Jorge L. Martínez

Approximating Kinematics for Tracked Mobile Robots

In this paper we propose a kinematic approach for tracked mobile robots in order to improve motion control and pose estimation. Complex dynamics due to slippage and track–soil interactions make it difficult to predict the exact motion of the vehicle on the basis of track velocities. Nevertheless, real-time computations for autonomous navigation require an effective kinematics approximation without introducing dynamics in the loop. The proposed solution is based on the fact that the instantaneous centers of rotation (ICRs) of treads on the motion plane with respect to the vehicle are dynamics-dependent, but they lie within a bounded area. Thus, optimizing constant ICR positions for a particular terrain results in an approximate kinematic model for tracked mobile robots. Two different approaches are presented for off-line estimation of kinematic parameters: (i) simulation of the stationary response of the dynamic model for the whole velocity range of the vehicle; (ii) introduction of an experimental setup so that a genetic algorithm can produce the model from actual sensor readings. These methods have been evaluated for on-line odometric computations and low-level motion control with the Auriga-α mobile robot on a hard-surface flat soil at moderate speeds.

Mobile robot localization based on Ultra-Wide-Band ranging: A particle filter approach

This article addresses the problem of mobile robot localization using Ultra-Wide-Band (UWB) range measurements. UWB is a radio technology widely used for communications, that is recently receiving increasing attention for positioning applications. In these cases, the position of a mobile transceiver is determined from the distances to a set of fixed, well-localized beacons. Though this is a well-known problem in the scientific literature (the trilateration problem), the peculiarities of UWB range measurements (basically, distance errors and multipath effects) demand a different treatment to other similar solutions, as for example, those based on laser. This work presents a thorough experimental characterization of UWB ranges within a variety of environments and situations. From these experiments, we derive a probabilistic model which is then used by a particle filter to combine different readings from UWB beacons as well as the vehicle odometry. To account for the possible offset error due to multipath effects, the state tracked by the particle filter includes the offset of each beacon in addition to the planar robot pose (x,y,@f), both estimated sequentially. We show navigation results for a robot moving in indoor scenarios covered by three UWB beacons that validate our proposal.

Experimental kinematics for wheeled skid-steer mobile robots

This work aims at improving real-time motion control and dead-reckoning of wheeled skid-steer vehicles by considering the effects of slippage, but without introducing the complexity of dynamics computations in the loop. This traction scheme is found both in many off-the-shelf mobile robots due to its mechanical simplicity and in outdoor applications due to its maneuverability. In previous works, we reported a method to experimentally obtain an optimized kinematic model for skid-steer tracked vehicles based on the boundedness of the instantaneous centers of rotation (ICRs) of treads on the motion plane. This paper provides further insight on this method, which is now proposed for wheeled skid-steer vehicles. It has been successfully applied to a popular research robotic platform, pioneer P3-AT, with different kinds of tires and terrain types.

Mobile robot motion estimation by 2D scan matching with genetic and iterative closest point algorithms

The paper reports on mobile robot motion estimation based on matching points from successive two-dimensional (2D) laser scans. This ego-motion approach is well suited to unstructured and dynamic environments because it directly uses raw laser points rather than extracted features. We have analyzed the application of two methods that are very different in essence: (i) A 2D version of iterative closest point (ICP), which is widely used for surface registration; (ii) a genetic algorithm (GA), which is a novel approach for this kind of problem. Their performance in terms of real-time applicability and accuracy has been compared in outdoor experiments with nonstop motion under diverse realistic navigation conditions. Based on this analysis, we propose a hybrid GA-ICP algorithm that combines the best characteristics of these pure methods. The experiments have been carried out with the tracked mobile robot Auriga-α and an on-board 2D laser scanner.

Pure-pursuit reactive path tracking for nonholonomic mobile robots with a 2D laser scanner

Due to its simplicity and efficiency, the pure-pursuit path tracking method has been widely employed for planned navigation of nonholonomic ground vehicles. In this paper, we investigate the application of this technique for reactive tracking of paths that are implicitly defined by perceived environmental features. Goal points are obtained through an efficient interpretation of range data from an onboard 2D laser scanner to follow persons, corridors, and walls. Moreover, this formulation allows that a robotic mission can be composed of a combination of different types of path segments. These techniques have been successfully tested in the tracked mobile robot Auriga- in an indoor environment.

