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- 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 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.
- A smooth variable structure control algorithm for robot manipulatorsPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins deA new sliding controller is proposed. Second order linear system sliding curves eliminate the reaching phase and consequently and associated problems of load sensitivity and high demanded torque. Moreover, the chattering usually present in the sliding phase also disappears with the new control law. Simulation results show a negligible coupling between axes, thus enabling an easier and more efficient controller adjustment. It is also shown that the controller parameter set can be easily adjusted, and there is a large set of possible quasi-optimal values. This is of utmost importance, when one thinks of the industrial applications of this type of algorithms. Experiments were developed based on the position control problem. Nevertheless, generalization to the trajectory tracking problem is trivial. In either case the controller computational requirements are low, thus well adapted to today's microprocessor based digital control technology.
- A real-time system for robot manipulator inverse dynamics computationPublication . Machado, J. A. Tenreiro; Carvalho, J. L. Martins de; Matos, J. A. SilvaA new robot manipulator inverse dynamics computational algorithm is announced. The novel feature resides in the computations which are a blend of ordinary and Boolean algebra. As such, this method may also be interpreted as a dedicated compiler that optimizes the on-line conputing time at expenses of the off-line stage. Nevertheless, the high off-line requirements are alleviated, through the derivation of some general ruls that stem from the structure of the robot manipulator equations. Moreover, the on-line computing time is further optimized through the use of Binary Decision Diagrass. The results show a considerable computational improvement on a conventional sequential machine. Furthermore, they clearly point out new computational parallel architectures, without schedualing problems, and where performance improvement is proportional to the number of processors. Finally, it is observed that the proposed algorithm is not restricted to robot inverse dynamic computations, but is also applicable to many other real-time computing structures.
- An Efficient algorithm for robot manipulators dynamic computationPublication . Tenreiro Machado, J. A.; Matos, J. S.; Carvalho, J. M.; Costa, A. C.Despite recent advances in robot manipulator inversc dynamic computing methods, the development of industrial implementations of real-time controllers is still highly difficult, and impractical, due to the large mumber of arithmetic and transcendental floating point operations involved. The paper presents a method based on the use of a combination of boolean ond ordinary algebra that leads to a considerable reduction of the on-line computing time. Terms of the link torque equations are calculated by boolean algebra, using Binary Decision Diagrams, and are then combinated by arithmetiic summations. The result is an efficient computational technique for real-time robot manipulator nonlinear control which is well suited to today's digital technology. The method, which is not restricted to the particular application described in the paper, is well adapted to implementation on a parallel architecture with performance improvement porportional to the number of processors, and without scheduling problems.
- 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.
- 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.
- Filosofias da Qualidade (Quality Gurus) - desenvolvimento de uma cultura da qualidade na empresaPublication . Fonseca, LuísSão analisadas as principias metodologias e abordagens de Deming, Juran, Crosby, Ishikawa e Taguchi, visando identificar quais as mais adequadas para diversos tipos de cultura organizacional.
- Robot manipulator dynamics - Towards better computational algorithmsPublication . Tenreiro Machado, J. A.; Carvalho, J. L. Martins de; Matos, J. A. Silva; Costa, António M. C.A new robot manipulator inverse dynamics computational algorithm is announced. The novel feature resides in the computations which are a blend of ordinary and Boolean algebra. As such, this method may also be interpreted as a dedicated compiler that optimizes the on-line computing time at expenses of the off-line stage. Nervertheless, the high off-line requirements are alleviated, through the derivation of some general rules that stem from the structure of the robot manipulator equations. In a practical implementation, a copmuter program based on a Quine-McCluskey truth table simplification method was used and experimented on a 2R robot manipulator. The results show a considerable computational improvement on a conventional sequential machine. Furthermore. they clearly point out new comptutational parallel architectures, without scheduling problems, and where performance improvement is porportional to the number of processors. Finally, it is observed that the proposed algorithm is not restricted to robot inverse dynamic computations, but also applicable to kinematic and control computations.
- A statistical approach to the analysis and design of robot manipulatorsPublication . Tenreiro Machado, J. A.; Carvalho, J. L. Martins deA new approach the the analysis and design of robot manipulators is announced. The novel feature resides on a non standard approach 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, can be very complex to tackle. This motivates the need of models based on other mathematical comcepts having distinct characteristics. The proposed statistical scheme is a step in that direction which gives clear guidelines towards the robot kinematic and dynamic optimization. Furthermore, the inherent use of histograms allows not only fast calculation procedures, but above all, the use of experimental data; consequently, complex dynamic modelling exercises can be avoided.