The Brick Assembly Machine (BAM) for the OPERA experiment in LNGS

The BAM project was conceived to face the problems of the brick construction of the OPERA detector target. An OPERA brick is made of a pile (interleaved lead and nuclear emulsion sheets), kept under a pressure of 3 bar. The brick must be a precise object (dimensional tolerance: ± 0.1 mm), weighting about 8.5 kg, which must be stable at micrometric level for 5 years (OPERA data taking time). The main purpose of the BAM project was to assembly 150.000 bricks in the planned time of one year. It was mandatory to keep bricks shielded from cosmic radiations and there was no way to store them out of the OPERA detector. Thereby it was decided to design an automatic machine for brick assembling, to place it close to the OPERA experiment (inside the underground laboratories of LNGS). Once defined the assembly technique, several technical problems were faced concerning the manipulation of both brick components and assembled bricks. The very challenging goal was due to the synergy of several technical difficulties to be solved in parallel: work in dark and clean room, micrometric precision, handling of heavy and fragile components, high level reproducibility, high production speed and long term stability. The use of anthropomorphic robots was the key choice to solve most of them. In fact those robots show outstanding feature of flexibility and reproducibility in positioning components in the space. Additional PLC and image processing controls were conceived to secure the demanded on line quality control of the production process. The BAM is equipped with 11 anthropomorphic robots and represents today the first application of this industrial technique in the particle physics research field. This approach can become a relevant solution for all future mass productions in the construction of components for future large size detectors in particle physic research. The final average production rate of 750 bricks/day was achieved. The BAM stopped the OPERA brick mass production in June 2008 at 146600 bricks produced, due to lack of lead caused by a severe accident in the lead supplier firm. The remaining 3400 bricks are planned to be produced, as soon as lead components will be available again.