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On 'Stability and control of elastic-joint robotic manipulators during constrained-motion tasks'
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Singular perturbation model of robots with elastic joints and elastic links constrained by rigid environment
No full textA robot with distributed flexibility in the links and lumped flexibility in the joints is considered in this paper. First the model of the system in free motion is formulated as a set of ordinary differential equations, adopting a finite number of modes of the link deformation. Then algebraic constraint equations on the generalized coordinates of the system are added, to account for the loss of degrees of freedom due to the contact with rigid environment. A reduced order model, expressed in the residual degrees of freedom is then derived, based on a coordinate partitioning procedure. The singularly perturbed model of the system is finally computed, and the expression of the fast subsystem is given. The special cases of a robot with rigid joints or rigid links are also addressed
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
Robust tuning of PID regulators based on step-response identification
No full textRobust control design requires an accurate knowledge of the uncertainty bound around the nominal model. While classical identification theory qualifies the uncertainty in identified models through confidence regions of the estimated parameters, recent works have studied frequency-domain error bounds for models identified via least-squares like techniques. In this paper a quantification of errors in models identified through step-response methods is proposed. A model error bound is derived based upon an elaboration of the step response of the process. This bound is then used to formulate simple rules for a robust tuning of PID controllers. A simulation example is also presented, where a comparison of the closed-loop performance obtained with the proposed tuning rules and with other common tuning rules is shown
Introduction to the special issue on modular physical modelling
No full textAn introduction to the special issue on modular physical modelling
INTEGRATED APPROACH TO RECYCLING AND CLEARANCE
No full textWaste management strategy based on recycling and clearance already applied to SEAFP-2 Plant Models is implemented in the following way: - For each activated component (or part of a component), the most appropriate management strategy is recommended, indicating the adequate cooling time, taken to be less than 100 years, required for the compliance with the limits. In some cases, two management options are suggested for the same material either allowing recycling or clearance, depending on different cooling times. - Clearance includes two possible paths: disposal as non-active waste, NAW, as for SEAFP-2, and recycling outside the nuclear industry or non-active recyclable material, NARM. For the former option, SEAFP-2 clearance levels are adopted, which are given in an IAEA interim document. For the latter option, different clearance levels defined in recent E.C.Recommendations are adopted. - An additional analysis concerns the possibility to attain conditions for clearance as non-active waste for the in-vessel V-4Cr-4Ti structures of PM-1. In this alloy most of the long-term activity arises from the impurities. It is shown that such conditions could be reached by: a) reduction of the impurities concentration in the alloy to extremely low levels, also below the actual detection limit, and b) reprocessing of the irradiated material to eliminate noxious nuclides deriving from the components of the alloy. The appendix contains a comparison of long-term risks, namely intrusion and degradation of containment, in fusion and fission wast
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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