Training a network of electronic neurons for control of a mobile robot

\u3cp\u3eAn adaptive training procedure is developed for a network of electronic neurons, which controls a mobile robot driving around in an unknown environment while avoiding obstacles. The neuronal network controls the angular velocity of the wheels of the robot based on the sensor readings. The nodes in the neuronal network controller are clusters of neurons rather than single neurons. The adaptive training procedure ensures that the input-output behavior of the clusters is identical, even though the constituting neurons are nonidentical and have, in isolation, nonidentical responses to the same input. In particular, we let the neurons interact via a diffusive coupling, and the proposed training procedure modifies the diffusion interaction weights such that the neurons behave synchronously with a predefined response. The working principle of the training procedure is experimentally validated and results of an experiment with a mobile robot that is completely autonomously driving in an unknown environment with obstacles are presented.\u3c/p\u3

Practical synchronization in networks of diffusively coupled non-identical systems

This document is attached as supplementary material to the manuscript entitled Training a network of electronic neurons for control of a mobile robot . In this document a general theoretical framework for practical synchronization in networks of diffusively coupled non-identical systems is described

Delay system modelling and analysis of a down-hole tool in drilling system

In this abstract, we present a delay systems model for the coupled axial-torsional dynamics of a drilling system including a down-hole tool. The down-hole tool directly affects the coupling between the axial and torsional dynamics and aims to improve the rate-of-penetration of the drilling system, thereby improving drilling efficiency. The results presented here provide physics-based insight in the working principle of the tool and confirm that indeed drilling efficiency can be improved by its usage

Analysis and control of stick-slip oscillations in drilling systems

\u3cp\u3eThis paper proposes feedback control strategies for the mitigation of torsional stick-slip oscillations in drilling systems using drag bits. Herein, we employ a model for the coupled axial-torsional drill-string dynamics in combination with a rate-independent bit-rock interaction law including both cutting and frictional effects. Using a singular perturbation and averaging approach, we show that the dynamics of this model generate an apparent velocity-weakening effect in the torque-on-bit, explaining the onset of torsional stick-slip vibrations. Based on this dynamic analysis, the (decoupled) torsional dynamics can be described by a delay-differential equation with a state-dependent delay. Using this model, we propose both state-and output-feedback control strategies for the mitigation of torsional stick-slip oscillations, where the latter strategy uses surface measurements only. The effectiveness of the proposed approaches is shown in a simulation study.\u3c/p\u3

Observer-based output-feedback control to eliminate torsional drill-string vibrations

Torsional stick-slip vibrations decrease the performance and reliability of drilling systems used for the exploration of energy and mineral resources. In this work, we present the design of a nonlinear observer-based output-feedback control strategy to eliminate these vibrations. We apply the controller to a drill-string model based on a real-life rig. Conditions, guaranteeing asymptotic stability of the desired equilibrium, corresponding to nominal drilling operation, are presented. The proposed control strategy has a significant advantage over existing vibration control systems in current drilling rigs as it only requires surface measurements instead of expensive down-hole measurements and can handle multiple modes of torsional vibration. Case study results using the proposed control strategy show that stick-slip oscillations can indeed be eliminated in realistic drilling scenarios

Nonlinear output-feedback control of torsional vibrations in drilling systems

\u3cp\u3eThis paper considers the design of a nonlinear observer-based output-feedback controller for oil-field drill-string systems aiming to eliminate (torsional) stick-slip oscillations. Such vibrations decrease the performance and reliability of drilling systems and can ultimately lead to system failure. Current industrial controllers regularly fail to eliminate stick-slip vibrations under increasingly challenging operating conditions caused by the tendency towards drilling deeper and inclined wells, where multiple vibrational modes play a role in the occurrence of stick-slip vibrations. As a basis for controller synthesis, a multi-modal model of the torsional drill-string dynamics for a real rig is employed, and a bit-rock interaction model with severe velocity-weakening effect is used. The proposed model-based controller design methodology consists of a state-feedback controller and a (nonlinear) observer. Conditions, guaranteeing asymptotic stability of the desired equilibrium, corresponding to nominal drilling operation, are presented. The proposed control strategy has a significant advantage over existing vibration control systems as it can effectively cope with multiple modes of torsional vibration. Case study results using the proposed control strategy show that stick-slip oscillations can indeed be eliminated in realistic drilling scenarios in which industrial controllers fail to do so. Moreover, key robustness aspects of the control system involving the robustness against uncertainties in the bit-rock interaction and changing operational conditions are evidenced.\u3c/p\u3

