ISEP – DEE – Livro, parte de livro, ou capítulo de livro
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- Dedicated compute system for robot manipulationsPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins de; Costa, António M. C.; Matos, José S.In the last decade, robot dynamic computational algorithms have been steadily improved. Lagrangian[1] and Newton-Euler [2,3] recursive numerical algorithms, Horak’s mixed calculation[4], Lisp symbolic derivation of the robot closed form equations[5,6] and recently, customized computing algorithms[7,9] have been important stages towards more efficient procedures. Nevertheless, the still existing high computational loads, have prevented the industrial application of such algorithms. A new robot computational system, which overcomes those limitations, is presented. This system is motivated by the following considerations: - Symbolic formulae pose a high computational burden, due to the large number of arithmetic and transcendental computations. – These computations, usually performed at a high level compiled computer language are complex, namely, they are compiled to a large number of the microprocessor’s machine code instructions. – Those computations must be performed with very high precision, in order to reduce problems with finite precision arithmetics, a large word lengh is required. – There are two situations, as far as precision is concerned: the computer internal representation having very high precision contrasting with the computer interface to the outside world, usually consisting of 8 to 16 bit precision.
- Robot Manipulator Systems: Analysis and ControlPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins deManipulator systems are rather complex and highly nonlinear which makes difficult their analysis and control. Classic system theory is veil known, however it is inadequate in the presence of strong nonlinear dynamics. Nonlinear controllers produce good results [1] and work has been done e. g. relating the manipulator nonlinear dynamics with frequency response [2–5]. Nevertheless, given the complexity of the problem, systematic methods which permit to draw conclusions about stability, imperfect modelling effects, compensation requirements, etc. are still lacking. In section 2 we start by analysing the variation of the poles and zeros of the descriptive transfer functions of a robot manipulator in order to motivate the development of more robust (and computationally efficient) control algorithms. Based on this analysis a new multirate controller which is an improvement of the well known “computed torque controller” [6] is announced in section 3. Some research in this area was done by Neuman [7,8] showing tbat better robustness is possible if the basic controller structure is modified. The present study stems from those ideas, and attempts to give a systematic treatment, which results in easy to use standard engineering tools. Finally, in section 4 conclusions are presented.
- Robot Manipulator Systems: Analysis and ControlPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins deManipulator systems are rather complex and highly nonlinear which makes difficult their analysis and control. Classic system theory is veil known, however it is inadequate in the presence of strong nonlinear dynamics. Nonlinear controllers produce good results [1] and work has been done e. g. relating the manipulator nonlinear dynamics with frequency response [2–5]. Nevertheless, given the complexity of the problem, systematic methods which permit to draw conclusions about stability, imperfect modelling effects, compensation requirements, etc. are still lacking. In section 2 we start by analysing the variation of the poles and zeros of the descriptive transfer functions of a robot manipulator in order to motivate the development of more robust (and computationally efficient) control algorithms. Based on this analysis a new multirate controller which is an improvement of the well known “computed torque controller” [6] is announced in section 3. Some research in this area was done by Neuman [7,8] showing tbat better robustness is possible if the basic controller structure is modified. The present study stems from those ideas, and attempts to give a systematic treatment, which results in easy to use standard engineering tools. Finally, in section 4 conclusions are presented.
- Dedicated Computer System for Robot ManipulatorsPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins de; Matos, J. A. Silva; Costa, António M. C.In the last decade, robot dynanic conputational algorithm have been steadily improved. Lagrangian [1] and Newton-Euler [2,3] recursive nunerical algorithns, Horak’s mixed calculation [4], Lisp based symbolic derivation of the robot closed forn equations [5,6] and recently, costumized conputing algorithns [7–9] have been important stages towards nore efficient procedures, Nevertheless, the still existing high computational loads, have prevented the industrial application of such algorithns.
- A Variable Structure Control Algorithm for Robot Manipulators Using Acceleration FeedbackPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins deA new variable structure control algorithm for robot manipulators is announced. Second order linear system sliding curves and a new control law, eliminate the reaching phase problems as well as the chattering usually present in the sliding mode. This controller architecture may also be interpreted as the result of the acceleration data integration on the VSS algorithm. Consequently, there is a shift from the computational burden, often present in sophisticated control schemes, towards a simpler but highly sensor based structure. The results show a remarkable improvement over conventional VSS controllers, maintaining, however, a low computational complexity which make it well suited for microcomputer implementation.
