated bus

This paper describes the perception system for an automatic articulated bus where an accurate tracking trajectory is desired. Among the most promising transport infrastructures of the autonomous or semi-autonomous transportation systems, the articulated bus is an interesting low cost and friendly option. This platform involves a mobile vehicle and a private circuit inside CSIC premises. The perception system, presented in this work, based on 2D laser scanner as a prime sensor generates local terrain maps, where the major concern lies in detecting and tracking a tunnel guide rail built-in the circuit, by using a hybrid-efficient line extraction algorithm and the obstacle detection to guide the vehicle down the lane.The authors acknowledge partial funding of this research under: Robocity2030-II S2009/DPI-1559 and IMADE PIE/62/2008 (Comunidad de Madrid, ALDESA CONSTRUCCIONES SA, MAXIMASDE); FORTUNA D/026706/09 (Agencia Española de Cooperación Internacional para el Desarrollo, AECID). Dr. Héctor Montes acknowledges support form Universidad Tecnológica de Panamá and from CSIC under grant JAE-Doc.Peer reviewe

Robust Cascade Controller for Nonlinearly Actuated Biped Robots: Experimental Evaluation

In this paper we consider the postural stability problem for nonlinearly actuated quasi-static biped robots, both with respect to the joint angular positions and also with reference to the gripping effect between the foot/feet against the ground during robot locomotion. Zero moment point based mathematical models are developed to establish a relationship between the robot state variables and the stability margin of the foot (feet) contact surface and the supporting ground. Then, in correspondence with the developed dynamical model and its associated uncertainty, and in the presence of non-modeled robot mechanical structure vibration modes, we propose a robust control architecture that uses two cascade regulators. The overall robust control system consists of a nonlinear robust variable structure controller in an inner feedback loop for joint trajectory tracking, and anH∞ linear robust regulator in an outer, direct zero moment point feedback loop to ensure the foot-ground contact stability. The effectiveness of this cascade controller is evaluated using a simplified prototype of a nonlinearly actuated biped robot in double support placed on top of a one-degree-of-freedom mobile platform and subjected to external disturbances. The achieved experimental results have revealed that the simplified prototype is successfully stabilized.In this paper we consider the postural stability problem for nonlinearly actuated quasi-static biped robots, both with respect to the joint angular positions and also with reference to the gripping effect between the foot/feet against the ground during robot locomotion. Zero moment point based mathematical models are developed to establish a relationship between the robot state variables and the stability margin of the foot (feet) contact surface and the supporting ground. Then, in correspondence with the developed dynamical model and its associated uncertainty, and in the presence of non-modeled robot mechanical structure vibration modes, we propose a robust control architecture that uses two cascade regulators. The overall robust control system consists of a nonlinear robust variable structure controller in an inner feedback loop for joint trajectory tracking, and anH∞ linear robust regulator in an outer, direct zero moment point feedback loop to ensure the foot-ground contact stability. The effectiveness of this cascade controller is evaluated using a simplified prototype of a nonlinearly actuated biped robot in double support placed on top of a one-degree-of-freedom mobile platform and subjected to external disturbances. The achieved experimental results have revealed that the simplified prototype is successfully stabilized

Methodology for Zero-moment Point Experimental Modeling in the Frequency Domain

Frequency domain methodology is applied to obtain a nominal model for the Zero-Moment Point (ZMP) stability index of a biped robot in an attempt to establish a relationship between the robot trunk trajectories and the stability margin of the contact surface of the foot (or feet) touching the supporting soil. To this end the biped robot trunk is excited with a variable frequency sinusoidal signal around several operating points. These input oscillations generate other output oscillations that can be analyzed with the help of the ZMP measurement system. The proposed ZMP modeling approach not only considers classical rigid body model uncertainties but also non-modelled robot mechanical structure vibration modes. The non-linear ZMP model is obtained following three consecutive stages: Equivalent inverted pendulum dynamics, where saturation and acceleration upper bounds are taken into account, non-modelled inverted pendulum dynamics, including non-linear effects, and low-pass dynamics defining the system cut-off frequency. The effectiveness of this method is demonstrated in practice with the SILO2 biped robot prototype, and a simple control strategy is implemented in order to validate experimentally the usefulness of the models developed.Frequency domain methodology is applied to obtain a nominal model for the Zero-Moment Point (ZMP) stability index of a biped robot in an attempt to establish a relationship between the robot trunk trajectories and the stability margin of the contact surface of the foot (or feet) touching the supporting soil. To this end the biped robot trunk is excited with a variable frequency sinusoidal signal around several operating points. These input oscillations generate other output oscillations that can be analyzed with the help of the ZMP measurement system. The proposed ZMP modeling approach not only considers classical rigid body model uncertainties but also non-modelled robot mechanical structure vibration modes. The non-linear ZMP model is obtained following three consecutive stages: Equivalent inverted pendulum dynamics, where saturation and acceleration upper bounds are taken into account, non-modelled inverted pendulum dynamics, including non-linear effects, and low-pass dynamics defining the system cut-off frequency. The effectiveness of this method is demonstrated in practice with the SILO2 biped robot prototype, and a simple control strategy is implemented in order to validate experimentally the usefulness of the models developed

