Crane by camera

1 October 2004

cientists at Fermilab are installing a camera to use a crane in a radioactive hall

The crane itself is nothing special. The 27t capacity double-girder KCI Konecranes crane was installed in a 67m by 9m hall in Batava, Illinois.

The only two special requests the scientists made were a low headroom and a motor-driven rotating hook.

So far operators have been able to use the crane in the hall using the standard radio remote control. It has lifted 6,350t of shielding, mostly in 9t blocks. But once the experiment begins later this year, the area will be sealed off.

The hall is cut in half along its length by a false floor of shielding. Above is the crane; below is the experimental equipment. A special particle gun will shoot a beam of particles that will be sampled once in the hall and again, 735 km away, at a research facility in Soudan, Minnesota. The change in the beam between the two detectors will make it possible to derive information about the mass of the particles – called neutrinos – and other fundamental properties. To produce the neutrino beam, Fermilab National Laboratory first accelerates protons (hydrogen with the electron stripped off) to very high energy. The protons are directed onto a target where they interact and produce pions. The pions are focused toward Soudan, and then quickly decay to neutrinos and other particles. “We need to distinguish between two conditions – radiation produced while the beam is on, and residual radiation that will be left after the beam is turned off,” says scientist Jim Hylen.

The centre of the target is expected to receive a radiation dose of 1014 Rad/year. Protected above the shielding, the crane is expected to only receive about 100 Rad/year, but this is still enough to fry the electrics – so the team will take away cameras and electrics when the beam is switched on.

Once or twice a year, the team will switch off the gun to replace the target or a focussing device – for which workers will need to open up the shielded chamber, releasing radiation. Although the cameras are mounted near the top of the chamber, they will still receive a dosage of several Rad/hr, according to Hylen – not enough to require special cameras, but far more than the 0.1 Rad maximum dose for personnel.

When fully installed later this year, there will be four cameras on the crane and several on the walls. Two cameras featuring remote tilt/pan/focus/zoom will watch the load from a vantage point on the crane bridge. Two black and white fixed cameras, one on the trolley, one on the bridge – will monitor long and cross travel by transmitting an image of a viewing scale.

The controls and video are wireless. The pan/tilt/zoom controls transmit at 5.8 GHz, and the video is transmitted back on 2.4 GHz bands, while the wireless crane control operates at 0.9 GHz. The camera receiver antennas are at a fixed location on the target hall wall, with cable running the rest of the way to the control station which is located behind a shield wall.

Once installed, technicians will check the video transmission quality using the antennas that come with the cameras. If the quality suffers as the crane moves away from the receiver, the team will passively multiplex the four video signals onto a high-gain antenna and de-multiplex them at the other end.

Fixed lasers mounted on the bridge will shine downward. The position of the spots on targets on the object being transported will indicate when the rotation angle of the object is correct for insertion into the target pile.

The camera/laser system will need to position objects to about 18mm initial accuracy. As objects are lowered, guide daggers will engage that will lead the object into final position with 0.05mm accuracy.