Steering control for haptic feedback and active safety functions

Steering feedback is an important element that defines driver–vehicle interaction. It strongly affects driving performance and is primarily dependent on the steering actuator\u27s control strategy. Typically, the control method is open loop, that is without any reference tracking; and its drawbacks are hardware dependent steering feedback response and attenuated driver–environment transparency. This thesis investigates a closed-loop control method for electric power assisted steering and steer-by-wire systems. The advantages of this method, compared to open loop, are better hardware impedance compensation, system independent response, explicit transparency control and direct interface to active safety functions.The closed-loop architecture, outlined in this thesis, includes a reference model, a feedback controller and a disturbance observer. The feedback controller forms the inner loop and it ensures: reference tracking, hardware impedance compensation and robustness against the coupling uncertainties. Two different causalities are studied: torque and position control. The two are objectively compared from the perspective of (uncoupled and coupled) stability, tracking performance, robustness, and transparency.The reference model forms the outer loop and defines a torque or position reference variable, depending on the causality. Different haptic feedback functions are implemented to control the following parameters: inertia, damping, Coulomb friction and transparency. Transparency control in this application is particularly novel, which is sequentially achieved. For non-transparent steering feedback, an environment model is developed such that the reference variable is a function of virtual dynamics. Consequently, the driver–steering interaction is independent from the actual environment. Whereas, for the driver–environment transparency, the environment interaction is estimated using an observer; and then the estimated signal is fed back to the reference model. Furthermore, an optimization-based transparency algorithm is proposed. This renders the closed-loop system transparent in case of environmental uncertainty, even if the initial condition is non-transparent.The steering related active safety functions can be directly realized using the closed-loop steering feedback controller. This implies, but is not limited to, an angle overlay from the vehicle motion control functions and a torque overlay from the haptic support functions.Throughout the thesis, both experimental and the theoretical findings are corroborated. This includes a real-time implementation of the torque and position control strategies. In general, it can be concluded that position control lacks performance and robustness due to high and/or varying system inertia. Though the problem is somewhat mitigated by a robust H-infinity controller, the high frequency haptic performance remains compromised. Whereas, the required objectives are simultaneously achieved using a torque controller

Optimized state feedback regulation of 3DOF helicopter system via extremum seeking

In this paper, an optimized state feedback regulation of a 3 degree of freedom (DOF) helicopter is designed via extremum seeking (ES) technique. Multi-parameter ES is applied to optimize the tracking performance via tuning State Vector Feedback with Integration of the Control Error (SVFBICE). Discrete multivariable version of ES is developed to minimize a cost function that measures the performance of the controller. The cost function is a function of the error between the actual and desired axis positions. The controller parameters are updated online as the optimization takes place. This method significantly decreases the time in obtaining optimal controller parameters. Simulations were conducted for the online optimization under both fixed and varying operating conditions. The results demonstrate the usefulness of using ES for preserving the maximum attainable performance

Tracking improvement based on the Proxy control scheme for bilateral teleoperation system under time-varying delays

International audienceThis paper addresses the problem of the position/force tracking in teleoperation system and proposes a haptic proxy control scheme. Compared to previous works, communication delays are assumed to be both time-varying and asymmetric, and the response of the synchronization and the transparency are improved. The control design is performed using Linear Matrix Inequality (LMI) optimization based on Lyapunov-Krasovskii functionals (LKF) and H1 control theory. With the designed controllers, the simulations of different working conditions, such as abrupt motion and wall contact, are performed and show the effectiveness of the proposed solution

H∞H_{\infty} Robust Control Design for Teleoperation Systems

International audienceThis paper deals with the problem of delay-dependent robust $H_{\infty}$ control for time-varying delay teleoperation system with norm-bounded and time-varying model uncertainties. Thanks to our proposed control scheme, Lyapunov-Krasovskii functionals (LKF) and $H_{\infty}$ theory, the delay-dependent stability and tracking performance analysis are proposed in terms of Linear Matrix Inequality (LMI) optimization. An illustrative example is given by various simulations to prove that, our proposed solution is efficient to handle time-varying delays and uncertainties under different working conditions, such as abrupt tracking and wall contact motion

A novel control scheme for teleoperation with guaranteed performance under time-varying delays

International audienceThis work deals with the stability and synchronization of systems with time-varying delays. We propose a novel control scheme with position/velocity information channel on the basis of Lyapunov-Krasovskii functional (LKF) and H1 control theory by using Linear Matrix Inequality (LMI). The proposed solution is efficient for different working conditions, such as abrupt motion and wall contact, and this is illustrated by various simulations