Determinantes da estrutura de capitais: o caso portugués - 1990 a 1995

Apesar do longo debate em finanças empresariais no que respeita à escolha da estrutura de capitals, ainda nao existe consenso sobre a existencia de urna estrutura óptima. No entanto, há unanimidade quanto à existência de vários factores que determinant a escolha de urna certa estrutura de financiamento por parte das empresas. Assim, neste artigo, mais do que discutirmos a problemática da existencia ou nào de uma estrutura óptima de capitals, analisamos, para uma amostra das maiores empresas Portuguesas, a importáncia e validade de diversos factores apontados na literatura como determinantes da estrutura de capitals das empresas (traduzida pelo rácio de endividamento): Dimensao, Crescimento, Risco de Negocio (Volatilidade), Rendibilidade, Composiçâo do Activo (Valor Colateral), Vantagens Fiscais Nao Resultantes do Endividamento, Sector de Actividade e Controlo Accionista. Utilizando dados em painel para o período de 1990 - 1995, procuramos descrever os efeitos que estas variáveis tém sobre o nivel de endividamento das empresas em cada ano da análise, tentando identificar relaçôes entre as variáveis, quer ao longo do tempo, quer entre empresas do mesmo sector de actividade, como também ainda analisar os efeitos particulares de cada empresa e de cada ano em análise, nao incluidos ñas variáveis explicativas dos modelos utilizados. Apesar de termos chegado a alguns resultados idénticos aos obtidos com outras metodologías aplicadas, para o mesmo efeito, a nivel internacional, também é um facto que nem sempre assim aconteceu, pensamos nós devido a características específicas das empresas da nossa amostra e, em geral, as do mercado Portugués.Despite the long debate in finance about the choice of the firm's capital structure, there is no agreement yet on the existence of such an optimal structure. However, there is a large unanimity as to the existence of several factors that can determine the choice of a certain capital structure by companies. Therefore, in this paper, more than discuss the problematic of the existence of an optimal capital structure, we analyse, for a large sample of Portuguese companies, the relevance and validity of several factors considered in the literature as determinants of the companies’ capital structure (represented by the debt ratio): Size, Growth, Business Risk (Volatility), Profitability, Assets Composition (Collateral Value), Non-Debt Tax Shields, Sector of Activity and Ownership Control. Using panel data for the period between 1990 and 1995, we seek to describe the effects that these variables have on companies’ debt level in each year of the analysis, trying to identify relationships among the variables, either through time or between companies in the same sector of activity. We also analyse the particular effects of each company and each year, that are not included in the explanatory variables of the models employed. Despite the fact that we have arrived at similar results as those obtained by other methodologies when applied internationally, it is also a fact that not always this has being so. We believe that, in particular, this was due to the specific characteristics of the companies in our sample and, in general, to those of the Portuguese market

Vertical Movement of Resonance Hopping Robot with Electric Drive and Simple Control System

In the paper vertical movements of resonance hopping robot with one leg and electric drive are considered. Special construction of hopping robot with compensation of losses during flight of the robot allows to employ a relatively simple control system as well as to get a stable regime of its operation. The designed robot has self-properties to maintain a specified height of jumping even with simple control system. Results of dynamical calculations, simulations and experimental testing are presented.In the paper vertical movements of resonance hopping robot with one leg and electric drive are considered. Special construction of hopping robot with compensation of losses during flight of the robot allows to employ a relatively simple control system as well as to get a stable regime of its operation. The designed robot has self-properties to maintain a specified height of jumping even with simple control system. Results of dynamical calculations, simulations and experimental testing are presented

