Control of a robot chain

Doctoral student : Martin Filliung

Funding: Doctoral school grant ED548, 2022-2025

Supervision : Nicolas Boizot (CNRS LIS) and Claire Dune (COSMER)


Recent advances in embedded technologies, miniaturization of sensors and decrease of their costs have accelerated the development of underwater mini-UAVs. Despite the loss of performance compared to current operational vehicles, their low weight and size are interesting because they can be deployed by a single person from small boats without expensive and cumbersome launching or recovery systems, which would require large vessels and a full crew.

The cable that connects the ROV to the boat at the surface is still the only way to communicate a significant amount of information underwater, as electromagnetic waves are absorbed within the first few centimeters. While for large industrial ROVs, of the working class type, the drag of the umbilical is easily countered by the mass and engine power of the system, this is no longer the case when considering small, low-cost devices. This is even more true when you move away from the boat and approach the coastal zone called surf zone with strong current and swell. However, this is the destination zone for these mini-robots that can evolve in shallow water. Their mission therefore requires them to be particularly exposed to marine disturbances. In order to help a mini-ROV to counter the disturbances of its umbilical, the COSMER laboratory is working on the concept of robot ropes. The idea is to add mini-ROVs regularly on the umbilical so that they erase in a coordinated way the disturbances of the cable on the leading robot. This also allows to position the cable in space taking into account the obstacles and to avoid that it gets tangled in the systems or on itself.

This thesis is therefore part of one of the mobile robotics themes of the COSMER laboratory, namely the consideration of the influence of the umbilical on the manoeuvre of a light ROV. This theme has already been addressed in previous works whose object was the estimation of the configuration of the umbilical in order to estimate the position of ROVs composing a string of ROVs{1}. A second thesis is in progress at COSMER. It deals with the localization of the rope by visual SLAM techniques. At this stage, it is possible to estimate in real time the position of the rope elements in a map of the environment. The next step is to command the rope to move towards a goal and avoid obstacles in these reconstructed environments.

The work we now propose focuses on the control of the robot rope as a single system, composed of actuated robots and passive rope portions. The objective is to propose a control that takes into account the specific dynamics of the rope, including a modeling of the gear dynamics and the cable dynamics by damping platooning effects (accordion effect of vehicle trains) and rejecting external disturbances, such as currents in the water body – see for example the robot catenary).

We will place ourselves at the intersection of robotics and control theory. The implementation of adaptive techniques or reinforcement learning could also be considered.


To contribute to the problem of dynamic control of tethered ROVs by proposing observers and commands adapted to these constrained flotilla systems


Predictive control, Dynamic Visual Servoing, Optimal Planning, Robust Controls, experimental implementation.

Key words

ROV rope; control theory; underwater robotics; underwater vision.