Nonlinear robust control of tendon–driven robot manipulators

This work addresses the position tracking control problem for tendon–driven robotic mechanisms in the presence of parametric uncertainty and additive external disturbances. Specifically, a full state feedback nonlinear robust controller is proposed to tackle the link position tracking problem for tendon–driven robot manipulators with uncertain dynamical system parameters. A robust backstepping approach has been utilized to achieve uniformly ultimately bounded tracking performance despite the lack of exact knowledge of the dynamical parameters and presence of additive but bounded disturbance terms. Stability of the overall system is proven via Lyapunov based arguments. Simulation studies performed on a two link planar robot manipulator driven by a six tendon mechanism are presented to illustrate the effectiveness and viability of the proposed approach.Scientific and Technological Research Council of Turkey (112E561

Robust dynamic positioning of surface vessels via multiple unidirectional tugboats

In this paper, the problem of accurate positioning of an unactuated surface vessel by using multiple uni-directional tugboats is investigated. Specifically a robust controller that ensures asymptotic position tracking is designed. The control design procedure is implemented in two steps: Initially by locating opposing tugboats to specific configurations, the overall problem is transformed into a second order system with an uncertain non-symmetric input gain matrix. Then via a matrix decomposition, a novel robust controller methodology is proposed. The stability of the overall system is ensured via rigorous stability analysis where asymptotic position tracking is ensured. Numerical simulation results are presented to demonstrate the efficiency of the proposed controller.Scientific and Technological Research Council of Turkey (113E147

A model independent observer based output feedback tracking controller for robotic manipulators with dynamical uncertainties

In this work, we propose the development and the corresponding stability analysis of a novel, observer-based output feedback (OFB), tracking controller for rigid-link robot manipulators. Specifically, a model-independent variable-structure-like observer in conjunction with a desired dynamic compensation technique have been utilized to remove the link velocity dependency of the controller formulation. Asymptotic stability of the observer - controller couple is then guaranteed via Lyapunov-based arguments. An adaptive controller extension is also presented to illustrate the expansiveness of the proposed scheme. Experimental studies performed on a two-link planar robot with dynamical uncertainties are included in order to demonstrate the performance and feasibility of the proposed method

A new objective function for obstacle avoidance by redundant service robot arms

The performance of task-space tracking control of kinematically redundant robots regulating self-motion to ensure obstacle avoidance is studied and discussed. As the subtask objective, the links of the kinematically redundant assistive robot should avoid any collisions with the patient that is being assisted. The shortcomings of the obstacle avoidance algorithms are discussed and a new obstacle avoidance algorithm is proposed. The performance of the proposed algorithm is validated with tests that were carried out using the virtual model of a seven degrees-offreedom robot arm. The test results indicate that the developed controller for the robot manipulator is successful in both accomplishing the main-task and the sub-task objectives.Scientific and Technological Research Council of Turkey (113E147

Robust output tracking control of an unmanned aerial vehicle subject to additive state dependent disturbance

In this study, an asymptotic tracking controller is developed for an aircraft model subject to additive, state-dependent, non-linear disturbance-like terms. Dynamic inversion technique in conjunction with robust integral of the sign of the error term is utilised in the controller design. Compared to the previous studies, the need of acceleration measurements of the aircraft have been removed. In addition, the proposed controller design utilises only the output of aircraft dynamics. Lyapunov based analysis is applied to prove global asymptotic convergence of the tracking error signal. Numerical simulation results are presented to illustrate the performance of the proposed robust controller