Alfonso García-Cerezo

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.

The autonomous mobile robot AURORA for greenhouse operation

AURORA has been conceived in order to substitute hard and unhealthy human work inside greenhouses by means of an autonomous mobile robot outfitted with appropriate sensors and operation devices. Emphasis has been put in the development of a new robotic platform specifically designed for greenhouse tasks, governed by a control architecture that supports both autonomous navigation and shared human control.

Using LEGO NXT Mobile Robots With LabVIEW for Undergraduate Courses on Mechatronics

The paper proposes lab work and student competitions based on the LEGO NXT Mindstorms kits and standard LabVIEW. The goal of this combination is to stimulate design and experimentation with real hardware and representative software in courses where mobile robotics is adopted as a motivating platform to introduce mechatronics competencies. Basic LabVIEW examples are proposed for three case-study laboratory practices. These are implemented with the NXT Toolkit and the NXT Direct Command programming libraries for standalone and remote execution, respectively. The application of this instructional material has been tested in two different experiences with senior undergraduate engineering students. A description of the courses as well as an assessment of student results are also included.

Stability indices for the global analysis of expert control systems

The stability of rule-based expert control systems is studied. A control structure with a nonlinear plant and a nonlinear controller, designed on the basis of logical rules incorporating the experience of designers and human operators, is considered. Two classes of indices are presented: one related to the relative stability of the equilibrium point at the origin, and the other to the global stability of the system. These indices can be used for the analysis and design of expert control systems. Some examples are included to illustrate the approach. >

Direct digital control, auto-tuning and supervision using fuzzy logic

Abstract We describe algorithms for the design and implementation of fuzzy logic controllers and present results of their application to temperature control of a heated air-stream. Auto-tuning methods are studied for adjustment of conventional parameters to compensate for actual values of control variables, or of external variables; and for improvement of performance from observation of results. Conditions for verifying the consistency of the linguistic protocol with its implementation are presented in an appendix.

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.

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.

A Large Area Tactile Sensor Patch Based on Commercial Force Sensors

This paper reports the design of a tactile sensor patch to cover large areas of robots and machines that interact with human beings. Many devices have been proposed to meet such a demand. These realizations are mostly custom-built or developed in the lab. The sensor of this paper is implemented with commercial force sensors. This has the benefit of a more foreseeable response of the sensor if its behavior is understood as the aggregation of readings from all the individual force sensors in the array. A few reported large area tactile sensors are also based on commercial sensors. However, the one in this paper is the first of this kind based on the use of polymeric commercial force sensing resistors (FSR) as unit elements of the array or tactels, which results in a robust sensor. The paper discusses design issues related to some necessary modifications of the force sensor, its assembly in an array, and the signal conditioning. The patch has 16 × 9 force sensors mounted on a flexible printed circuit board with a spatial resolution of 18.5 mm. The force range of a tactel is 6 N and its sensitivity is 0.6 V/N. The array is read at a rate of 78 frames per second. Finally, two simple application examples are also carried out with the sensor mounted on the forearm of a rescue robot that communicates with the sensor through a CAN bus.

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.