Alessio Salerno

A New Family of Two-Wheeled Mobile Robots: Modeling and Controllability

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

THE RABIT: A RAPID AUTOMATED BIODOSIMETRY TOOL FOR RADIOLOGICAL TRIAGE

In response to the recognized need for high throughput biodosimetry methods for use after large-scale radiological events, a logical approach is complete automation of standard biodosimetric assays that are currently performed manually. The authors describe progress to date on the RABIT (Rapid Automated BIodosimetry Tool), designed to score micronuclei or &ggr;-H2AX fluorescence in lymphocytes derived from a single drop of blood from a fingerstick. The RABIT system is designed to be completely automated, from the input of the capillary blood sample into the machine to the output of a dose estimate. Improvements in throughput are achieved through use of a single drop of blood, optimization of the biological protocols for in situ analysis in multi-well plates, implementation of robotic-plate and liquid handling, and new developments in high-speed imaging. Automating well-established bioassays represents a promising approach to high-throughput radiation biodosimetry, both because high throughputs can be achieved, but also because the time to deployment is potentially much shorter than for a new biological assay. Here the authors describe the development of each of the individual modules of the RABIT system and show preliminary data from key modules. System integration is ongoing, followed by calibration and validation.

On the nonlinear controllability of a quasiholonomic mobile robot

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.

The control of semi-autonomous two-wheeled robots undergoing large payload-variations

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.

Driftless 3-D Attitude Determination and Positioning of Mobile Robots By Integration of IMU With Two RTK GPSs

This paper focuses on the integration of inertial measurement unit (IMU) with two real-time kinematic global positioning system (GPS) units in an adaptive Kalman filter (KF) for driftless estimation of a vehicles attitude and position in 3-D. The observability analysis reveals that 1) integration of a single GPS with IMU does not constitute an observable system; and 2) integration of two GPS units with IMU results in a locally observable system provided that the line connecting two GPS antennas is not parallel with the vector of the measured acceleration, i.e., the sum of inertial and gravitational accelerations. The latter case makes it possible to compensate the error in the estimated orientation due to gyro drift and its bias without needing additional instrument for absolute orientation measurements, e.g., magnetic compass. Moreover, in order to cope with the fact that GPS systems sometimes lose their signal and receive inaccurate position data, the self-tuning filter estimates the covariance matrix associated with the GPS measurement noise. This allows the KF to incorporate GPS measurements in the data fusion process heavily only when the information received by GPS becomes reliably available. Finally, test results obtained from a mobile robot moving across uneven terrain demonstrate driftless 3-D pose estimation.

Experimental Validation of an Underactuated Two-Wheeled Mobile Robot

Reported in this paper are the implementation and testing of the real-time control of a two-wheeled mobile robot. The robot is underactuated, its mobility and control inputs being three and two, respectively. The control challenge faced here is to reduce the oscillations of the intermediate body while following a desired path. A controller, introduced elsewhere, is implemented using a real-time operating system on a novel control architecture. The control algorithm was tested using three different test motions: translational, rotational, and uphill.

Design Considerations for a Minimally Invasive High-Throughput Automation System for Radiation Biodosimetry

Design aspects of a minimally invasive high-throughput automation system for radiation biodosimetry are reported. The system, currently under development, relies on robotic devices and advanced high-speed automated image acquisition to perform mass triage following a radiological event. A design concept of the automation system is proposed based on the use of an input stage, a centrifuge module, a cell harvesting system, a liquid handling module, an imaging system and a service robot. The biological assays are described along with an analysis of the throughput requirements. The special requirements imposed by bioassay automation, system throughput and minimal invasiveness lead to the design of a custom-made multipurpose gripper and a cell harvesting module. Results on the embodiment design of these modules are provided. A prototype of the automation system is described.

Attitude determination and localization of mobile robots using two RTK GPSs and IMU

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.

The development of quasiholonomic wheeled robots

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.

Design and Implementation of a Quasiholonomic Mobile Robot

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