Fuzzy Supervisory Path Tracking of Mobile Robots 1

Abstract In this paper a new method for automatic path tracking of mobile robots and autonomous vehicles is proposed. The paper also includes the application to RAM-1, a new mobile robot testbed designed and built for research and applications in indoor and outdoor industrial enviroments. The method generates the appropriate vehicle steering angle command by combining fuzzy logic with the geometric pure-pursuit technique and the generalized predictive control method. In the proposed fuzzy path-tracking strategy the control parameters of these methods are inferred automatically in real time from the characteristics of the current segment of the path to follow, the vehicles velocity and its current relative position and orientation.

Steering Limitations for a Vehicle Pulling Passive Trailers

Motion control of articulated vehicles composed of a nonholonomic tractor and several passive trailers is a difficult underactuated problem. This paper proposes the application of steering limitations to the tractor to avoid inter unit collision during forward motion. This method can be used for systems that combine any type of on-axle and off-axle joints. We propose an algorithm to compute curvature bounds based on the analysis of steady and transient responses. These limitations can be introduced at the path tracking and path planning levels for autonomous navigation. Thus, the tractor can be controlled to follow admissible paths much in the same way as when it does not tow any trailer. The method has been validated experimentally with an off-axle two-trailer setup attached to the tracked mobile robot Auriga-alpha.

Power Consumption Modeling of Skid-Steer Tracked Mobile Robots on Rigid Terrain

Power consumption is a key element in outdoor mobile robot autonomy. This issue is very relevant in skid-steer tracked vehicles on account of their large ground contact area. In this paper, the power losses due to dynamic friction have been modeled from two different perspectives: 1) the power drawn by the rigid terrain and 2) the power supplied by the motors. Comparison of both approaches has provided new insight on skid steering on hard flat terrains at walking speeds. Experimental power models, which also include traction resistance and other power losses, have been obtained for two different track widths over marble flooring and asphalt with Auriga- beta, which is a full-size mobile robot. To this end, various internal probes have been set at different points of the power stream. Furthermore, new energy implications for navigation of these kinds of vehicles have been deduced and tested.

Combination of UWB and GPS for indoor-outdoor vehicle localization

GPS receivers are satellite-based devices widely used for vehicle localization that, given their limitations, are not suitable for performing within indoor or dense urban environments. On the other hand ultra-wide band (UWB), a technology used for efficient wireless communication, has recently being used for vehicle localization in indoor environments with promising results. This paper focuses on the combination of both technologies for accurate positioning of vehicles in a mixed scenario (both indoor and outdoor situations), which is typical in some industrial applications. Our approach is based on combining sensor information in a Monte Carlo localization algorithm (also known as particle Filter), which has revealed its suitability for probabilistically coping with a variety of sensory data. The performance of our approach has been satisfactorily tested on a real robot, endowed with a UWB master antenna and a GPS receiver, within an indoor-outdoor scenario where three UWB slave antennas were placed in the indoor area.

Driver assistance system for backward maneuvers in passive multi-trailer vehicles

Drivers of vehicles with one or several passive trailers, like truck-and-trailer or articulated luggage carriers, have difficulties in backward maneuvers due to jackknife and lack of visibility. Advanced driver assistance systems (ADAS) can be helpful to improve both safety and driver comfort in these complex operations. In this paper, we propose an ADAS that adopts our curvature limitation method for backward multi-trailer vehicles, where the last trailer is considered a virtual tractor and steering limits are established to avoid jackknife and inter-unit collisions. In the proposed solution, when the driver puts the vehicle in reverse, the steering wheel and pedals can be used as if the vehicle was driven from the back of the last trailer with visual feedback from a camera. This system can be implemented in drive-by-wire vehicles, where the steering-wheel feedback force can be customized for the curvature limitation of a given combination of one or several trailers. The system has been tested to tele-operate a mobile robot with two off-axle trailers.