- 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.
- An Intelligent Distributed System for Environmental ManagementPublication . Malheiro, Benedita; Oliveira, EugénioEnvironmental management is a complex task. The amount and heterogeneity of the data needed for an environmental decision making tool is overwhelming without adequate database systems and innovative methodologies. As far as data management, data interaction and data processing is concerned we here propose the use of a Geographical Information System (GIS) whilst for the decision making we suggest a Multi-Agent System (MAS) architecture. With the adoption of a GIS we hope to provide a complementary coexistence between heterogeneous data sets, a correct data structure, a good storage capacity and a friendly user’s interface. By choosing a distributed architecture such as a Multi-Agent System, where each agent is a semi-autonomous Expert System with the necessary skills to cooperate with the others in order to solve a given task, we hope to ensure a dynamic problem decomposition and to achieve a better performance compared with standard monolithical architectures. Finally, and in view of the partial, imprecise, and ever changing character of information available for decision making, Belief Revision capabilities are added to the system. Our aim is to present and discuss an intelligent environmental management system capable of suggesting the more appropriate land-use actions based on the existing spatial and non-spatial constraints.
- Improving Assumption based Distributed Belief RevisionPublication . Malheiro, Benedita; Oliveira, EugénioBelief revision is a critical issue in real world DAI applications. A Multi-Agent System not only has to cope with the intrinsic incompleteness and the constant change of the available knowledge (as in the case of its stand alone counterparts), but also has to deal with possible conflicts between the agents’ perspectives. Each semi-autonomous agent, designed as a combination of a problem solver – assumption based truth maintenance system (ATMS), was enriched with improved capabilities: a distributed context management facility allowing the user to dynamically focus on the more pertinent contexts, and a distributed belief revision algorithm with two levels of consistency. This work contributions include: (i) a concise representation of the shared external facts; (ii) a simple and innovative methodology to achieve distributed context management; and (iii) a reduced inter-agent data exchange format. The different levels of consistency adopted were based on the relevance of the data under consideration: higher relevance data (detected inconsistencies) was granted global consistency while less relevant data (system facts) was assigned local consistency. These abilities are fully supported by the ATMS standard functionalities.
- Consistency and Context Management in a Multi Agent Belief Revision TestbedPublication . Malheiro, Benedita; Oliveira, EugénioMulti-agent architectures are well suited for complex inherently distributed problem solving domains. From the many challenging aspects that arise within this framework, a crucial one emerges: how to incorporate dynamic and conflicting agent beliefs? While the belief revision activity in a single agent scenario is concentrated on incorporating new information while preserving consistency, in a multi-agent system it also has to deal with possible conflicts between the agents perspectives. To provide an adequate framework, each agent, built as a combination of an assumption based belief revision system and a cooperation layer, was enriched with additional features: a distributed search control mechanism allowing dynamic context management, and a set of different distributed consistency methodologies. As a result, a Distributed Belief Revision Testbed (DiBeRT) was developed. This paper is a preliminary report presenting some of DiBeRT contributions: a concise representation of external beliefs; a simple and innovative methodology to achieve distributed context management; and a reduced inter-agent data exchange format.
- Intelligent Distributed Environmental Decision Support SystemPublication . Malheiro, Benedita; Oliveira, EugénioThis article discusses the development of an Intelligent Distributed Environmental Decision Support System, built upon the association of a Multi-agent Belief Revision System with a Geographical Information System (GIS). The inherent multidisciplinary features of the involved expertises in the field of environmental management, the need to define clear policies that allow the synthesis of divergent perspectives, its systematic application, and the reduction of the costs and time that result from this integration, are the main reasons that motivate the proposal of this project. This paper is organised in two parts: in the first part we present and discuss the developed Distributed Belief Revision Test-bed — DiBeRT; in the second part we analyse its application to the environmental decision support domain, with special emphasis on the interface with a GIS.