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- 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.
- Statistical Modelling of Robotic ManipulatorsPublication . Machado, J. A. Tenreiro; Galhano, Alexandra M. S. F.The article presents a new approach to the analysis and design of robotic manipulators. The novel feature resides on a non-standard formulation to the modelling problem. usually, system descriptions are based on a set of differential equations which, due to their nature, lead to very precise results and strategies but require laborious camputations. This motivates the need of alternative models based on other methematical concepts. The proposed statistical method gives clear guidelines towards the robot kinematic and dynamic optimsation. Furthermore, the results point out strutural characteristics of the trajectory planning algorithm as well as ideal-actuator properties.
- 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
- Evaluation of manipulator direct dynamics using customized Rung-Kutta MethodsPublication . Machado, J. A. Tenreiro; Galhano, Alexandra M. S. F.This paper studies the efficiency of customized Runge-Kutta methods on the evaluation of the direct dynamics of robot manipulators. Customizing consists not only on the elimination of unnecessary and redundant calculation but also on the development of efficient integration methods. In this perspective, we investigate numerical algorithms with high order expansion and integration with adaptive step size based on the embedded estimated of the local truncation error.
- Benchmarking computer systems for robot controlPublication . Machado, J. A. Tenreiro; Galhano, Alexandra M. S. F.The high computational burden posed by modern control algorithms often precludes their industrial application using present day microcomputers. We evaluate the computational load of different logical and arithmetic operations and the capabilities of several computing systems (software and hardware). Real-time limitations are alleviated through the adoption 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 toward future computer control architectures
- Variable structure control of manipulators with joints having flexibility and backlashPublication . Machado, J. A. TenreiroThis article studies the variable structure control of robot manipulators with joints having flexibility and bcklash. A second order reference model and smoth control law eliminate the reaching phase problems and the chattering usually present in the sliding mode. The results show a remarkable improvement of the stability over conventional variable structure controllers, while the algorithm maintains a low computational load that makes it well suited for microcomputer implementation.
- Analysis and design of fractional-order digital control systemsPublication . Machado, J. A. TenreiroThe paper presents a novel method for the design of fractional-order digital controllers. The theory oof fractional derivatives and integrals (FDI's) is still in a research stage but the recent progress in the areas of chaos and fractal reveals promising aspects for future developments. In the field of automatic control systems some preliminary work has been carried out but the results are restricted to the frequency domain. The algorithms z-transform analysis and digital implementation. For a prototype mechanical system the control algorithm based on the new concepts reveals that classical P, I and D actions are, in fact, special cases of a more brad paradigm. In this line of thought, this study represents a first stage towards the development of motion controol systems based on the theory of FDI's
- Winrob: An educational program for roboticsPublication . Tenreiro Machado, J. A.; Galhano, AlexandraThe paper presents a program for robotics education that runs on standard IBM-PCs under the Microsoft Windows enviroment. The WinRob package is designed for undergraduate students and emphasises the fundamental aspects of robot modelling and control. The software is self-explanatory and uses menus, dialog boxes and context-dependent on-line help.
- Fractional-order derivative approximations in discrete-time control systemsPublication . Machado, J. A. TenreiroThe theory of fractional calculus goes back to he beginning of the theory of differential calculus but its inherent complexity postponed the application of the associated concepts. in the last decade the progress in the areas of chaos and fractals revealed subtle relationships with the fractional calculus leading to an increasing interest in the development of the new paradigm. in the area of automatic control preliminay work has already been carried out but the proposed algorithms are restricted to the frequency domain. The paper discusses the design of fractional-order discrete-time controllers. the algorithms and discrete-time implementation.
- On the Statistical/Harmonic modelling of mechanical manipulatorsPublication . Machado, J. A. Tenreiro; Galhano, Alexandra M. S. F.A new approach to the analysis and design of robot manipulators is presented. The novel feature resides on a non-standard formulation to the modelling problem. Usually, system descriptions are based on a set of differential equations which in general, require laborious computations and may be difficult to analyze. These facts motivate the need of alternative models based on different mathematical concepts. The proposed statistical approach to the Fourier modelling gives clear guidelines towards the optimization of the robot kinematics and point out structural characteristics of the trajectory planning algorithms.