Robust output-feedback control to eliminate stick-slip oscillations in drill-string systems

\u3cp\u3eThe aim of this paper is to design a robust output-feedback controller to eliminate torsional stick-slip vibrations. A multi-modal model of the torsional dynamics with a nonlinear bit-rock interaction model is used. The controller design is based on skewed-μ DK-iteration and the stability of the closed-loop nonlinear system is analyzed. The proposed controller design strategy offers significant advantages compared to existing strategies. First, it requires only surface measurements, second, it can effectively deal with multiple torsional flexibility modes, third, it provides robustness with respect to uncertainties in the bit-rock interaction and finally, control performance specifications can be taken into account. Simulation results confirm that stick-slip vibrations are indeed eliminated using the designed controller.\u3c/p\u3

Experimental validation of torsional controllers for drilling systems

\u3cp\u3eTorsional stick-slip vibrations decrease the performance, reliability and fail-safety of drilling systems used for the exploration and harvesting of oil, gas, min- erals and geo-thermal energy. Current industrial controllers regularly fail to eliminate stick-slip vibrations, especially when multiple torsional flexibility modes in the drill- string dynamics play a role in the onset of stick-slip vibrations. This chapter presents the experimental validation of novel robust output-feedback controllers designed to eliminate stick-slip vibrations in the presence of multiple dominant torsional flexibility modes. For this purpose, a representative experimental test setup is designed, using a model of a real-life drilling rig as a basis. The model of the dynamics of the experimental setup can be cast in Lure-type form with set-valued nonlinearities representing an (uncertain) model for the complex bit-rock interaction and the interaction between the drill-string and the borehole. The proposed controller design strategy is based on skewed-m-DK-iteration and aims at optimizing the robustness with respect to uncertainty in the non-smooth bit-rock interaction. Moreover, a closed-loop stability analysis for the non-smooth drill-string model is provided. Experimental results confirm that stick-slip vibrations are indeed eliminated using the designed controller in realistic drilling scenarios in which state-of-practice controllers have failed to achieve the same.\u3c/p\u3

Mitigation of torsional vibrations in drilling systems:a robust control approach

\u3cp\u3eStick-slip vibrations decrease the performance, reliability, and fail safety of drilling systems. The aim of this paper is to design a robust output-feedback control approach to eliminate torsional stick-slip vibrations in drilling systems. Current industrial controllers regularly fail to eliminate stick-slip vibrations, especially when multiple torsional flexibility modes play a role in the onset of stick-slip vibrations. As a basis for controller synthesis, a multimodal model of the torsional dynamics for a real drill-string system is employed. The proposed controller design strategy is based on skewed-\mu DK iteration and aims at optimizing the robustness with respect to uncertainty in the nonlinear bit-rock interaction. Moreover, a closed-loop stability analysis for the nonlinear drill-string model is provided. This controller design strategy offers several benefits compared with existing controllers. First, only surface measurements are employed, therewith avoiding the need for down-hole measurements. Second, multimodal drill-string dynamics are effectively dealt with in ways inaccessible to state-of-practice controllers. Third, robustness with respect to uncertainties in the bit-rock interaction is explicitly provided and closed-loop performance specifications are included in the controller design. Case study results confirm that stick-slip vibrations are indeed eliminated in realistic drilling scenarios using the designed controller in which state-of-practice controllers fail to achieve this.\u3c/p\u3