Developing rugged robots for the nuclear industry

Achieving the ruggedness, reliability and real time control required of these autonomous systems has always posed a challenge. French industrial consortium INTRA Groupe has been facing this problem for many years with a series of robots for repairing nuclear power stations, especially after accidents. These systems have to operate from a considerable distance to keep the operators safe from any contamination while providing real time response over many kilometres. Devices ranging from exploratory robots to giant earth removal trucks not only have to be controlled remotely, but also have to operate reliably in harsh environments. Until now, many systems in these robots have been proprietary, as standard equipment has not met system performance requirements. However, this has made it difficult to evolve the system without changing the software. However, commercial boards and software are becoming viable for use in the most challenging designs. INTRA, with the help of ECA, is replacing 15 year old systems with Pentium 4 based boards, linked to specialist interface and communications boards, while moving to a new software architecture. This combination is allowing robot systems to be updated quickly and efficiently without introducing bugs and problems. A long lifetime is required for the boards, With the robots remaining in service for 20 years, a long lifetime is needed for the boards, so additional stocks have been purchased and are ready to replace any faults. Moving to commercial software also means there is the potential to upgrade the boards in the future while maintaining the same software base, allowing the systems to evolve in a controlled way. INTRA, owned by a consortium of the French nuclear equipment companies, develops, builds and maintains the fleet of robots ready for action. It previously used the Irmx OS real time operating system, developed specifically for the nuclear industry. Because moving to a commercial OS opens up long term development and support and a wider range of tools, INTRA evaluated other embedded operating systems and the open source Linux software before selecting Wind River's VxWorks. Determinism, stability and low footprint, combined with maintenance and life cycle support programs, makes VxWorks suitable for the application, matching specific control system requirements. VxWorks runs across multiple control units in the system – from the screens in the control centre to control units in the robots – wherever real time response is required. The robots are controlled by a wireless link that runs a robust, high performance proprietary coding scheme developed in the 1990s. This uses a band of 20 frequencies provided by the French army so availability can be guaranteed during an emergency. The robots can also be controlled over a 5km optical fibre and the same protocol is used to give identical latency and determinism. To give the operator guaranteed real time control, the system needs a response time of less than 100ms for all data, three channels of high resolution video from the robot and any startup operations. This is a challenge for any OS and a key reason why INTRA Groupe chose VxWorks. The VERI II, ERASE (pictured), and ERELT remote robots, used to investigate buildings in the contamination zone and to collect samples for further study, have already been upgraded to VxWorks. Because they can stay in contamination zones for up to 80 hours, each robot has to be rugged, with high levels of protection against cumulative software errors from radiation particle strikes The next move is to integrate VxWorks into EBENNE, a 20tonne, 10m long remote control earth moving truck which features six cameras. These robotic systems have to operate reliably and effectively in some of the worst environments known to man. In the past, this has meant developing proprietary hardware and software. However, the availability of high performance real time systems is allowing these systems to move to commercial implementations to meet the high requirements of latency and ruggedness and to allow new features to be added in the future.