Browsing by Issue Date, starting with "1991"
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- Refinamento de valore próprios de operadores integrais e diferenciaisPublication . Vieira, Maria Isabel CoutinhoRefinamento de valore próprios de operadores integrais e diferenciais
- Towards the real-time control of robotic systemsPublication . Tenreiro Machado, J. A.; Carvalho, J. L. Martins de; Galhano, AlexandraIn the last decades robot control has been an area of active research and development. Mechanical manipulators have a complex dynamics which makes difficult the design efficient controllers. Linear PID algorithms are still used in industrial robotics however, they are inappropriate for high performances. The limited efficiency of these systems motivated the development of controllers based on different concepts Dubwsky and DesForges (1), Luh e tal. (2), Freund (3). Nevertheless, the high computational load posed by many of the modern algorithms precludes its industrial application using present day microcomputers. In fact, the use of powerful monoprocessor computers is expensive while, on the other hand, multi-microprocessor architectures Luh and Lin (4), Binder and Herzog (5), Watanabe et al. (6) are still in a research stage. This situation can be overcome through the development of control strategies more adapted to the microcomputer. In this line of thought, this article compares the computational capabilities of several computers and introduces techniques capable of rendering more efficient practical implementations. It is organized as follows. In section two we evaluate the computational load posed by different operations to several computer systems. Based on the results, in section three, we present general techniques amenable to robot control implementation. Finally, in section four conclusions are drawn.
- Statistical modelling of robot manipulatorsPublication . Galhano, Alexandra; Tenreiro Machado, J. A.; Carvalho, J. L. Martins deRobotics is an area encompassing a wide range of industrial, technological and scientific applications. Still, many of them pose challenging issues to the available industrial manipulators. The superior performances of the human arm induced an extensive research towards better mechanical structures. In this line of thought, considerable research has been done either on the kinematics Tsai and Soni (1), Asada (2) or the dynamics Yoshikawa (3,4), Youcef-Toumi and Asada (5). However, a simple optimization criterion comprising both the kinematics and the dynamics is still lacking. In the present paper we address this problem, and our presentation is organized as follows. In section two the robot manipulator model and the associated optimization criterion are discussed. In section three a new model leading to natural optimization criterion is formulated and applied to a 2R robot manipulator. Finally, in section four conclusions are drawn.
- A multi-agent environment in roboticsPublication . Oliveira, Eugénio; Camacho, R.; Ramos, CarlosThe use of Multi-Agent Systems as a Distributed AI paradigm for Robotics is the principal aim of our present work. In this paper we consider the needed concepts and a suitable architecture for a set of Agents in order to make it possible for them to cooperate in solving non-trivial tasks. Agents are sets of different software modules, each one implementing a function required for cooperation. A Monitor, an Acquaintance and Self-knowledge Modules, an Agenda and an Input queue, on the top of each Intelligent System, are fundamental modules that guarantee the process of cooperation, while the overall aim is devoted to the community of cooperative Agents. These Agents, which our testbed concerns, include Vision, Planner, World Model and the Robot itself.
- Portugal na década de 80. Metamorfoses e o amortecimento e deslocamento da conflitualidade social no trabalhoPublication . Ramos, Geraldo DiasPortugal na década de 80. Metamorfoses e o amortecimento e deslocamento da conflitualidade social no trabalho
- Pesquisa automática da sequência óptima de produção el linhas galvânicasPublication . Duarte, Manuel Pedro de AlmeidaPesquisa automática da sequência óptima de produção el linhas galvânicas
- Microprocessor-Based Controllers for Robotic ManipulatorsPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins deRobotic manipulators pose a challenging problem to control system theory. Classical controllers, such as the well know PID controller still used in present day industrial robots, are inadequate for high performance manipulators. This problem motivated the emergence of a new class of controllers based on different concepts, namely non-linear and adaptative controllers. Unfortunately, these complex algorithms require powerful computer structures. While monoprocessor systems may be non-economical, multi-microprocessor architectures are still in a research stage and the total computional efficiency is far from desirable. To surpass these limitations new controller structures were devised. Some are based on the reformulation of the overall control concepts. In this line of thought methods like sliding controllers and learning controllers are being actively investigated. In the former the algorithms are easy to implement using standard hardware and applications have already been reported. With respect to learning controllers, they are still in a research stage; nevertheless, preliminary results indicate that a considerable computational reduction can be achieved by a more intelligent use of the microprocessor memory. Alternative strategies based on a more sound allocation of the computing tasks were also suggested~: Techniques such as multirate sampling, preview schemes and dedicated compilers have achieved promising results. This chapter focuses on the aforementioned control methods having in mind its real-time implementation on microprocessor-based structures.
- O Mundo da História 9Publication . Rothes, Luís; Cardoso, Fernando; António, MarinhoLivro escolar da disciplina de história para o nono ano do ensino básico
- Towards the statistical modelling of robotic manipulatorsPublication . Galhano, Alexandra; Carvalho, J. L. Martins de; Tenreiro Machado, J. A.A novel approach to the modelling of robot manipulators is presented. Usually, system descriptions are based on a set of differential equations which, due to their nature, lead to very precise results and strategies. However, they need laborious computations and, therefore, methods based on alternative mathematical concepts are required. The proposed statistical model overcomes thes problems and gives clear guidelines towards the optimization of the robot performances.
- On the evaluation of computer systems for robot controlPublication . Tenreiro Machado, J. A.; Carvalho, J. L. Martins de; Galhano, AlexandraThe high computational burden posed by modern control algorithms precludes its industrial application using present day microcomputers. In this paper we evaluate the calculation load of different logical and arithmetic operations and the capabilities of several computer systems. Thisanalysis reveals that some limitations can be alleviated through the adoptation of techniques associated with data representation. Such techniques achieve not only a more efficient management of the computational resources but also provide a deeper insight on developments towards future control architectures.