Robust Autonomous Robot Localization Using Interval Analysis

This paper deals with the determination of the position and orientation of a mobile robot from distance measurements provided by a belt of onboard ultrasonic sensors. The environment is assumed to be two-dimensional, and a map of its landmarks is available to the robot. In this context, classical localization methods have three main limitations. First, each data point provided by a sensor must be associated with a given landmark. This data-association step turns out to be extremely complex and time-consuming, and its results can usually not be guaranteed. The second limitation is that these methods are based on linearization, which makes them inherently local. The third limitation is their lack of robustness to outliers due, e.g., to sensor malfunctions or outdated maps. By contrast, the method proposed here, based on interval analysis, bypasses the data-association step, handles the problem as nonlinear and in a global way and is (extraordinarily) robust to outliers.Luc Jaulin: on leave from Laboratoire d'Ingénierie des Systèmes Automatisés, Université d'Angers, 2 bd Lavoisier, 49045 Angers, FranceLuc Jaulin: on leave from Laboratoire d'Ingénierie des Systèmes Automatisés, Université d'Angers, 2 bd Lavoisier, 49045 Angers, FranceLuc Jaulin: on leave from Laboratoire d'Ingénierie des Systèmes Automatisés, Université d'Angers, 2 bd Lavoisier, 49045 Angers, France     

Identification and spatial distribution of glycine receptor subunits in human sperm

The human sperm surface glycine receptor (GLR) plays a role in an important fertilization event, the sperm acrosome reaction. Here, by western blot analysis, we report the presence of GLRA1, GLRA2, GLRA3, and GLRB subunits in human sperm. Immunolocalization studies showed that the GLRA1 and GLRA2 subunits are present in the equatorial region, the GLRA3 subunit in the flagellar principal piece, and the GLRB subunit in the acrosomal region of sperm. This first demonstration of isoforms of the sperm GLRA subunit and of a differential spatial distribution of the alpha and beta subunits on the surface of mammalian sperm suggests the possibility that human sperm GLRs have more than one function.     

Progesterone initiation of the human sperm acrosome reaction: the obligatory increase in intracellular calcium is independent of the chloride requirement

The progesterone-initiated human sperm acrosome reaction (AR) requires a rise in intracellular Ca2+ ([Ca2+]i), extracellular Cl- and apparently increased Cl- flux through a unique steroid receptor/Cl- channel resembling but not identical to a GABA(A)/Cl- channel complex. The present study uses fura-2 loaded human sperm, GABA(A)/Cl- channel blockers (picrotoxin and pregnenolone sulfate) and Cl(-)-containing and Cl(-)-deficient media to determine whether the progesterone-mediated increase in [Ca2+]i is dependent on the Cl- requirement. There was no significant difference between the progesterone-mediated increases of [Ca2+]i obtained in Cl(-)-containing and Cl(-)-deficient media. Picrotoxin did not significantly inhibit the progesterone-mediated increase in [Ca2+]i, and pregnenolone sulfate increased [Ca2+]i to the same extent as progesterone. These results strongly suggest that the increase in [Ca2+]i essential to the AR is independent of the AR Cl- requirement and could be explained by the existence of two different sperm plasma membrane progesterone receptors.     

Virtual sensor: application to vehicle sideslip angle and transversal forces

This paper compares four observers (virtual sensors) of vehicle sideslip angle and lateral forces. The first is linear and uses a linear vehicle model. The remaining observers use an extended nonlinear model. The three nonlinear observers are: extended Luenberger observer, extended Kalman filter and sliding-mode observer. Modeling, model simplification, and observers are described, and an observability analysis is performed for the entire vehicle trajectory. The paper also deals with three different sets of sensors to see the impact of observers results. Comparison is first done by simulation on a valid vehicle simulator, and then observers are used on experimental data. Our study shows that observers are more accurate than simple models as regards unmeasurable variables such as sideslip angle and transversal forces. It also shows that speed of center of gravity is not an indispensable variable here.     

Guaranteed robust nonlinear estimation with application to robot localization

When reliable prior bounds on the acceptable errors between the data and corresponding model outputs are available, bounded-error estimation techniques make it possible to characterize the set of all acceptable parameter vectors in a guaranteed way, even when the model is nonlinear and the number of data points small. However, when the data may contain outliers, i.e., data points for which these bounds should be violated, this set may turn out to be empty, or at least unrealistically small. The outlier minimal number estimator (OMNE) has been designed to deal with such a situation, by minimizing the number of data points considered as outliers. OMNE has been shown in previous papers to be remarkably robust, even to a majority of outliers. Up to now, it was implemented by random scanning, so its results could not be guaranteed. In this paper, a new algorithm based on set inversion via interval analysis provides a guaranteed OMNE, which is applied to the initial localization of an actual robot in a partially known two-dimensional (2-D) environment. The difficult problems of associating range data to landmarks of the environment and of detecting potential outliers are solved as byproducts of the procedure.     

Path following with a security margin for mobile robots

This paper addresses the problem of determining a feedback control law, robust with respect to localization errors, allowing a mobile robot to follow a prescribed path. The model that we consider is a dynamic extension of the usual kinematic model of a mobile robot in the sense that the path curvature is defined as a new state variable. The control variables are the linear velocity and the derivative of the curvature. By defining a sliding manifold we determine a stabilizing controller for the nominal system, that is when the exact configuration is supposed to be known. Then, we prove that the system remains stable when the feedback control inputs use estimated values instead of the exact values, and we characterize the control robustness with respect to localization and curvature estimation errors. The control robustness is expressed by determining a bounded attractive domain containing the configuration error as the closed-loop control is performed with the estimated state values. Two control laws are successively proposed. The former is deduced from Lyapunov's direct method, and the latter is based on variable structure control techniques. Using variable structure control we show that the size of the attractive domain can be easily minimized while keeping the balance between short response time, low output oscillation, and large stability domain. Knowledge of this attractive domain allows us to compute easily a security margin to guarantee obstacle avoidance during the path following process. Experimental results are presented at the end of the paper.