Browsing by Issue Date, starting with "1996-09-11"
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- A statistical approach to the harmonic modelling of mechanical manipulatorsPublication . Tenreiro Machado, J. A.; Galhano, AlexandraA 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 labirous computations and may be difficult to analyse. Thes 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.
- Control of robots with nonlinear friction and backlash in the jointsPublication . Azenha, Abílio; Tenreiro Machado, J. A.This paper investigates the control of robots with nonlinear friction and dynamic backlash in the joints. The study is based on the describing function (DF) of nonlinear systems. The controllers studied are the first order model and the second order model variable structure controllers (FOM-VSC and SOM-VSC). We start by studying nonlinear systems consisting of a mass subjected to coulomb plus viscous friction or two masses subjected to backlash. The worst case of the limit cycle generation is found to be the closed-loop system having two masses with backlash. On the other hand, the closed-loop system of a mass with nonlinear friction is found to be amenable to control without limit cycles. By decoupling the joints of the robot we find similar results within a good accuracy range.
- Design of fractional-order digital controllersPublication . Tenreiro Machado, J. A.The paper presents a novel method for the design of fractional-order digital controllers. The theory of fractional derivatives and integrals (FDI's) is still in a research stage but recent progress in the areas of chaos and fractal reveals promissing 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 proposed in the paper adopt the time domain, which makes them well suited for 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 broad algorithm. In this line of thought, this study represents a first stage towards the development of motion control systems based on the theory of FDI's.
- Research issues in natural and artificial biped locomotion systemsPublication . Silva, Filipe M.; Tenreiro Machado, J. A.This paper presents a review on biological and robotic biped locomotion systems. The main purpose is to study the achievements attianed in the last years and to develop a deeper insight towards future research. In the past decade a significant progress in the cooperation between biology and robotics has been made as researchers recognise the synergies in the two scientific areas. This cooperation stmilated the development of experimental legged vehicles and adequate control algorithms. The ultimate purpose of this article is to contribute toward the productive interaction between these two fields.