1,721,221 research outputs found
FIR based causal design of 2-d.o.f. controllers for optimal set point tracking
No full textThe Base Function approach, recently proposed in the literature, is an effective method for set point tracking optimisation with two degrees of freedom regulators. Following this framework, the manuscript proposes an approach based on a Finite Impulse Response digital filter, that allows for an automatic selection of the feedforward path structure and for the optimisation of its parameters, thus overcoming the limitations inherent in the continuous time approaches recently presented in the literature. Based on a nonparametric model of the control loop, which is independent of the technique used to synthesise the feedback controller and of the set point signal, the method is simple enough to be suitable for systems where the limits imposed by the hardware and/or software architecture are relevant. Simulation and physical examples illustrate the usefulness of the proposal
End-point vibration sensing of planar flexible manipulators through visual servoing
No full textA visual servoing approach to the control of planar flexible robotic manipulators is adopted in this paper, based on the composite control theory, where the camera sensor is used together with the strain gauge measurements, to estimate the tip deformation. A fast Kalman filter, built on an integral manifold approximation of the manipulator model, can be used to fuse in the most effective way the measurements coming from different sensors, each one perturbed by its own noise. As a consequence, the signal to noise ratio of the deformation measurements can be effectively improved. A difficulty however arises in deriving a linear relation between the camera output and the state variables: the specific contribution of this paper is the derivation of such a linear relation in the fast time scale. Simulation results based on a two link planar flexible manipulator show the potential of the proposed approach to gain a more effective suppression of the tip vibrations, while an experimental example demonstrates its practical feasibility
Two-time scale visual servoing of eye-in-hand flexible manipulators
No full textVisual servoing of eye-in-hand flexible manipulators is addressed in this paper. Dynamic effects of both the rigid and the flexible motion of the manipulator are fully taken into account in a control solution where the two-time scale nature of the problem is exploited. The visual information is used in the "slow" subsystem for a task-space-oriented control law, where computationally expensive operations, such as inverse and time derivative of the Jacobian, are avoided. A constructive proof of stability of this control scheme, based on Lyapunov theory, is also presented. The effectiveness of the proposed controller is shown by means of a numerical simulation concerning a trajectory tracking problem. Some experimental results finally demonstrate the precision enhancement achieved by the proposed algorithm on a single-link flexible manipulator
Modelling flexible manipulators with motors at the joints
No full textA computationally efficient recursive model of a flexible manipulator with motors at the joints is described in this paper. The model adopts a mixed Eulerian and Lagrangian formulation of the equations of a flexible body and exploits the chained structure of the equations for a serial manipulator. The dynamic effects of the motors at the joints, including gyroscopic terms, are fully taken into account. Symbolic manipulation is used
in a newly developed package, whose performance in detailed reproduction of the dynamic effects due to the interplay between the motors and the flexible links is assessed through simulation. A comparison between the complete model and a simplified one, where the motors are considered as simple inertias rotating around their own axis, has been carried out, using both a time domain analysis and a frequency domain analysis, in order to show the relevance of gyroscopic effects in modelling flexible robots
On the design of the feedforward compensator in two-degree-of-freedom controllers
No full textThis paper presents an innovative methodology to design the feedforward path of two-degree-of-freedom (2-d.o.f.) regulators for ‘optimal’ set point tracking. The proposed methodology is totally independent of the structure of the feedback controller, of the way it is designed, and of the characteristics of the set point signal. By using a nonparametric model of the control loop, that can be easily identified on-line, various tracking problems can be cast into a unified, and easily interpreted optimisation framework. Simulated and physical examples demonstrate the simplicity and efficacy of the proposal
Revising the robust-control design for rigid robot manipulators
No full textRobust controllers for robot manipulators ensure stability of the closed-loop system, even if only partial knowledge of the dynamic model of the manipulator is available. Existing derivations of robust-control laws, while guaranteeing the stability result, present an undesired dependence of the robust-control term on the gains of the controller for the nominal system. This dependence forces larger robust-control terms when the nominal control gains are large. Based on a structured representation of the model uncertainty, this paper proposes a derivation of the robust-control law, where these limitations are removed. Experimental results on the COMAU SMART 3S industrial robot in a 3-degree-of-freedom (DOF) configuration confirm the advantages of the proposed controller
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