Realistic Autofarming Closed-Loop Tractor Control over Irregular Paths Using Kinematic GPS

Abstract

High-precision ‘autofarming’ makes possible farming techniques previously impractical using metre-level Differential GPS-based control systems: techniques such as tape irrigation, the elimination of guess rows, and precise contour farming. A Carrier-Phase Differential gps positioning and attitude system with centimetre-level and 0·1° accuracy was installed in a large farm tractor. Four types of trajectories (lines, arcs, spirals, and curves) were identified as basic building blocks necessary to generate a ‘global’ trajectory for a realistic autofarming path. Information about each trajectory type was translated into reference state specifications that a linear controller used to control the tractor over velocities between 0·7 and 2·8 m/s to within approximately 6 cm (1 σ) without implement and 10 cm (1 σ) with implement on sloped terrain using a previously developed tractor model. These results are a significant step towards a realistic autofarming system because they not only demonstrate accurate control over various realistic operating speeds but over different types of trajectories necessary for a commercial system.

Curved Path Following of a Farm Tractor Using a CP-DGPS

“…Some rely on 2D information extracted from the image plane (Debain, 1996), (Khadraoui et al, 1998) and (Ollis and Stentz, 1997). Other are based on 3D sensors, for instance made of a laser scanning and a video camera (Chateau et al, 1999). Two kinds of difficulties arise: the first one is the reference extraction.…”

“…Farm tractor control along curved paths has already been addressed in some particular cases (Bell et al, 1997). We use hereafter a more general approach: we convert the non linear model ( 1) into a chained form.…”

Untitled

“…The tractor model (10) is clearly nonlinear. In Bell et al (1997), the authors propose to linearize it around the equilibrium y =θ = 0, in order that celebrated linear systems theory could be used. In that case, control design does not rely on the actual tractor model, but on an approximated one.…”

Automatic guidance of a farm tractor along curved paths, using a unique CP-DGPS

“…The tractor model (1) is clearly nonlinear. In [1], the authors propose to linearize it around the equilibrium y =θ = 0, in order that celebrated linear systems theory could be used. In this case, control design does not rely on the actual tractor model, but on an approximated one.…”