@conference {GFB08, title = {Anytime Control Algorithms for Real-Time Embedded Systems}, booktitle = {Int Conf of Hybrid Systems: Computation and Control}, series = {Lecture Notes in Computer Science}, volume = {4981/2008}, year = {2008}, pages = {158 - 171}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {St. Louis, MO}, abstract = {

In this paper we consider the problem of designing controllers for linear plants to be implemented in embedded platforms under stringent real-time constraints. These include preemptive scheduling schemes, under which the maximum execution time allowed for control software tasks is uncertain. We propose an {\textquoteleft}{\textquoteleft}anytime control{\textquoteright}{\textquoteright} design approach, consisting in a hierarchy of controllers for the same plant. Higher controllers in the hierarchy provide better closed-loop performance, while typically requiring a larger worst-case execution time. We provide a procedure for the design of controllers which, together with a conditioning process of the stochastic scheduling, provides better performance than prevailing worst case-based design, while guaranteeing almost sure stability of the resulting switching system.

}, keywords = {Embedded Control, Robotics}, author = {D. Fontanelli and L. Greco and A. Bicchi}, editor = {M. Egerstedt and B. Mishra} } @conference {GFB07, title = {Almost Sure Stability of Anytime Controllers via Stochastic Scheduling}, booktitle = {Proc. IEEE Int. Conf. on Decision and Control}, year = {2007}, month = {December}, pages = {5640-5645}, abstract = {

In this paper we consider scheduling the execution of a number of different software tasks implementing a hierarchy of real-time controllers for a given plant. Controllers are considered to be given and ordered according to a measure of the performance they provide. Software tasks implementing higher-performance controllers are assumed to require a larger worst-case execution time. Control tasks are to be scheduled within given availability limits on execution time, which change stochastically in time. The ensuing switching system is prone to instability, unless a very conservative policy is enforced of always using the simplest, least performant controller. The presented method allows to condition the stochastic scheduling of control tasks so as to obtain a better exploitation of computing capabilities, while guaranteeing almost sure stability of the resulting switching system.

}, keywords = {Embedded Control, Robotics}, author = {L. Greco and D. Fontanelli and A. Bicchi} } @conference {FontanelliVGCB06, title = {Adaptive non Linear Control of Dynamic Mobile Robots with Parameters Uncertainty}, booktitle = {Int. IFAC Symp. on Robot Control}, year = {2006}, month = {September}, address = {Bologna, Italy}, abstract = {

Research of a modular stabilizing control law for uncertain, nonholonomic mobile systems with actuators limitation has been investigated. Modular design allows the definition of a stabilizing control law for the kinematic model. The presence of uncertainties in the actuators parameters or in the vehicle dynamics has been treated both adding suitable components to the Lyapunov function and using parameters adaptation laws (e.g. adaptive control and backstepping techniques). Simulations are reported for the set point stabilization of a unicycle like vehicle showing the feasibility of the proposed approach. Torque limitations for a unicycle like vehicle has been investigated using backstepping techniques for the vehicle tracking problem. Simulations are reported.

}, keywords = {Embedded Control, Robotics}, author = {D. Fontanelli and R. Viviani and L. Greco and A. Caiti and A. Bicchi} } @booklet {FontanelliG-TR06, title = {Any Time Control}, year = {2006}, month = {March}, publisher = {Interdepartmental Research Center E. Piaggio, University of Pisa}, address = {Pisa, Italy}, abstract = {

It is widely accepted in the control community that the Computer Controlled Systems (briefly, CCSs), have a lot of advantages based primarily on the high reconfigurability of the controller platform and the ability of making complex yet fast decisions. Such positive features make the CCS a useful platform for multitasking control, i.e. using only one single-processor platform to control several plants. Within this framework, the computer has to share its computational time to solve several critical tasks, each one with its priority. Taking into account schedulability and real time operating systems problems, it is just a step forward to realize that tasks with low priority could be interrupted any time, with unpredictable distributions, and it is just a logical intuition that not all the tasks can be at the highest priority. From a control point of view, each control task should compute a control input to the controlled system to prevent instability or to ensure the performances. This field seems to be at the border between the control community and the computer science community and it has not been widely investigated. Some work has been presented introducing more general scheduling models and methods for control systems, where control design methodology takes the availability of computing resources into account and allows the trade{\textendash}offs between control performance and computer resources utilization, and also introducing the idea of any time CCS without solutions. In literature, the Control Server is introduced, allowing the separation between scheduling and control design by treating the controllers as scalable real{\textendash}time components. Jitter and latency is included in the model and cannot be taken over. Furthermore, the interrupt time, the I/O operations and the overrun handling are not taken into account, simply imposing only soft real time control tasks. Useful tools for the analysis of real time control performance are the Jitterbug and the True Time that analyze the control performance once the control tasks are implemented as soft real time tasks.

}, keywords = {Embedded Control, Robotics}, author = {D. Fontanelli and L. Greco} } @booklet {BCFGV05, title = {Adaptive nonlinear control of dynamic mobile robots with parameters uncertainty}, year = {2005}, publisher = {Dipartimento di Sistemi Elettrici e Automazione, Universit\à di Pisa}, abstract = {

Research of a modular stabilizing control law for uncertain, nonholonomic mobile systems with actuators limitation has been investigated. Modular design allows the definition of a stabilizing control law for the kinematic model. The presence of uncertainties in the actuators parameters or in the vehicle dynamics has been treated both adding suitable components to the Lyapunov function and using parameters adaptation laws (e.g. adaptive control and backstepping techniques). Simulations are reported for the set point stabilization of a unicycle like vehicle showing the feasibility of the proposed approach. Torque limitations for a unicycle like vehicle has been investigated using backstepping techniques for the vehicle tracking problem. Simulations are reported.

}, keywords = {Embedded Control, Robotics}, author = {A. Bicchi and A. Caiti and D. Fontanelli and L. Greco and R. Viviani} }