Browsing by Author "Carvalho, J. L. Martins de"
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- An efficient computational scheme for robot manipulatorsPublication . Tenreiro Machado, J. A.; Carvalho, J. L. Martins de; Matos, J. A. SilvaA new robot manipulator computational scheme which is a blend of ordinary and Boolean algebra is presented. This method may also be interpreted as a dedicated compiler that optimizes the on-line computing time at expenses of the off-line stage. The off-line requirements are alleviated, by the implementation of some general rules that stem from the structure of the robot manipulator equations, and the on-line computing time is optimized through the use of Binary Decision Diagrams. The results show a considerable computational improvement on conventional sequential machines but, furthermore, they clearly point out new computational parallel architectures. Finally, it is observed that the proposed algorithm is not restricted to robot dynamic computations, but is also applicable to many other computing structures.
- Analysis of Robot Dynamics and Compensation Using Classical and Computed Torque TechniquesPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins de; Galhano, Alexandra M. S. F.A classical analysis of the dynamics of robot manipulators is presented. It is shown that these systems have configuration-dependent properties and can be open-loop unstable. Due to this fact, present day linear controllers are inefficient. On the other hand, nonlinear hardware and software compensation methods also are shown to have some limitations. Controllers based on the direct design algorithm and the computed torque method have superior performances. These algorithms have nonlinear loops, yet it is shown that a linear analysis is still feasible. Therefore, classical design tools can be adopted in order to develop practical implementations
- Computer system evaluation in robot controlPublication . Tenreiro Machado, J. A.; Carvalho, J. L. Martins de; Galhano, AlexandraThe high computational burden posed by mordern control algorithms preclude its industrial application using present day microcomputers. In this paper we evaluate the computational load of different logical and arihmetic operations and the capabilities of several computing systems (software & hardware). This study reveals that real-time limitations can be alleviated through the adoption of general techniques achieve not only a more efficient management of the computational resources but also provide a deeper insight on developments towards future real-time control architectures.
- 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.
- 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.
- Engineering Design of a Multirate Nonlinear Controller for Robot ManipulatorsPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins deA new multirate nonlinear controller for robot manipulators is described. The algorithm stems from the computed torque method, but has several modifications on its structure, resulting in a more robust controller. The man philosophy behind those improvements resides on a sound engineering and management of the system resources. Consequently, the use of multirate sampling, memory tables, and predictive action arises naturally from that methodology. The resulting controller is easy to tune using standard industrial engineering practice; moreover, by alleviating the computational burden its implementation es feasible with present day microprocessors.
- Microcomputer evaluation in robot controlPublication . Tenreiro Machado, J. A.; Carvalho, J. L. Martins de; Galhano, AlexandraThe high computational burden posed by modern control algorithms preclude its industrial application using present day microcomputers. In this paper we evaluate the computational load of different logical and arithmetic operations and the capabilities of several computing systems (software and hardware). This study reveals that real-time limitations ca be alleviated through the adoptation of general techniques associated with the 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 real-time control architectures.
- 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.
- A new variable structure controller for robot manipulatorsPublication . Tenreiro Machado, J. A.; 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. The results show a remarkable improvement over conventional VSS controllers, maintaining, however, a low computationla complexity which make it well suited for microcomputer implementation. Furthermore, the well known standard heuristic procedures of controller adjustment can be used in the proposed scheme. This is of utmost importance in an industrial environment.
- On statistical analysis of biological armsPublication . Galhano, Alexandra; Carvalho, J. L. Martins de; Tenreiro Machado, J. A.The statistical analysis of robot manipulators reveals the limitations of joint-actuated machines. Steming from the results, in this paper we apply the statistical concepts on the study of biological arms. The superior performances of muscle-actuated arms over standard joint-actuated manipulators are demonstrated.