This paper focuses on the design and test results of an adaptive variation of Kalman filter (KF) estimator based on fusing data from Inertial Measurement Unit (IMU) and two Real Time Kinematic (RTK) Global Positioning Systems (GPS) for driftless 3-D attitude determination and robust position estimation of mobile robots. GPS devices are notorious for their measurement errors vary from one point to the next. Therefore in order to improve the quality of the attitude estimates, the covariance matrix of measurement noise is estimated in real time upon information obtained from the differential GPS measurements, so that the KF filter continually is ¿tuned¿ as well as possible. No a priori knowledge on the direction cosines of the gravity vector in the inertial frame is required as these parameters can be also identified by the KF, relieving any need for calibration. Next, taking advantage of the redundant GPS measurements, a weight least-squares estimator is derived to weight the GPS measurement with the ¿good¿ data more heavily than the one with ¿poor¿ data in the estimation process leading to a robust position estimation. Test results are presented showing the performance of the integrated IMU and two GPS to estimate the attitude and location of a mobile robot moving across uneven terrain.

Aspects of the mechatronic design and prototyping of a robot designed and realized with the quasiholonomy property are discussed here. After an overview of the motivation and applications of the project at hand, we show how we faced the challenges encountered in the mechatronic design and implementation of the prototype. The actuation system and power supply dimensioning are then described, along with the selection of the on-board control unit and programming of the real-time operating system. Advantages of quasiholonomic robotic systems are substantiated

This paper introduces a new family of two-wheeled mobile robots. The mathematical model of the proposed robots is formulated along with a controllability analysis, also taking into account the oscillations of the intermediate body. We prove that it is possible to completely control these robots using only the wheel motors, while tracking a desired path

We report on the control of semi-autonomous two-wheeled mobile robots undergoing large variations of the payload. These robots being underactuated, their control poses some challenges when resorting to a simple controller. The latter being a linear controller, its robustness with respect to model uncertainty needs to be investigated. To do this, we conducted a time-domain analysis of robustness of the foregoing controller with respect to parametric and unmodeled dynamics uncertainty. The controller, which is designed by a dominant second-order pole technique, turns out to be fragile (as opposed to robust) with respect to unmodeled dynamics uncertainty. In order to cope with this problem, a linear-quadratic regulator is designed. By numerical simulation we show that the latter features robustness with respect to both types of uncertainty.

We report on the controllability of a novel mobile robot which comprises two driving wheels and an intermediate body carrying the payload. By virtue of quasiholonomy, a concept introduced elsewhere, the robot is underactuated by design. One challenge here is the control of the motion of the intermediate body, which will tend to rotate about the wheel axis as the wheels are actuated. We prove that it is possible to completely control the robot using only the wheel motors, while tracking a desired trajectory, with apparent advantages in terms of cost, weight and efficiency. To do this, we show that every linearization of the robot dynamics model around an equilibrium point verifies the Kalman rank condition for controllability. Moreover, using modern results from nonlinear control theory, we prove that the robot is locally accessible and small-time locally controllable.

We report the holonomy analysis of three wheeled mobile robots. Two of these, Vuton II and Nomad, have full mobility and are claimed by their inventors to be holonomic. We show that, in fact, they are nonholonomic. Nevertheless, conditions are given under which these robots can be designed for quasiholonomy, a concept introduced elsewhere and recalled here. The third robot, Quasimoro, has a mobility of two and is unconditionally quasiholonomic. It is shown that if the wheel mechanism of a robot with full mobility is designed in such a way that the platform is much heavier than the wheel mechanism, then the underlying mathematical models are free of the nonholonomy term.