A path following algorithm for mobile robots

Abstract

This paper considers path following control for a robotic platform. The vehicle used for the experiments is a specially designed robotic platform for performing autonomous weed control. The platform is four-wheel steered and four-wheel driven. A diesel engine powers the wheels via a hydraulic transmission. The robot uses a Real Time Kinematic Differential Global Positioning System to determine both position and orientation relative to the path. The deviation of the robot to the desired path is supplied to two high level controllers minimizing the orthogonal distance and orientation to the path. Wheel angle setpoints are determined from inversion of the kinematic model. At low level each wheel angle is controlled by a proportional controller combined with a Smith predictor. Results show the controller performance following different paths shapes including a step, a ramp, and a typical headland path. A refined tuning method calculates controller settings that let the robot drive as much as possible along the same path to its setpoint, but also limit the gains at higher speeds to prevent the closed loop system to become unstable due to the time delay in the system. Mean, minimum and maximum orthogonal distance errors while following a straight path on a paving at a speed of 0.5 m/s are 0.0, −2.4 and 3.0 cm respectively and the standard deviation is 1.2 cm. The control method for four wheel steered vehicles presented in this paper has the unique feature that it enables control of a user definable position relative to the robot frame and can deal with limitations on the wheel angles. The method is very well practical applicable for a manufacturer: all parameters needed are known by the manufacturer or can be determined easily, user settings have an easy interpretation and the only complex part can be supplied as a generic software module.

VFO Path following Control with Guarantees of Positionally Constrained Transients for Unicycle-Like Robots with Constrained Control Input

“…It seems justified because F (p) is zero if and only if p ∈ S d , while a sign of a value of F (p) for p ∈ S d depends on a side on which the robot position stays relative to the reference path. 1 Let us define the path following error as follows…”

“…Upon definitions (19), (20), (29), and according to the first equation of Eq. 1 one can write: e a (19) =θ a −θ (1) =θ a − u 1 (29) =θ a − ςh θ (20) =θ a − ςk a e a − ςθ an = −ςk a e a (31) where we have used the factθ a = ςθ an (see Appendix C). Defining a positive definite function…”

Multi-scenario optimization approach for fuzzy control of a robot-car model

“…Besides there are some solution to measure another kind of quality, for example in [14]: "by logging the GPS coordinates, orthogonal distances and orientation errors during path following with a time interval of 50 ms".…”

“…Mostly PID (like in [13,14,20,23]) and Fuzzy (like in [3,6,12,16,17,18,21,23]) controllers are used in various levels of vehicle controlling based on the literature: • Motor controller level -called as low level control system • Path or route control level -called as high level control system. Example can be found in [14,16,17,21] The exception is model-based solutions published, like in [9,10,11,13,15,19,22].…”

Fleets of robots for environmentally-safe pest control in agriculture

“…and integrated intervention mechanisms for specific agricultural applications. Some of these developments will be operative in the coming years (Bakker et al 2010;Ruckelshausen et al 2009). …”