Faiz Ben Amar

Modeling robot-soil interaction for planetary rover motion control

In aim to optimize the control for an off-road robot and specially a robot with a crawling motion mode named peristaltical motion, it is essential to understand robot-soil interaction. We present an efficient method for simulating this interaction. This method can simulate the dynamic behavior of a 6-wheeled/3-axles Marsokhod type robot on different kinds of soils. With this simulation, we have defined the necessary conditions for using the peristaltical motion on sand or loose soil.

Dynamic Analysis of Off-Road Vehicles

This paper deals with the simulation of off-road robots while taking into account the mechanical behavior of the locomotion system and its interaction with its environment. This interaction is studied and discussed for different behaviors of wheel-soil contact. The analysis considers phenomena of slips, of soil shear deformations, of soil compaction and wheel elastic deformation. Wheel-soil contact models are expressed by analytical relationships which link each contact force components (radial, longitudinal and lateral forces) to relative displacements (radial displacement, longitudinal slip ratio and side slip angle). These laws are then coupled to the dynamic equations of the mechanical system in order to characterize the behavior of the whole system. These models are implemented on a graphic simulation system which provides a basic tool for the design of the mechanical system, for the path planning and for the definition of control schemes.

Kinematic analysis and stability optimization of a reconfigurable legged-wheeled mini-rover

This paper deals with the optimization of locomotion performances of vehicle used for planetary exploration. The design of an innovative reconfigurable mini-rover is presented. Then, a control process that optimize the stability and the global traction performances is developed. A method to identify in-situ the wheel-ground mechanical contact properties is proposed and used to determine an optimal traction torque. Results on experiments and simulations show that the rover stability is significantly enhanced by using the proposed control method.

Designing Modular Lattice Systems with Chiral Space Groups

We propose to use the concept of chiral space groups used by crystallography science to define and design lattice robots. Chiral space groups are of great interest because they give all possible sets of discrete displacements having a group structure and a translational symmetry. We explain the analogy between lattice robot kinematics and crystal symmetry, and identify three fundamental properties of lattice robots: (1) discreteness; (2) translational symmetry; and (3) composition. Then we give the possible connector symmetries and orientations into a chiral space group, and the possible sliding and hinge joint locations and orientations compatible with the displacements in the groups. We present a framework for the design of lattice robots by assembling compatible joints and connectors into a chiral space group. Several two-dimensional and three-dimensional examples of designs are given to illustrate the framework. Moreover, we list the symmetries of the two chiral space groups P432 and P622 because they contain the symmetries of all the 65 chiral space groups and allow the design of any lattice system.

Modeling and Control Design of a Robotic Sailboat

This paper presents a method to obtain a full 6 degrees of freedom dynamic model of a robotic sailing boat starting from the description of forces and torques acting on it. A general 6-DOF model is first described and then simplified to obtain a 3-DOF control-oriented one. Relying on it, a rudder controller and a sail’s trimming calculator are proposed. This controller has been validated using a numerical implementation of the proposed dynamic model.

Accurate and stable mobile robot path tracking: An integrated solution for off-road and high speed context

This paper is focused on the problem of accurate and reliable path tracking control of a 4-wheels car-like mobile robot moving off-road at high speed. Dynamic and extended kinematic models that take into account the effects of wheel skidding are presented. Based on the extended kinematic model, an adaptive and predictive controller for path tracking is derived. This control law is combined to a stabilization algorithm of yaw motion, based on the dynamic model and the modulation of driven wheel forces. The overall control architecture is experimentally evaluated on a slipping terrain. Results demonstrate enhanced performances as the robot succeed in following the path at high speed, accurately and without loss of control.

Experimental Evaluation of Obstacle Clearance by a Hybrid Wheel-Legged Robot

This paper deals with the problem of frontal obstacle crossing by a poly-articulated wheeled robot. We focus on the particular architecture of hybrid wheel-legged robots that are redundantly actuated systems. In this paper, experimental results that show the climbing capabilities of such system when crossing large obstacle are presented. We focus on the case of a step like obstacle whose height is superior to the diameter of the wheels. In this case, the adhesion properties have a large impact on the crossing capabilities. First, we introduce our control methodology which is based on the optimization of both the robot posture and the distribution of internal forces. The optimization criterion represents the maximum allowable force disturbance that the system can support before violating the frictional contact constraint. Then, our experimental prototype, the robot Hylos2 and the experimental setup are presented. As our approach is based on the control of the contact forces, experiments used to quantify the level of friction in the mechanical transmissions are first reported. Then a step-crossing trial on the real system is presented.

Routing and course control of an autonomous sailboat

In this paper, we present a layered control scheme for an autonomous sailboat. The high level control uses a custom cost function with a PRM-Dijkstra algorithm for the routing (global path planning) of autonomous sailboat. This algorithm exploits the sailboat kinematics and wind distribution on a map. For the low level control, we design a new nonlinear course (direction of the velocity vector) controller that exhibits superior performance compared to conventionally used heading controller. A smoothing function is also introduced in the design of the controller to switch easily from course control to heading control, especially when course measurements are noisy at low speed.

Characterization of lattice modular robots by discrete displacement groups

The paper provides a method to determine and compare the reconfigurability of lattice systems. First it shows the difference that exists between the reconfigurability and self-reconfigurability features of a lattice system. Then a method using displacement groups is introduced to characterize these features. Based on this method, these features are then compared for some existing lattice systems.

Adaptive Sampling with a Fleet of Autonomous Sailing Boats Using Artificial Potential Fields

Autonomous sailing boats are an attractive solution to perform measurements at sea thanks to their low energy consumption. A fleet of such vehicles can also be used for adaptive sampling of an environmental field. In previous work, artificial potential fields have been used successfully in a local and real-time planner to carry out the autonomous navigation of one sailing boat. In this paper, we first extend the previous method to include marine current in the local planning and show how this extension can improve the safety and navigation performances in the case of strong marine current. Next we show how the same planning method can be used to control a formation of sailboats and perform adaptive sampling of some natural quantities and can be easily tuned to exhibit different behaviors such that way-point reaching, gradient or isoline following.