When designing an accurate automated guidance system for vehicles, a major problem is sliding and pseudosliding effects. This is especially the case in agricultural applications, where five-centimetre accuracy with respect to the desired trajectory is required, although the vehicles are moving on slippery ground.It has been established that RTK GPS was a very suitable sensor to achieve automated guidance with such high precision: several control laws have been designed for vehicles equipped with this sensor, and provide the expected guidance accuracy as long as the vehicles do not slide. In previous work, further control developments have been proposed to take sliding into account: guidance accuracy in slippery environments has been shown to be preserved, except transiently at the beginning/end of curves. In this paper, the design of this control law is first recalled and discussed. A Model Predictive Control method is then applied in order to preserve accuracy of guidance even during these curvature transitions. Finally, the overall control scheme is implemented, and improvements with respect to R. Lenain ( ) · C. Cariou Cemagref, 24 av. des Landais BP50085, 63172 Aubière Cedex,

Precision agriculture involves very accurate farm vehicle control along recorded paths, which are not necessarily straight lines. In this paper, we investigate the possibility of achieving this task with a CP-DGPS as the unique sensor. The vehicle heading is derived according to a Kalman state reconstructor, and a nonlinear velocity independent control law is designed, relying on chained systems properties. Field experiments, demonstrating the capabilities of our guidance system, are reported and discussed.

In this article, we review the dynamic control of parallel kinematic machines. It is shown that the classical control strategies from serial robotics generally used for parallel kinematic machine have to be rethought. Indeed, it is first shown that the joint space control is not relevant for these mechanisms for several reasons such as mechanical behavior or computational efficiency. Consequently, Cartesian space control should be preferred over joint space control. Nevertheless, some modifications to the well-known Cartesian space control strategies of serial robotics are proposed to make them perfectly suited to parallel kinematic machines, particularly a solution using an exteroceptive measure of the end-effector pose. The expected improvement in terms of accuracy, stability and robustness are discussed. A comparison between the main presented strategies is finally performed both in simulation and experiments.

Visual servoing requires an object in the field of view of the camera, in order to control the robot evolution. Otherwise, the virtual l i i is broken and the control loop ,cannot continue to be closed.In this paper, a novel approach is presented in order to guarantee that the object remains in the field of view of the camera during the whole robot motion. It consists in t r d n g an iteratively computed trajectory. A position based modeling adapted to a moving target object is established, and is used to control the trajectory. A nonlinear decoupliig approach is then used to control the robot. Experiments, demonstrating the capabilities of thiS a p proach, have been conducted on a Cartesian robot connected to a real time vision system, with a CCD camera mounted on the end effector of the robot.

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Optimizing the inter-distances between vehicles is very important to reduce traffic congestion on highways. Variable spacing and constant spacing are the two policies for the longitudinal control of platoons. Variable spacing doesn't require a lot of data (position, speed...) from other vehicles, and string stability can be obtained using on-board information only. However, inter-vehicle distances are very large, and hence traffic density is low. Constant spacing offers string stability with high traffic density, but it requires data communication between the vehicles, at least from the leader. In this paper, a new platoon model and a modification of the variable spacing policy are proposed. This modification is effective to decrease the distances between the cars, making them nearly equal to the constant spacing policy. It also enables increasing string stability. This new approach doesn't require heavy communication between the vehicles. The new model is based on an unidirectional spring-damper model between vehicles, with the vehicles loaded on a virtual flatbed tow truck. From this configuration, conditions of stability and safety of homogeneous platoon are derived. Based on this new model, a control has been derived and evaluated by simulation with a perfect system model using Matlab, and with a more realistic vehicle model using TORCS (The Open Racing Car Simulator). The simulation consists of a platoon of ten vehicles, moving on highways, with a desired inter-vehicle distance equal to 1 meter. The stability and the safety of the platoon are tested during platoon creation, changing the speed and emergency stop. The good results demonstrate the effectiveness of the new approach.

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Many environmental problems require assessment of extensive reaction systems within natural subsurface flow systems exhibiting large physical and biogeochemical heterogeneity. We present an approach to couple stochastic advective-reactive modeling of physical solute transport (LaSAR) with the geochemical model PHREEQC for modeling solute concentrations in systems with variable flow velocity and multicomponent reactions. PHREEQC allows for general and flexible quantification of a multitude of linear and nonlinear geochemical processes, while LaSAR efficiently handles field-scale solute spreading in stochastic heterogeneous flow fields. The combined LaSAR-PHREEQC approach requires very modest computational efforts, thereby allowing a large number of reactive transport problems to be readily assessed and facilitating handling of quantifiable uncertainty in environmental model applications. Computational efficiency and explicit handling of field-scale dispersion without introduction of excessive fluid mixing that may impair model results are general advantages of the LaSAR compared with alternative solute transport modeling approaches. The LaSAR-PHREEQC approach is restricted to steady or unidirectional flow fields, and our specific application examples are limited to homogeneous reaction systems without local or transverse dispersion-diffusion, although these are not general methodological limitations. As a comprehensive application example, we simulate the spreading of acid mine drainage in a groundwater focusing on Zn2+ and including relevant, major-component geochemistry. Model results show that Zn2+ may be substantially attenuated by both sorption and precipitation, with flow heterogeneity greatly affecting expected solute concentrations downstream of the mine waste deposit in both cases.