Observatorio Astrofísico de Javalambre (OAJ) is a highly unique astronomical research facility. The observatory is operated by the Centro de Estudios de Física del Cosmos de Aragón (CEFCA) foundation, whose main research goal is to survey several thousand square degrees of sky photometrically.
Two Javalambre telescopes will make it possible for the first time to record the positions of hundreds of millions of galaxies and their development in order to supply the first full 3D map of the universe. To ensure high quality and efficiency, the telescopes operate with robotic assistance, based on an industrial PC control platform.
The CEFCA observatory is equipped with two telescopes: the JST/T250 with a mirror diameter of 2,55 m and a 3-degree field of view, and the smaller JAST/T80, with a mirror diameter of 83 cm and a 2-degree field of view. All data from the sky surveys is sent wirelessly to the main server in Teruel.
EtherCAT network connects all systems and subsystems
The observatory’s control system is based on a C6640 Industrial PC (IPC) as the master control platform and various CX5000 series embedded PCs provide decentralised control. The PC platform ensures the reliable control, monitoring and management of all systems and subsystems installed in the observatory.
All control nodes are linked via EtherCAT in a ring topology, as well as via an Ethernet network with a star topology. The latter links the control units of the C250 camera with the observatory’s EtherCAT network over EtherCAT Automation Protocol (EAP). Communication takes place via a fibre optic cable using EtherCAT or Ethernet protocols. The high bandwidth of EtherCAT enables the transmission of status information with each cycle. A remote control centre is installed at the CEFCA headquarters in Teruel, from which the observatory can be managed, controlled and operated.
Embedded PC facilitates complex control of telescopes
The smaller of the two telescopes, the T80, performs some sky surveys, beginning with the planned photometric multiband survey of the entire sky, with expected completion in two to three years’ time. The results will be used to support the calibration of the astrophysical J-PAS survey, which is to be carried out with the JST/T250 telescope. In the next five years this telescope will have surveyed 800 square degrees, or one fifth of the entire sky.
Installed on the T250 is a JPCam wide-field camera. It consists of a mechanical filter shutter unit and camera system. The latter consists of the cooling and vacuum systems, the CCD detector field, an optically controlled entrance window and electronics. Filter inserts, the shutter and the interface with the telescope form the mechanical basis for the unit. A total of four CX5020 embedded PCs are used to control the optical lenses, the camera and the hexapod on which the camera is mounted.
Control of the dome – an entire world of automation
The dome that covers the T250 telescope is almost 13 metres in height and weighs 17 tons. It is controlled by a CX5020 embedded PC with TwinCAT software. The compact PC-based controller controls the azimuth movement, which reaches a speed of 27 m/min, the opening and closing of the windshield and the observation window, as well as the rotary movement of the dome. The entire system is driven by Beckhoff servo drives with integrated safety option card and servo motors. Safety I/Os are also integrated seamlessly into the control system via TwinSAFE terminals.
Mirror maintenance necessitates high-precision transport
The mirror of the T250 telescope has a diameter of 2,55 metres – a precision instrument whose surface must be polished with extremely high accuracy to ensure that the deviation of the reflected beams is as small as possible. In view of the size and weight of the mirror, its transport to the maintenance room some 16,5 metres away represents a remarkable challenge. The lifting system that moves the mirror up and down is controlled with the highest precision by an embedded PC and a servo drive with integrated safety functionality. The speed is only 15 cm per minute. However, each minute acceleration or deceleration could cause tiny scratches on the glass, which would result in sky observation errors.
Extensions already planned
Axel Yanes, head of engineering at the OAJ, is already devising plans for the future. “We are very pleased to have Beckhoff as a technology partner. They have more than fulfilled our requirements with regard to a high quality, reliable and flexible, easy to maintain system,” he says.
For more information contact Kenneth McPherson, Beckhoff Automation, +27 (0)11 795 2898, [email protected], www.beckhoff.co.za
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