An adaptive technique for trajectory tracking control of a wheeled mobile robots without velocity measurements

This paper addresses an adaptive method for designing a sensorless trajectory tracking control scheme for a wheeled mobile robot. In order to reduce the cost of the robot, a new Nonlinear Observer (NOB) is used to leave out velocity sensors in the robot. Also, an adaptive model reference technique is used for designing the dynamic controller. In order to ensure the implementability of proposed controller, dynamic controller and nonlinear observer are designed in the presence of uncertainties. In addition, the Observer-based Kinematic Controller (OKC) is designed in the presence of sliding velocity. In order to improve the performance of the kinematic controller, sliding velocity is estimated and used for modification of kinematic controller. Finally, the effectiveness of the proposed method is demonstrated by simulations.     

Robust finite-time tracking control of nonholonomic mobile robots without velocity measurements

The problem of robust finite-time trajectory tracking of nonholonomic mobile robots with unmeasurable velocities is studied. The contributions of the paper are that: first, in the case that the angular velocity of the mobile robot is unmeasurable, a composite controller including the observer-based partial state feedback control and the disturbance feed-forward compensation is designed, which guarantees that the tracking errors converge to zero in finite time. Second, if the linear velocity as well as the angular velocity of mobile robot is unmeasurable, with a stronger constraint, the finite-time trajectory tracking control of nonholonomic mobile robot is also addressed. Finally, the effectiveness of the proposed control laws is demonstrated by simulation.     

Trajectory tracking control of mobile robots without using longitudinal velocity measurements

We propose a new robust trajectory tracking control scheme for wheeled mobile robots without longitudinal velocity measurements. In the proposed controller, a velocity observer is used to estimate the longitudinal velocity of a wheeled mobile robot. A wheeled mobile robot model, including motor dynamics, is used to develop the controller. The developed controller has the following useful properties. (1) The developed controller does not require any accurate knowledge of the robot parameters or the motor parameters. Even if there are uncertainties in the robot dynamics, including the motor properties, it is certain that tracking errors ultimately become uniformly bounded in a closed-loop system using the developed controller. (2) It is shown theoretically that the ultimate norms of tracking errors can easily be reduced by setting only one design parameter.     

A nonlinear trajectory tracking controller for mobile robots with velocity limitation via fuzzy gains

This paper proposes a fuzzy controller for trajectory tracking with unicycle-like mobile robots. Such controller uses two Takagi–Sugeno (TS) fuzzy blocks to generate its gains. The controller is able to limit the velocity and control signals of the robot, and to reduce the errors arising from its dynamics as well. The stability of the developed controller is proven, using the theory of Lyapunov. Experimental results show that the use of the proposed controller is attractive in comparison with the use of a controller with fixed saturation function.     

Spacecraft relative rotation tracking without angular velocity measurements

We present a solution to the problem of tracking relative rotation in a leader-follower spacecraft formation using feedback from relative attitude only. The controller incorporates an approximate-differentiation filter to account for the unmeasured angular velocity. We show uniform practical asymptotic stability (UPAS) of the closed-loop system. For simplicity, we assume that the leader is controlled and that we know orbital perturbations; however, this assumption can be easily relaxed to boundedness without degrading the stability property. We also assume that angular velocities of spacecraft relative to an inertial frame are bounded. Simulation results of a leader-follower spacecraft formation using the proposed controller structure are also presented.     

Distributed formation control of nonholonomic mobile robots without global position measurements

This paper proposes a new class of distributed nonlinear controllers for leader-following formation control of unicycle robots without global position measurements. Nonlinear small-gain design methods are used to deal with the problem caused by the nonholonomic constraint of the unicycle robot and yield simple conditions for practical implementation. With the proposed distributed controllers, the formation control objective can be achieved without assuming any tree sensing structures. More interestingly, the distributed controller is robust to position measurement errors and the linear velocities of the robots can be restricted to specific bounded ranges.     

Global trajectory tracking control of VTOL-UAVs without linear velocity measurements

This paper deals with the position control of Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) without linear velocity measurements. We propose a multistage constructive procedure, exploiting the cascade property of the translational and rotational dynamics. More precisely, we consider the force as a virtual control input for the translational dynamics, from which we extract the required (desired) system attitude and thrust achieving the tracking objective. Thereafter, the control torque is designed to drive the actual attitude to the desired one. A nonlinear observer, as well as some instrumental auxiliary variables are used to obviate the need for the linear velocity. Global asymptotic stability of the overall closed loop system is achieved. Simulation results are provided to show the effectiveness of the proposed control scheme.     

Cooperative adaptive consensus tracking for multiple nonholonomic mobile robots

This paper addresses the cooperative adaptive consensus tracking for a group of multiple nonholonomic mobile robots, where the nonholonomic robot model is assumed to be a canonical vehicle having two actuated wheels and one passive wheel. By integrating a kinematic controller and a torque controller for the nonholonomic robotic system, a cooperative adaptive consensus tracking strategy is developed for the uncertain dynamic models using Lyapunov-like analysis in combination with backstepping approach and sliding mode technique. A key feature of the developed adaptive consensus tracking algorithm is the introduction of a directed network topology into the control constraints based on algebraic graph theory to characterise the communication interaction among robots, which plays an important role in realising the cooperative consensus tracking with respect to a specific common reference trajectory. Furthermore, a novel framework is proposed for developing a unified methodology for the convergence analysis of the closed-loop control systems, which can fully ensure the desired adaptive consensus tracking for multiple nonholonomic mobile robots. Subsequently, illustrative examples and numerical simulations are provided to demonstrate and visualise the theoretical results.     