Reliable, Built-in, High-Accuracy Force Sensing for Legged Robots

An approach for achieving reliable, built-in, high-accuracy force sensing for legged robots is presented, based on direct exploitation of the properties of a robot’s mechanical structure. The proposed methodology relies on taking account of force-sensing requirements at the robot design stage, with a view to embedding force-sensing capability within the mechanical structure of the robot itself. The test case is ROBOCLIMBER, a bulky, quadruped climbing and walking machine whose weighty legs enable it to carry out heavy-duty drilling operations. The paper shows that, with finite-element analysis of ROBOCLIMBER’s mechanical configuration during the design stage, candidate positions can be selected for the placement of force transducers to measure indirectly the contact forces between the feet and the ground. Force sensors are then installed at the theoretically best positions on the mechanical structure, and several experiments are carried out to calibrate all sensors within their operational range of interest. After calibration, the built-in sensors are subjected to experimental performance evaluation, and the final best sensor option is found. The built-in force-sensing capability thus implemented is subjected to its first test of usability when it is employed to compute the actual centre of gravity of ROBOCLIMBER. The method is shown to be useful for determining variation during a gait (due to the non-negligible weight of the legs). Afterwards the force sensors are shown to be useful for controlling foot-ground interaction, and several illustrative experiments confirm the high sensitivity, reliability and accuracy of the selected approach. Lastly, the built-in sensors are used to measure ground-reaction forces and to compute the zero-moment point for ROBOCLIMBER in real time, both while standing and while executing a dynamically balanced gait.An approach for achieving reliable, built-in, high-accuracy force sensing for legged robots is presented, based on direct exploitation of the properties of a robot’s mechanical structure. The proposed methodology relies on taking account of force-sensing requirements at the robot design stage, with a view to embedding force-sensing capability within the mechanical structure of the robot itself. The test case is ROBOCLIMBER, a bulky, quadruped climbing and walking machine whose weighty legs enable it to carry out heavy-duty drilling operations. The paper shows that, with finite-element analysis of ROBOCLIMBER’s mechanical configuration during the design stage, candidate positions can be selected for the placement of force transducers to measure indirectly the contact forces between the feet and the ground. Force sensors are then installed at the theoretically best positions on the mechanical structure, and several experiments are carried out to calibrate all sensors within their operational range of interest. After calibration, the built-in sensors are subjected to experimental performance evaluation, and the final best sensor option is found. The built-in force-sensing capability thus implemented is subjected to its first test of usability when it is employed to compute the actual centre of gravity of ROBOCLIMBER. The method is shown to be useful for determining variation during a gait (due to the non-negligible weight of the legs). Afterwards the force sensors are shown to be useful for controlling foot-ground interaction, and several illustrative experiments confirm the high sensitivity, reliability and accuracy of the selected approach. Lastly, the built-in sensors are used to measure ground-reaction forces and to compute the zero-moment point for ROBOCLIMBER in real time, both while standing and while executing a dynamically balanced gait

Channel estimation and prediction in a pilot-less massive MIMO TDD using non-coherent DMPSK

A novel time division duplex massive MIMO technique is proposed based on performing a pilot-less channel estimation in the uplink (UL) utilizing reconstructed differentially encoded data. Spatial multiplexing and differentially encoded data is applied both in the UL and in the downlink (DL). In this system, a reference signal is the first one of the differentially encoded streams in the UL and DL, and the pilots for data estimation are avoided while maintaining spatial multiplexing capabilities. To improve the channel estimation we propose to use a linear Wiener filter and we also propose different symbols placing strategies in an OFDM grid. We also propose a detection improvement of the UL data utilizing the predicted channels. We perform an analysis of the MSE of the blind channel estimation using the differentially encoded data and analyze the symbol-error-rate for both the UL and the DL when channel aging is considered. The analysis is corroborated via numerical results and the proposed scheme is shown to outperform its pilot-based counterpart.This work was supported in part by the European Union Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie European Training Network (ETN) TeamUp5G under Grant 813391, and in part by the Spanish National Project IRENE-EARTH (MINECO/AEI/FEDER/UE) under Grant PID2020-115323RB-C33

Excess volatility, cointegration and investor sentiment closed-end fund discounts-premiums.

Neste trabalho pretende-se analisar o comportamento dos descontos/prémios dos fundos de investimento fechados ao longo do tempo e identificar os factores que justifiquem a sua variabilidade. Tendo em consideração os argumentos apresentados pela corrente híbrida sobre a existência dos descontos/ prémios, a qual alega que estes se devem quer a factores ditos racionais quer comportamentais, pretende-se investigar se factores como o sentimento do investidor e liquidez dos fundos poderão justificar/explicar a variabilidade dos fundos ao longo do tempo. Nesta pesquisa utiliza-se uma amostra de 346 fundos fechados norte-americanos para o período de 2 de Janeiro de 1987 a 18 de Junho de 1999. Como o “sentimento do investidor” não é uma variável observável, emprega-se proxies como o fluxo líquido de fundos de investimento abertos (Mutual funds) bem como o índice composto do sentimento do investidor construído por Baker & Wurgler (2006) que conjugam algumas proxies usuais do sentimento do investidor. In this work we intend to analyse the closed-end funds discounts/premiums behaviour along time and to identify the factors that justify their variability. Having into consideration the arguments presented by hybrid framework about the existence of discounts/premiums which says that they are due to so-called rational factors as behaviour factors, we aim to investigate if factors such as investor sentiment and funds liquidity may explain the variability of discounts along time. In this research, we use a sample of 346 US closed-end funds for the period of January, 2 of 1987 to June, 18, 1999. As investor sentiment is a non observable variable, we employ proxies such as open-end funds (mutual funds) net flow as well as compound investor sentiment index constructed by Baker & Wurgler (2006) that mix some usual proxies of investor sentiment