Path-tracking of a tractor-trailer vehicle along rectilinear and circular paths: A Lyapunov-based approach

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Tracking Control of Uncertain Nonholonomic Mobile Robots: Smooth Switching Approach

ABSTRACT Backstepping based adaptive tracking control of nonholonomic mobile robots in the presence of both kinematic and dynamic parametric uncertainty is presented. The major challenge is the possible singularity phenomenon due to the approach of zero of the estimated input vector field entering the denominator of the control input, a common drawback of adaptive linearization-based schemes. A hybrid control approach, which switches between an adaptive and a robust control schemes, is developed for solving such a problem. It retains the advantage of an adaptive control approach to a greatest extent while avoiding the possible blowup of the torque inputs simultaneously. A case study on a specific Type (2; 0) mobile robot is provided in the final to verify the usefulness of the proposed design

Design and Development of an Integrated Mobile Robot System for Use in Simple Formations

In recent years, formation control of autonomous unmanned vehicles has become an active area of research with its many broad applications in areas such as transportation and surveillance. The work presented in this thesis involves the design and implementation of small unmanned ground vehicles to be used in leader-follower formations. This mechatronics project involves breadth in areas of mechanical, electrical, and computer engineering design. A vehicle with a unicycle-type drive mechanism is designed in 3D CAD software and manufactured using 3D printing capabilities. The vehicle is then modeled using the unicycle kinematic equations of motion and simulated in MATLAB/Simulink. Simple motion tasks are then performed onboard the vehicle utilizing the vehicle model via software, and leader-follower formations are implemented with multiple vehicles

Trajectory tracking and formation control of a platoon of mobile robots

This thesis is concerned with controlling a platoon of wheeled mobile robots (WMR), where the robots are aimed to follow a trajectory while they maintain their formation intact. The control design is carried out by considering unicycle kinematics for each robot, and the leader-follower structure for the formation. It is assumed that every robot except the one located at the end of each platoon can potentially be the leader to the one behind it. It is also assumed that each follower is capable of sensing its relative distance and relative velocity with respect to its preceding robot. The stability of the proposed control law is investigated in the case of perfect sensing and in the presence of input saturation. The impact of measurement noise on the followers is then studied assuming that a known upper bound exists on the measurement error, and a linear matrix inequality (LMI) methodology is proposed to design a control law which minimizes the upper bound on the steady-state error. The problem is then investigated in a more practical setting, where the control input is subject to delay, and that the tracking trajectory can be different in distinct time intervals. It is to be noted that delay often exists in this type of cooperative control system due to data transmission and signal processing, and if neglected in the control design, can lead to poor closed-loop performance or even instability. Furthermore, switching in tracking trajectory can be used as a collision avoidance strategy in the formation control problem. Delay dependent stability conditions are derived in the form of LMIs, and the free-weighting matrix approach is used to obtain less conservative results. Simulations are presented to demonstrate the efficacy of the results obtained in this thesis

Model Predictive Control of Nonholonomic Mobile Robots

In this work, we investigate the possibility of using model predictive control (MPC) for the motion coordination of nonholonomic mobile robots. The contributions of this dissertation can be summarized as follows.A robust formation controller is developed for the leader-following formation of unmanned aerial vehicles (UAVs). With the assumption that an autopilot operating in holding mode at the low-layer, we present a two-layered hierarchical control scheme which allows a team of UAVs to perform complex navigation tasks under limited inter-vehicle communication. Specifically, the robust control law eliminates the requirement of leader's velocity and acceleration information, which reduces the communication overhead.A dual-mode MPC algorithm that allows a team of mobile robots to navigate in formations is developed. The stability of the formation is guaranteed by constraining the terminal state to a terminal region and switching to a stabilizing terminal controller at the boundary of the terminal region. With this dual-mode MPC implementation, stability is achieved while feasibility is relaxed.A first-state contractive model predictive control (FSC-MPC) algorithm is developed for the trajectory tracking and point stabilization problems of nonholonomic mobile robots. The stability of the proposed MPC scheme is guaranteed by adding a first-state contractive constraint and the controller is exponentially stable. The convergence is faster and no terminal region calculation is required. Tracking a trajectory moving backward is no longer a problem under this MPC controller. Moreover, the proposed MPC controller has simultaneous tracking and point stabilization capability.Simulation results are presented to verify the validity of the proposed control algorithms and demonstrate the performance of the proposed controllers.School of Electrical & Computer Engineerin

Adaptive robust control of an omnidirectional mobile platform for autonomous service robots in polar coordinates

This paper presents an adaptive robust control method for trajectory tracking and path following of an omni-directional wheeled mobile platform with actuators' uncertainties. The polar-space kinematic model of the platform with three independent driving omnidirectional wheels equally spaced at 120 from one another is briefly introduced, and the dynamic models of the three uncertain servomotors mounted on the driving wheels are also described. With the platform's kinematic model and the motors' dynamic model associated two unknown parameters, the adaptive robust controller is synthesized via the integral backstepping approach. Computer simulations and experimental results are conducted to show the effectiveness and merits of the proposed control method in comparison with a conventional PI feedback control method

Adaptive Polar-Space Motion Control for Embedded Omnidirectional Mobile Robots with Parameter Variations and Uncertainties

This paper presents an adaptive polar-space motion controller for trajectory tracking and stabilization of a three-wheeled, embedded omnidirectional mobile robot with parameter variations and uncertainties caused by friction, slip and payloads. With the derived dynamic model in polar coordinates, an adaptive motion controller is synthesized via the adaptive backstepping approach. This proposed polar-space robust adaptive motion controller was implemented into an embedded processor using a field-programmable gate array (FPGA) chip. Furthermore, the embedded adaptive motion controller works with a reusable user IP (Intellectual Property) core library and an embedded real-time operating system (RTOS) in the same chip to steer the mobile robot to track the desired trajectory by using hardware/software co-design technique and SoPC (system-on-a-programmable-chip) technology. Simulation results are conducted to show the merit of the proposed polar-space control method in comparison with a conventional proportional-integral (PI) feedback controller and a non-adaptive polar-space kinematic controller. Finally, the effectiveness and performance of the proposed embedded adaptive motion controller are exemplified by conducting several experiments on steering an embedded omnidirectional mobile robot