67 research outputs found
Distributed Fault-Tolerant Control for Networked Robots in the Presence of Recoverable/Unrecoverable Faults and Reactive Behaviors
The paper presents an architecture for distributed control of multi-robot systems with
an integrated fault detection, isolation, and recovery strategy. The proposed solution is
based on a distributed observer-controller schema where each robot, by communicating
only with its direct neighbors, is able to estimate the overall state of the system; such
an estimate is then used by the controllers of each robot to achieve global missions
as, for example, centroid and formation tracking. The information exchanged among
the observers is also used to compute residual vectors that allow each robot to detect
failures on anyone of the teammates, even if not in direct communication. The proposed
strategy considers both recoverable and unrecoverable actuator faults as well as it
properly manages the possible activation of reactive local control behaviors of the
robots (e.g., the activation of obstacle avoidance strategy), which generate control inputs
different from those required by the global mission control. In particular, when the robots
are subject to recoverable faults, those are managed at a local level by computing a
proper compensating control action. On the other side, when the robots are subject to
unrecoverable faults, the faults are isolated from anyone of the teammates by means of a
distributed fault detection and isolation strategy; then, the faulty robots are removed from
the team and the mission is rearranged. The proposed strategy is validated via numerical
simulations where the system properly identifies and manages the different cases of
recoverable and unrecoverable actuator faults, as well as it manages the activation of
local reactive control in an integrated case study
Ultrasound imaging classifications of thyroid nodules for malignancy risk stratification and clinical management : state of the art
Assessing the risk of malignancy in the thyroid with ultrasound (US) is crucial in patients with nodules, as it can aid in selecting those who should have a fine-needle aspiration (FNA) biopsy performed. Many studies have examined whether the US characteristics of thyroid nodules are useful indicators of histological malignancy. Overall, these investigations have identified a few US features that are significantly more frequent in malignant thyroid nodules which can be coalesced into a defining set to be used as an indicator of a higher risk of malignancy. Despite these efforts, none of these classifications have been widely adopted worldwide, and there are still conflicting recommendations from different institutions. Understanding the role and appropriate utilization of these systems could facilitate the effective interpretation and communication of thyroid US findings among referring physicians and radiologists. In this comprehensive review, we outline the major US classification systems of thyroid nodules published in the last few years
A decentralized fault detection and isolation strategy for networked robots
This paper presents a distributed Fault Detection
and Isolation (FDI) strategy, applied in conjunction with a
distributed controller-observer schema, for a team of networked
robots. Differently from other works in literature, the proposed
FDI approach makes each robot of the team able to detect
and isolate input faults of other robots even if not directly
connected to it. The residual dynamics of the FDI observers are
analytically investigated, and adaptive thresholds are derived to
avoid the occurrence of false alarms in the presence of nonzero
initial observer estimation errors. The approach is validated
via numerical simulations in the case of time-varying centroid
and formation control tasks
Distributed fault detection and recovery for networked robots
The paper deals with the problem of decentralized fault detection, isolation and recovery for teams of networked robots. The proposed strategy is a combination of distributed and local approaches that allow the robots to deal with both recoverable and unrecoverable faults. A local adaptive fault observer is used to locally compensate recoverable faults, while a distributed fault detection and isolation strategy is used to allow each robot to detect unrecoverable faults on other teammates even if not directly connected; once the faulty robots have been isolated, they are removed from the team and the mission is rearranged. Results of numerical simulations and experiments involving a team of 5 mobile robots are provided to show the effectiveness of the approach
How to Investigate Constraints and Motions in Assemblies by Screw Theory
The use of the screw theory to do constraint analysis is described. Screw theory uses a matrix representation to describe, for any mating features, the part's degrees of freedom (twist-matrix) and the directions along which the constraint reacts (wrench-matrix). From these screw-matrices it is possible to individuate the exact constraint conditions of parts into the assembly. Starting from the basics of this theory, how to get screw parameters (constrained directions and degrees of freedom) from screw-matrices is analyzed and how to make the constraint analysis for several serial and parallel constraint configurations is described. Finally, a MATLAB algorithm to analyze possible constraints and motions in assemblies with any complexity is presented
Distributed fault-tolerant strategy for networked robots with both cooperative and reactive controls
The paper presents a controller-observer architecture with decentralized fault tolerance strategy for a networked team of autonomous robots. In the proposed architecture, each robot runs a decentralized observer to estimate the overall system state and a distributed control law for centroid and formation tracking control. The decentralized observer is used to compute a set of residuals in charge of detecting and isolating actuator faults affecting the other robots, even if not directly connected. The fault detection strategy is designed so as to distinguish between actuator faults and activation of local reactive controls e.g., to manage the presence of obstacles. The strategy is validated via numerical simulations
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