Improving the safety of AUVs

The cost of autonomous underwater vehicles is generally high. Therefore, safety, defined as the ability of being able to physically retrieve the AUV if an emergency situation arises, should be one of the main concerns in the design of such systems. On a hardware architecture based on the field bus controller area network, we introduce two different safety layers that are orthogonal to the rest of the system operation and that can be implemented using low-cost resources. The first layer is called critical safety layer (CSL) and reacts autonomously in front of extremely hazardous situations. All the functionality related to detecting these critical situations and triggering the AUV surfacing mechanism is located in a single hardware module, called the emergency hardware module, that presents internal redundancy for fail-safe behaviour. As the AUV could be affected by an internal failure not immediately leading to a critical situation, we introduce a second layer, called preventive safety layer (PSL), to avoid waiting until the situation becomes critical. The PSL monitors the system, and on finding a permanent failure it triggers the surfacing mechanism as well. Moreover, the PSL is designed not to interfere with the critical operation of the CSL. These two safety layers can be taken as a set of services provided to the designer that can decide whether to use them or not. On top of these services, the AUV software designer can add all the application specific safety mechanisms that he considers necessary for the particular mission having a minimum guaranteed by the two aforementioned layers