THE ACTIVE SURFACE SYSTEM
The actuator has the electronics and mechanics parts close together, this avoids a huge amount of cable spreaded on the antenna structure.The Noto antenna , 32m in diameter and 244 actuators, uses less than 1km of 10mm diameter cable to distribute power supply and communication. This solution also avoids long cables and thus interference signals.
Software - The software packages used are two. The first one runs on the master computer. It is a C program running on DOS OS, a solution we thought the most reliable. This program controls the network, inquiring the actuators and receiving back their position and status. Moreover, the program updates the actuator position every one degree of elevation. Mostly the master computer communicates with the actuators in an addressed mode. About 30msec are necessary to address, command and receive back the answer from each actuator. It also provides the possibility to send a broadcast command to the network in order to start the zero procedure, in which all actuators are moved to a mechanical reference and the step motor counter cleared.
The second program runs on the host computer and allows the operator interaction, for maintenance for example. The host communicates with the master computer via a RS485 link and with the observation computer in order to get the elevation value to be issued to the master. This program is written in the graphical language TCL/TK.
244 actuators mounted under the primary mirror, commanded by a master computer located in the secondary focus cabin. (pict) The master computer stores the actuators positions for all elevations and manages the update of the surface when the elevation value is issued.
The actuators network is firstly subdivided in four branches, organized in a star topology. (pict) Each branch has 12 arms each one composed of 5 (or 6) actuators arranged in a bus topology. The master computer sends the command, in the simplest way it can be seen "address + position", to each actuator by using a demultiplexer board routing to the arm containing the addressed device. All the actuators in that arm receive the command but only that one matching the address will move. The master computer regularly controls the network status and communicates it to the host. Every 1° of elevation updates the position network.
Junction box, placed on the antenna structure. It contains the transformer converting the 220Vac to 48Vac. (pict) 48 Vac is merged with the the communications line in a same cable and routed to the actuators. The junction box has 2 input connectors and 12 output connectors.
View of the rack containing the PC embedded master computer and the demultiplexer board, (pict) the boards and the junction box are also showed.
View of the screen panel of the program running on the host computer. This program can be used for maintenance, for sending (pict) a broadcast command to the network to start the zero procedure, for loading files to be added to the deformation file. A complete network refresh takes about 7 sec.