An adaptive tracking controller using neural networks for a classof nonlinear systems

A neural-network-based adaptive tracking control scheme is proposed for a class of nonlinear systems in this paper. It is shown that RBF neural networks are used to adaptively learn system uncertainty bounds in the Lyapunov sense, and the outputs of the neural networks are then used as the parameters of the controller to compensate for the effects of system uncertainties. Using this scheme, not only strong robustness with respect to uncertain dynamics and nonlinearities can be obtained, but also the output tracking error between the plant output and the desired reference output can asymptotically converge to zero. A simulation example is performed in support of the proposed neural control scheme.     

A linear-interpolation-based controller design for trajectory tracking of mobile robots

This work presents a novel linear interpolation based methodology to design control algorithms for the trajectory tracking of mobile robotic systems. Particularly, a typical nonlinear multivariable system—a mobile robot—is analysed. The methodology is simple and can be applied to the design of a large class of control systems. Simulation and experimental results are presented and discussed, demonstrating the good performance of the proposed methodology.     

On global tracking control of a VTOL aircraft without velocity measurements

This note develops a nonlinear output-feedback controller to force a nonminimum phase, underactuated vertical take-off and landing aircraft to globally asymptotically track a reference trajectory generated by a reference model. The control development is based on a global exponential observer, some global coordinate transformations, Lyapunov's direct method and an extension of the backstepping technique. Interestingly, the proposed methodology also yields new results for the previously studied problems of stabilization and output tracking or regulation. Numerical simulations illustrate the effectiveness of the proposed controller.     

Dynamics of a learning controller for surface tracking robots onunknown surfaces

An extended Kalman filter is applied to simulated sensor information as an approach to the surface estimation problem. It is assumed that a robotic probe equipped with a tactile sensor is given the task of working with a completely unknown surface. Kinematics and control based on tactile measurements are briefly discussed. An estimator which provides surface information as obtained by an inherently noisy force sensor is designed. From these estimates, a controller is given the capability of learning the constraint surface, thereby rejecting the noisy sensor data. After a short time, surface tracking is similar to the case of constrained motion on known surfaces     

A tracking controller for flexible joint robots using only linkposition feedback

A dynamic output feedback controller for flexible joint robots is presented which guarantees asymptotic tracking of a desired trajectory, starting from arbitrary initial conditions. The controller needs only the measurements of the positions of the links and the knowledge of an upper bound on the initial tracking error     

Extremum seeking for moderately unstable systems and for autonomous vehicle target tracking without position measurements

We remove the long standing restriction that plant dynamics in extremum seeking control must be stable and provide an extension that allows single integrators, double integrators, and moderately unstable single poles. An application of the result for single and double integrators is in control of autonomous vehicles. Extremum seeking is used for finding a source of a signal (chemical, electromagnetic, etc.) whose strength decays with the distance. This is achieved without the measurement of the position vector and using only the measurement of the scalar signal.     

Unified nonsingular tracking and stabilization controller design for unicycle-type wheeled mobile robots

A unified, singularity-avoidant controller which enables simultaneous trajectory tracking and posture stabilization of unicycle-type wheeled mobile robots is proposed. The design scheme is based on phase portrait analysis, dynamic feedback linearization and sliding mode control. Path planning via phase portrait analysis plays a key role in choosing the control parameters and the initial value of the extended state in avoiding any singularity. Simulation results on posture stabilization as well as an eight-shaped trajectory tracking are presented to demonstrate the performance of the proposed controller.     

An adaptive controller for nonlinear teleoperators

In Chopra et al (2008) [Chopra, N., Spong, M. W., & Lozano, R. (2008). Synchronization of bilateral teleoperators with time-delay. Automatica, 44(8), 2142-2148], an adaptive controller for teleoperators with time-delays, which ensures synchronization of positions and velocities of the master and slave manipulators, and does not rely on the use of the ubiquitous scattering transformation, is proposed. In this paper it is shown that this controller will tend to drive to zero the positions of the joints where gravity forces are non-zero. Hence, the scheme is, in general, applicable only to systems without gravity. We also prove in this paper that this limitation can be obviated, replacing the positions and velocities-that are used in the coordinating torques and the adaptation laws-by their errors. Simulation results illustrate the performance of both schemes.     

Robust adaptive controller with zero residual tracking errors

The adaptive control of a plant whose dominant part has transfer function with relative degreen^{ast} = 1has been considered in the presence of parasitics and disturbances. A new adaptive law is proposed which guarantees the existence of a large region of attraction from which all signals are bounded and the tracking error converges to a small residual set. In contrast to the adaptive law used in [1], [2] the new adaptive law guarantees a smaller residual set for the tracking error, which reduces to zero when the parasitics and disturbances disappear.     

End-effector trajectory tracking of flexible link parallel robots using servo constraints

Multibody System Dynamics -     

A data-driven controller for position tracking of a long-stroke piezoelectric actuator

Microsystem Technologies - Hysteresis and other nonlinearities exhibited by piezoelectric materials significantly limit the tracking capability of piezoelectric actuators (PAs). To eliminate these...     

A flexible controller for robots

The structure of a flexible microprocessor-based controller for a low-cost robot for component handling is described. The robot demonstrates three degrees of freedom within cylindrical coordinate motion. One axis uses end-stop pneumatic actuation with the remaining two axes being actuated by specially designed hydropneumatic drives. By using hydropneumatic actuation and incremental encoder feedback, point-to-point positioning is provided through a real-time closed-loop control algorithm designed and implemented within the controller structure. Interactive programming aids have also been implemented within the control structure to allow operatives to describe robot handling tasks by using a shop floor oriented language. Both hardware and software for the controller have been developed in a modular form to increase its flexibility allowing the modules produced to be used for the control of other work-handling systems.