Research Activity 

For many people with mobility impairments, essential and simple tasks, as dressing or feeding, require the assistance of dedicated people; thus, the use of robotic devices providing independent mobility can have a large impact on their quality of life. We are working on the development of control architecture for assistive robotic systems operated via high-level Human Machine Interface. In particular, we used a lightweight robot manipulator (7DOF Kinova Jaco2) operated via a Brain Computer Interface (Emotiv Epoc+) to perform autonomous mission. Using the BCI, the user selects an element from a GUI by focusing attention on it and counting how many times it flashes (P300 potential generated via oddball paradigm). The motion of the manipulator is controlled relying on a closed loop inverse kinematic algorithm that simultaneously manages multiple set based and equality-based tasks. The objects and the user's mouth are recognized and localized using an RGB-D sensor (Kinect one). The software architecture is developed relying on widely used frameworks to operate BCIs and robots (namely, BCI2000 for the operation of the BCI and ROS for the control of the robot) integrating control, perception and communication modules developed for the application at hand. 

We developed a distributed Fault Detection and Isolation (FDI) strategy for a team of networked robots that builds on a distributed controller-observer schema. The proposed FDI approach makes each robot of the team able to detect and isolate faults occurring on other robots, even if they are not direct neighbors. By mean of a local observer, each robot can estimate the overall state of the team and it can use such an estimate to compute its local control input in order to achieve global tasks. The same information used by the local observers are also used to compute residual vectors whose aim is to allow the detection and the isolation of actuator faults occurring on any robot of the team. The approach is validated via experiments involving four Khepera III mobile robots commanded to perform a formation control mission even in the case on of the robots is subject to failure. 

We developed a distributed controller-observer schema for tracking control of the centroid and of the relative formation of a multi-robot system. Each robot of the team uses a distributed observer to estimate the overall system state and a motion control strategy for tracking control of time-varying centroid and formation. Proof of the overall convergence of the observer-controller schema for different kinds of connection topologies, as well as for the cases of unsaturated and saturated control inputs is presented. In particular, the solution is proven to work in the case of strongly connected topologies, in the case of non-switching topologies, and with balanced strongly connected topologies, in the case of switching topologies. In order to complete the work, the approach is validated by experimental tests with a team of five wheeled mobile robots. 

The field of cooperation and coordination of multi-robot systems has been object of considerable research efforts in the last years. The basic idea is that multi-robot systems can perform tasks more efficiently than a single robot or can accomplish tasks not executable by a single one. Moreover, multi-robot systems have advantages like increasing tolerance to possible vehicle fault, providing flexibility to the task execution or taking advantage of distributed sensing and actuation.

The Null-Space-based Behavioral control (NSB) We developed a behavior-based approach, namely the Null-Space-based Behavioral control (NSB), aimed at guiding a mobile robots platoon. The approach, using a hierarchy based logic to combine multiple conflicting tasks, is able to fulfill or partially fulfill each task according to their position in the hierarchy. This approach has been extensively studied and simulated with different kinds of vehicles (i.e. mobile robots, underwater robots and surface vessels) while performing several formation control missions.

NSB for cooperative control with centralized system Extensive experiments have been performed with a multi-robot systems composed by a team of 7 Khepera II mobile robots controlled from a central unit with vision system. The videos, at the right side of this table, concern different kind of missions and task functions:

• Escorting a moving target (a tennis ball pushed by hand); Active tasks: Obstacle avoidance - Centroid on the target - Circle of fixed radius - Regular distribution

• Rigid formation and obstacle avoidance; Active tasks: Obstacle avoidance - Centroid in a fixed position- Rigid formation (linear)

• Rigid formation and obstacle avoidance; Active tasks: Obstacle avoidance - Centroid in a fixed position- Rigid formation (circular)

NSB to control individual robots The NSB approach has been used to control individual robots, i.e. not cooperating one with each other, to perform move to goal and obstacle avoidance missions. These represented preliminary test with Khpera III robots on the way to built a completely distributed architecture.