Mobile Robotics

 

General Information

The Monsun is an AUV (Autonomous Underwater Vehicle) developed at the Institute of Computer Engineering, primarily for use in robot swarms. It differs from other systems primarily in its small size, which makes it also known as a micro AUV. In addition to high mobility, thanks to six brushless motors housed in the wings, the robot is distinguished by its flexibility and adaptability to different missions. With the help of a modular extension system, a wide variety of sensors and modules can be accommodated, enabling a wide range of tasks to be performed.

 

 

Construction

The shell of the robot consists of glass-fibre reinforced plastic and simultaneously serves as a pressure body to a maximum intended depth of 20m. The body consists of two parts, which are connected by a bayonet ring in the rear area. The motors and sensors mounted outside are connected to the shell via watertight connectors, thus allowing the components to be replaced quickly in the event of damage.

 

 

Commercial brushless motors from aircraft model construction are used as motors. These have the advantage of a small design and the possibility of a simple evaluation of the motor values, such as speed and power consumption. The internal structure of the robot is very modular. The main part of the electronics is a base board on which a bus-based architecture is implemented. Electronic modules can thus be connected to each other via several connectors, allowing the robot to be flexibly adapted to its respective area of application.

 

 

The adaptability of the system to different missions is achieved by the modular extension package, which is divided into three different device types:

At the bow of the robot different front modules can be integrated by means of a small bayonet ring, e.g. an optical distance sensor (i), a sonar (ii) or imaging sensors (iii). Below the robot is an equipment carrier that allows external components and payloads to be attached to the robot. In this case, a CTD-48 probe (a) and a commercial underwater modem (b) are placed underneath. In addition, an OceanKit consisting of a carrying handle and external antennas can be attached from the outside. In the middle of the robot, so-called body modules can also be integrated using bayonet rings. Illustrated are a sonar module (1), a module for taking water samples (2), an internal underwater modem (3), a visual feedback module (4) and an environmental monitoring module (5).

 

 

Control

A Raspberry Pi 3B is currently used as the control unit, on which an Ubuntu 16.04 operating system does its work. This allows to use the Robot Operating System (ROS). Thus a simple modular control software can be realized, which can be adapted to the used hardware.

The software architecture is divided into three hierarchical levels: the Sense/Act Level, the Behaviour Level and the Task Level. At the lowest level, the device drivers and specific basic functionalities as well as position and speed controllers are implemented. These capabilities are accessed at the middle level for the implementation of specific behaviors, such as driving to a given waypoint, before at the highest abstraction level whole missions are defined as a sequence of behaviors in finite automata.

 

 

Swarm behaviour and communication

On the water surface, WLAN is used for communication between the MONSUN AUVs in the swarm and with an operating notebook on land or on a boat. The localization of the swarm members is done by GPS. Neither is possible under water, therefore acoustic modems are used. These allow not only a (narrow band) communication, but also a rather exact distance measurement between the AUVs.

The MONSUN localization concept now provides that some AUVs remain on the surface and determine their absolute position via GPS. The other swarm members under water locate themselves relative to them by distance measurement. New methods have been developed, implemented and evaluated within the MONSUN project. It should be noted that acoustic communication is very unreliable. The developed methods are therefore very robust against longer interruptions of the communication connections. Failed swarm members can also be tolerated.

A V-formation of three MONSUNs has already been successfully tested at a lake near Ratzeburg. Two AUVS travel parallel to each other on the water surface using GPS. The third MONSUN follows them under water at a given distance using distance measurements based on acoustic communication. It is also possible to take bends with not too tight a radius.

 

 

 

Applications and Projects

As one of the first applications, two MONSUNs (one on the surface, one submerged) were used in 2016 in the Baltic Sea off Bornholm as part of the Clockwork Ocean project of the Helmholtz Centre Geesthacht to measure submesoscale eddys.

In the BMBF-funded joint project MoSAIk (9/2016 - 11/2018), the MONSUN swarms were further developed for use in the measurement of hazardous substances in harbours. The project partner TUHH developed a new low-cost acoustic micro-modem especially for the communication in MONSUN swarms. This will replace the commercial acoustic modem of Evologics. Project partner Sea&Sun Technology has designed a MONSUN intermediate ring to integrate its sensors for measuring water quality and determining pollutants.

In the course of the BMVI funded IHATEC project SecurePort (10/2017 - 9/2020) the use of MONSUN for the inspection of quay walls and ship hulls is investigated in cooperation with the LHG (Lübecker Hafengesellschaft). The aim is to use an autonomously working swarm for this task, which is still performed manually by divers today. In addition, high-resolution multibeam sonars and cameras with LED headlights are used as sensors.

In the EU.SH project Modular Autonomous Underwater System - MAUS (3/2019 - 2/2022) MONSUN is used together with the AUV HANSE, also developed at the ITI, as a test system for novel control and navigation software for heterogeneous AUV teams. This software will later be ported to newly developed AUVs together with the project partners FH Kiel, University of Kiel and the companies SubCtech and Emma technologies.

 

 

Videos

On the Youtube Channel of the Institute of Computer Engineering you can find various videos of current tests and experiments, which illustrate the possible properties of the system: Go to Youtube