Bearing Persistently Exciting formation and Relaxed Bearing Rigidity
We developed a new framework for vision-based formation control and localization problems relying on inter-agent bearing (direction) measurements, which loosens the constraints significantly on the graph topology required by the classical Bearing Rigidity. The key contribution lies in improving and extending the well-known Bearing Rigidity concept by introducing the new concepts of Bearing Persistently Exciting (BPE) formation and Relaxed Bearing Rigidity. These concepts relax the classical bearing rigid conditions on graph topology, remove the scale ambiguity on bearing-based formations and extend the current bearing formation control and localization solutions (typically restricted to rigid shapes and constant bearing references) by encompassing dynamic shapes and time-varying bearing references. The proposed concepts were exploited not only to determine whether the formation can be uniquely determined by the available sensor measurements but also to derive efficient decentralized controllers.
Examples of graph topologies of BPE formations in two (a1 − b3) and three-dimensional space (c1 − d3). Red (blue) lines represent edges for which the corresponding bearing vector are PE (not necessarily PE, resp.)
The video shows simulation results of the proposed bearing formation controllers under assumptions that the desired formation is BPE.
Related journals:
Z. Tang, R. Cunha, T. Hamel, C. Silvestre, Relaxed bearing rigidity and bearing formation control under persistence of excitation, Automatica, accepted, Jan. 2022.
Z. Tang, R. Cunha, T. Hamel, C. Silvestre, Formation control of a leader-follower structure in three dimensional space, Automatica, 128, 109567, 2021.
Image-Based Visual Servo (IBVS) control for Unmanned Aerial Vehicles
The novel IBVS controllers guarantee obstacle-free navigation abilities for UAVs in urban or congested environments. The key idea is to directly exploit the centroid of the spherical image points of the observed pattern together with the optical flow, thereby preventing the need to estimate the UAVs' position and velocity. Particularly, optical flow measurements are exploited for the purpose of avoiding collision.
The video shows the implementation of the proposed IBVS algorithms on a real quadrotor equipped with two on-board cameras and an IMU, with real-time image processing ability. The quadrotor automatically crosses the window and land on the target, without collision with the wall nor the window.
Related journals:
Z. Tang, R. Cunha, D. Cabecinhas, T. Hamel, C. Silvestre, Quadrotor going through a window and landing: An image-based visual servo control approach, Control Engineering Practice, 112, 104827, 2021.
Z. Tang, R. Cunha, T. Hamel, C. Silvestre, Aircraft landing using dynamic two-dimensional image-based guidance control, IEEE Transactions on Aerospace and Electronic System, 55 (5), 2104-2117, 2018.