A robot lawnmower includes a body and a drive system carried by the body and configured to maneuver the robot across a lawn. The robot also includes a grass cutter and a swath edge detector, both carried by the body. The swath edge detector is configured to detect a swath edge between cut and uncut grass while the drive system maneuvers the robot across the lawn while following a detected swath edge. The swath edge detector includes a calibrator that monitors uncut grass for calibration of the swath edge detector. In some examples, the calibrator comprises a second swath edge detector.

Lawn care robot

This work aims at improving real-time motion control and dead-reckoning of wheeled skid-steer vehicles by considering the effects of slippage, but without introducing the complexity of dynamics computations in the loop. This traction scheme is found both in many off-the-shelf mobile robots due to its mechanical simplicity and in outdoor applications due to its maneuverability. In previous works, we reported a method to experimentally obtain an optimized kinematic model for skid-steer tracked vehicles based on the boundedness of the instantaneous centers of rotation (ICRs) of treads on the motion plane. This paper provides further insight on this method, which is now proposed for wheeled skid-steer vehicles. It has been successfully applied to a popular research robotic platform, pioneer P3-AT, with different kinds of tires and terrain types.

Experimental kinematics for wheeled skid-steer mobile robots

This paper presents a novel vector-field-orientation (VFO) feedback control method and its application to a differentially driven wheeled vehicle. It describes the control concept and the control design methodology originating from simple geometrical interpretations connected with the vehicle model structure. The novelty of the VFO method allows one to treat two considered control tasks - trajectory tracking and point stabilization - in a unified manner. Control systems with VFO controllers reveal several practically desirable features like fast and nonoscillatory error convergence, simple interpretation of control input effect, and, as a consequence, particular simplicity of the controller parametric synthesis. The theoretical considerations included in this paper are validated by simulation and experimental results.

Vector-Field-Orientation Feedback Control Method for a Differentially Driven Vehicle

Skid-steered vehicles are often used as outdoor mobile robots due to their robust mechanical structure and high maneuverability. Sliding, along with rolling, is inherent to general curvilinear motion, which makes both kinematic and dynamic modeling difficult. For the purpose of motion planning, this paper develops and experimentally verifies dynamic models of a skid-steered wheeled vehicle for general planar (2-D) motion and for linear 3-D motion. These models are characterized by the coefficient of rolling resistance, the coefficient of friction, and the shear deformation modulus, which have terrain-dependent values. The dynamic models also include motor saturation and motor power limitations, which enable correct prediction of vehicle velocities when traversing on hills. It is shown that the closed-loop system that results from inclusion of the dynamics of the [proportional--integral--derivative (PID)] speed controllers for each set of wheels does a much better job than the open-loop model of predicting the vehicle linear and angular velocities. For a vehicle turning with small linear and angular accelerations, the model provides accurate predictions of velocities and reasonable predictions of torques. Hence, the closed-loop model is recommended for motion planning.

Analysis and Experimental Verification for Dynamic Modeling of A Skid-Steered Wheeled Vehicle

Optical 3D laser measurement system for navigation of autonomous mobile robot

A mathematical model of a 4-wheel skid-steering mobile robot is presented in a systematic way. The robot is considered as a subsystem consisting of kinematic, dynamic and drive levels. Next, a designing process of a kinematic controller based on the algorithm introduced by (Dixon et al., 2001) is shown. An extension of the kinematic control law at the dynamic and motor levels using the Lyapunov analysis and the backstepping technique is developed. To validate the designed algorithm, extensive simulation results for trajectory tracking and set-point cases are discussed. Some deliberations concerning the tuning of the controller are presented, too.

/pdf/modeling-and-control-of-a-4-wheel-skid-steering-mobile-robot-1tx1v95y68.pdf

Modeling and control of a 4-wheel skid-steering mobile robot

This paper presents kinematic control problem of skid-steering mobile robot using practical smooth and time-varying stabilizer. The stability result is proved using Lyapunov analysis and takes into account both input signal saturation and uncertainty of kinematics. In order to ensure stable motion of the robot the condition of permissible velocities is formulated according to dynamic model and wheel-surface interaction. Theoretical considerations are illustrated by simulation results.

Practical Stabilization of a Skid-steering Mobile Robot - A Kinematic-based Approach

This paper considers problem of approximation of admissible trajectory for skid-steering mobile robot at kinematic level. Nonholonomic constraints at kinematic and dynamic level are taken into account. The trajectory tracking control problem is solved using practical stabilizer using tunable oscillator with novel method of tuning. The stability result is proved using Lyapunov analysis and takes into account uncertainty of kinematics. In order to ensure stable motion of the robot the scaling method is used. Theoretical considerations are illustrated by simulation results.

/pdf/trajectory-tracking-of-underactuated-skid-steering-robot-1ja3zaea81.pdf

Trajectory tracking of underactuated skid-steering robot

The article is devoted to a motion control problem for a differentially driven mobile robot in the task of trajectory tracking in the presence of skid-slip effects. The kinematic control concept presented in the paper is the Vector Field Orientation (VFO) feedback approach with a nonlinear feed-forward skid-slip influence compensation scheme. The VFO control law guarantees asymptotic convergence of the position tracking error to zero in spite of the disturbing influence of skid-slip phenomena. The paper includes a control law design description, stability and convergence analysis of a closed-loop system, and practical verification of the proposed control concept. The experimental results illustrate control quality obtained on a laboratory setup equipped with vision feedback, where the Kalman filter algorithm was used in order to practically estimate skid-slip components.

/pdf/trajectory-tracking-for-a-mobile-robot-with-skid-slip-4p7evjb45d.pdf

Trajectory tracking for a mobile robot with skid-slip compensation in the vector-field-orientation control system

In this paper a unified motion control strategy dedicated for the waypoint following task realized by a differentially driven robot is presented. It is assumed that the vehicle moves with limited velocities and accelerations in order to reduce excessive slip and skid effects. In order to include operational constraints, a motion planner is combined with a universal stabilizer taking advantage of transverse functions. To improve tracking precision translated transverse functions are deployed and a new adaptive technique for the controller tuning is proposed. During the motion planning stage an auxiliary trajectory connecting points in the configuration space and satisfying assumed phase constraints is generated. The resulting motion execution system has been implemented on a laboratory-scale skid-steering mobile robot, which served as platform for experimental validation of presented algorithms.

/pdf/waypoint-following-for-differentially-driven-wheeled-robots-k54oxth33i.pdf

Dariusz Pazderski

Papers

Modeling and control of a 4-wheel skid-steering mobile robot

Practical Stabilization of a Skid-steering Mobile Robot - A Kinematic-based Approach

Trajectory tracking of underactuated skid-steering robot

Trajectory tracking for a mobile robot with skid-slip compensation in the vector-field-orientation control system

Waypoint Following for Differentially Driven Wheeled Robots with Limited Velocity Perturbations