Article de revue scientifique à comité de lecture

GUILLET, A., LENAIN, R., THUILOT, B., ROUSSEAU, V. – 2017. Formation control of agricultural mobile robots: A bidirectional weighted constraints approach. Journal of Field Robotics, vol. 34, n° 7, p. 1260 – 1274 [ ]

This paper focuses on the formation control of several mobile robots in off-road conditions. A control strategy based on bidirectional referencing is proposed, where each robot combines a velocity controlw.r.t. the immediate preceding neighbor with a control w.r.t. the immediate following neighbor. Two virtual leaders, respectively, at the head and at the tail of the fleet, are propelling the fleet at the desired velocity. The fleet stability is investigated using Lyapunov techniques, pending on combination coefficients. The stability is theoretically proven for constant coefficients as weights of the respective velocity controls and tested through simulations and full-scale experiments. It is shown that this control strategy permits us to reduce the error propagation problem often encountered in formation control, while limiting the communication problems of the global strategies. As a result, a stable formation control architecture is defined, which requires each vehicle to be refereed only to two other robots. This limited communication need is particularly interesting for agricultural operations. The proposed approach is implemented in this paper on agricultural tractors.


LENAIN, R., DEREMETZ, M., BRACONNIER, J. B., THUILOT, B., ROUSSEAU, V. – 2017. Robust sideslip angles observer for accurate off-road path tracking control. Advanced Robotics, vol. 31, n° 9, p. 453 – 467 [ ]

This paper proposes a control strategy to achieve high accurate path tracking in off-road conditions. The approach is based on adaptive and predictive techniques to account for sliding effects and actuator properties. An extended kinematic model is designed using sideslip angles definition. An observer is proposed to estimate online these variables, independently from the reference path and robot velocity. Thanks to the proposed approach, high accurate path tracking can then be achieved whatever the shape of the reference path and the task to be achieved (practical stabilization or moving object tracking).



Communication scientifique avec actes

DEREMETZ, M., LENAIN, R., COUVENT, A., CARIOU, C., THUILOT, B. – 2017. Path tracking of a four-wheel steering mobile robot: A robust off-road parallel steering strategy. ECMR The European Conference on Mobile Robotics, 06/09/2017 – 08/09/2017, Paris, FRA. [ ]

In this paper, the problem associated with accurate control of a four-wheel steering mobile robot following a path, while keeping different desired absolute orientations and ensuring different desired lateral deviations, is addressed thanks to a backstepping control strategy. In particular, the control of each steering angle is investigated through a new parallel steering approach based on an extended kinematic model of a bicycle-model robot assuming that the two front steering angles are equal and likewise for the two rear ones. Two control laws are then proposed to ensure a suitable path following according to orientation and position conditions. In order to balance the lateral effects, notably the sideslip angles, an observer has been used to estimate the sliding. This estimation permits to feed the proposed control laws appropriately, enabling an accurate path tracking and orientation keeping along the trajectory. This new point of view permits to achieve difficult manoeuvres in narrow environments such as a parallel parking or sharp turns. Previous approaches have focused on the control of four-wheel steering mobile robots with respect to the trajectory but do not combine path following with independent heading angle control and slippery conditions.


DEREMETZ, M., LENAIN, R., THUILOT, B., ROUSSEAU, V. – 2017. Adaptive trajectory control of off-road mobile robots: A multi-model observer approach. IEEE Robotics Conference on Robotics and Automation (ICRA), 29/05/2017 – 03/06/2017, Singapor, SGP. p. 4407 – 4413 [ ]

In this paper, the problems associated with accurate path tracking control in off-road conditions is addressed with model-based adaptive control. In particular, the estimation of grip conditions is investigated through the derivation of a new observer and by gathering kinematic and dynamic models into a single framework. This new reference point employs a unique observer regardless of the velocity of the robots. Previous approaches necessitated the switching of models depending upon the phenomena encountered as well as robot dynamics. The observer proposed here allows an accurate and reactive estimation of sliding. This permits to feed relevantly a control law based on an extended kinematic model, enabling accurate path tracking, even in harsh conditions and when facing significant dynamic effects such as spin around.



Article de revue scientifique à comité de lecture

DEREMETZ, M., LENAIN, R., THUILOT, B. – 2017. Stiffness and damping real-time control algorithms for adjustable suspensions: A strategy to reduce dynamical effects on vehicles in off-road conditions. IFAC-PapersOnLine, vol. 50, n° 1, p. 1958 – 1964 [ ]

In this paper, the problem of dynamical effects of ground irregularity or stability of vehicles in off-road conditions is addressed thanks to a dynamic analysis of the vehicle. In particular, the choice of suitable real-time values for the stiffness and the damping of adjustable suspensions, in order to reduce dynamical effects, is investigated thanks to the analysis of a Laplace transfer function describing the mechanical behaviour of the vehicle. Moreover, a decoupled load transfer computation to identify the suspended masses on each suspension is used and a way to modify in real time suspension parameters by modifying the settling time value in order to drive over obstacles is proposed. This new point of view may permit to use effectively adjustable suspensions in off-road context. Previous approaches indeed only focus on the control of adjustable suspensions on road or by using an actuator in parallel of the suspension and are often dedicated to the driver comfort.