PhD Defense of Maxime Chalvin, July the 9th

Additive manufacturing of tubes by multi-axis robotized wire deposition :
Trajectory generation and optimization

Additive manufacturing through Directed Energy Deposition (DED) enables small batches
of parts to be rapidly manufactured. However, manufacturing trajectories usually used
for the manufacture of overhanging parts require the use of supports, material which
is not useful for the finished part and time consuming. If multi-axis trajectories can be
used to avoid them, they present generally a heterogeneous local inter-layer distance, thus
requiring a variation of the deposition parameters to adapt the layer height ; variation that
can be harmful to the mechanical characteristics of the final part. This thesis first proposes
a constant local inter-layer trajectory generation method for DED additive manufacturing
of tubular parts defined by parametric curves and which can have profile radius variations.
The proposed trajectories have been validated by robotized manufacturing trials of polymer
parts. Since the rotation about a coaxial deposition tool axis has no impact on the deposit,
the use of 6-axis robots offers a redundancy. Using this redundancy, a layer by layer
optimization of the trajectory in the robot space is then proposed. In a constrained robot
configuration, the trajectory optimization allows the manufacturing of parts that cannot
be manufactured in the usual way, and improves the geometrical quality of the parts with
a better repeatability.

April, the 26th : Matheus LARANJEIRA PHD Defense

Matheus LARANJEIRA will defend his PHD thesis, on the 26th of April at 10.30 AM, in the amphitheatre of the M building.
Visual Servoing on Deformable Objects :An Application to Tether Shape Control

“This thesis addresses the problem of tether shape control for small remotely operated underwater vehicles (mini-ROVs), which are suitable, thanks to their small size and high maneuverability, for the exploration of shallow waters and cluttered spaces. The management of the tether is, however, a hard task, since these robots do not have enough propulsion power to counterbalance the drag forces acting on the tether cable. In order to cope with this problem, we introduced the concept of a Chain of mini-ROVs, where several robots are linked to the tether cable and can, together, manage the external perturbations and control the shape of the cable.

We investigated the use of the embedded cameras to regulate the shape of a portion of tether linking two successive robots, a leader and a follower. Only the follower robot deals with the tether shape regulation task. The leader is released to explore its surroundings. The tether linking both robots is assumed to be negatively buoyant and is modeled by a catenary. The tether shape parameters are estimated in real-time by a nonlinear optimization procedure that fits the catenary model to the tether detected points in the image. The shape parameter regulation is thus achieved through a catenary-based control scheme relating the robot motion with the tether shape variation. The proposed visual servoing control scheme has proved to properly manage the tether shape in simulations and real experiments in pool.”

Research Show in Toulon

This year again, the University of Toulon invites you to the Théâtre Liberté for an evening event around the research activities of doctoral students and young researchers. 12 doctoral students and 7 researchers will undergo a perilous exercise: present their research in a limited time in a theatrical and imaginative way for all audiences.

The COSMER laboratory will be represented by Ornella Tortorici and Mathieu Richier. Come and support them!